VLTI Spectro Imager

VLTi Spectro-Imager

Technical Proposal for a second generation VLTI instrument

in response to ESO Call for Phase-A Proposals for 2nd generation VLTI instruments

Document No VSI-PRO-001 Issue: 1.0 Date: 30/01/2006

from a consortium composed of the following institutes:

– Laboratoire d’Astrophysique de Grenoble (LAOG, France) – Cavendish Laboratory, University of Cambridge (United Kingdom) – Max-Planck Institut fürRadioastronomie in Bonn (MPIfR, Germany) – Centro de Astrof´ısicada Universidade do Porto (CAUP, Portugal) – Istituto Nazionale di Astrofisica (INAF, Italy) – Institut d’Astrophysique et de Géophysique de Liège (IAGL, Belgium) – Institut für Astronomie, UniversitätWien (IfA, Austria) – Astrophysikalisches Institut und Universitäts-Sternwarte (AIU Jena, Germany) Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 2 / 118

Change record

Issue Date Update sections Reason / remarks Draft 0.3 05/01/2006 all ﬁrst draft (PKe) 1.0 30/01/2006 all validation (FMa) Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 3 / 118

Table of contents

Change record 2

Executive summary 7

1 Introduction 9 1.1 Scope of the document ...... 9 1.2 VLTi Spectro-Imager objectives ...... 9 1.3 VLTI infrastructure ...... 10 1.4 Context ...... 11 1.4.1 Pre-phase A studies, EII colloquium ...... 11 1.4.2 Presentation to the 60th meeting of the ESO Science Technical Committee ...... 11 1.4.3 Consortium ...... 12 1.4.4 International complementarity and competition ...... 13 1.5 Glossary ...... 13 1.6 References ...... 13 1.6.1 Applicable and Reference Documents ...... 13 1.6.2 Abbreviations and Acronyms ...... 15

2 Science cases 17 2.1 Summary from science cases ...... 17 2.1.1 The formation of stars and planets ...... 17 2.1.2 Imaging stellar surfaces ...... 17 2.1.3 Evolved stars, stellar remnants & stellar winds ...... 18 2.1.4 Active galactic nuclei & supermassive black holes ...... 18 2.2 Comparison with existing instrument capabilities ...... 18 2.3 Astrophysical speciﬁcations ...... 19 2.4 Required tasks for Phase A ...... 19 2.4.1 Top level requirements ...... 19 2.4.2 Operational model ...... 20 2.4.3 Image reconstruction ...... 20 2.4.4 Science cases ...... 20

3 System analysis 21 3.1 High level speciﬁcation ...... 21 3.1.1 The imaging paradigm ...... 22 3.1.2 Recall: VLTI infrastructure ...... 22 3.1.3 Image complexity ...... 23 3.1.4 Dynamic range ...... 23 3.1.5 Spectral coverage and dispersion requirement ...... 23 3.1.6 Limiting magnitude ...... 23 3.1.7 Field of view ...... 23 3.1.8 Time resolution ...... 24 3.2 VLTi Spectro-Imager external constraints ...... 24 3.2.1 Atmospheric refraction and dispersion ...... 24 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 4 / 118

3.2.2 Atmospheric dispersion ...... 25 3.2.3 Field of View ...... 25 3.2.4 Pupil properties ...... 25 3.2.5 Beam optical quality ...... 25 3.2.6 OPD ...... 25 3.2.7 Polarization ...... 25 3.2.8 VLTI throughput ...... 26 3.3 Functional analysis ...... 26 3.3.1 Atmospheric dispersion compensator ...... 26 3.3.2 Spatial ﬁltering ...... 27 3.3.3 Optical path scanner ...... 28 3.3.4 Wavefront correction ...... 28 3.3.5 Beam injection ...... 28 3.3.6 Fringe tracking ...... 29 3.3.7 Beam combination ...... 30 3.3.8 Polarization control ...... 31 3.3.9 Spectral dispersion ...... 32 3.3.10 Detection ...... 32 3.3.11 Control software ...... 33 3.3.12 Data processing ...... 33 3.3.13 Image reconstruction ...... 33 3.3.14 Calibration and alignment tools ...... 33 3.4 Expected performances ...... 34 3.5 VLTi Spectro-Imager and PRIMA ...... 34 3.6 General system studies ...... 34 3.7 Summary of required tasks for phase A ...... 34 3.7.1 Wavefront Quality ...... 34 3.7.2 Spatial ﬁlter module ...... 35 3.7.3 Optical path compensation ...... 35 3.7.4 Beam injection module ...... 35 3.7.5 Beam combination module ...... 35 3.7.6 Fringe tracker ...... 35 3.7.7 Polarization control ...... 35 3.7.8 Spectrometer ...... 35 3.7.9 Detector ...... 35 3.7.10 Data Reduction ...... 35 3.7.11 Image Reconstruction ...... 36 3.7.12 Calibration requirements ...... 36 3.7.13 Performances ...... 36 3.7.14 PRIMA ...... 36 3.7.15 Global System Studies ...... 36

4 Beam combiner conceptual design: Integrated Optics solution 38 4.1 Overall description ...... 38 4.2 Atmospheric dispersion compensator ...... 38 4.3 Beam injection module ...... 40 4.4 Spatial ﬁltering ...... 40 4.5 Integrated Optics science beam combiners ...... 41 4.5.1 IO combiners ...... 41 4.5.2 Combining concept ...... 41 4.5.3 Preliminary results ...... 41 4.5.4 IO combiner mechanical support ...... 42 4.5.5 Phase A studies ...... 42 4.6 Polarization control ...... 43 4.7 Spectrograph and detector ...... 44 4.7.1 Spectrograph ...... 44 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 5 / 118

4.7.2 Detector ...... 45 4.7.3 Cryostat ...... 45 4.8 Calibration and alignment tools ...... 45 4.8.1 Calibration tools ...... 45 4.8.2 Alignment tools ...... 46 4.9 Degrees of freedom ...... 46 4.10 Software ...... 46 4.10.1 Control command ...... 46 4.10.2 Data reduction ...... 47 4.11 Additional functionalities ...... 47 4.11.1 Option 6T/8T ...... 47 4.11.2 Beam shaper with adaptive optics ...... 48 4.12 General means ...... 49 4.13 Interfaces ...... 49 4.13.1 VLTI interfaces ...... 49 4.13.2 Subsystem interfaces ...... 50 4.14 Phase A tools ...... 50 4.14.1 Experimental setup ...... 50 4.14.2 Numerical simulator ...... 50 4.15 Required tasks for phase A ...... 50 4.15.1 Atmospheric dispersion compensator ...... 51 4.15.2 Injection module ...... 51 4.15.3 Beam combiner ...... 51 4.15.4 Polarization control ...... 51 4.15.5 Spectrograph ...... 51 4.15.6 Detector ...... 51 4.15.7 Data reduction ...... 51 4.15.8 Additional functionalities ...... 51

5 Beam combiner conceptual design: Bulk Optics solution 54 5.1 Overall description ...... 54 5.2 Atmospheric dispersion compensator ...... 56 5.3 Alignment/calibration module ...... 56 5.4 Beam switchyard ...... 56 5.5 Bulk Optics science beam combiner ...... 56 5.6 Path modulators ...... 57 5.7 Spatial ﬁltering/Beam injection module ...... 57 5.8 Detector and Spectrograph ...... 57 5.9 Software ...... 57 5.10 Other tasks ...... 57 5.11 Interfaces ...... 58 5.12 Required tasks for phase A ...... 58 5.12.1 Beam switchyard ...... 58 5.12.2 Beam combiner ...... 58 5.12.3 Path modulators ...... 58 5.12.4 Spatial ﬁltering/Beam injection module ...... 58 5.12.5 Other tasks ...... 58

6 Internal fringe tracker conceptual design 59 6.1 Role of the fringe tracker ...... 59 6.1.1 Fringe acquisition ...... 59 6.1.2 Hardware phase tracking ...... 59 6.1.3 Hardware coherencing ...... 60 6.2 System analysis ...... 60 6.3 Dichroics ...... 61 6.4 Beam switchyard ...... 61 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 6 / 118

6.5 Fringe-tracking combiner ...... 62 6.6 Fast pathlength modulators ...... 62 6.7 Low-resolution spectrograph and detector ...... 62 6.8 Control system ...... 62 6.8.1 User interface ...... 63 6.8.2 Quasi-static control of motorised elements ...... 63 6.8.3 Real-time servo loops ...... 63 6.8.4 Mode switching ...... 63 6.8.5 Data archiving ...... 63 6.9 OPD corrector ...... 63 6.10 Required studies for Phase-A ...... 64 6.10.1 System analysis ...... 64 6.10.2 Dichroics ...... 64 6.10.3 Low-resolution spectrographs and detectors ...... 64

7 Preliminary development plan 65 7.1 Project organization ...... 65 7.2 Manpower ...... 66 7.2.1 Required manpower for VLTi Spectro-Imager ...... 66 7.2.2 Estimation of the available manpower in the consortium ...... 68 7.3 Tentative planning ...... 68 7.4 Documentation and deliverable ...... 70 7.5 Financial budget ...... 70 7.5.1 Cost evaluation ...... 70 7.5.2 Financial contributions ...... 71 7.6 Requirements on VLTI infrastructure ...... 71

8 Phase-A management plan 73 8.1 Scope of the chapter ...... 73 8.2 Organization of the phase A study ...... 73 8.3 Planning of the phase A ...... 74 8.4 Financial needs ...... 74 8.5 Summary of phase A studies ...... 75 8.6 Consortium contribution to the studies ...... 75 8.7 Phase A deliverable ...... 75

A Experience from the proposing consortium 81 A.1 Laboratoire d’Astrophysique de Grenoble ...... 81 A.2 Cavendish Laboratory, University of Cambridge ...... 83 A.3 Infrared Interferometry Group at the Max-Planck Institute for Radioastronomy ...... 84 A.4 Centro de Astrof´ısicada Universidade do Porto ...... 85 A.5 Istituto Nazionale di Astrofisica ...... 86 A.6 Institut d’Astrophysique et de Géophysique de Liège ...... 87 A.7 Institut für Astronomie, UniversitätWien ...... 88 A.8 Astrophysikalisches Institut und Universitäts-Sternwarte ...... 89

B Bibliography 91 B.1 Astrophysical drivers ...... 91 B.2 Optical interferometry and related techniques ...... 94 B.3 Instrumental projects ...... 101 B.4 Observations and Interpretation ...... 108 B.5 Other technical papers ...... 116 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 7 / 118

Executive summary

VLTi Spectro-Imager is proposed as second generation VLTI instrument providing the ESO community with the capability of performing image synthesis at milli-arcsecond angular resolution. Image synthesis is the standard operation of radio and (sub-)mm interferometers. VLTi Spectro-Imager is the result of the merging of two previous concept studies, VITRUV and BOBCAT, led by Grenoble and Cambridge, respectively. They where previously presented at the ESO workshop in 2005 and at the 60th meeting of the ESO Science and Technical Committee. VLTi Spectro-Imager provides the VLTI with an instrument able to combine 4 telescopes in a baseline version and optionally up to 6 telescopes in the near-infrared spectral domain with moderate to high spectral resolution. The instrument contains its own fringe tracker in order to relax the constraints onto the VLTI infrastructure. VLTi Spectro-Imager will do imaging at the milli-arcsecond scale with spectral resolution of: a) the close environments of young stars probing the initial conditions for planet formation; b) the surfaces of stars; c) the environment of evolved stars, stellar remnants and stellar winds, and d) the central region of active galactic nuclei and supermassive black holes. The science cases allowed us to specify the astrophysical requirements of the instrument and to define the necessary studies of the science group for phase A. A preliminary system analysis of the VLTi Spectro-Imager, allowed us to clarify the high level specifications of the system, the external constraints and to perform a functional analysis. In particular, the instrument was separated into 14 functions, the context of PRIMA was addressed and the system tasks for the required phase-A study were defined. Two solutions for the science beam combiner where identified one based on integrated optics and another on bulk optics:

• The integrated optics science beam combiner solution has been validated with astrophysical results at high performance on IOTA and VLTI. It emphasizes the maintainability of the instrument (apart from the injection devices, there are no degrees of freedom left for the beam combination); it is well suited to feed a conventional infrared spectrograph; enhancing the number of telescopes from 4 to 6 just requires a different IO device which can be fed by different fibers and the duplication of 2 more injection modules. • The bulk optics science beam combiner solution has an emphasis on the commonality with the integrated optics solution. It is based on a 4-way working prototype in Cambridge. Although having a larger number of degrees of freedom, it has high optical throughput and interferometric contrast. To work with 6 telescopes, the beam combiner requires fast switching optics in order to select subsets of the input beams to feed the 4-way beam combiner. The 4 outputs of the beam combiner are injected in fibers to feed a similar spectrograph as the one designed for the IO solution.

These two solutions are inherited from the two concepts merged. One of the goals of the Phase A study is to define which of them will be used by the VLTi Spectro-Imager. VLTi Spectro-Imager have an internal fringe tracker which relaxes the constraints on the VLTI interfaces by allowing to servo optical path length differences of the input beams to the required level. An optical switchyard allows the operator to choose the best configuration of the VLTI co-phasing scheme in order to allow phase bootstrapping for the longest baseline on over-resolved objects. In this proposition, a preliminary development plan is presented, based on our system analysis to estimate the financial, manpower costs and the foreseen planning. The instrument has been divided in 6 subsystems for which 3 subsystem managers have already been identified. We think that we will be able to deliver the VLTi Spectro-Imager at Paranal by the end of 2010 for a budget of 3251 ke for the IO solution or 3173 ke for the bulk optics option, and, a Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 8 / 118 total of 54.8 FTE. Based on the Letters of Intent from the consortium institutes, we estimated that the consortium can provide at least 62 FTE. On the financial side, the institutes will submit proposals to their funding agencies. Minimum ESO contribution will be requested for procurements of ESO standard control boards and eventually for detectors and controllers of the science and the fringe tracker cameras. All scientific and technical chapters of the proposal end with a summary of the tasks to be fulfilled during the phase-A study. The organization proposed is based on a science group and a system group coordinated by a management team. Several meetings during the expected 9 months of the phase A are planned, for which we request 51ke to ESO. The estimation of the required manpower is 122 men-months matching the available man power of the consortium (as stated in the Letters of Intent). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 9 / 118

Chapter 1

Introduction

1.1 Scope of the document

This document describes a proposal to ESO for a second generation VLTI instrument in response to ESO Call for Phase-A Proposals for 2nd generation VLTI instruments published on the ESO web site [AD1]. The main driver for this call is long-baseline interferometry at the VLTI in the available 1-20 microns spectral regions, and aims at combining a number of telescopes between 4 and 6. What is expected in the Call for Phase A Proposal is reproduced below:

ESO requests the project to be conceived with the goal of developing end-to-end general use facilities, operated inside the ESO data flow system [REF3, Chap. 10] in place at Paranal and Garching and based on the VLTI interface description [AD2]. The project should underline the instrument concept, its capabilities and operating modes, with a basic description of calibration & data reduction strategy and a compelling scientific case, spelling out the significant astronomical advances that the proposed facility should permit. The response for the call for proposal should include a description of any technical area that would require significant R&D advances and/or prior prototyping, and the strategy to pursue it, and, a preliminary implementation plan and cost estimate. Of particular importance is to establish the likely availability of an adequate team to carry out the project, and possible time scale including the earliest starting date. Finally, the proposal should outline the requirements on the VLTI infrastructure, observing strategies, telescope configurations and observing time requirements required to conduct the key scientific programs.

The proposal for the VLTi Spectro-Imager is composed of 3 documents:

– The technical and managerial proposition [VSI-PRO-001, this volume]; – The science cases [VSI-PRO-002] which details the science objectives of the instrument; – The document which gathers all Letters of Intent [VSI-PRO-003] from the institutes involved in the consortium.

This document has been written with contributions from all participating institutes with main contributions from the Science Group, LAOG and Cavendish Laboratory.

1.2 VLTi Spectro-Imager objectives

The VLT interferometric facility is unique in the world, since it offers giant 8m telescopes, 2m auxiliary telescopes and the necessary infrastructure to combine them. With four 8m unit telescopes (UTs) equipped with adaptive optics systems, four 1.8m auxiliary relocatable telescopes (ATs) equipped with tip-tilt correction, a maximum separation of 130m for UTs and 200m for ATs, 6 available delay lines, slots foreseen for 2 more ones, a dual feed capability (PRIMA) and a complete system control, the VLTI is the best site to propose the first optical interferometer to deliver Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 10 / 118 routinely aperture synthesis images like the millimeter wave interferometers are already doing for more than 10 years. The quality of the images will be as good as the ones delivered by the IRAM Plateau de Bure Interferometer with six 15m antennas and a maximum baseline of 500m at 1-3mm. The VLTI will be for a long time the only facility with four 10m class telescopes able to provide 1mas angular resolution in optical wavelength. It is interesting to notice that the VLTi Spectro-Imager will have similar and even better resolution than ALMA of the order of 1 mas. We propose a spectro-imager for the VLTI aimed at taking the best profit of the imaging capability of the array, especially in the PRIMA framework. The science objectives of the instrument are focused on the kinematics and morphology of compact astrophysical objects at optical wavelengths like the environment of AGN, star forming regions, stellar surfaces and circumstellar environments. The instrument will aim at delivering aperture synthesis images with spectral resolution as the final data product to the astronomer. The baseline for the specifications is:

• beam combiners for 4T (speciﬁcation) and 6T (goal) operation, • a temporal resolution of the order of 1 day, • 2 or 3 spectral resolutions from 100 to 10000, • internal fringe tracking • image dynamics from 100 to 1000, • a ﬁeld of view corresponding to a few hundred of milli-arcsec • wavelength coverage from 1 to 2.5 microns

One of the interesting feature of this instrument is the possibility to use integrated optics technology (contemplated at this stage for the beam combination) because this proved technology offers simplicity, stability especially for phases, operational liability, and high performances. This technology was successfully validated on the 3 telescope IOTA interferometer where the system delivers routinely visibilities for 3 baselines and a closure phase (Monnier et al. 2004 [REF19]; Kraus et al. 2005 [REF18]) and at VLTI to replace the fiber coupler of VINCI (Le Bouquin et al. 2004 [REF21], 2005 [REF22]). However in the phase A study, we plan to compare the integrated optics solution (chapter 4) with the bulk optics one (chapter 4) not only on performances but also in terms of actual implementation and maintainability. A decision will be made during phase A. Our strategy is to provide an instrument which combines in a first phase 4 telescopes and secondly 6 telescopes. The design opens also the way to operation with the full VLTI array, i.e. 4 UTs and 4ATs, providing that 2 more delay lines are installed to fulfill the initial VLTI implementation plan.

1.3 VLTI infrastructure

The VLTI infrastructure is the one described by the VLT white-book [REF3] and updated in the appendix of the call for proposals [AD1]. The Very Large Telescope Interferometer (VLTI) oﬀers a facility with a collecting power signiﬁcantly greater than any other interferometer available at present or being planned at visible and infrared wavelengths. It is based on an array of the four identical, 8.2-m VLT Unit Telescopes (UT) and four dedicated 1.8-m Auxiliary Telescopes (AT). The main elements of the VLTI are:

• Four 8.2-m Unit Telescopes (UT), all with Adaptive Optics (AO) correction at their Coudéfocus. • Four 1.8-m Auxiliary Telescopes (AT). AO for ATs is being considered. • Six Delay Lines (DL) installed. Variable Curvature Mirrors (VCM) in the cat’s eye of the DL are used to relay the pupil. VCMs are currently operational on 2 DLs, and will be extended to all DLs. • two Differential Delay Lines (DDL) units have been contracted and are under development. • The Test instrument VINCI with an integrated optics beam combiner in the K-band (IONIC). • The mid-infrared two beam combiner MIDI in regular science operation. • The near-infrared three beam combiner AMBER in commissioning and offered in the Call for Proposals for science operations starting in October 2005. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 11 / 118

• A Fringe Tracker with on-axis guide star (FINITO) under extensive testing at Paranal. • A near-infrared tip-tilt sensor (IRIS) in the lab. • PRIMA is a dual-feed system to perform accurate relative phase measurements between objects separated by up to 1 arcminute. Star Separators Systems (STS) for two ATs and two UTs are under development; a third STS/UT (and possibly a fourth one) are externally ﬁnanced; Fringe Sensor Units (FSU) A&B in development. Metrology in development.

The call for proposal specifies that if properly justified by the scientific case, proposers may consider extensions to the above VLTI infrastructure in the scenarios of their Phase-A studies.

1.4 Context

1.4.1 Pre-phase A studies, EII colloquium

The project which we are presenting in this document does not come from nowhere. Some initial ideas have already been published in 2001 at the ESO workshop on Scientiﬁc Drivers for ESO Future VLT/VLTI Instrumentation1. These ideas have been developed since in several SPIE conferences. In the OPTICON FP6 European program, the European Interferometry Initiative (EII) Joint Research Activity (JRA) was proposed to focused on European interferometry development. Its main objective, namely Integrating interferometry into mainstream astronomy2, is to help preparing the future of European Interferometry including the VLTI. One of the work package, Advanced Instruments, is dedicated to the study of new generation instruments. In this framework, two concepts of near-infrared imager have been proposed:

• VITRUV [REF5] a concept for a near-infrared integrated optics combiner designed for imaging with 4 to 8 telescopes. • BOBCAT [REF9] a concept for a near-infrared (JHK) bulk-optics combiner designed for eﬃcient model-independent imaging of faint sources.

In April 2005, ESO in collaboration with EII has organized a workshop on The power of optical/IR interferometry: recent scientific results and 2nd generation VLTI instrumentation in Garching. The purpose of the Workshop was to present and discuss the additional instrumentation required in the next 5-8 years to optimize the scientific return of the VLTI. For the EII, this Workshop doubled as an internal reviewing process of the instrumental projects that were currently being studied as possible VLTI Instruments at the conceptual level in the frame of the Joint Research Activity #4 (Interferometry) of the OPTICON FP6 program (see above). On the ESO side, this was the starting point of the process for selecting and building 2nd generation VLTI instruments since the Scientific and Technical Committee (STC) of ESO has recommended the extension of PRIMA facility to more than 2 ATs and 2 UTs and the development of a 4-way fringe tracker. The instruments proposed through the JRA4 work package, in particular the two proposals VITRUV [REF10] and BOBCAT [REF11], were presented with addition of new instrument concepts. The result of this workshop has been sent to the ESO Science Technical Committee (STC) which decided that the next generation instruments should focus on infrared wavelength. It was the first step before the presentation at the 60th meeting of STC on 17 October 2005.

1.4.2 Presentation to the 60th meeting of the ESO Science Technical Committee

VITRUV and BOBCAT have then been presented to the committee together with two other instrumental concepts, MATISSE and GRAVITY. After deliberation, STC recommended to ESO:

The STC appreciates the presentations by the four groups working on second generation instruments for VLTI, and underlines the importance these instruments could have for the development of the VLTI programs in the next decade. In this framework, the STC acknowledge the relevance of instruments with

1See Haniﬀ & Buscher p. 293; Malbet et al. p. 303 2JRA4 see website at eii-jra4.ujf-grenoble.fr Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 12 / 118

imaging and spectroscopic capabilities for the near- and mid-IR, exploiting the extensive multi-beam capabilities of VLTI. The STC also recognize the importance of the science cases presented, including in particular the Galactic center case for general relativity, and those for star and planet formation, and active galactic nuclei. In these fields the unique characteristics of VLTI may allow important breakthroughs, that should not be unnecessarily delayed. The STC recommends that ESO solicit formal proposals for Phase A studies for next generation instruments with a deadline early in 2006, so that they can be reviewed by ESO in time for the April STC meeting. These proposals should address not only the scientific capabilities and technical descriptions of the proposed instruments, but also the requirements on the VLTI infrastructure, observing strategies, telescope configurations and observing time requirements required to conduct the key scientific programs. ESO should continue to engage with the instrument teams and encourage them to search for possible synergies between the different projects.

Preceding STC request, the VITRUV and BOBCAT teams met in October 2005 in Cambridge to discuss the possibility to collaborate. The merging of the two concepts was finalized in a meeting organized by ESO staff in November 2005 to find synergies among the different NIR concepts. The agreement was based on the fact that the two teams had complementary objectives in their instrument: integrated optics beam combination and control software for LAOG, and, bulk optics beam combination and fringe tracking for Cavendish Laboratory with a common interest in the system design. This is the basis of our common today proposition. Additionally, including fringe tracking in the instrument became a strong requirement. It can be seen also as a willing to relax the interfaces between the instrument and the VLTI infrastructure both in OPD but also in the quality of the incoming wavefront. By relaxing these constraints we think that the chances to have working up to 6 telescopes and DLs are largely increased. We do believe that this association between the two proposals is a very strong commitment that will help to define an instrument with the best instrumental design and performance, and, with the experience of the two groups. Given the limited amount of time, we chose to postpone some decisions on the system design to the phase A. Therefore the proposition which is made here is, for the moment, a mere juxtaposition of the two proposals where the common parts have to be worked out. We are conscious that this might be a weak point, but on the other hand merging the two concepts was also a strong requirement from STC and the ESO community. Anyhow, we tried as much as possible to have a common project path (for example see Chapter 3 in the system analysis), but for the conceptual design of the beam combiner we decided to separate the integrated optics solution from the bulk optics solution. As a matter of fact, depending on which solution is finally chosen, the organization of the project might change completely as indicated in the preliminary development plan (see Chapter 7).

1.4.3 Consortium

The main partners of this proposition are the ones which have been proposing VITRUV and BOBCAT, respectively LAOG/CAUP and Cavendish Laboratory. Since the 2005 ESO workshop, other partners have expressed their interests to be part of such a project. The name of the institutes are listed below, with their contact person:

– Laboratoire d’Astrophysique de Grenoble (France): Dr. F. Malbet – Cavendish Laboratory, University of Cambridge (United Kingdom): Dr. D. Buscher – Max-Planck Institut fürRadioastronomie in Bonn (Germany): Pr. G. Weigelt – Centro de Astrof´ısicada Universidade do Porto (Portugal): Dr. P. Garcia – Istituto Nazionale di Astrofisica (Italy): Dr. M. Gai – Institut d’Astrophysique et de Géophysique de Liège (Belgium): Pr. J. Surdej – Institut für Astronomie, UniversitätWien (Austria): Dr. J. Hron – Astrophysikalisches Institut und Universitäts-Sternwarte in Jena (Germany): Pr. R. Neuhäuser

More details about the competences, experience and resources of the diﬀerent institutes are given in Appendix A. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 13 / 118

1.4.4 International complementarity and competition

The VLTi Spectro-Imager will be competing with several other interferometers: the Keck interferometer when the outriggers will be operational, but also the CHARA and phase-I MROI arrays. The latter instruments however will be less sensitive because of smaller apertures, will provide less (u, v) coverage with 6 telescope, although their maximal baselines are about 10% to 75% longer. As the spectro-imaging instrument of PRIMA, the VLTi Spectro-Imager will have no other competitors for a few years. More quantitative details on the comparison with existing facilities are given in the science cases [REF1 and Chapter 2].

1.5 Glossary

In this section we clarify some key points of the instrument by deﬁning what we mean under speciﬁc terms.

– Beam combination. Beam combination is the heart of the instrument. This is the subsystem which is in charge to combine the different beams carried individually by the VLTI to the interferometric lab. By combining the beams, we can measure complex visibilities, that means the correlation of the electric field sampled by the different telescopes and gives the astronomer information on the spatial distribution of intensity of the source. – Visibilities. Visibilities are complex quantities which correspond to the value of the Fourier transforms of the spatial intensity distribution of the source sampled at different spatial frequencies (= baselines, i.e. pairs of telescopes, divided by the wavelength). The interferometric fringes are overimposed on the total photometric flux coming from all beams. A fringe is characterized by its period, its amplitude and its phase. The period of the fringe is given by the instrumental setup and is chosen in order to distinguish between the different pairs of telescopes. The fringe amplitude is measured in intensity unit whereas the phase is measured in radian. The visibility amplitude is the fringe amplitude normalized by the total photometric flux coming from the source. – Integrated optics. Integrated optics is a particular type of optics. It is part of guided optics which also includes fiber optics. Like in fiber optics, the light propagates in integrated optics devices within optical guides. But in addition integrated optics can perform different functions on the light: beam splitting, beam combination, mirrors, chromatic coupling,...in one single solid substrate. It is the analog of integrated circuits in micro- electronics, when fibers are the analog of electrical wires. – Bulk optics. Traditional optics where the light propagates freely in the air and the functions are applied by individual optical elements like lenses, mirrors, beam splitters,... – Fringe tracking. Due to atmospheric turbulence, the fringes are jittering: the optical path difference (OPD) between two telescopes varies because of the changes of the refractive index of the air both spatially and temporally. The result is that the fringes move. A fringe tracker is a subsystem which is able to measure the instantaneous phase of the fringes and send a command to an OPD actuator which will compensate the motion. When the loop is closed, the fringes are frozen. There are different flavors of fringe tracking, mainly phase tracking and group delay tracking (see Chapter 6). In phase tracking, one measures the phase and one ensures that the fringe does not move more than a small percentage of the fringe so that the science beam combiner can increase the SNR with long integration time. In group delay tracking, data is recorded only if the fringe is within the coherence length of the interferometer (a few fringes) and one ensures that it does not escape from this length. The requirements are less stringent than those for fringe tracking, but since the fringe is always present, the idea is to average many short exposures to increase the SNR. In the VLTi Spectro-Imager, we contemplate using both techniques so that we can have access both to high sensitivity (group delay tracking) and high spectral resolution on relatively bright objects (phase tracking).

1.6 References

1.6.1 Applicable and Reference Documents

[AD1] ESO call for Proposals http://www.eso.org/projects/vlti/instru/2ndgeneration/cfp-2ndgeneration-vlti-instruments.htm Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 14 / 118

[AD2] Interface Control Document between the VLTI and its instruments, VLT-ICD-ESO-15000-1826, Issue 4, date: 11/08/2005 http://www.eso.org/projects/vlti/instru/2ndgeneration/vlt-icd-eso-15000-1826 iss4.pdf

[REF1] VLTI Spectro-Imager - Science Cases VSI-PRO-002, Issue 1.0, Date: 27/01/2006 (companion document). [REF2] VLTI Spectro-Imager - Letters of Intent from the Institutes of the consortium VSI-PRO-003, Issue 1.0, Date: 26/01/2006 (companion document). [REF3] The VLT White Book http://www.eso.org/outreach/ut1fl/whitebook [REF4] PRIMA Reference Mission Report by the VLTI Implementation http://www.eso.org/gen-fac/commit/stc/stc-58th/8-STCPRIMA2004.pdf [REF5] VITRUV - Concept Study Report EII-JRA4 document, JRA4-TRE-1160-0001, Issue 1, date: 15/02/2005 http://eii-jra4.ujf-grenoble.fr/doc/approved/JRA4-TRE-1160-0001.pdf [REF6] VITRUV - Science cases EII-JRA4 document, JRA4-TRE-1160-0002, Issue 1, date: 03/2005 http://eii-jra4.ujf-grenoble.fr/doc/approved/JRA4-TRE-1160-0002.pdf [REF7] VITRUV - Preliminary Management Plan EII-JRA4 document, JRA4-TRE-1160-0003, Issue 1, date: 25/03/2005 http://eii-jra4.ujf-grenoble.fr/doc/approved/JRA4-TRE-1160-0003.pdf [REF8] VITRUV - Preliminary System Studies EII-JRA4 document, JRA4-TRE-1160-0004, Issue 1, date: 03/2005 http://eii-jra4.ujf-grenoble.fr/doc/approved/JRA4-TRE-1160-0004.pdf [REF9] Bulk-Optics - Concept Study Report EII-JRA4 document, JRA4-TRE-1120-0001, Issue 1, date: 03/03/2005 http://eii-jra4.ujf-grenoble.fr/doc/approved/JRA4-TRE-1120-0001.pdf [REF10] VITRUV - Imaging close environments of stars and galaxies with the VLTI at milli-arcsec resolution in Proc. of ESO/EII workshop on “ The power of optical/IR interferometry: recent scientific results and 2nd generation VLTI instrumentation” http://arxiv.org/abs/astro-ph/0507233 [REF11] BOBCAT - a photon-efficient multi-way beam combiner for the VLTI in Proc. of ESO/EII workshop on “ The power of optical/IR interferometry: recent scientific results and 2nd generation VLTI instrumentation” [REF12] AMBER ESO/VLTI Conceptual Design Review (AMB-REP-004) http://amber.obs.ujf-grenoble.fr/IMG/pdf/amb-rep-004.pdf [REF13] AMBER Instrument Analysis Report, VLT-TRE-AMB-15830-0001, Issue 2.0, DATE: 19/06/2001 http://amber.obs.ujf-grenoble.fr/PLAIN/pae/Documents FDR/Documents/1 TRE IAR.pdf [REF14] J.-B. Le Bouquin PhD thesis “Imagerie par synthèsed ouverture optique, application aux étoiles chimiquement particulières”. Part II: “Un spectro-polarimètre imageur au VLTI” http://www-laog.obs.ujf-grenoble.fr/ jblebou/These/these LeBouquin 2005.pdf [REF15] Improvements for group delay fringe tracking, Basden, A. G. and Buscher, D. F., MNRAS 357, 656 (2005) [REF16] Low light level limits to tracking atmospheric fringe wander Buscher, D.F., in “Quantum Limited Imaging and Information Processing”, 1989 Technical Digest Series (OSA), vol. 13, 67 (1989) Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 15 / 118

[REF17] An introduction to closure phase in Principles of long Baseline Interferometry, JPL Publication 00-009 07/00 http://olbin.jpl.nasa.gov/iss1999/coursenotes.html [REF18] Infrared Imaging of Capella with the IOTA Closure Phase Interferometer Kraus, S. et al., AJ 130, 246 (2005) [REF19] First Results with the IOTA3 Imaging Interferometer: The Spectroscopic Binaries lambda Virginis and WR 140, Monnier, J. -D., ApJ 602, L57 (2005) [REF20] The calibration of interferometric visibilities obtained with single-mode optical interferometers. Com- putation of error bars and correlations, Perrin, G., A&A 400, 1173 (2003) [REF21] First observations with an H-band integrated optics beam combiner at the VLTI, Le Bouquin, J.B. et al., A&A 424, 719 (2004) [REF22] Integrated optics for astronomical interferometry - VI. Coupling the light of the VLTI in K band, Le Bouquin, J.B. et al., A&A in press, astro-ph/0512544 (2006) [REF23] Fringe Visibility Estimators for the Palomar Testbed Interferometer, Colavita M.M., PASP 111, 111 (1999)

1.6.2 Abbreviations and Acronyms

ADC Atmospheric Dispersion Compensator AGN Active Galactic Nucleus AIT Assembly Integration and Tests AIU Astrophysikalisches Institut und Universitäts-Sternwarte in Jena ALMA Atacama Large Millimeter Array AMBER Astronomical Multi-BEam Recombiner AO Adaptive Optics APRES-MIDI Instrumental concept for an upgrade of MIDI AT Auxiliary telescopes (1.8m) AU Astronomical Unit BLR Broad-Line Regions BO Bulk Optics BOBCAT Bulk Optics Beam Combiner And Tracker, project of an instrument of second generation. CAUP Centro de Astrof´ısicada Universidade do Porto CHARA Center for High Angular Resolution Aastronomy CONICA COudéNear Infrared CAmera CRIRES Cryogenic High-Resolution IR Echelle Spectrometer DDL Differential Delay Lines DL Delay Lines EGP Extra-Solar Giant Planet EII European Interferometry Initiative ESO European Southern Observatory FDR Final Design Revew FINITO First generation fringe tracking unit FOV Field of View FP6 Sixth Framework Programme (European) FPA Focal Plane Array FSU Fringe Sensor Unit FT Fringe Tracker FTU Fringe Tracker Unit FTE Full Time Equivalent FWHM Full Width at Half Maximum Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 16 / 118

GRAVITY One of the proposed concepts for the 2ng generation VLTI instrument HR Hertzsprung-Russell (effective temperature-luminosity diagram) HST Hubble Space Telescope IAGL Institut d’Astrophysique et de Géophysique de Liège ICD Interface Control Document IfA Institut für Astronomie, UniversitätWien INAF Istituto Nazionale di Astrofisica IO Integrated Optics IONIC Integrated Optics Near-Infrared Combiner IOTA Infrared Optical Telescope Array IR Infra-Red IRAM Institut de Radio-Astronomie Millimétrique IRIS Infra-Red Image Sensor JMMC Jean-Marie Mariotti Center JRA Joint Research Activity KI Keck Interferometer LAOG Laboratoire d’Astrophysique de l’Observatoire de Grenoble LCU Local Control Unit LETI Laboratoire d’Electronique et de Technologies de l’Information LN2 Liquid Nitrogen MATISSE One of the proposed concepts for the 2ng generation VLTI instrument MHD Magneto-Hydro-Dynamics MIDI MID-Infrared VLTI first generation instrument MOS Multi-Object Spectroscopy MPIfR Max-Planck Institut fürRadioastronomie MROI Magdalena Ridge Observatory Interferometer MS Main Sequence NACO NAOS/CONICA NAOS Nasmyth Adaptive Optics System NGST New Generation Space Telescope NIR Near Infrared NPOI Navy Prototype Optical Interferometer OPD Optical Path Difference OPTICON Optical Infrared Coordination Network for Astronomy PAE Preliminary Acceptance Europe PdBI Plateau de Bure Interferometer PDR Preliminary Design Revew PMS Pre-Main Sequence PNe Planetary Nebulae PRIMA Phase-Reference Imaging and Micro-arcsecond Astrometry PSF Point Spread Function RV Radial Velocity SINFONI Spectrograph for INtegral Field Observations in the Near Infrared SNR Signal to Noise Ratio SPIE International Society for Optical Engineering SR Strehl Ratio STC Science and Techincal Committee STS Star Telescope Separator TBC To Be Confirmed TBD To Be Defined TBW To Be Written UT Unit Telescope (8m) VCM Variable Curvature Mirror VINCI VLT Interferometer Near-Infrared Commissioning Instrument VITRUV Not an acronym. Project of an instrument of second generation. VLT Very Large Telescope VLTI Very Large Telescope Interferometer WBS Work Breakdown Structure WFS Wavefront Sensor Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 17 / 118

Chapter 2

Science cases

2.1 Summary from science cases

VLTi Spectro-Imager concept is a general purpose instrument aimed at exploiting the full capability of the VLTI infrastructure including the faint science space enabled by PRIMA. VLTi Spectro-Imager is up to 5 times faster than current interferometric instrumentation (AMBER) because it combines up to 6 telescopes. The wavelength range is JHK. Three spectral resolutions are available ∼100, ∼1000 and ∼10000. The dynamic range of the reconstructed images is 10-100 with a goal of 100-1000. There is a goal of retaining polarization information. The current science cases deﬁnition methodology was to concentrate in a few ﬁelds where VLTi Spectro-Imager can make a substantial contribution, without being exhaustive. In this respect the PRIMA reference mission document [REF4] is highly complementary to this one. A detailed presentation of the science cases is given in “Science Cases - VSI-PRO-002” [REF1] accompanying this document. The main science cases for VLTi Spectro-Imager are listed below.

2.1.1 The formation of stars and planets

The early evolution of stars and the initial conditions for planet formation are determined by the interplay of accretion and outﬂow processes. Due the small spatial scales where these processes engines actuate, very little is known about the actual physical and chemical mechanisms at work. Interferometric imaging at 1 mas (milli-arcsecond) will directly probe the regions responsible for the bulk of continuum emission excess from these objects therefore constraining the currently highly degenerate models for the spectral energy distribution. In the emission lines a variety of processes will be probed, in particular outﬂow and accretion magnetospheres. The inner few AUs of evolved planetary systems will also be studied, providing additional information on their formation and evolution processes, as well as on the physics of extrasolar planets.

2.1.2 Imaging stellar surfaces

Optical imaging instruments are a powerful means to resolve stellar features at the generally patchy surfaces of stars throughout the HR diagram. Optical interferometry has already proved its ability to derive surface structure parameters such as limb darkening or others atmosphere parameters. VLTi Spectro-Imager, as an imaging device, is of strong interest to study various speciﬁc features as vertical and horizontal temperature proﬁles, abundance inhomogeneities and detect their variability as the star rotates and pulsates. This will provide important keys to address stellar activity processes, mass-loss events, magneto-hydrodynamic mechanisms, pulsation and stellar evolution. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 18 / 118

Figure 2.1: Left: VLTi Spectro-Imager’s place within the ESO instrumentation/facilities suite. Right: compared timelines for VLTi Spectro-Imager and other relevant instruments/facilities.

2.1.3 Evolved stars, stellar remnants & stellar winds

HST and ground-based observations revealed that the geometry of young and evolved PNe and related objects (e.g. nebulae around symbiotic stars) show an incredible variety of elliptical, bi-polar, multi-polar, point-symmetrical, and highly collimated (including jets) structures. The proposed mechanisms explaining the observed geometries (disks, MHD collimation and binarity) can only be tested by interferometric imaging at 1 mas resolution. Extreme cases of evolved stars are stellar black holes. In microquasars the stellar black-hole accretes mass from a donor. The interest of these systems lies in the small spatial scales and high multi-wavelength variability. Milli- arcsecond imaging in the NIR will allow disentangling of dust from jet synchrotron emission, compare the observed morphology with radio maps and correlate it with the variable X-ray spectral states.

2.1.4 Active galactic nuclei & supermassive black holes

AGN are complex systems composed of different interacting parts powered by accretion onto the central supermassive black hole. The imaging capability will allow study of the geometry and dust composition of the obscuring torus, testing radiative transfer models. Milli-arcsecond resolution imaging will allow to probe the collimation at the base of the jet and the energy distribution of emitting particles. Supermassive black holes masses in nearby (active) galaxies can be securely measured and it will be possible to detect general relativistic effects for the stellar orbits closer to the galactic center black hole. The wavelength-dependent differential-phase variation of broad emission lines will provide strong constraints to the size and geometry of the Broad Line Region. It will then be possible to establish a secure size-luminosity relation for the BLR, a fundamental ingredient to measure supermassive black hole masses at high redshift.

2.2 Comparison with existing instrument capabilities

Figure 2.1 places VLTi Spectro-Imager in the context of the ESO instrumentation/facilities, as well as of other scientifically relevant past/present/future ground-based and space facilities. The general purpose spectral range and resolution of VLTi Spectro-Imager combined with its 2-5 times higher efficiency makes it a natural successor to AMBER. This second generation VLTI instrument will fully exploit the faint science parameter space opened up by PRIMA. VLTi Spectro-Imager imaging complements spectroscopy with adaptive optics angular resolution (NACO, SINFONI), as well as spectro-imaging with ALMA. It will provide a zoom-in capability on parts of a target that Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 19 / 118 remain unresolved by AO and/or ALMA, which is often critical for the interpretation of the large scale imaging and spectroscopy. Once equipped with VLTi Spectro-Imager, the VLTI will be more capable than any competing near-infrared imaging array. For example, the VLTI will be much more sensitive than NPOI, and will provide better image fidelity than CHARA and the Keck Interferometer, thanks to its relocatable ATs. With regard to future arrays, the augmented VLTI will be more than competitive with the six-telescope MROI Phase I since the inclusion of the larger diameter UTs will provide better sensitivity.

2.3 Astrophysical speciﬁcations

The top level astrophysical speciﬁcations identiﬁed at this stage are:

• Three spectral resolution modes: ∼100, ∼1000, ∼10 000. • Three imaging modes: parametric (no images and only a list of visibility measurements including V2, closure phase, diﬀerential phase or visibility phase), snapshot imaging (dynamic range up to ∼100), high dynamic range imaging (up to ∼1000). • Field of view a few times the diﬀraction limit of a UT: ∼0.1 arcsec. • Limiting K magnitude of at least 13 at low spectral resolution.

2.4 Required tasks for Phase A

The science cases and astrophysical specifications presented form a framework where VLTi Spectro-Imager is a plausible instrument with an outstanding scientific potential. However, they remain in some aspects very qualitative and incomplete. It is therefore clear that a Phase-A study is required. It should focus, quantify and complete the present science cases, top level requirements, operational model and image reconstruction. In the following subsections, we pass in review the science group tasks for the Phase-A study already identified allowing a more precise and systematic approach than the current document.

2.4.1 Top level requirements

The following tasks quantify the instrument top level requirements.

[Task 1] Define the three spectral resolution modes The science cases identified a low, intermediate and high spectral resolution modes. The exact values for the instrument resolutions setup will be defined balancing sensitivity and parametric versus imaging modes. [Task 2] Calibrators Identify calibrators that allow baseline bootstrapping (can calibrate large/small simultaneous baselines). Statistical study of faint calibrators and very large baseline calibrators. [Task 3] Define the maximum time in which an image must be taken Limiting factors can be the movement of the object (e.g. binary rotation) or connected to calibration issues. [Task 4] Define data products There are two possible end data products for the instrument: a) calibrated spectrally dispersed visibilities/(closure) phases and b) data cubes. Is b) viable? What is the use of the ALMA experience? [Task 5] Polarization Will linear polarization be a data product? Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 20 / 118

2.4.2 Operational model

[Task 6] Observing modes We can anticipate three observing modes: parametric visibility, snapshot image, high dynamic range image. How do they translate in terms of operations and calibrations? [Task 7] Complementary observations Pre-imaging is a natural precursor observation to MOS observations. Is AO pre-imaging required for our science? How important are the incoherent/coherent contributions for image reconstruction? How contemporary must it be? Same question applies to (spectro)photometry. [Task 8] Target of opportunity The feasibility of a target of opportunity mode will be assessed.

2.4.3 Image reconstruction

The following tasks have to be shared between the science and system groups. We will accomplish these tasks thanks to a strong connection to the JMMC image reconstruction group and thanks to the EII-JRA4 eﬀort.

[Task 9] Science image strategy Deﬁne array conﬁgurations, imaging time requirements, number of simultaneous telescopes used, dynamic range and image quality. [Task 10] Image reconstruction algorithm selection Several image reconstruction algorithms are already developed in the context of optical interferometry within the consortium. They should bench-marked and one of them will be selected for open use. [Task 11] AO data How can the AO data be used for the image reconstruction process? Study data combination with AO and other interferometers. [Task 12] FOV and mosaicing Identify the required FOV and the viability of mosaicing.

2.4.4 Science cases

[Task 13] Define legacy programmes The science case will be focused in a few (∼10) key legacy programmes in representative areas of astrophysics. These programmes can be undertaken under GTO, large programme or public survey mode. [Task 14] Target lists For each programme, target lists will be built including relevant information (e.g. position, multi-band magnitude, spectra, variability, geometry, statistical significance) for the end-to-end simulation. [Task 15] Generate synthetic images Radiative transfer models (in the lines or continuum), hydrocode simulations or simple geometrical models will be used to generate synthetic images for the science cases. [Task 16] End-to-end simulation and feedback The target information and an end-to-end simulation tool will allow to feedback the analysis on: a) attainability of scientific goals; b) top level requirements; c) operational model. [Task 17] Identify preparatory programmes relevant for the instrument Preparatory programmes for the instrument using AMBER/SINFONI/NACO/CRIRES with an intrinsic scientific potential will be identified and pursued. [Task 18] Complementary and competition Quantify the level of competition from other optical interferometers (MROI, CHARA) and complementary from existing/planned ESO/space instrumentation. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 21 / 118

Chapter 3

System analysis

We have carried out a system study aimed at defining a preliminary conceptual design for a multipurpose near-infrared spectro-imager for the VLTI. These studies, matching as much as possible the science case requirements, have raised several mandatory questions that will have to be addressed during the phase A study. The simple idea behind this work is to provide the astronomical community with an efficient spectro imager able to fulfill a broad science program. One additional important constraint has been and will be continuously taken into consideration: the requirement that VLTi Spectro-Imager should be an easy to maintain instrument. This system study has taken benefit of the extensive experience of members of the consortia past experience in previous successful facilities and instruments (e.g. COAST, AMBER/VLTI, IONIC/IOTA and IONIC/VLTI). In the initial VITRUV study the fringe tracking instrument was not included, BOBCAT study included it. It appears that the capability of VLTi Spectro-Imager to carry out its science program depends heavily on the VLTI ability to cophase its telescopes. We have therefore considered that a phase-A study should include an analysis of what is expected as far as VLTI cophasing is concerned. As required by the call for proposal, the VLTi Spectro-Imager is conceived with the goal of developing end-to-end general use facility. In the following four chapters, we describe the instrument system analysis and a preliminary conceptual design encompassing hardware description, science capabilities, calibration strategy and data reduction strategy.

3.1 High level speciﬁcation

Although the initial work done by the science group has allowed us to better constrain what should be the range of performance of VLTi Spectro-Imager further work is needed, the science case phase-A study will have to answer the following questions that will directly impact the instrument observing modes.

1. expected image complexity; 2. dynamic range; 3. spectral coverage and dispersion requirement; 4. limiting magnitude; 5. ﬁeld of view; 6. time resolution (i.e duration to obtain an image);

This in turn will allow the system study to deﬁne high-level technical requirements. These requirements will concern mainly

1. what is the level of (u,v) coverage expected to access to a given complexity; Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 22 / 118

2. what is the level of visibility and phase (closure-phase) accuracy expected; 3. what is the level of array cophasing accuracy that is expected.

At the time of the study we consider that the VLTi Spectro-Imager should be able to combine four telescopes as a basic requirement but should include a detailed description of its ability to combine six telescopes (goal). In the following subsections we recall what can be said about the diﬀerent science requirements from the system study.

3.1.1 The imaging paradigm

VLTi Spectro-Imager is intended to be an imager with spectral resolution. The final astronomical product should therefore be an image at each spectral channel. VLTi Spectro-Imager will be able to measure sufficient visibilities and phase information to permit model-independent image reconstruction. This puts a strong constraint on the number of (u,v) points for which one needs to obtain visibility, closure phase and differential-phase measurements. In particular increasing the number of telescopes has an immediate impact on the amount of phase information that can be retrieve through the use of closure phases quantities. The importance of retrieving phase information is considerable and three options arise:

1. using a second source as a phase reference; 2. using the closure phase technique; 3. in peculiar cases using spectral diﬀerential phases;

The closure-phase technique [REF17] allows us to retrieve atmosphere-free phase information. In a standard interferometer absolute phase information is lost due to multiple wave-front perturbations, (optomechanical instability, atmospheric piston). Using combination of at least three telescopes allows to extract the so-called closure-phases by summing up each baseline interferogram phases. This summation cancels out all the parasitic phase perturbation and produces the closure phase. Figure 3.1 shows how using an increasing number of telescopes allows to reduce the amount of phase information difference between phase and closure phases. Although extracting phase information from closure phase measurements is a tough work a considerable amount of research to find efficient algorithms has been carried (radio) and is still underway. We believe that the considerable relaxation of instrumental/operation constraints introduced by the use of closure phase quantities instead of phases is worth the already successful effort to find numerical ways to reduce the degeneracy when phases are extracted from closure phases. Of course the possibility of accessing directly to phase measurements is very interesting and the phase-A study should include a detailed study of the impact of phase vs. closure phase measurements on the final image reconstruction capability. However we can anticipate that the gain in terms of image quality due to the use of phase instead of closure phase might not be as important as the gain due to the increase in the number of telescopes. See figure 3.2 and caption for an illustration. It should be remembered that imaging with the VLTI, which requires a good level of cophasing will have an important impact on VLTI operation.

3.1.2 Recall: VLTI infrastructure

VLTI can provide 4 UT telescope and 4 AT telescope. Six delay lines are available. Our starting point is considering that VLTi Spectro-Imager should be able to manage the combination of four telescopes. An additional mode where VLTi Spectro-Imager can combine six telescopes to take full beneﬁt of the current infrastructure will be also considered. This latter should not be taken lightly since the impact on imaging capability of switching from 4T to 6T is considerable. VLTI oﬀers the possibility of phase referencing thanks to the PRIMA mode. Two Star Separator Systems (STS) are already available but two additional ones are foreseen (see Sect. 1.3). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 23 / 118

Percentage of phase information 100

200

Phases 50

100

Independent closure phases

0 0 5 10 15 20

Number of telescopes

Figure 3.1: Percentage of phase information that can be theoretically recovered from the use of closure phases alone. Histograms show respectively the number of independent closure phases and phases as a function of the number of telescopes. Filled line shows the ratio of closure phases over phases.

3.1.3 Image complexity

Image complexity depends directly on the ability to cover the (u,v) plane with a great number of independent visibility, phase/closure phases measurements.

3.1.4 Dynamic range

The science case has determined that imaging with a dynamic range of 100 should allow to full ﬁll a signiﬁcant fraction program. The conditions at which a dynamic range of 1000 can be reached should be studied.

3.1.5 Spectral coverage and dispersion requirement

The science case study has defined operation at J, H and K bands with two to three spectral resolution spanning the [100,10000] domain as the minimum configuration. Some programs in the different legacy surveys may require R≈ 30000.

3.1.6 Limiting magnitude

Currently the faintest objects contained in the science case have magnitudes of H,K ≈ 14.

3.1.7 Field of view

The science case is mainly focused towards “compact” sources i.e sources that are not individually resolved by the UTs at their diffraction limit. Currently most of the science programs require a field of view no bigger than 0.2”. During phase A the science group will have to define: Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 24 / 118

Figure 3.2: : Image reconstruction from simulated high-SNR data of an elliptical star with a companion which is approximately 3.4 magnitudes fainter than the primary. The upper images are reconstructed from simulated data using the beams from only 4 telescopes (i.e 6 instantaneous baselines), while the lower images are reconstructed from an array of 6 telescopes (i.e 15 instantaneous baselines). In each case an earth-rotation synthesis of 6 hours duration was simulated. The leftmost images are reconstructed from uncorrupted phase data, simulating data from a phase reference system, while the rightmost images are reconstructed from closure-phase data. All images have the same greyscale levels. It can be seen that the diﬀerence between images reconstructed from 4-telescope data and those reconstructed from 6-telescope data is far greater than the diﬀerence between images constructed from phase-referenced data and from closure phase data.

• if the sources are indeed unresolved by individual apertures; • the interest in increasing the field of VLTi Spectro-Imager, so that it is able to map extended structures (in the sense of bigger than individual diffraction fields of view).

3.1.8 Time resolution

VLTi Spectro-Imager will be able to provide an image within one night. However the phase A science study should take into consideration the impossibility to move the telescope configuration during the night (especially with four telescopes) and should evaluate the impact on science of observing the same object with different configurations obtained at different epochs. Currently preliminary science cases has pointed out objects with intrinsic variability ranging from 1 hour to 1 month.

3.2 VLTi Spectro-Imager external constraints

3.2.1 Atmospheric refraction and dispersion

Since stellar light passes through a prism of atmosphere, the different wavelengths are refracted with different angles that depend upon zenithal angle. These refraction angles significantly vary from a spectral band to another, and even through a spectral band, as detailed and shown in the AMBER studies [REF13]. So, the resulting image spots in the J and H bands are spectrally dispersed and thus appear elongated of an order of a few Airy disks. In the particular Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 25 / 118 case of a single-mode instrument this leads to a coupling efficiency degradation at the extreme wavelengths of these bands. Another consequence lies in the fact that the angle between the beam direction provided by the adaptive optics device to the image sensor and the direction of the actual observing wavelength varies with time, inducing a variation of the coupling efficiency.

3.2.2 Atmospheric dispersion

Since stellar light does not follow the same horizontal optical path in the air, an optical path diﬀerence (OPD) proportional to the interferometric baseline and to the projection of the zenithal angle on the meridian plane exists. As computed in the AMBER studies [REF13], this eﬀect is rather negligible with the exception of long baselines and at low spectral resolution. In these cases, visibility loss can reach several percents but quickly decrease with spectral resolution. Moreover the corresponding bias can be well modeled.

3.2.3 Field of View

Whatever the telescopes, the unvigneted field of view (FOV) at the instrument input has a diameter of 2”. The ESO facility PRIMA allows a dual-feed mode with two FOV of 2”, separated by an Airy disk at least and picked up anyway on the global Coudéfield of 2’ [AD2].

3.2.4 Pupil properties

Whatever the instrumental conﬁguration, the pupil at the instrument input has a diameter of 18 mm. Thanks to the Variable Curvature Mirrors, the pupil can be re-imaged at any location in the focal lab with a precision of ± 6.4 mm with the UTs, and of ± 125 mm with the ATs in the single feed mode. The nominal lateral position lies 1.46 ± 0.01 m above the lab ﬂoor level and depends upon the considered beam. The lateral distance between beams equals 240 mm. Accuracy and stability of these pupil positions are provided in [AD2].

3.2.5 Beam optical quality

The typical tip-tilt error budget provides errors smaller than 21 mas rms on the sky with the UTs, and than 30 mas rms on the sky with the ATs, in the single feed mode. Details on tip-tilt corrections and wave front error corrections are given in [AD2]. Based on the current experience with AMBER it seems reasonable to reassess the tip/tilt performances at VLTI in order to determine the need for an additional module integrated to VLTi Spectro-Imager that would allow additional tip/tilt and/or higher order modes adjustment.

3.2.6 OPD

The VLTI has been designed to be intrinsically stable and, without fringe tracking, internal VLTI OPD ﬂuctuations of 338 nm in K band are expected for an exposure time of 48 ms [AD2].

3.2.7 Polarization

The VLTI has been designed to minimize the differential polarization effects thanks to symmetric optical trains. Nevertheless due to multiple reflections in each arm, various optical coatings, aging of these coatings, etc. residual polarization effects as partial polarization and phase shifts between the two perpendicular directions of linear polarization and/or between two different interferometric arms remain. Estimations are provided in the ICD [AD2]:

• partial polarization rate of 10%, • absolute linear retardation in one arm lower than 100◦ in H band and than 80◦ in K band: cross talks between linear and circular polarizations can occur throughout the propagation along the optical train, Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 26 / 118

• diﬀerential linear retardation between two arms smaller than 20◦ in H band and than 10◦ in K band: instrumental polarization induces a slight instrumental contrast decrease (smaller than 1.5% in H band and than 0.4% in K band).

3.2.8 VLTI throughput

The VLTI throughput with the UTs and the ATs equals from 20% up to 35% over the J, H and K bands, according to the wavelength and the optical conﬁguration [AD2].

3.3 Functional analysis

We have carried out a sub-system breakdown in order to define for each of the instrument functions what were the studies that had to be addressed during the phase A study. At the current level of the study we have not merged any of the two different concepts (BOBCAT and VITRUV) but we can reasonably agree on the following subsystem breakdown illustrated in Fig. 3.3. As we will see in next chapter the preliminary conceptual designs arising from that are quite different and the phase A study will have to define the best concept. The VLTi Spectro-Imager 14 subfunctions are made of:

1. atmospheric dispersion compensator; 2. spatial ﬁltering; 3. wavefront correction; 4. fringe tracking; 5. optical path scanner; 6. beam injection; 7. beam combiner; 8. polarization control; 9. spectral dispersion; 10. detector; 11. data processing; 12. calibration and alignment tools;. 13. control module; 14. image reconstruction.

It should be stated that some of the previous subsystems might be irrelevant depending on the ﬁnal beam combination concept adopted. Also the fringe tracking instrument should be seen as an instrument by itself (see section 3.3.6).

3.3.1 Atmospheric dispersion compensator

While the atmospheric refraction is quite negligible for the K band, it has been shown in section 3.2.1 that the effect is more critical in the J and H band. The scientific instrument operating one band at a time, no compensation is required for the atmospheric refraction effect between two bands. In the case of the fringe tracker, the operating spectral bands have to be defined in the next study phase. Nevertheless, if this one needs to work simultaneously with two spectral bands, the atmospheric refraction will have to be compensated on a larger band. As a consequence, an atmospheric compensator will have to be implemented and its specifications must have to be defined in the next phase taking into account the scientific instrument and the fringe tracker. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 27 / 118

Figure 3.3: Functional diagram that describes the VLTi Spectro-Imager subsystem breakdown.

3.3.2 Spatial ﬁltering

The ability to spatially filter the incoming beams associated with a proper calibration has been identified as a key function to reach accurate visibility measurements (of the order of 1% [REF20]). Spatial filtering allows incoming perturbed wavefronts to be filtered in order to remove high spatial frequencies perturbations and therefore improve the flatness of the wavefront. The extraction of the beam coherent flux through spatial filtering associated with a proper photometric calibration are the essential steps to improve the visibility accuracy. At the present state of the study the two different beam combination concepts lead to two different ways of spatially filtering the wavefronts:

• In the case of a bulk optics combiner this can be done through the use of a pinhole or a waveguide. It is simplest to perform the spatial filtering by focusing the light onto a fiber or pinhole after rather than before beam combination. In this way, the path length, dispersion and polarization properties of the fibers are immaterial, and the fiber/pinhole can act as the “slit” for the subsequent spectrograph. However, calibration of the beam-coupling efficiency (photometry) is not simultaneous with fringe measurement but requires interleaving calibration and fringe-measurement exposures on timescales of seconds to minutes. • In the case of an integrated optics combiner the use of single-mode waveguides provides natural spatial (better named modal) filtering. The IO combining circuit will allow to calibrate simultaneously the photometry.

We identify two phase A tasks in relation with spatial ﬁltering.

[Task 19] Compare pinhole vs. single-mode fiber spatial filtering capability (included in the BO beam combination strategy study); [Task 20] If relevant define the pinhole requirement in particular the need for several pinholes to accommodate different operating wavelengths. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 28 / 118

3.3.3 Optical path scanner

The science instrument should have an internal path scanner in order to allow to:

1. cophase fringe tracker and science instrument (residual OPDs can be caused by diﬀerential longitudinal dispersion, mechanical instability etc...) 2. scan through the fringe packet for calibration purposes.

In the current view of the instrument the OPD scanner will be included in the beam injection module in the case of an IO combiner and will be an independent module in the case of a Bulk Optics combiner. In addition to that the fringe tracker/science instrument might require a common optical path scanner in order to servo the OPD control commands sent by the fringe tracker.

[Task 21] Specify the diﬀerent optical path compensation requirements.

3.3.4 Wavefront correction

The wavefront correction will be a particularly sensitive issue in the context of a spatially ﬁltering instrument. Strehl Ratios performances will have to be carefully monitored since they aﬀect the global throughput and photometric stability.

[Task 22] During the phase A, the VLTI ability to deliver stable and sufficiently flat wavefronts will have to be assessed; [Task 23] If this study demonstrates that a significant gain could be obtained with an internal active optics system, the phase A will have to specify it (expected performances).

3.3.5 Beam injection

This module is required in the context of a single-mode instrument where light coming from the telescope has to be injected into single-mode fibers. We have voluntarily split the beam injection module and spatial filtering module although both of them have common functionalities. However the conceptual design of such a module differs between the integrated optics and the bulk optics option (see next two chapters). The beam injection module will have to ensure several other functions which are described below:

• light injection in the fibers; • coupling optimization; • spatial filtering (in the IO-based concept); • fiber selection (J, H or K); • orientation of the fiber neutral axis; • OPD correction; • OPD scan;

Specific comments: Injection and optimization of the flux: The opto-mechanical design of the injection unit have to be defined to ensure the coupling of the 18 mm VLTI beams in the fibers. It should allow also a fine adjustment of the flux on a regular basis. Wavelength selection: As described in the ”beam combination” section, two/three IO components are needed to cover the three spectral bands. As a consequence, depending on the operating band, the injection unit will have to Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 29 / 118 direct the flux in the corresponding fiber J,H or K. A motorized mechanical stage must therefore ensure the switching from the different fibers. Polarization direction adjustment: Due to polarization control constraints the single mode fibers used before the combination are polarization-maintaining type. Therefore their birefringence axis need to be aligned at the beam injection position. Whether this should be a degree of freedom or an imposed feature is still to be defined. OPD scanning In the integrated optics version of the instrument we consider implementing an optical path exploration capability to the beam injection module. This is motivated by the interest in being able to retrieve instrument internal fringes and correct for optical path differences between the fringe tracker and science instrument.

[Task 24] Specify the precise functionalities of the beam injection module.

3.3.6 Fringe tracking

A fringe tracker, which measures and actively corrects time-varying OPD errors arising from atmospheric phase perturbations and instrumental eﬀects, is essential for the proper functioning of the instrument. VLTi Spectro-Imager incorporates a fringe tracker as part of the instrument, as an alternative to using an external fringe tracker such as an upgraded version of PRIMA capable of tracking fringes on up to 6 telescopes. This allows the operation of the fringe tracker to be tailored to the science mission of the instrument, and reduces the demands on VLTI infrastructure. The fringe tracker will have at minimum the following distinct modes:

1. “Fringe acquisition” in which a finite region of OPD space is scanned in order to find the fringe coherence envelope in the presence of atmospheric and instrumental delay uncertainties. 2. “Hardware phase tracking” in which the delay errors are actively compensated at high speed so that the level of stability of the science combiner fringes is sufficient to allow on-chip integration of the fringe signal over periods of many atmospheric coherence times. 3. “Hardware coherencing” in which the delay errors are compensated in real time but at a lower speed, with sufficient precision to ensure that the loss in fringe contrast due to temporal coherence effects is small over incoherent integration periods of many minutes.

The hardware coherencing mode will use group-delay tracking to allow access to the faintest objects, while the hardware phase tracking mode will be used for high-spectral-resolution observation of brighter objects. The fringe tracker will be able to switch automatically between these modes based on the SNR in the fringe-tracking channels. In all modes, the fringe-tracker fringe sensing data will be time-tagged and archived with the science data in order to allow “software phase tracking” and “software coherencing” to be used to “phase up” and coherently integrate the science fringe data during post-processing. The on-board fringe tracker unit (FTU) will use light from the science target, but in a different near-infrared bandpass from the science bandpass, in order to determine the OPD errors. It will use the H band for fringe tracking when the J or K bands are being used for science and will use the K band for fringe tracking when H-band science is required. Ultra-efficient (> 98% throughput in both transmission and reflection) dichroics will be used to separate the fringe-tracking light from the science combiner light. The fringe tracker should track the fringes on at least 3 connected baselines in order to cophase 4 telescopes, and at least 5 connected baselines in order to cophase 6 telescopes. The fringe tracker will be based on a pairwise beam combination scheme, which can be readily expanded from a 4-telescope fringe tracker to a 6-telescope fringe tracker. A “beam switchyard” will allow the telescope pairs used for fringe tracking to be selected so as to track fringes on baselines where the source is least resolved, in a “baseline bootstrapping” configuration. The fringe tracker unit will be optimized for the highest-possible SNR for tracking on faint objects. It does not need to be optimized for visibility calibration accuracy or baseline coverage. We have identified the following tasks to be carried out during the phase A study.

[Task 25] specify high level requirements (group delay vs. phase tracking, limiting magnitude performances etc...); Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 30 / 118

[Task 26] specify the fringe tracker in detail (operating wavelength, combination concept, bootstrapping strategy, performances).

3.3.7 Beam combination

In the four telescope configuration VLTi Spectro-Imager should measure simultaneously six visibilities and three independent closure phases. In the six telescope configuration it should measure fifteen visibilities and ten independent closure phases1. The beam combiner encodes the fringe signal into a recordable format, the interferogram, from which visibilities and phases are later extracted. Beam combination schemes are numerous but two major characteristics can be pointed out:

• Interferogram fringe encoding strategy: spatial, temporal or matricial; • Beam combining strategy: all-in-one, pairwise, intermediate.

At the present level of the study we consider two technical options presented in the BOBCAT and VITRUV propo- sitions. The first one is based on compact adhesive bulk optics technology the second one on integrated optics technologies. Although the phase A study will have to refine the numbers it is reasonable to say based on the already existing science that: the beam combiner should be capable of combining 4 to 6 beams (goal) and retrieve all visibilities and closure phases with an accuracy of 1% for the visibilities (goal 0.1%) and 1 degree for the closure phase (goal: 0.1 degree) on most of science targets2. These specifications will have to be translated into throughput, instrumental contrast, visibility and phase stability, coherent and incoherent crosstalk, biases requirements.

Bulk optics combiner

The design of the bulk optics combiner proposed is based on the 4-way beam combiners used at COAST to make the first optical and infrared aperture synthesis images. The “all in one” combination mode characteristic of this design means that the measured closure phases are free of instrumental systematics to first order, yielding sub-degree closure phase accuracy without calibration. This design has subsequently been improved to use contacted optics for mechanical stability and to use improved coatings for ultra-high throughput. A prototype combiner demonstrating high throughput and requiring no adjustment of any parts has been demonstrated in the laboratory in Cambridge. An additional component of the bulk optics concept that has been developed as part of the preliminary system study is the use of a “beam switchyard” which allows a straightforward upgrade to 6-telescope operation by rapidly selecting subsets of beams to feed into the existing 4-way combiner. In this way all the u-v coverage offered by the 6-telescope array is exploited with good observing efficiency and minimal hardware changes. It should be noted that it would also be possible to use this switchyard design to upgrade the 4-way integrated optics combiner to use more telescopes.

Integrated optics combiner

Integrated optics beam combiners have been used successfully at VLTI and IOTA for the combination of respectively two and three telescopes. This experience associated with extensive laboratory experimentation has brought an important amount of experience on the actual performances that are to be expected from an IO combiner. The motivation behind the use of IO beam combiner is that it is expected and demonstrated that the combination of modal ﬁltering, proper photometric calibration and intrinsic stability leads to excellent visibility and closure phase accuracy measurements. Science oriented image reconstructions using the IOTA interferometer equipped with an IO 3-way beam combiner have already been published and demonstrate that IO technologies have reach a mature development[REF18, REF19].

1In the eight telescope case the number of visibilities amounts to 28 and 21 independent closure phases. 2An additional information on what are the smallest visibilities to be measured will have to be provided Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 31 / 118

For the purpose of the VITRUV preliminary system study on beam combination strategy we have carried out an extensive analysis of all the beam combination scheme possible with a focus on signal to noise eﬃciency and technological feasibility. Our starting point was the requirement that all visibilities and closure phases should be simultaneously recorded [REF14]. The conclusion of this system study together with preliminary laboratory experiments are detailed in section 4.5. Our analysis pointed out a 4-way (matricial-ABCD) pairwise combiner as our best combining scheme while for more beams the competition between matricial-ABCD and multi-axial all-in-one is opened. It should be recalled that the overall performances will be evaluated once the fringe tracker performances will be known but also once several issues related to the use of bandpass limited, birefringent and dispersive waveguides have been demonstrated to be controllable to the required levels. An optical end-to-end simulator and numerical end-to end simulator are already being exploited to address these questionings.

[Task 27] The phase A study will have to deﬁne a common grid and carry out a detailed comparison of the two concepts taking into account pure throughput eﬃciency, beam combination scheme, practical implementation; expected visibility/phase accuracy, the logistical aspects of their operation (etc...). The end product should be a decision on the beam combination concept. [Task 28] Study on the best beam combination concept for 6 telescopes and specify how the 4T version of the instrument could be upgraded.

3.3.8 Polarization control

Due to potential residual polarization eﬀects of the VLTI optical trains, polarimetric behavior of the instrument to partially polarized light has to be controlled at the instrument level. In fact cross talks between polarization directions can signiﬁcantly damage the instrumental contrast, produce beat phenomena between these directions and/or parasitic interferograms. In the IO version of the combination two important considerations argue in favor of some level of polarization control.

1. Planar integrated optics components exhibit two neutral axes corresponding to the normal to the component plane and the direction in this plane that is perpendicular to the propagation direction. As such they behave as polarization-maintaining fibers. We thus plug each input of integrated optics beam combiner to a polarization- maintaining fiber. For maintenance purpose, an additional fiber cord is plugged from the injection device to each fibered input of the beam combiner, and the neutral axes are aligned together. Cross-talks can occur due to misalignment of these neutral axes at the fiber connection level. With such a device, we have shown in laboratory and modeled with a numerical simulator (VITRUVSim) that fiber birefringence can induce contrast degradation if the different polarization directions are not separated. Moreover due to fiber sensitivity to temperature and pressure variation, instrumental contrast can fluctuate with time [REF14]. 2. As far as science is concerned, it could be of great interest to couple polarimetric measurements with high angular resolution to be able to partially resolve polarized structures at the surface or in the environment of stars. This implies to access to the linear and/or circular polarization emitted by the target. Our preliminary study of the whole instrumental polarization (including the VLTI optical train and the focal instrument) shows [REF14]: • for astrophysical circular polarization, the large number of reflections in the VLTI optical train which couples both circular polarizations together and converts a part of them in linear ones seems to make impossible the interpretation of the obtained polarized visibilities. • for astrophysical linear polarization, the large number of reflections in the VLTI optical train only induces a small partial polarization (10%). Polarized visibilities, which would be biased, may be used in a parametric approach to bring new constraints on object models.

To summarize, we recommend to simultaneously record visibilities in two perpendicular linear polarization directions since it appears as a diagnosis tool for better understanding and modeling the instrumental contrast answer. We have also proved in lab and at VLTI and IOTA that such a polarization separation allows to signiﬁcantly improve the instrumental contrast stability with time. Finally, the simultaneous record of polarized visibilities can bring new constraints on astrophysical polarizing phenomena as scattering, dichroism, etc. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 32 / 118

[Task 29] interact with VLTI to constrain as much as possible VLTI optical train eﬀect on polarization; [Task 30] simulate polarization behavior of IO combiner; [Task 31] assess bulk optics combiner polarization behavior.

3.3.9 Spectral dispersion

The scientific goals impose to cover the J, H and K bands but no specific requirements have been made to observe in two or more bands simultaneously. The amount of complexity required to observe in two or more of these bands simultaneously is therefore not worth of consideration (strengthened by AMBER experience). At the present level we are considering two to three spectral resolutions in the [100,10000] range (extension to 30000 to be confirmed) that need to be specified. A particular care should be taken by the science group to describe precisely the specific need as far as spectral resolution is required. As an example the calibration requirements to measure a radial velocity or measure a line profile are not the same and have a direct incidence on the spectrometer calibration unit design.

[Task 32] specify the exact spectral resolution requirements (both min and max) as recommended by the science group; [Task 33] specify the calibration constraint required for each spectral mode (in particular stability).

3.3.10 Detection

Detection performance will depend on fringe tracker performances and we can already anticipate two major modes where fringe tracker is performing group-delay tracking and fringe tracking. In the ﬁrst case readout will have to be fast whatever the beam combination scheme in order to avoid fringe blurring, in the second case (required for high spectral resolution) it will be possible to integrate the coherent ﬂux. One of the critical aspects of this sub-system is the strong requirement to include from the beginning of the phase-A study the need for adequate calibration. This statement is reinforced by our current experience with AMBER. The science detector is located inside the spectrograph cryostat, local calibrations must be possible :

• bias calibration (shutter or dark position) • flat-field calibration (extended flat illumination with integrated sphere) • bad pixel calibration (idem) • pixel linearity calibration (idem)

Science detector characteristics to be taken into consideration

• Spectral range • Read-out noise • Read-out time • Number of pixels and pixel size: The preliminary analysis shows that the HAWAII format could comply with the integrated optics combiners speciﬁcations. The complete system analysis led during the A phase will have to conﬁrm this choice.

[Task 34] deﬁne the detector required performance and operating modes in relation with the fringe tracker performances; Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 33 / 118

3.3.11 Control software

Software control role will be to:

• control instrument degrees of freedom (ﬁlter wheels, gratings, scanners, translations); • control the data acquisition (camera control, both fringe tracker and science instrument); • provide data quick-look capability; • dialog with the super OS; • control calibration tools (light sources, scanners, degrees of freedom);

3.3.12 Data processing

Data processing for the instrument includes image cosmetics, ABCD- like algorithms for extraction of correlated fluxes, algorithms for real-time estimates of pistons, and further computation of all available interferometry observables, V 2, differential visibilities, closure phases. The final products will be delivered in the OI FITS format for further data analysis (image reconstruction, etc...) with available public-domain packages. The consortium benefits here of the strong expertise deployed within the data processing software for the AMBER instrument at ESO and for the IONIC beam combiner at IOTA.

[Task 35] specify the observable expected accuracy (visibility, phases, closure phases) in terms of data reduction requirements (algorithms , etc ...).

3.3.13 Image reconstruction

At the present level of our evaluation we consider sub-contracting the study of image reconstruction tools to JMMC which manages a European eﬀort (JRA4/OPTICON) to provide the community with image reconstruction software tools. We will therefore interact with JMMC in order to carry on the following task in close collaboration with the science group:

[Task 36] specify the incidence of imaging requirements on system choices and VLTI operation. In particular assess the importance of the number of telescopes and PRIMA availability on imaging capability. In close interaction with science group.

3.3.14 Calibration and alignment tools

This is an essential part of the instrument that needs improvements with respect to what has been done for AMBER. The overall stability of the instrument will act directly on the need for complex and time-consuming calibration steps an important amount of phase A time should therefore be spent on assessing the level of calibration requirement. VLTi Spectro-Imager will require several layers of alignment/calibration:

1. aligning VLTi Spectro-Imager and fringe tracker with VLTI; 2. VLTi Spectro-Imager internal alignment (here we can note that both beam combination concepts are considerably simpler to align than any previous beam combiner); 3. VLTi Spectro-Imager internal interferometric response calibration; 4. spectrometer calibration; 5. detector calibration.

[Task 37] Deﬁne the alignment/calibration requirements, specify the corresponding subsystems. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 34 / 118

3.4 Expected performances

At the current level of the study the expected performances evaluation of the VLTi Spectro-Imager instrument is not available since several critical subsystems are still to be deﬁned (e.g beam combiner). However preliminary work carried by VITRUV [REF10] and BOBCAT [REF11] teams on their speciﬁc concepts shows that expected performances are compatible with the science cases.

[Task 38] Assess expected performances including the science instrument and the fringe tracker description;

3.5 VLTi Spectro-Imager and PRIMA

When used in association with PRIMA, VLTi Spectro-Imager operation mode will differ from the standard one in the sense that the fringe tracker will be fed with light coming from a different object than the one observed with the science instrument. Figure 3.4 shows two different implementation schematics of VLTi Spectro-Imager, on the left implementation without PRIMA, on the right with PRIMA. It should be noted that extension to 6 beams is not fully compatible with a PRIMA mode.

[Task 39] Assess the system consequences of the availability of PRIMA.

3.6 General system studies

We identify here the studies which are transverse to all subsystems and which needs to be tackled at the general level.

[Task 40] general design: translation of science requirements into high level system and subsystems specifications; [Task 41] selection of observing modes; [Task 42] consistency of system choices: error budget distribution, subsystem specification, critical vs. routine studies definition; [Task 43] assessing control requirements in particular the dialog between internal fringe tracker, science combiner and VLTI; [Task 44] assessing the instrumental stability requirements in order to reach expected performances; [Task 45] interface with the VLTI: identify all the instrument characteristics that have direct impact on the VLTI or are sensitive to VLTI system (footprint, wavefront quality, beam stability, cophasing);

3.7 Summary of required tasks for phase A

We summarize all tasks which have been listed in this chapter.

3.7.1 Wavefront Quality

Task 22: Assessing wavefront quality; Task 23: If relevant specify Additional beam shaper module. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 35 / 118

3.7.2 Spatial ﬁlter module

Task 19 Compare pinhole vs. single-mode ﬁber spatial ﬁltering capability (included in the BO beam combination strategy study); Task 20: If relevant specify pinhole subsystem.

3.7.3 Optical path compensation

Task 21: Specify the diﬀerent optical path compensation requirements.

3.7.4 Beam injection module

Task 24: Specify the beam injection module functionalities.

3.7.5 Beam combination module

Task 27: Beam combiners concept comparisons, ﬁnal recommendation. Task 28: Evaluation of the upgrading to 6/8 beams

3.7.6 Fringe tracker

Task 25: Specify high level requirements (group delay vs. phase tracking, limiting magnitude performances); Task 26: Specify the fringe tracker in detail (operating wavelength, combination concept, bootstrapping strategy, performances).

3.7.7 Polarization control

Task 29: interact with VLTI to constrain as much as possible the polarizing properties of the VLTI train; Task 30: Simulate polarization behavior of IO combiner; Task 31: Assess bulk optics combiner polarization behavior.

3.7.8 Spectrometer

Task 32: Specify the spectral resolution requirements in collaboration with science group; Task 33: Specify the calibration level required for each spectral mode.

3.7.9 Detector

Task 34: Deﬁne the detector required performances and operating modes;

3.7.10 Data Reduction

Task 35: Specify the observable expected accuracy (visibility, phases, closure phases) in terms of data reduction requirements;. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 36 / 118

3.7.11 Image Reconstruction

Task 36: Specify the incidence of imaging requirements on system choices and VLTI operation.

3.7.12 Calibration requirements

Task 37: Deﬁne the alignment/calibration requirements;

3.7.13 Performances

Task 38: Assess expected performances;

3.7.14 PRIMA

Task 39: Assess the system consequences of the availability of PRIMA.

3.7.15 Global System Studies

Task 40: general design: translation of science requirements into high level system and subsystems speciﬁcations; Task 41: selection of observing modes; Task 42: consistency of system choices; Task 43: assessing control requirements; Task 44: assessing the instrumental stability requirements; Task 45: interface with the VLTI; Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 37 / 118

VLTi Imager VLTi Imager

Fringe Fringe tracker tracker

Ref Target VLTI beams VLTI/PRIMA beams

Figure 3.4: VLTi Spectro-Imager with or without PRIMA Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 38 / 118

Chapter 4

Beam combiner conceptual design: Integrated Optics solution

4.1 Overall description

This chapter presents the technical solutions selected for the sub-systems of the VLTi Spectro-Imager. This selection was based on our experience with several of the precursors build by members of the consortium among which AM- BER(VLTI). The combination proposed here is realized with Integrated Optics technology. This one is well suitable to the combination of four telescopes or more and the performances in terms of stability and eﬃciency have been demonstrated at several occasion (VLTI, IOTA) [REF18, 19, 21, 22]. The ﬁgure 4.1 describes a conceptual study of the science beam combiner derived from our system analysis. This last is composed of the following subsystems:

• Atmospheric dispersion compensator modules; • Alignment/calibration module; • Beam switchyard/Fringe tracker; • Beam injection module; • Spatial ﬁltering; • Beam combination module; • Polarization control module; • Spectrograph; • Spectral calibration module; • Detector; • Control software;

The control Software and data reduction aspects are not represented in the ﬁgure but their functions are approached in the next sections. The degrees of freedom are in brackets in Fig. 4.1.

4.2 Atmospheric dispersion compensator

We have identified that an atmospheric dispersion compensator is required on the system. The spectral range to correct will depend on the operating mode of the fringe tracker and particularly if it has to work simultaneously on two bands. In this case, the angular residual variation appearing during the rotation of the prisms has to be minimized to avoid a degradation of the coupling with the fiber. If the final design of the compensator produces a large angular Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 39 / 118

Figure 4.1: Schematic view of the beam combiner concept Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 40 / 118 residual variation during its rotation, the implementation of an active correction at the ﬁber level will have to be considered.

[Task 46] Analyze the need of an active correction (tip/tilt), compensating the angular residual variation of the ADC.

4.3 Beam injection module

The figure 4.2 presents a possible conceptual design of the injection unit. This work has inherited from the design successfully used at IOTA. The philosophy for this assembly is to facilitate the integration. Each module is consequently easily interchangeable and can be aligned independently of the system. The focus is made thanks to off axis parabolic mirror to discard chromatic effect. The fiber positioning is ensured by a two axis motorized translation stage Tx and Ty. This last Ty translation has also to ensure the selection of the operating fiber J, H or K as described on the right part of the figure 4.2. A manual stage will achieve the Tz focus adjustment. Further to these stages, the implementation of an optical path exploration is required to ensure the internal fringe search when the interferometric calibration mode is used (see 4.8.1). This motorized stage will be integrated in the injection module as well. At this level of the analysis the type of stages are not defined. The degrees of freedom of the injection module are presented in the section 4.9 (see figure 4.2 for the reference axis). Even if the construction of this assembly is not critical, the injection module is subjected in the phase A, to a study to ensure the most reliable and stable mount.

[Task 47] Design study of the injection module.

Nota: LAOG has developed a compact ”ﬁne” positioner able to ensure accurate positioning and servoing of ﬁbers. This system would be potentially usable if any dynamic correction is required (stroke:+/- 20 µm).

Figure 4.2: Preliminary design of the injection module

4.4 Spatial ﬁltering

In our design, the spatial filtering is done at two levels. A first filtering is ensured at the entrance of the optical fiber. Main of the work is however ensured by the single mode propagation property of the Integrated Optics combiner [REF18, 19]. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 41 / 118

4.5 Integrated Optics science beam combiners

4.5.1 IO combiners

As it is proposed in the system analysis, the combination of 4 VLTI beams is our baseline while the combination of 6 or 8 beams is proposed as an additional option (see section 4.11). We have considered IO technology as our solution to combine the 4 to 6/8 VLTI beams. This choice is based on LAOG experience on this type of combination which has been successfully exploited at VLTI (2-way beam) and IOTA (2,3-way beam combiners). The main advantages of this technology are:

• possibility to integrate on single chip almost all combination schemes; • it is easy to implement the modal ﬁltering function associated to photometric calibration which has proved to be a key element in the improvement to the visibility accuracy (xx reference); • the very compact size of the combining chip allows a remarkable stability of phase properties and a small combining footprint; • easy to install since only the alignment with the spectrograph has to be ensured;

Each beam combiner is made of an integrated optics chip connected to a ﬁber V-groove. At the present state of the study, the capability to use only one chip to recombine both the J and H bands has not been demonstrated. Our baseline is consequently to ensure the combination of the 4 VLTI beams with three components, one component per spectral band. In the global study of the combiner, we foresee to study however the use only one IO component for both J and H bands. The use of optical ﬁbers coupled to the integrated optics chip induces several constraints:

• this introduces a differential birefringence and dispersion that will have to be characterized carefully; • the fibers are cemented at one end to the IO combiner, and at the other end to the connector of the injection module. The maintenance strategy of such a critical system has to be considered; • alignment of fiber neutral axis together has to be ensured at the connector level; • the fibers have to be chosen in order to match the numerical aperture defined by the off axis parabola for each spectral band;

These points are included in the combiner study (see section 4.5.5).

4.5.2 Combining concept

Among all the beam combination concepts, our system study (REF14) has pointed out that a four way pairwise ABCD beam combiner was the best compromise as far as signal to noise and biases are concerned. Our industrial partner LETI has designed such a combination concept which can be seen in figure 4.3. The combination chip has 4 inputs and 24 outputs (6 baselines x 4 A,B,C,D samples). The use of achromatic phase shifters allows to sample simultaneously four different phase states across the central fringe as it is described figure 4.4 (this is a spatial version of the widely known ABCD concept [REF23]). No temporal modulation is then required for this concept.

4.5.3 Preliminary results

LETI has manufactured a prototype 4-way pairwise ABCD beam combiner similar to what will be proposed for the phase A. The beam combiner was optimized for the H band. We will perform a detailed study of the beam combiner properties with the help of different tools that have been specifically developed (see section 4.14). Figure 4.5 shows an actual image of the 24 interferometric outputs. As a first validation of the concept we have scanned the optical path of three out of the four beams which leads to spatially encode 6×4 interferograms (a subset of 6 interferograms for each baseline is shown here in figure 4.6). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 42 / 118

Figure 4.3: Schematic design of a 4-way pairwise ABCD beam combiner.

Figure 4.4: Description of the ABCD concept

4.5.4 IO combiner mechanical support

The degrees of freedom identiﬁed for the beam combiner mechanical support are described ﬁgure 4.1. A two axis motorized stage Tx, Ty, is needed to ensure the centering of waveguide outputs on the detector pixels while a manual stage is foreseen to make the focus adjustment.

4.5.5 Phase A studies

During phase A studies we propose to check the compatibility of beam combiner properties with the science case requirements. That includes:

[Task 48] Full characterization of a 4T ABCD H beam combiner (throughput, instrumental contrast, closure phase biases, chromatic behavior, polarization measurements) [Task 49] Design study of the beam combiner sub-system for all bands (ﬁbers, combiners, chromatic dispersion constraint, maintenance) Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 43 / 118

Figure 4.5: Image of the output of a 4-way pairwise beam combiner on an infrared detector.

Figure 4.6: Scanned interference fringes obtained with the 4-way pairwise beam combiner (subset of 6 out of the 24 outputs).

4.6 Polarization control

We propose to separate the two perpendicular polarization directions with a Wollaston prism to be able to simultaneously detect and analyze the two linearly polarized interferograms. This prism has its neutral axes aligned with those of the fibered beam combiner. A preliminary study of the bias introduced by the instrumental polarization effects has been done for two solutions: a polarization separation before the combination and a polarization separation after the combination [REF14]. The polarization after the combiner is chosen for the 4T-ABCD component since it simplifies the system and it leads to acceptable bias. The angular deviation at the prism output is chosen to allow to interlace the 24 outputs in one polarization direction with the 24 outputs in the other one (see figure 4.7). This allows to reduce the total number of pixels and to use a single slit at the spectrograph entrance.

Phase A studies

Thanks to the numerical simulator VitruvSim, we have demonstrated that splitting the polarization at the output induces no major bias. Our first tests in laboratory confirm this analysis, but an exhaustive study has to be made to valid this issue. More generally, we have to go deeper into the study of the bias introduced by the instrumental polarization effects. More accurate values of polarization of the VLTI optical train would be very useful for these works. We have also to conduct a thorough study of the observing strategy and the calibration steps for polarized Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 44 / 118

Figure 4.7: Interlacing the two polarizations on the detector by inserting a Wollaston prism. astrophysical targets.

[Task 50] Experimental validation of the polarization separation placed at the output of the beam combiner.

4.7 Spectrograph and detector

4.7.1 Spectrograph

The implementation of a relay optics imaging the IO combiner waveguide outputs is required (see 4.1). This one allows to place the polarization separator in a small pupil and it gives the possibility to have a cooled entrance spectrograph slit. A preliminary optical design of the spectrograph and its image quality is proposed ﬁgure 4.8. This layout has the following speciﬁcations:

• dioptric layout correcting the image quality over the whole spectral domain on a 1k x 2k detector (pixel size: 18 µm); • focal magniﬁcation of about γ=7, to guarantee the spatial sampling on the pixels; • pupil diameter: about 40 mm; • size: 650 x 400 mm; • Strehl ratio: ≥ 97%;

To achieve the spectral requirements, we propose to use two diffraction gratings for the high and medium resolution (R = 1000 and 10000) and a variable prism able to provide a low resolution from R=0 to R=200. The order separation is realized with interferential filters placed in a filter wheel in the cryostat. In the current design, our goal is to have the degrees of freedom on the IO combiner output level and at the detector level. The other adjustments would be obtained machined wedges (degrees of freedom are presented in section 4.9).

[Task 51] Concept study of the spectrograph. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 45 / 118

4.7.2 Detector

The detector format chosen for the preliminary analysis is 1k x 2k with a pixel size of 18 microns, corresponding to an Engineering grade Hawaii-2RG with 2 running quadrant. We think that the implementation of the ESO New Generation Controller would be a major improvement. According to the acquisition modes, several readout modes could be considered such as:

• fast double correlated • slow double correlated • low noise optimized multiple read

[Task 52] Search of the best suitable detector according the format and frame rate speciﬁcations.

4.7.3 Cryostat

The cooling of the spectrograph is preferred to minimize the background emission. No design is proposed for the cryostat at this point of the project but several constraints have to be taken into account:

• A LN2 tank is preferred for cooling process in order to minimize vibrations; • Each sub-assembly (detector, calibration boxes, etc) has to be integrated independently of the system to simplify the alignment/integration in the cryostat; • The design has to be optimized to facilitate and limit the maintenance of the cryostat;

The final specifications of the cryostat will be accurately defined during the next phase.

4.8 Calibration and alignment tools

4.8.1 Calibration tools

Internal calibrations

This includes the spectral calibration and the detector and interferometric calibrations. Spectral calibration: A spectral lamp can be inserted to spectrally calibrate the spectrum. It has to be chosen to provide enough identified lines in each spectral band, for all the spectral modes. This calibration is mandatory for each dispersive mode change. Detector calibration: A broad band source is foreseen to provide flat field and thus allow to measure the detector response. The accurate specifications of this detector calibration box should be defined in the phase A study. An analysis will be required to defined the position of this calibration source mainly if it has to be placed in the cryostat. Interferometric calibration: An unresolved source allowing to check the contrast for each pair of telescopes can be inserted to estimate the instrument performances during assembly, integration, tests and maintenance. The design proposed at this point of this analysis is based on a Mach Zehnder interferometer which can be put at the place of the stellar beams coming from the VLTI (see figure 4.9). In this design the injection modules have been placed in order to compensate the optical path difference between each channel. The final configuration will have to be confirmed however during next phase. The necessity to have this interferometric calibration permanently usable on the bench or occasionally mounted has also to be defined in the phase A. The accurate specifications, operating modes of these three calibration tools have to be studied during the phase A study. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 46 / 118

4.8.2 Alignment tools

Internal alignments

The beams coming from interferometric calibration system could be used to light up the four injection modules with a red laser source and to allow alignment of the instrument up to the spectrograph and the detector (sensitive in the visible too). The use of this system has to be validated however during the next phase. The optimization of the coupling with the fibers is made by maximizing the flux and the alignment procedure from the beam combiner to the detector will be defined during this same phase.

Alignment with the VLTI

Our experience at IOTA shows that a capability allowing to align the VLTI beams with the injection fibers would allow to minimize the time spent to align the instrument with the telescopes. We consequently propose to install a movable LED enlightening the output of the integrated optics beam combiners. This allows to back illuminate the beam injection modules and to gather on an imaging detector both the VLTI beams and the injection beams as described figure 4.10. In the phase A, the studies relative to these calibration/alignment tools, concern mainly the definition of the specifications. A preliminary design study of these tools will be performed however in parallel of the spectrograph design study.

4.9 Degrees of freedom

The degrees of freedom listed in at this stage of the project are detailed in table 4.1. At this point of the analysis the number of degrees of freedom and motorized functions listed are:

• Number of degrees of freedom: 41 (11 manual stages) • Number of motorized functions: 30 + (TBC) functions

4.10 Software

4.10.1 Control command

Electronics

The electronics cabinets required for the controlled functions will conform to the ESO standard. If piezo-electric actuations are needed, the control system will have to be studied speciﬁcally.

Control software

As prescribed in [AD2], the control software supplied with instrument will conform to the general requirements and specifications contained in [AD1] and the references contained therein. The control software will benefit of our valuable experience acquired during AMBER instrument development. During the phase A, we will study the impact of the integration specific sub-systems such beam shaper or fringe tracker inside of the instrument. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 47 / 118

Table 4.1: Summary of the degrees of freedom and motorized functions of the instrument (TBC) Sub-system Function Type Degree of Required stroke Accuracy freedom (mm) TBC (µm) TBC ADC Prism rotation motorized -Rz 4 x 2 TBD TBD Switchyard motorized - ?? TBD TBD TBD Fiber positioning motorized - Tx 4 x 1 1 0.1 Injection Fiber positioning and fi- motorized - Ty 4 x 1 1 0.1 module ber selection Fiber focusing manual - Tz 4 x 1 1 0.1 OPD scan motorized - Tz 4 x 1 10 0.1 IO combiner Combiner positioning motorized - Tx, Ty 2 Tx=15, Ty=1 0.1 support and Combiner positioning manual - Tz 1 2 0.1 relay optics Polarization prism swit- motorized - Tx 1 TBD TBD chyard Calibration flip mirror 1 motorized - Ry or 1 TBD TBD ?? Calibration flip mirror 2 motorized - Ry 1 TBD TBD Spectrograph filter wheel rotation motorized - Rz 1 TBD TBD Grating turntable motorized - Ry 1 TBD TBD Low resolution variable motorized - Rz 2 TBD TBD prism rotation Focus adjustment motorized - Tz 1 TBD TBD Detector Prism rotation Manual Tx, Ty, Tz, 6 TBD TBD Rx, Ry, Rz

4.10.2 Data reduction

The data reduction strategy will have to be deﬁned during the phase A study. The expertise deployed within the data processing software for AMBER and for the IONIC beam combiner will be helpful in this analysis. Moreover the data obtained on the 4T ABCD combiner currently under characterization should allow to better approach this issue.

[Task 53] Deﬁne the data reduction strategy

4.11 Additional functionalities

4.11.1 Option 6T/8T

As it is described in the system analysis, a signiﬁcant gain could be reached by combining more than 4 telescopes. The Integrated Optics technologies allow to realize complex circuitry and thus to design combinations for more than 4 beams. A combination for 6 or 8 telescopes can therefore be proposed. The technology developed by LETI allows to manufacture either co-axial or multi-axial combiner. We consequently propose to manage a study during the phase A which compares the implications of the two combination options as described below.

6 beam combination

For a 6 beam combination, both co-axial and multi-axial combination will be studied. For the co-axial option the ABCD concept is the most attractive since no modulation of the optical path is required. Nevertheless, it should be validated with the system analysis, considering that in ABCD 60 interferometric outputs (15 baselines x 4 A,B,C,D samples) will be available and 120 areas will be imaged on the detector and read if we separate the two polarizations. The multi-axial combination can be considered for 6 beams also. This scheme would provide spatially sampled fringes Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 48 / 118

Table 4.2: Options for the 6T/8T study Combiner combination scheme Sub-system - Fringe tracker Co-axial - Spectrograph - Fringe tracker 6T - Polarization Multi-axial - Spectrograph - Data reduction - Fringe tracker - Polarization 8T Multi-axial - Spectrograph - Data reduction

at the output of the integrated optics beam combiner that can be dispersed by the spectrograph deﬁned for the 4T-ABCD beam combiner. In this case the following points have to be considered: Polarization separation: The angular separation given by the Wollaston prism of the 4T ABCD allows to interlace the waveguide outputs on the detector. With the multi-axial concept the fringes are spread out on a large width. If we use the 4T ABCD Wollaston prism, the small angular separation interlacing the polarizations, would smear the multi-axial fringe pattern. Several solutions have thus to be studied during the Phase A: - removing the Wollaston prism to analyze the spatial fringes in natural light (i.e. without selecting a linear polarization);

removing the Wollaston prism, putting a polarization selector at the beam injection level and providing a single beam combiner, operating with a fixed single polarization direction; -- replacing the Wollaston prism with a polarization selector at the beam combiner output level, the latter operating with a fixed single polarization direction; - putting the Wollaston prism at the beam injection level and providing two identical beam combiners, one per polarization direction; - replacing the 4T Wollaston prism by a different one allowing to separate the two polarized multi-axial areas on the detector. This solution would require to turn the Wollaston prism of 90◦ and a large angular separation between the two polarizations. Data reduction: The data reduction to implement for the multi-axial combination is quite different of those developed for the 4 telescope co-axial combination, our baseline. If the multi-axial scheme is finally chosen, a complete data reduction software will have to be implement again.

8 beam combination

For the combination of 8 beams the co-axial scheme is not adapted and the multi-axial concept is preferred. The constraints noticed for the 6 beam multi-axial combination will have to be considered as well.

[Task 54] Paper study of the option 6/8T beam combiners

4.11.2 Beam shaper with adaptive optics

The performance of the instrument will be estimated during the phase A study. At this occasion it would be interesting in having an analysis end to end of the VLTI to have a performance budget as realistic as possible. If this final budget reveals a poor performance, LAOG proposes to define the specifications of the adaptive optics system required to improve the performances of the global system. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 49 / 118

[Task 55] If required, make a concept study of an optional adaptive optics system

4.12 General means

This section gathers the items which have not been studied yet, but which are identiﬁed to be treated during the phase A study. These issues include:

• Instrument implantation • Optical bench height • Bench size • Bench enclosure • Weight of the instrument • Environment interactions (thermal dissipation, electro-magnetic constraints, Vibration and acoustic constraints) • Safety constraints

Maintenance: The preliminary analysis shows that several issues have to be considered with care: Beam combiner fibers: In our design the fibers are cemented, at one end to the IO combiner and at the other end in a connector and each fiber has approximately the same length to discard chromatic dispersion effect (specification to be defined). As a consequence, if a fiber is broken, we can’t shorten the fiber and then the assembly become unusable. We have thus chosen to limit the risk by adding a sleeve in the pigtail as described in the figure 4.1. We have to notice however that if a fiber breaks, either the IO combiner sub-assembly or the injection connector will have to be replaced. To limit the fiber breakage the study has to take into account the use a cable ensuring a good protection of the fiber. The spares parts will have to be considered for this issue. Remote control stages: Remote stages and particularly stages which are placed in the cryostat can induce a critical maintenance. The design performed should therefore limit the number of motorized functions in the cryostat. Calibration lamps: During the phase A study, the position and type of the calibration boxes will have to be defined in order to facilitate the maintenance operations.

4.13 Interfaces

4.13.1 VLTI interfaces

Optical: The design of the injection modules will be done taking into account the specifications given in [AD2]. An analysis end to end of the VLTI could be useful to make a realistic budget of the performances of the instrument. Mechanical: The constraints defined in the [AD2] will be taken in account for the definition of the optical bench (height,size). The degree of freedom of the crane of the VLTI lab will have to be considered for the integration phase. Supplying: Easy access to electrical power and cryogenic liquid will be required for the instrument. The vacuum needs will be defined during the phase A study. Data flow: Assuming the readout of complete 2k x 2k detector format, 4 quadrants with frame pixel of 1Mpx/sec, the maximum data flow is estimated at about 500Go/night and about 100Go/night in average. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 50 / 118

Table 4.3: Interface to be considered in the phase A

ADC Fringe Injection Beam Polarization Spectrograph Detector tracker modules combiner control and cryostat ADC O O Fringe TBD O C tracker Injection O modules Beam O O/C O/C combiner Polarization O O/C control Spectrograph O/M/C and cryostat Detector Control C C C C C (TBC) C C system O: optical, M: mechanical, C: control

4.13.2 Subsystem interfaces

The interface document will be created during the phase A study. The table 4.13.2 establish the interfaces which have to be considered. The nature of the interface is deﬁned as O for Optical, M for Mechanical and C for Control.

4.14 Phase A tools

4.14.1 Experimental setup

We have setup an end to end laboratory interferometer simulator that allows us to simulate a four to eight beam interferometer and the corresponding integrated optics beam combiner with its polarization and spectral analysis module. We should therefore be able to provide the essential information on the characterization of an H band 4-way prototype beam combiner.

4.14.2 Numerical simulator

We have developed a VLTi Spectro-Imager numerical simulator VitruvSim that allows us to describe precisely beam propagation inside the instrument taking into consideration numerous important physical parameters such as incoming polarization state, coupling eﬃciency, waveguides dispersion and birefringence and temperature sensitivity. Phase A study will be devoted into validating our numerical simulator with laboratory experiments and simulate realistic observables in order to check the capability of the instrument to fulﬁll the science program it has been designed for. ram it has been designed for.

4.15 Required tasks for phase A

At the end of the phase A study we will have to answer the speciﬁc questions that will allow us to present a detailed conceptual design. This chapter summarizes the tasks which have been pointed out along the conceptual design chapter. The phase A study will be mainly dedicated to answer these speciﬁc issues. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 51 / 118

4.15.1 Atmospheric dispersion compensator

Task 46: Analyze the need of an active correction (tip/tilt), compensating the angular residual variation.

4.15.2 Injection module

Task 47: Design study of the injection module.

4.15.3 Beam combiner

Task 48: Full characterization of a 4T ABCD H beam combiner (throughput,instrumental contrast, closure phase biases, chromatic behavior, polarization measurements) Task 49: Design study of the beam combiner sub-system (ﬁbers, combiners, chromatic dispersion constraint, maintenance)

4.15.4 Polarization control

Task 50: Experimental validation of the polarization separation placed at the output of the beam combiner.

4.15.5 Spectrograph

Task 51: Concept study of the spectrograph.

4.15.6 Detector

Task 52: Search of the best suitable detector according the format and frame rate speciﬁcations.

4.15.7 Data reduction

Task 53: Deﬁne the data reduction strategy

4.15.8 Additional functionalities

Task 54: Paper study of the option 6/8T beam combiners Task 55: If required, make a concept study of an optional adaptive optics system Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 52 / 118

Entrance Collimator slit Variable prisms or diffraction gratings

Chamber Folding Folding 0

0 mirror #1 mirror #2 4

Detector

650

Figure 4.8: Preliminary layout of the spectrograph and corresponding spot diagrams from J to K (the ﬁeld is in x-axis) - size of a cross (200 microns) Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 53 / 118

Figure 4.9: Preliminary layout of the interferometric calibrator

Figure 4.10: Preliminary layout of the alignment module Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 54 / 118

Chapter 5

Beam combiner conceptual design: Bulk Optics solution

5.1 Overall description

The bulk-optics (BO) option is an alternative to the integrated-optics (IO) science combiner which offers a number of potential advantages. Chief amongst these is the combination of high photon throughput (>96%) and high fringe contrast (>95%) which has been demonstrated in working prototypes. This high “interferometric throughput” is particularly critical to science cases which require the observation of targets which are intrinsically faint, for example AGN or faint M-dwarfs. The BO science combiner has the same basic functionality as the IO combiner. The main difference in implementation is the use of free-space optics rather than guided-wave optics for producing the interference patterns. A number of beam combination modes are possible within the BO concept, including image-plane and pupil-plane combination, as are a number of spatial filtering modes such as pinhole and fibre filtering. For simplicity we describe here mainly the baseline option, which uses pupil-plane beam combination and fibre spatial filtering. A schematic diagram of the overall instrument is shown in Figure 5.1. Light entering the instrument is split using dichroics between the science beam combiner and the fringe tracker. The dichroics form part of a “beam switchyard” which feeds light into the main beam combiner. This is a 4-way pupil-plane design using beam splitters which produces 4 outputs, each being the superposition of all 4 input beams, i.e. interference patterns corresponding to all 6 possible baselines are present in each output. The fringes are “fluffed out” i.e. each output beam is either all light or all dark depending on the phases of the fringes. Path modulators serve to rapidly scan the phase of the input beams such that a temporally-modulated intensity is observed, with each of the 6 fringe patterns appearing at a separate frequency. The collimated outputs from the combiner are focused onto single-mode fibres, serving to spatially filter the fringes and also to inject light into the input “slit” of a cooled spectrograph. The spectrograph illuminates a detector which is read out synchronously with the fringe modulation to produce a spectro-interferogram. This can be processed to yield fringe amplitude and phase information for all 6 baselines at a large number of wavelengths simultaneously. This design is described further below in terms of a system analysis into a number of different functions:

• Atmospheric dispersion compensator modules; • Alignment/calibration module; • Beam switchyard/Fringe tracker; • Science beam combiner; • Fast path modulators • Beam injection module; Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 55 / 118

4 x (Tx, Tz) Light dump Fringe tracker OPD Tracker Switchyard

ADC 6 x (Tz, Tx) ADC

ADC

ADC Beam switchyard Components may need 6 x (2 x Rz) tip/tilt adjustments.

Slabs

Beam Combiner Fiber injection

Cryostat − Spectrograph

Detector

Entrance slit X Grating turntable (Ry) Z HR Y

Motorised functions are in brackets T − Translation Filter (order selction) (Rz) MR R − Rotation

Figure 5.1: Schematic layout for the bulk-optics combiner. The layout for an instrument accepting 6 input beams is shown, including a switchyard for selecting a subset of the beams to feed into a 4-way combiner. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 56 / 118

• Spatial ﬁltering; • Spectrograph; • Spectral calibration module; • Detector; • Control software;

It can be seen that there is a large amount of commonality with the IO solution, so in many cases the reader will be referred to the IO sections for further detail (see Chapter 4). The only module in the IO concept for which there is no equivalent in the BO concept is the polarisation control module: the BO solution requires no compensation for instrumental birefringence. The fast path modulators are present only in the BO concept as path modulation is done statically in the IO combiners.

5.2 Atmospheric dispersion compensator

The requirements for the dispersion compensator are identical to those for the IO combiner, except that it is possible to place the ADCs in the optical train after the beams have been combined. This somewhat relaxes the manufacturing requirements for the ADCs as they do not need to have matched thicknesses.

5.3 Alignment/calibration module

The functionality of this module is identical to that for the IO concept. Due to the use of stable contacted optics in the BO combiner, the number of degrees of freedom of the combiner which need frequent calibration are similar in the BO and IO cases.

5.4 Beam switchyard

The functionality of this module is similar to that in the IO beam combiner, except where a 6-beam concept is implemented. With 6 input beams, the science beam combiner in the BO concept remains a 4-way design, but the switchyard serves to select subsets of the input beams to feed to the combiner. Interferometric data are accumulated with different subsets of input beams, with rapid (timescales of under a minute) switching between subsets. This allows sampling of all possible baselines and closure phases in a short period. Compared with an option which makes all possible combinations of 6 input beams simultaneously, the switched 4-way combiner offers easier upgrading, greater flexibility and simplicity, lower baseline-to-baseline crosstalk and, surprisingly, allows coverage of all baselines at similar signal-to-noise ratios in less or approximately the same total amount of observing time. As a result, the switchyard needs to be designed for rapid reconfiguration. The baseline option to implement this functionality is using mirrors and dichroics mounted on commercial slides, but some studies are required to investigate the feasibility of the commercial solution. Each slide includes 1 translational degree of freedom, plus the mirror mounts on the slides will each have motorised control in tip and tilt (it may be possible to have tip and tilt control on one slide only, depending on the pitch and yaw of the slide system). If only 4 input beams are used, reconfiguration is on much longer timescales (perhaps nightly) and this significantly reduces the repeatability requirements on the slides.

[Task 56] Design study of fast/slow switchyard options, including suitability of commercial slides.

5.5 Bulk Optics science beam combiner

The optical arrangement which allows all 4 input beams to be superimposed using beam splitters is shown in the box labelled “beam combiner” in Figure 5.1. The design uses custom-designed coatings at low angles of incidence for Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 57 / 118 high eﬃciency and low polarisation sensitivity, and components are connected using contacted-optics technology to achieve exceptional path length and alignment stability. The wide-band nature of the coatings means that only one combiner is needed to cover the J, H and K bands. The design is based on a working prototype in Cambridge which has demonstrated the required high throughput and stability. The work in the phase-A study would mainly involve looking at scaling issues for the larger VLTI beams.

[Task 57] Design study of options for manufacture of scaled-up contacted-optics beam combiner.

5.6 Path modulators

The optical path diﬀerence between beams is modulated at rates of several hundred Hertz using mirrors mounted on piezoelectric actuators. Laboratory tests have shown that the scanning of these mirrors can achieve the required accuracy and repeatability by appropriately controlling the harmonics of the drive waveform. Studies thus far have used feedback from direct measurements of the resulting modulation using a metrology laser, but injecting laser metrology to all the modulators could be problematic within the space envelope. Alternative options for performing the calibration of the drive waveform include use of capacitive or strain-gauge sensors.

[Task 58] Study of options for modular drive waveform calibration.

5.7 Spatial ﬁltering/Beam injection module

The injection of light into fibres in the BO design occurs after beam combination, so the phase and birefringence properties of the fibres are of little concern. If suitable fibres (e.g. chalcogenide photonic crystal fibres) can be procured, then only a single set of fibres may be needed to cover all wavebands. The beam injection technology described for the IO combiner would be appropriate for application in the BO concept.

[Task 59] Investigate options for single mode ﬁbres covering all wavebands simultaneously.

5.8 Detector and Spectrograph

The detector and spectrograph layout and requirements in the BO concept are similar to that for the IO concept. One diﬀerence is that the BO spectrograph has fewer outputs which are read out more often than the IO spectrograph, but the overall pixel rate is similar.

5.9 Software

The overall functionality and architecture of the control and data reduction software for the BO option is similar to that for the IO design, yielding similar outputs at the end of the data reduction pipeline. The number of degrees of freedom to be controlled are similar to that for the IO combiner, except the switchyard, which adds 8/10 additional motorised translation stages (for 4/6 input beams respectively) and 16/20 motorised degrees of freedom of tip/tilt.

5.10 Other tasks

While there is a lot of commonality of modules with the IO concept, an additional task is to make sure that the concepts for the modules within the IO system are fully compatible with the requirements of the BO concept.

[Task 60] Monitor common tasks for BO/IO concepts for commonality of speciﬁcation. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 58 / 118

5.11 Interfaces

The external and internal interfaces for the BO concept are similar to that for the IO concept.

5.12 Required tasks for phase A

Below we summarise the required Phase-A studies as detailed in the previous sections.

5.12.1 Beam switchyard

Task 56: Design study of fast/slow switchyard options, including suitability of commercial slides.

5.12.2 Beam combiner

Task 57: Design study of options for manufacture of scaled-up contacted-optics beam combiner.

5.12.3 Path modulators

Task 58: Study of options for modulator drive waveform calibration.

5.12.4 Spatial ﬁltering/Beam injection module

Task 59: Investigate options for single mode ﬁbres covering all wavebands simultaneously.

5.12.5 Other tasks

Task 60: Monitor common tasks for BO/IO concepts for commonality of speciﬁcation. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 59 / 118

Chapter 6

Internal fringe tracker conceptual design

6.1 Role of the fringe tracker

A fringe tracker performs a similar role within an interferometer as an adaptive optics (AO) system performs within a single telescope. It measures wavefront errors due to the atmosphere and instrument (in the case of a fringe tracker, these OPD errors are the differences between telescopes of the amplitudes of their respective Zernike “piston” modes) and corrects these errors in real time. Like an AO system, a fringe tracker requires a bright reference object to sense the wavefront errors, and also like an AO system there are strong fundamental limits to how faint this reference object is allowed to be before the fringe tracker fails to operate. If the fringe tracker does not work, little or no science can be done, and so the range of science targets accessible to the instrument is typically most strongly limited by the performance of the fringe tracker, especially its magnitude limit. Because of this intimate relationship between fringe tracker performance and the science performance of the system as a whole, the VLTi Spectro-Imager will incorporate its own fringe tracking subsystem. The combined system of fringe tracker and science beam combiner will be optimised as a whole to meet the science requirements. In order to fulfill the science goals of high-throughput acquisition of data, high-SNR high-spectral-resolution imaging, and imaging of complex faint objects, the fringe tracker will operate in a minimum of three distinct modes defined as follows:

6.1.1 Fringe acquisition

This is a mode in which a finite region of OPD space is scanned in order to find the fringe coherence envelope in the presence of atmospheric and instrumental delay uncertainties. This mode will typically use a either a continuous or stepped scan of the delay lines together a group-delay algorithm to efficiently detect the presence of fringes over a region of delay space set by the coherence length of a single spectral channel.

6.1.2 Hardware phase tracking

This is a mode in which the delay errors are actively compensated at high speed so that the level of stability of the science combiner fringes is suﬃcient to allow on-chip integration of the fringe signal over periods of many atmospheric coherence times. Typically hardware phase tracking requires a high SNR fringe phase measurement to be made in a short integration time in to allow the high-precision (typically of order λ/20) correction required. This means that a bright (mH < 10) reference object is required, but providing such a reference is available, then the long coherent integration times aﬀorded on the science combiner allow high-spectral-resolution measurements to be made relatively rapidly. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 60 / 118

Figure 6.1: Conceptual layout of the fringe tracker optics

6.1.3 Hardware coherencing

This is a mode in which the delay errors are compensated in real time but at a lower speed, with sufficient precision to ensure that the loss in fringe contrast due to temporal coherence effects is small over incoherent integration periods of many minutes. Using group-delay tracking methods on spectrally-dispersed fringes [REF15], the fringes can be tracked using reference stars at least 2.5 magnitudes fainter than are usable with phase-tracking methods [REF16]. In addition, in the presence of short-term Strehl “dropouts” and phase branch point effects due to imperfect AO correction, group delay methods are considerably more robust. Thus the hardware coherencing mode will be most beneficial for science on faint targets and/or in moderate to poor seeing. In this mode, the science combiner will need to be read out at rates comparable to the atmospheric coherence time, rather than the longer integration times afforded by the phase-tracking mode.

6.2 System analysis

A conceptual layout for the fringe tracker is shown in ﬁgure 6.1.The subcomponents of the fringe tracker are described in the following sections and have been separated into:

• Dichroics Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 61 / 118

• Beam switchyard; • Fringe-tracking beam combiner; • Fast path modulators • Low-resolution spectrograph and detector; • Control system; • OPD corrector;

A number of system-level tasks need to be undertaken to validate the proposed fringe tracker concept. A complete optical and mechanical design of the fringe-tracking combiner optics is needed to ensure that the combiner can be ﬁtted within the space envelope at the VLTI. A key parameter of the science case for the instrument as a whole will be the list of which potential science targets can be observed in a high-spectral-resolution phase-tracking mode and which can be observed in a faint-object coherencing mode. Detailed calculations of the magnitude limits for both these modes will feed into the determination of these potential target lists. The maximum coherent integration time, and hence SNR, for the science combiner when the fringe combiner is in phase-tracking mode will be strongly limited by drifts in the relative OPD as measured by the fringe tracker and as seen by the science beam combiner. Various methods of “tying together” the beam combiners using either mechanical means or laser metrology will be evaluated to determine the practical limits to achieving long coherent integrations and the most cost-eﬀective means for achieving these.

[Task 61] Space envelope design study for fringe tracker [Task 62] Prediction of fringe tracking magnitude limits [Task 63] Design study of methods of mitigation of non-common-path OPD drifts

6.3 Dichroics

The fringe tracker uses light from the whole of a near-IR waveband, selectable between H and K, to derive the OPD errors, while the science combiner will work in one of the remaining wavebands. The fringe-tracking light is separated from the light for the science combiner using optimised dichroics. Two possible sets of dichroics are needed to allow all possible sets of fringe tracking/science wavelength splits. The baseline is for these dichroics to be switched manually, but a motorised switching option would minimise the need for operators to enter the instrument area.

[Task 64] Cost/beneﬁt analysis of motorised switching of dichroics.

6.4 Beam switchyard

Light not taken by the science combiner enters the fringe tracker beam switchyard, consisting of a pair of movable ﬂat mirrors in sequence for each beam which performs the following three functions:

1. It allows beams from each of the delay lines to be fed into diﬀerent inputs to the fringe tracking beam combiner. This allows the set of baselines to be used for fringe tracking to be optimally conﬁgured for the set of telescopes in use, for example to allow “baseline bootstrapping” on a set of nearest-neighbour telescopes. 2. It adapts the spacing of the beams coming from the delay lines to that required at the input of the fringe-tracking beam combiner. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 62 / 118

3. It allows the relative pathlengths between the diﬀerent beams entering the fringe tracking beam combiner to be adjusted so that when the OPDs are equalised in the science combiner they are also equalised in the fringe tracking combiner.

The switchyard is very similar in function to that in the science combiner, so phase A studies of the science switchyard will be equally applicable to the fringe tracker switchyard.

6.5 Fringe-tracking combiner

The fringe tracking combiner is a pairwise pupil-plane combiner arranged as shown in the figure. The figure shows a 6-beam combiner but the arrangement can be straightforwardly adapted for different numbers of incoming beams by adding or removing stages. In the 6-beam arrangement, only the 5 nearest-neighbour pairs of input beams are combined, yielding 10 interference patterns, and the “outermost” pair of input beams are discarded. The fringes are “fluffed out” so that the output beams are either all dark or all light.

6.6 Fast pathlength modulators

The fringe phase is temporally modulated using mirrors mounted on piezoelectrically-actuated stages.

6.7 Low-resolution spectrograph and detector

The output beams of from the beam combiner constitute a single pixel of information: this enters a low-resolution spectrograph which disperses the light into a low resolution spectrum incident on a near-infrared array detector. The optics are designed such that reading out approximately five pixels of the detector corresponds to reading 5 spectral sub-bands across a photometric band (i.e. R ∼ 20). These 5 pixels of spectral information are read out synchronously with the phase modulation waveform. The detectors for the fringe tracking beam combiner are perhaps the most critical factor in achieving high performance fringe tracking, particularly for the faintest sources. An evaluation of existing and planned infrared focal-plane arrays, particularly with regard to minimising read noise, will be performed, resulting in a recommendation as to the best array technology for the fringe tracker and the most effective readout strategy to employ. The most straightforward scheme for using detectors would be to have one spectrograph and detector for each of the 6-10 outputs of the fringe tracking beam combiner. Since only 5 pixels of each detector will be used, there is an opportunity to significantly reduce the system cost by multiplexing multiple beam combiner outputs onto a single detector. The optimum trade between multiplexing advantage and losses in fringe tracking performance resulting from changes in throughput, crosstalk and detector read noise will be determined by designing in some detail a number optical arrangements for multiplexing and evaluating their effects on system performance.

[Task 65] Evaluation of detectors for the fringe tracker [Task 66] Cost/beneﬁt trade of multiplexing multiple beam combiner outputs onto a single detector

6.8 Control system

The software system for the fringe tracker controls all the basic functions of the fringe tracker. The subtasks within the control system are summarised in the subsections below. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 63 / 118

6.8.1 User interface

Control of the fringe tracker during observing will be part of an integrated interface to the entire instrument, but engineering-mode software will allow detailed access to system parameters.

6.8.2 Quasi-static control of motorised elements

The control system adjusts the motorised degrees of freedom of the fringe tracker on roughly a nightly basis for alignment purposes and also to change operating modes. The degrees of freedom to be controlled include:

• Adjustment of the beam switchyard (10 translational degrees of freedom and 20 tilt degrees of freedom for a 6T solution). • Adjustment of internal alignment mirrors (12 rotational degrees of freedom). • Changes of ﬁlter to allow for changes in fringe-tracking wavelength (6 ﬁlter slide changes). This may not be necessary depending on the design of the spectral dispersion system.

6.8.3 Real-time servo loops

The real-time component of the fringe tracker derives adjustments to the OPD from the pixel data stream arriving from the detectors. In both the coherencing or phase-tracking modes the fringe amplitude and phase are derived for each of the 5 spectral sub-bands at rates of up to several hundred Hz. Typically 4 fringe samples need to be taken synchronously with the OPD modulation in order to derive the fringe parameters, so that 20 pixels in total need to be processed per coherent integration per baseline being tracked. For 5 baselines being tracked at a sample rate of 500Hz, the data rate is 50ksamples/sec. This is not a demanding computational task, and so specialised computing hardware (e.g. DSP arrays) is not necessary — it should be possible to perform all the real-time computation on a single Pentium-class processor running a hard real-time operating system.

6.8.4 Mode switching

Switching between the acquisition, coherencing and phase-tracking modes can either be done automatically based on real-time evaluation of the fringe signal-to-noise ratio, or can be performed under external control. Switching between these modes requires no hardware changes, only software algorithm and parameter changes within the fringe tracking computer, and so can be accomplished in fractions of a second.

6.8.5 Data archiving

The fringe tracking computer archives the sensed fringe signals and correction signals. This archived data can be used for diagnostics or for post-processing of the science data using software phase rotation algorithms.

6.9 OPD corrector

The fringe-tracking computer ﬁlters the derived OPD errors and sends the appropriate signals to the a two-stage OPD correction system consisting of:

1. A mirror mounted on a fast piezo-electric stage connected which takes out rapid pathlength ﬂuctuations. 2. Error signals sent to the delay line signals to correct long-term large-amplitude OPD errors. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 64 / 118

6.10 Required studies for Phase-A

Much of the hardware and software required for the fringe tracker has already been demonstrated on the VLTI and other interferometers, and experience from the FINITO fringe tracker (especially that available from the members of the FINITO team who are members of the VLTi Spectro-Imager consortium) will provide good information as to the external constraints on the fringe tracker. However, a number of speciﬁc points need to be addressed in the Phase-A study in order to determine the optimum speciﬁcation of the fringe tracker hardware and software to allow maximum science throughput for the system as a whole. These tasks are summarised below.

6.10.1 System analysis

Task 59: Investigate options for monomode ﬁbres covering all wavebands simultaneously. Task 61: Space envelope design study for fringe tracker Task 62: Prediction of fringe tracking magnitude limits Task 63: Design study of methods of mitigation of non-common-path OPD drifts

6.10.2 Dichroics

Task 64: Cost/beneﬁt analysis of motorised switching of dichroics.

6.10.3 Low-resolution spectrographs and detectors

Task 65: Evaluation of detectors for the fringe tracker Task 66: Cost/beneﬁt trade study of multiplexing multiple beam combiner outputs onto a single detector Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 65 / 118

Chapter 7

Preliminary development plan

This chapter gives the main guidelines for the expected development plan of the whole VLTi Spectro-Imager project. We have identiﬁed the main phases of the project as the following:

– Phase A studies – Design studies – Manufacturing – Assembly Integration and Tests

During the proposed phase A studies, the main critical points will be analyzed1. A complete list of the foreseen analysis is detailed in the next chapter (Chapter 8).

7.1 Project organization

The competence and experience of the consortium is detailed for each institute in Annex A. The management of the project is presented in the preliminary Work Bench Structure (WBS) of Fig. 7.1. This development plan is preliminary since formal commitments are not yet available from some partners of the consortium. These commitments are possibly subject to changes according to the chosen solution. If the IO solution is chosen, the main part of the project management will be provided by LAOG (Principal Investigator, Project Manager, System Engineer) as well as the integration and its management, whereas trade no management plan has been deﬁned for the BO concept option. Phase A will allow to complete the management plan for all identiﬁed subsystems. The possible responsibilities are the followings:

- Instrument feeding optics: TBD - Fringe tracker: Cavendish (David Buscher) - Beam Combiner module: LAOG (Jean-Philippe Berger) - Spectrograph and detector: TBD - Detector: MPfIR (Udo Beckmann) - Spectrograph: TBD - Cryostat: TBD - Software: LAOG (G´erard Zins)

1We provide also a comparison between an Integrated Optics and a Bulk Optics concept. According to the result of this comparison a diﬀerent management plan is proposed. The required expertise for each concept as well as the available manpower to built the instrument diﬀers for each concept. LAOG will provide a strong involvement for the manufacturing of an Integrated Optics instrument, but cannot provide the required manpower for a Bulk Optics instrument that requires an important opto-mechanics contribution. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 66 / 118

VLTi Imager PI : Fabien Malbet LAOG

Project Manager Co-PIs Pierre Kern D.Buscher, G. Weigelt, LAOG P. Garcia, M. Gai, J. Surdej, J. Hron, R. Neuhaüser

Science group System Engineer Chair : Paulo Garcia Laurent Jocou CAUP LAOG

AIT Karine Perraut LAOG

Instrument Feeding Optics Fringe tracker Beam Combiner Spectrometer & IR Detector Software Alignments & calibration tools TBD David Buscher Jean Philippe Berger TBD Gérard Zins TBD Cavendish LAOG LAOG

Atmospheric Dispersion Switchyard 4T IO combiner IR camera Control software Compensator J, H & K Udo Beckmann Gérard Zins MPfIR LAGO

Beam Injection modules Combining Optics Fiber Optics Bundles Spectrograph Data reduction TBD Gilles Duvert LAOG

Spatial Filtering Spectrograph &detector Relay Optics & support Image reconstruction Eric Thiébaut JMMC

Optical Path Scanner Control Software Polarization Control

Component Selection

6/8T IO combiners J, H &K

Figure 7.1: WBS of the VLTi Spectro-Imager for the IO solution. The green box corresponds to the optional deliverable, and the darker blue one to an external contribution.

- Alignment and calibration tools: TBD

For the bulk optics solution the management team has to be reconsidered as well as the responsibilities of the main subsystems. The system activity will be conducted according to the system WBS presented in Fig. 7.2. The purpose of this breakdown is to achieve all the required budget and performance estimations described in Sect. 7.5, 7.3 and 7.2. The system design will allow us to deﬁne the interfaces between the subsystems and with the VLTI. Maintenance procedures will be deﬁned during this phase. Some prototyping activities can be foreseen for the most critical functions.

7.2 Manpower

7.2.1 Required manpower for VLTi Spectro-Imager

An evaluation of the required resources is given in Table 7.1. It has been obtained thanks to FTE aﬀectation to each subsystem or activities of Fig. 7.2. These values will be analyzed more accurately during the phase A studies. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 67 / 118

Figure 7.2: System main activities Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 68 / 118

Table 7.1: Project estimated required manpower expressed in Full Time Equivalent (FTE) in the case of the 4 telescope instrument baseline. Subsystems Estimated required FTE (expressed in years) IO solution BO solution Project management 2 FTE Science Group 2 FTE System Engineering 3 FTE Fringe tracker 6.65 FTE Opto-mechanics 2.4 FTE Control software 2 FTE Real time software 1.5 FTE Data archiving 0.75 FTE Feeding optics 5.2 FTE 5.2 FTE Beam Combiner 2.4 FTE 2.4 FTE Spectrograph / Detection 12 FTE Detection 3.5 Spectrograph 6.5 Cryostat 2 Software 18 FTE Control 5 Data reduction 5 Image reconstruction 8 AIT 4.5 FTE AIT tools 2 AIT Europe 2 AIT Paranal 0.5 Total 54.8 FTE

7.2.2 Estimation of the available manpower in the consortium

Table 7.2 lists the competences and the possible contributions of each institute of the consortium. This based on the content of the Letters of Intent which comes with this document [REF2]. Some contributions for the phase after the phase A are subjects to formal commitment of the projects and decision from funding authorities. Final decision will be made at the end of the Phase A.

7.3 Tentative planning

Gantt chart of ﬁgure 7.3 presents the proposed planning for the whole project. It includes the following phases:

- Phase A Studies: Concluded by the Phase A review. Phase A is aimed to prove the feasibility of the proposed conceptual design. During these 9 months, most critical aspects of the considered designs will be addressed and the organization of the project will be ﬁnalized and each member of the consortium will commit to the project. - Preliminary design studies: This one year study is concluded by a Preliminary Design Review (PDR). An important issue of this phase is the release of the main critical component orders (feeding optics, integrated optics beam combiners, spectrograph optics, detectors) - Detailed design studies: After this one year study concluded by a Final Design Review (FDR), the complete design of the instrument will be available, and will be released for manufacturing. - Manufacturing: The whole instrument is manufactured during this phase. At the end all parts of the instrument are available for assembly. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 69 / 118

Table 7.2: Possible consortium contributions for the project design and manufacturing, and related manpower expressed in FTE (in years) over the 4 years of the project.

Institute Activities FTE (over 3-4 years) Management LAOG Integrated Optics 20 (Grenoble) System studies Science Objectives Image reconstruction CAUP Integrated Optics 6∗ (Porto) Science Objectives Fringe tracker Cavendish System studies 12∗ (Cambridge) Science Objectives Nears infrared detectors systems Detector electronics MPfIR Opto mechanical sub-systems 9 (Bonn) Electronics sub systems Software Science Objectives Optical and opto-mechanical cryogenics and detector INAF instrument modeling: error budget and performance analysis TBD (Italy) Software Science Objectives Fiber optics IAGL System studies 6∗ (Li`ege) Software Science Objectives IfA Software 3∗ (Vienna) Science Objectives Integrated Optics AIU Software 6∗ (Jena) Science Objectives Total ≥ 62 ∗ subject to funding agencies agreement Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 70 / 118

2006 2007 2008 2009 2010 2011 Numéro de Titre Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 plan VLTi Imager 1 Project Management 2 Science 3 System Engineering 4 Sub-systems 5 Phase A studies 6 Phase A review 7 Design 8 Preliminary Design review 9 Final Design Review 10 Realization 11 AIT Europe 12 Preliminary Acceptance Europe 13 Packing and Shipping 14 AIT Paranal 15 Commissionning

Figure 7.3: Tentative planning of the VLTi Spectro-Imager

- AIT Europe: During this phase the instrument is assembled, and fully characterized in all operating modes. This phase ends by the Preliminary Acceptance in Europe (PAE), that allows the consortium shipping to Paranal. - AIT Paranal: During this phase the instrument is assembled in the interferometric laboratory in Paranal, and characterized. At the end of this phase the instrument is ready for commissioning. - Commissioning: These on-sky tests and characterizations allow the consortium to establish that the instrument is operational and can be oﬀered to the ESO community.

Table 7.3 gives the main milestones of the project.

Table 7.3: Project milestones

Milestones Dates Kick-oﬀ Meeting t0 PDR t0 + 12 months FDR t0 + 24 months PAE t0 + 44 months

7.4 Documentation and deliverable

Phase A studies will detail the required documentation for the whole project. It will mainly include the usual progress reports over a period to be deﬁned with ESO, and the PDR, FDR and PAE documentation packages.

7.5 Financial budget

7.5.1 Cost evaluation

Table 7.4 gives the estimated costs for the main instrument sub-systems and project related activities in the case of a 4 telescope conﬁguration operated in the J, H and K band. A more accurate cost estimation will be provided at the end of the phase A depending to the system choices. The provided estimation has been established according to previous instrument experience (NAOS, IOTA, AMBER and VLT-PF ). For this estimation we have considered standard component costs down to motorized displacement Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 71 / 118

Table 7.4: Project estimated costs in the case of the 4 telescope instrument baseline.

Subsystems Estimated costs IO solution BO solution Fringe tracker 1200 ke Optomechanics 200 Detection∗ (x2∗∗) 900 Cryostat (x2∗∗) 100 Spectrograph (x2∗∗) 100 Feeding optics 207 ke Beam injection Modules 93 ADC 62 OPD Scanner 52 Beam Combiner 342 ke 264 ke IO Beam Combiners 300 BO Beam Combiners 240 Support 12 12 Polarization Control 10 - Fiber Optics Bundles 20 12 Spectrograph/Detection 877 ke Detection 670 Spectrograph 137 Cryostat 70 Spare parts 40 ke Software 70 ke AIT tools 95 ke Operation 420 ke Travels 200 Transport 20 Overheads 120 Contingencies 80 (TBC) Total 3251 ke 3173 ke ∗ on the basis of two 1Kx1K FPA ∗∗ for possible cost reduction see task 66

stages, or regular optical components such as oﬀ-axis parabolas or ADC prisms. For example we consider that the cost for a remote controlled translation or rotation stage is around 5 ke/axis to be ESO compliant.

7.5.2 Financial contributions

The ﬁnancial contributions from the consortium members are not yet deﬁned (see letters of intent [REF2]). Budget requests will be submitted to the national funding agencies at the end of phase A. ESO will be solicited at least to contribute for ESO standard control boards procurements and eventually for detectors and controllers both for the science and the fringe tracker cameras.

7.6 Requirements on VLTI infrastructure

VLTi Spectro-Imager needs the current VLTI available facilities (see Sect. 1.3). For faint object observation (PRIMA combined operation), VLTi Spectro-Imager requires the use of 4 star telescope separators (STS) on UTs and/or ATs which means presently the procurement by ESO of two additional STS for UTs. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 72 / 118

If necessary, depending of phase A studies, we may require Adaptive Optics systems on all ATs2.

2LAOG associated with Floralis/AlpAO can eventually provide on ESO request a design and manufacturing of AO systems for ATs. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 73 / 118

Chapter 8

Phase-A management plan

8.1 Scope of the chapter

This chapter details the organization of the phase A study. This is based on the intentions given by the diﬀerent institutes of the consortium in their Letters of Intent [REF2] and the list of tasks deﬁned in chapters 2 to 6.

8.2 Organization of the phase A study

The organization of the project will be split in three parts as indicated in Fig. 8.1:

– The science group is in charge of specifying the astrophysical high level requirements. It has a special and important role in VLTi Spectro-Imager since one has to define a strategy for the best use of the VLTI infrastructure leading to consequences on the image quality. The group will be helped with external consultants, specialists in their astrophysical domains and by internal consultants. A special link is foreseen with the Image Reconstruction group. – The system group is in charge of solving all the issues raised in chapters 3 to 6. It is made of the subsystem leaders and the identified persons who work at the system level (system engineer, interfaces engineer and integration manager). The TBD leaders will be identified before or at the kick-off meeting depending on the competences of the available resources and the motivation of the participating consortium. – The management is in charge of the project so that information circulates fluently between the groups and also to organize the work of the consortium at higher level. The management will participate to the meetings of each group as necessary. The management is also responsible to build the structure of the project for the following phase. The management is the main contact point for ESO.

The science group will have two face-to-face meetings, at the beginning of its work and near the end. The rest of the time, communication will be done through email or by audio-conference. We plan to have most of the science work done by the middle of the phase A study so that inputs are given in advance to the system group. The system group will have a telephone meeting of half a day every two weeks to follow the progress of the tasks and discuss main issues. We plan to have also two face-to-face meetings for general discussion, in particular to discuss the choice of the solution for the beam combiner. Many “easy” issues will be tackled at the beginning in order not to depend on the progress of the science group. At the end of the phase-A study, the diﬀerent subsystem leaders will specify the high level requirements of their subsystems. We plan also have a meeting of the co-Is for the construction of the ﬁnal management of the project. An important question will have to be solved, namely the management which depends on the technical solution chosen (integrated optics or bulk optics). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 74 / 118

VLTi Imager Phase A PI : Fabien Malbet PM : Pierre Kern

Science Group Instrument System

Chair : Paula Garcia / CAUP Chair :Jean Philippe Berger

Olivier Absil / IAGL System Engineer : L. Jocou Thierry Forveille / LAOG Interfaces : E. Lecoarer GAspard Duchêne / LAOG Integration and tests: K. Perraut Joseph Hron / IfA John Young / Cavendish Leonardo Testi / INAF Fringe tracker : D. Buscher Alessandro Marconi / INAF Instrument feeding Optics : TBD Pierre-Olivier Petrucci / LAOG IO Beam Combiner: J-P Berger Ralph Neuhäuser / AIU BO Beam Combiner: D. Buscher Gerd Weigelt / MPfIR Software: G. Zins Spectrograph : TBD External Consultants: Detection: U. Beckmann Karel Schrijver, Sebastian Wolf, AIT Tools : TBD Tim Harries, Romano COrradi COnsultants: Internal consultants: O. Absil Karine Perraut, Jean Philippe Berger, Eric Thiébaut, Michael De Becker, Werner Weiss

Figure 8.1: Structure of the phase A study

Figure 8.2: Planning of the phase-A study

8.3 Planning of the phase A

We estimate the phase-A study to last 9 months. We plan to have 3 meetings with ESO at the beginning (kick-oﬀ meeting), in the middle of the phase A (mid-term meeting), and at the end for the phase A review (see milestones in Fig. 8.2). We plan to have continuous contact with ESO especially on issues concerning interfaces with the VLTI and detectors.

8.4 Financial needs

In order to fulﬁll the objectives of the phase A, we have some ﬁnancial needs. There are of three kinds:

- travel and subsistence for the internal meetings of the group; - funding for the contract extension of one student and one postdoc in Cavendish Laboratory; - funding for the management (travels of PI/PM) in addition to the regular meetings.

Table 8.1 summarizes our needs. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 75 / 118

Table 8.1: Financial needs of the consortium for the phase A study Nature Quantity Total Kick-Oﬀ meeting (Grenoble) 13 x 0.8 ke 10.4ke Science meeting (Cambridge?) 10 x 0.8 ke 8.0ke System meeting (Germany?) 8 x 0.8 ke 6.4ke 2 months of PhD+Postdoc (Cavendish) 10+5ke 15ke Travel for PI and PM to visit the consortium 7x2x0.8ke 11.2ke Total 51ke

8.5 Summary of phase A studies

Tables 8.2 to 8.6 summarize identified tasks for the phase A studies as defined in chapters 2 through 6. Beside identification of the tasks, they also report the amount of work required for each task. For most of the tasks, the main contributors have been identified. The repartition of the tasks between all participants of the consortium will be completed for the kick off meeting. Table 8.7 gives the total manpower needs required for the completion of the for the phase A tasks. We found a total of 122 men-months.

8.6 Consortium contribution to the studies

We have listed in table 8.8, the resources and skills which are oﬀered by the members of the consortium. We found a total of 136 men-months. We think that this matches to the need declared in the previous section.

8.7 Phase A deliverable

We expect to submit for the phase A review the following documents:

1. Science cases: update of the current science cases [REF1]. 2. Science analysis report: analysis of the tasks identiﬁed in chapter 2. 3. Technical Speciﬁcations 4. User’s requirements 5. Instrument Conceptual Design (initial version) 6. Instrument analysis report (initial version) 7. Interface control document (initial version) 8. Management Plan Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 76 / 118

Table 8.2: Summary of phase-A studies and required manpower (in men-months) for the science analysis.

Estimated Subsystem Task # Designation duration (men-months) Task 1 Define the three spectral resolution modes 0.5 Task 2 Calibrators 1 Top level Task 3 Define the maximum time in which an image must be 0.5 requirements taken Task 4 Define data products 1 Task 5 Polarization 0.5 sub-total 3.5 Task 6 Observing modes 1 Operational model Task 7 Complementary observations 1 Task 8 Target of opportunity 0.5 sub-total 2.5 Task 9 Science image strategy 6 Task 10 Image reconstruction algorithm selection 0.5 Image reconstruction Task 11 AO data 0.5 Task 12 FOV and mosaicing 0.5 sub-total 7.5 Task 13 Define large programmes 2 Task 13 Target lists 1 Task 15 Generate synthetic images 1 Science cases Task 16 End-to-end simulation and feedback 1 Task 17 Identify preparatory programmes relevant for the instru- 1 ment Task 18 Complementary and competition 0.5 sub-total 6.5 Total 40 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 77 / 118

Table 8.3: Summary of phase-A studies and required manpower (in men-months) for the system analysis.

Estimated Subsystem Task # Designation duration (men-months) Task 22 Assessing wavefront quality 2 Wavefront Quality Task 23 If relevant specify additional beam shaper module 1 Task 19 Compare pinhole vs. single-mode fiber spatial filtering 1 Spatial filter module capability Task 20 If relevant specify pinhole subsystem 0.5 Optical path Task 21 Specify the different optical path compensation require- 0.5 compensation ments

Beam injection Task 24 Specify the beam injection module functionalities 0.5 module Beam combination Task 27 Beam combiners concept comparisons, final recommen- 6 module dation Task 28 Evaluation of the upgrading to 6 beams 2 Task 25 Specify high level requirements (group delay vs. phase 0.5 Fringe tracker tracking, limiting magnitude performances) Task 26 Specify the fringe tracker in detail (operating wavelength, 1 combination concept, bootstrapping strategy) Task 29 Constrain as well as possible VLTI optical train polar- 1 ization Polarization control Task 30 Simulate polarization behavior of IO combiners, specify 2 system consequences Task 31 Assess bulk optics combiner polarization behavior 0.5 Task 32 Specify the spectral resolution requirements in collabo- 0.5 Spectrometer ration with science group Task 33 Specify the calibration level required for each spectral 0.5 mode defined by the science group Detector Task 34 Define the detector required performances and operating 0.5 modes Data Reduction Task 35 Specify the expected accuracy of observables (visibility, 1 phases, closure phases) in terms of data reduction requirements Image Task 36 Specify the incidence of imaging requirements on system 4 Reconstruction choices and VLTI operation Calibration Task 37 Define the alignment/calibration requirements 1 requirements Performances Task 38 Assess expected performances for each science modes 0.5 PRIMA Task 39 Assess the system consequences of the availability of TBD PRIMA Task 40 General design: translation of science requirements into 0.5 high level system and subsystems specifications Task 41 Selection of observing modes 0.5 Global System Task 42 Consistency of system choices 1.0 Studies Task 43 Assessing control requirements 0.5 Task 44 Assessing the instrumental stability requirements 1 Task 45 Interface with the VLTI 0.5 Total 29.5 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 78 / 118

Table 8.4: Summary of phase-A studies and required manpower (in men-months) for the IO solution.

Estimated Subsystem Task # Designation duration (men-months) Injection module Task 47 Design study of the injection module 2 Task 48 Full characterization of a 4T ABCD H beam combiner 5 (throughput, instrumental contrast, closure phase biases, Beam combiner chromatic behavior, polarization measurements) Task 49 Design study of the beam combiner sub-system (fibers, com- 7 biners, chromatic dispersion constraint, maintenance) Polarization control Task 50 Experimental validation of the polarization separation lo- 1 cated at the output of the beam combiner Spectrograph Task 51 Concept study of the spectrograph 3 Task 52 Search of the best suitable detector according the format and 1 Detector frame rate specifications Data reduction Task 53 Define the data reduction strategy 1 Task 54 Paper study of the option 6/8T beam combiners 2 Additional Task 55 If required, make a concept study of an optional adaptive 2 functionalities optics system Total 24

Table 8.5: Summary of phase-A studies and required manpower (in men-months) for the BO solution.

Estimated Subsystem Task # Designation duration (men-months) Task 56 Design study of fast/slow switchyard options (suitability of 1.5 Beam switchyard commercial slides) Science beam Task 57 Design study of manufacturing options of scaled-up cont- 2 combiner acted-optics beam combiner Path modulators Task 58 Study of options for modular drive waveform calibration 0.5 Beam injection / Task 59 Investigate options for single mode fibers covering all wave- 1 Spatial filtering bands simultaneously Task 60 Monitor common tasks for BO/IO concepts for commonality 1 Other tasks of specification Total 6 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 79 / 118

Table 8.6: Summary of phase-A studies and required manpower (in men-months) for the fringe tracker.

Estimated Subsystem Task # Designation duration (men-months) Task 59 Investigate options for single-mode fibers covering all wave- 0.5 bands simultaneously Task 61 Space envelope design study for fringe tracker 2 Subsystem analysis Task 62 Prediction of fringe tracking magnitude limits 1 Task 63 Design study of methods of mitigation of non-common-path 0.5 OPD drifts Dichroics Task 64 Cost/benefit analysis of motorized switching of dichroics 0.5 Low-resolution Task 65 Evaluation of detectors for the fringe tracker 1 spectrographs and Task 66 Cost/benefit trade study of multiplexing multiple beam com- 1 detectors biner outputs onto a single detector Total 6.5

Table 8.7: Summary of required manpower for phase A task completion Task group required manpower (men-months) Science 40 System 29.5 Fringe tracker 6.5 IO combiner solution 24 BO combiner solution 6 Management 10 Documentation & Meetings 6 Total 122 Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 80 / 118

Table 8.8: Consortium contributions for the Phase A studies, and related manpower expressed in FTE (in men-months) over the 9 months of the project.

Institute Activities FTE (over 9 months) Management LAOG Integrated Optics 40 (Grenoble) System studies Science Objectives Image reconstruction CAUP Integrated Optics (Porto) 18 Science Objectives Fringe tracker Cavendish System studies 8+4∗ (Cambridge) Science Objectives Nears infrared detectors systems Detector electronics MPfIR Opto mechanical sub-systems 18 (Bonn) Electronics sub systems Software Science Objectives Optical and opto-mechanical cryogenics and detector INAF instrument modeling: error budget and performance analysis 9 (Italy) Software Science Objectives Fiber optics IAGL System studies 18 (Li`ege) Software Science Objectives IfA Software 3 (Vienna) Science Objectives Integrated Optics AIU Software 18 (Jena) Science Objectives Total 136 men-months ∗ subject to funding agencies agreement Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 81 / 118

Appendix A

Experience from the proposing consortium

A.1 Laboratoire d’Astrophysique de Grenoble

LAOG has strong scientiﬁc and technical implications in high angular resolution techniques for astronomy and has developed over the past ten years its experience and expertise in several areas important in achieving the goals of the VLTi Spectro-Imager.

Teams interested in the VLTi Spectro-Imager

LAOG is composed of 4 main teams, 3 devoted to astrophysical research (FOST, SHERPAS and ASTROMOL) and one to instrumental research (GRIL), and a technical group. Three of these teams are focused on research which can be tackled with the VLTi Spectro-Imager:

– FOST (= star and planet formation, brown dwarfs) team focuses on later stages of star formation, mainly the physics of star-disk interactions, evolved disks and the conditions for planet formation (structural features like gaps and rings, dust grain evolution in disks, etc.; timescale ≈ 106 − 107 yrs), and also on the formation mechanisms of binaries and the Initial Mas Function (IMF). A specific activity within the team is the study of brown dwarfs, both as astronomical objects by themselves, and as intermediate bodies between low-mass stars and exoplanets. The search and characterization of exoplanets are themselves an increasing part of the FOST activities. The team contributes a lot to observations made with LAOG-built instruments and to their interpretation. Permanent staff : 13 + 7 shared with GRIL. PhDs in 2001-2005 completed : 5 + 1 with GRIL; underway: 9 + 3 with GRIL + 1 with SHERPAS. Team leader: F. Ménard (CNRS). – SHERPAS (=sources of high energies and relativistic physics in accretion-ejection structures , in full) team is essentially involved in MHD theory calculations, with particular emphasis on the accretion-ejection phenomenon in astrophysics. Here it mainly applies models to star-disk interactions and disk-driven jets, where magnetic fields, instead of gravitation, play a dominant role. The team has an interest in high angular resolution observations of AGN and micro-quasars in order to constrain their models. Permanent staff : 7. PhDs in 2001-2005 completed: 2; underway: 2 + 1 with FOST. Team leader: Pr. G. Pelletier (University J. Fourier). – GRIL (= instrumental research group at LAOG) team concentrates on strategic issues in research & development (R&D) for future instruments and detectors. GRIL’s responsibility has been to contribute to the development of optical and near-IR instruments for large ground-based telescopes (ESO, CFHT) with the highest spatial resolution (for instance with the goal to resolve the inner parts of protoplanetary disks, i.e., within 1 AU at 450 pc, say), by way of adaptive optics and interferometry, and/or the highest dynamic range (adaptive optics to image exoplanets as closely as possible from their host star). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 82 / 118

Permanent staﬀ : 9 (including 8 engineers) + 7 shared with FOST. PhDs in 2001-2005 completed: 3 + 1 with FOST; underway: 8 + 3 with FOST. Team leader: Dr. C. Perrier (Astronomer).

The key persons from LAOG involved in the VLTi Spectro-Imager are: J.-P. Berger, G. Duvert, L. Jocou, P. Kern, E. Le Coarer, F. Malbet, K. Perraut all of them part of GRIL. J.-P. Berger, G. Duvert and F. Malbet are also part of FOST. G. Duchˆene,T. Forveille from FOST and P.O. Petrucci from SHERPAS are part of the science group.

Instrumental experience

Technically, LAOG has been involved in the development of two ﬁrst generation VLT/VLTI instruments:

– NAOS, the Nasmyth Adaptive Optics System for the VLT, which was delivered to ESO in the fall of 2001 and is now being installed on UT4. LAOG was responsible for the instrument opto-mechanical design and realization, the system interfaces, the visible wavefront sensor, the overall instrument control and the preliminary integration. NAOS was developed in collaboration with LESIA and ONERA. – AMBER, a VLTI near-infrared instrument, which has been delivered to ESO in spring 2004. LAOG was responsible for the system design, the ﬁnal integration and testing, the high-level control software and the data reduction software. AMBER was developed in collaboration with OCA/LUAN in Nice, Max-Planck Institute for Radioastronomy (Bonn) and Arcetri Observatory (Florence).

For this two projects, LAOG astronomers also played a key role in the definition of the scientific drivers and high level requirements of the instruments. LAOG has been chosen by ESO to lead the development of the VLT Planet Finder, one the of the second generation instrument of the VLT, under the leadership of Dr. J.-L. Beuzit. Compared to NAOS, the main emphasis is on a very high dynamic range to reach the scientific goal of direct detection of dozens of Jupiter-mass planets, possibly in multiple systems (as a few are already known from the radial-velocity method). It is expected to be completed in 2009-2010. The persons involved in the VLTi Spectro-Imager are mostly not involved in the VLT-PF project. LAOG also took part to the development of the Wide-field Infrared Camera (WIRCAM) for the CFHT (Canada- France-Hawaii Telescope), in collaboration with LAE at Universitéde Montréaland LESIA, among others. LAOG activities on this project included the overall mechanical design, realization and testing (including the cryostat) and the preliminary integration. LAOG is currently leading Research and Development efforts on critical components for astronomical instruments, such as deformable micro-mirrors for adaptive optics (with up to 10000 actuators) and integrated optics combiners for interferometry, in collaboration with other institutional and industrial partners. The IO work led to the manufacturing of 3 beam combiners, 2 of them being currently in operation:

• a 3T beam combiner which is the the science combiner of the IOTA interferometer. Two astrophysical papers have already been published in major journals and several others are in preparation [REF18, REF19]. • a 2T beam combiner which replaced the MONA ﬁber coupler of VINCI on the VLTI. This beam combiner was used for example for the ﬁrst fringes of the ATs (see press release).

LAOG hosts the service part and the direction of Jean-Marie Mariotti Center, the French Center for Infrared and Optical Interferometry. It provides support for the users of the astronomical interferometers currently in operation around the world. JMMC plays a leading role in the Joint Research Activity 4 of the European Interferometry Initiative (EII). This project, centered on the VLTI, is one of the 6 JRAs of the European programme OPTICON. Twelve countries participate in this programme (Austria, Belgium, Czech Republic, France, Germany, Hungary, Israel, Italy, Nederlands, Poland, Portugal, United Kingdom), as well as ESA and ESO, for a total of more than twenty laboratories. The resources of the JRA4 are distributed evenly on two work packages Advanced instruments and Oﬀ-line data reduction software. In 2006, the technical personnel at LAOG include a total of 17 engineers and technicians. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 83 / 118

Short biographies of the Principal Investigator and the Project Manager

Dr. Malbet graduated in 1992 on the astrophysical topic Circumstellar environments of young stars under the direction of Pr. Lénaand Dr. Bertout. In 1993-1994, Research Associate at JPL in the group of Dr. Shao, he proposed the dark hole method in space-based stellar coronography and took part to the construction of the Palomar Testbed Interferometer (PTI) under the supervision of Dr. M. Colavita. Entered in CNRS in 1995, he worked on T Tauri disk modeling showing the importance of infrared interferometry for such objects. In 1998, with Dr. R.G. Petrov, he put in place a European consortium to build AMBER the near infrared instrument of the VLT Interferometer. He occupied the function of Project Scientist, and, after 2000, led the science group. He took part to the commissioning of the AMBER instrument, and, conducted the work leading to the first AMBER result, where for the first time evidence for spatially resolved wind was found together with the presence of a disk around the young star MWC 297. F. Malbet is part of the LAOG team working on the new technology promising for astronomical interferometry especially with a large number of telescopes. F. Malbet has been responsible for the interferometry activity in LAOG since 1998. Dr. Kern graduated in 1990 with a thesis demonstrating for the first time that adaptive optics worked in astronomy (first observations at OHP in 1989). Hired by LAOG to take an active part to the VLTI development, and, P. Kern took the leadership of the optomechanical part of the VLT project NAOS because of the delay of the VLTI. In the same time Dr. Kern started an important research and technology development in the integrated optics technology. He organized the AstroFib’96 workshop where all specialists from this domain met for the first time. In 2002-2004, P. Kern has been deputy project manager of AMBER during its integration phase in LAOG. P. Kern is also at the origin of the development of micro deformable mirrors which are now manufactured for several labs in Europe. P. Kern has been the technical director of LAOG since 2003.

Internet webpages

More details can be found on the Internet at the following places:

• LAOG: http://www-laog.obs.ujf-grenoble.fr • AMBER: http://amber.obs.ujf-grenoble.fr • JMMC: http://www.mariotti.fr

A.2 Cavendish Laboratory, University of Cambridge

Background

Members of the Cambridge Optical Aperture Synthesis Telescope (COAST) team have been key players in the field of optical aperture synthesis since the early 1980’s. Then, under the leadership of Professor John Baldwin, they were responsible for the first measurements of optical and near-infrared closure phases, for delivering the first images from optical aperture synthesis and for the design and deployment of the world’s first optical separated element synthesis telescope, COAST. Subsequently, their work has spanned the full range of activities associated with the delivery of a synthesis imaging capability for astronomers, including system design, design, prototyping and delivery of hardware and software components of interferometers, as well as astronomical observations using COAST and other interferometric arrays. The group has also made significant contributions to the development of the OIFITS standard for interferometer data exchange under the auspices of the IAU, and won the first IAU-organized “Imaging Beauty Contest” in 2004 with their BSMEM software package. The group’s astrophysical interests have been mainly directed towards understanding the surface activity and mass loss from cool evolved stars and confronting theories of stellar pulsation, in particular of Mira variables. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 84 / 118

Current activities

Most recently, the COAST group has been focusing mainly on two parallel technical eﬀorts: (i) with US colleagues, as key participants of the Magdalena Ridge Observatory Interferometer (MROI) and (ii) with European colleagues as participants of the European Interferometry Initiative (EII). The group’s role in the MROI is as provider of top- level technical and scientiﬁc oversight, as well as being responsible for the design and delivery of a number of critical subsystems, in particular the long-stroke vacuum delay lines and the beam combiners. Under the EII’s umbrella, the team have been participating in the technical activities associated with second-generation instrument design for the VLTI, with fringe tracking, and with the testing and development of novel image reconstruction algorithms for optical/IR interferometric data.

Team

The current COAST team comprises two full time tenured academic staff (Buscher and Haniff), three post-doctoral workers (Young, Seneta and Baron), two engineers and, typically, around two graduate students. For this proposal we expect that one of our graduate students and one of our post-docs will provide significant inputs of effort, together with oversight, direction and top-level contributions from Buscher, Haniff and Young. Further details of our group’s activity and research record can be found at our web site at:

http://www.mrao.cam.ac.uk/telescopes/coast/

Short biography of the Co-I

Dr. David Buscher has been closely involved in astronomical aperture synthesis for close to 20 years. He was a key contributor to the design of the Cambridge Optical Aperture Synthesis Telescope (COAST) and has worked at the MkIII interferometer on Mt Wilson, California and contributed to the design and construction of the NPOI interferometer in Flagstaﬀ, Arizona. From 1994-1999 he lead the team responsible for the design and commissioning of the University of Durham MARTINI and ELECTRA adaptive optics systems for the William Herschel Telescope and participated in the NAOMI common-user adaptive optics project. From 1999 he has worked on next-generation optical and infrared synthesis telescopes at the Cavendish Laboratory. He has authored papers on imaging the surfaces of supergiant stars and stellar envelopes, aperture masking techniques, atmospheric seeing, image reconstruction, laser- guide-star adaptive optics, and the design and optimization of optical interferometers.

A.3 Infrared Interferometry Group at the Max-Planck Institute for Ra- dioastronomy

Group web page: http://www.mpifr-bonn.mpg.de/div/ir-interferometry

Research areas

Our Infrared Interferometry Group at the Max-Planck Institute for Radioastronomy conducts a wide range of research in the following ﬁelds: star formation, evolved stars, active galactic nuclei, radiative transfer modeling, and development of methods for high angular resolution imaging

Development of instrumentation for high angular resolution imaging

Our group developed the following instruments for high-resolution imaging at visible and near-infrared wavelengths:

• Speckle cameras for speckle imaging at visible wavelengths: based on optical photon-counting detectors and electron-multiplying CCD cameras. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 85 / 118

• Speckle cameras for speckle imaging at near-infrared wavelengths: based on NICMOS, PICNIC, and Hawaii Array detectors. • K-band beam combiner instrument for the GI2T interferometer. • JHK-band beam combiner instrument for the IOTA interferometer (see movie on the web page of our group). • Hawaii Array detector system and detector software for the AMBER instrument. • Hawaii Array fringe tracker detector and science software for the LINC-NIRVANA interferometry instrument (Large Binocular Telescope).

The team

Head of the group: Gerd Weigelt - Director at the MPIfR (http://www.mpifr-bonn.mpg.de/staff/gweigelt); Staﬀ members: 6 astronomers; Postdocs: 4 astronomers; students: 3 PhD students; number of engineers and technicians: 6.

Curriculum Vitae of the CoI Gerd Weigelt:

February 7, 1947 born in Erlangen, Germany 1969 - 1975 Study of Physics, Erlangen-Nuremberg University 1978 Ph.D. in Physics, Erlangen-Nuremberg University 1978 - 1981 Postdoc at Erlangen-Nuremberg University 1982 - 1989 Professor, Erlangen-Nuremberg University 1989 - present Director at the Max Planck Institute for Radioastronomy in Bonn

A.4 Centro de Astrof´ısica da Universidade do Porto

CAUP is the largest astronomical centre in Portugal, with a staﬀ of 14 permanent scientists, 4 post-docs and 16 PhD students. It also attracts yearly 10 short term (1-2 weeks) visitors. The centre is one of the top Portuguese research units in Earth and Space Sciences - evaluated as excellent by National Science Foundation - FCT. Its main areas of research are star formation, cosmology and asteroseismology. CAUP supports the training in astronomy via Astronomy BSc, MSc and PhD programmes. CAUP shares a building with the town Planetarium actively participating in outreach and spreading of scientiﬁc culture.

Instrumentation experience

CAUP has started in early 2004 a collaboration with INESC-Porto optoelectronics unit (located 500m from CAUP) in guided optics R&D for astronomical interferometry. This collaboration is being highly successful and rapid prototyping of recombiners for the J band using sol-gel technologies is underway.

Scientiﬁc domains related to VLTI

CAUP is actively involved in the scientific exploitation of the VLTI since 2001 in the fields of star formation and asteroseismology. Activities include: a) participation in the definition of the AMBER instrument guaranteed time; b) scientific exploitation of VINCI, MIDI and AMBER; c) participation in the radiative transfer and asteroseismology working groups of the OPTICON interferometry networking; d) participation in the OPTICON interferometry JRA; e) Coordination of the Marie Curie VLTI summer schools (2006-2008). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 86 / 118

Team description

Paulo J.V. Garcia Assistant professor star formation CAUP Margarida Cunha Post-doc asteroseismology CAUP Samira Rajabi PhD student radiative transfer CAUP Ines Carvalho Assistant professor system studies FEUP Ant´onio Leite Associate professor integrated optics INESC-Porto Jos´eSantos Associate professor guided optics INESC-Porto Paulo Marques Assistant professor integrated optics INESC-Porto Paulo Moreira Post-doc integrated optics CAUP/INESC-Porto Askari Ghasempour PhD student guided optics CAUP/INESC-Porto

Short bio of the co-I

Paulo J.V. Garcia scientiﬁc interests lie in the modelisation and high angular resolution observation of the circumstellar environments of pre-main-sequence stars. He completed his PhD on models and observations of jets from young stars under the supervision of Renaud Foy in 1999. During the year 2000 was support astronomer and deputy instrument specialist of the ISIS and IDS spectrographs at the Isaac Newton Group of Telescopes, La Palma Observatory. During the year 2001 was Post-doc at CAUP. From 2001 to 2005 was Assistant Professor on contract with 340h/yr teaching. Since 2005 is tenure track Assistant professor with 250h/yr teaching. Edited two proceedings and co-authored 16 ISI articles. Has served in several national and international committees. Coordinator of several projects totaling ∼ 1 Meuro.

Relevant publications

CAUP/INESC-Porto publications relevant to the theme: Planar and UV written channel optical waveguides prepared with siloxane Polly(oxyethylene)-zirconia organic-inorganic hybrids Molina C, Moreira PJ, et al., 2005, Journal of Materials Chemistry, 15, 3937 Photosensitive materials for integrated optic applications, 2005, Marques PVS, Moreira PJ, Alexandre D, et al., Fiber and integrated optics, 24 (3-4): 149-169 Observations of 51 Ophiuchi with MIDI at the VLTI, 2005, astro-ph/8052, Gil, C.; Malbet, F., et al. The Very Large Telescope Interferometer - Challenges for the Future, 2003, Eds. Garcia, P. J. V.; Glindemann, A.; Henning, Th.; Malbet, F. ISBN 1-4020-1518-6 Interferometry and asteroseismology: The radius of tau Cet, 2003, A&A, 406, 15, Pijpers, F. P.; Teixeira, T. C.; Garcia, P. J.; Cunha, M. S.; Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.

A.5 Istituto Nazionale di Astroﬁsica

The INAF team is composed by the Observatories of Arcetri (OAA), Rome (OAR), Turin (OATo) and Catania (OACt), supported by the Universities of Padova (UPD) and Bologna. Such Institutes are playing an important role in the construction and use of VLTI and LBT instrumentation. All institutes are interested to contribute to both scientiﬁc case and instrument development.

Technological expertise

OAA is responsible for the cold spectrograph of AMBER (AMBER-SPG). OATo was responsible for the construction of FINITO, the ﬁrst instrument designed for fringe stabilization, which allows the other instruments to have exposures longer than the atmospheric coherence time. OATo is part of the team (with Alenia Spazio) building the two Fringe Sensor Units (FSU) for PRIMA, the instrument for Phase Referenced Imaging and Microarcsecond Astrometry. OATo has been involved in characterization and testing of NIR and MIR detection systems, including optimization of Read- Out electronics for high-speed, low noise operations. OAR is responsible for the camera system on the Medium-High- Wavefront Sensor (MHWS) of the beam combiner LINC-NIRVANA on LBT. UPD has started a series of training Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 87 / 118 activities dedicated to the formation of interferometric expertise. The Observatory of Catania (OACt) has a signiﬁcant experience on development, characterisation, maintenance and usage of astronomical instrumentation and detection systems at visible wavelengths, and wishes to achieve an active involvement in near IR interferometric instrumentation.

Data analysis expertise

Data reduction and analysis, from the calibration of the raw data to the extraction of the astrophysical parameters, are critical to the successful scientiﬁc utilisation of interferometric instruments. A large part of the team members has developed speciﬁc expertise in handling data reduction tools of the present VLTI instruments (VINCI, MIDI, AMBER) and in developing procedures for the visibility computation from 2D physical models.

Scientiﬁc expertise

Scientiﬁc topics which we have already investigated with the present high resolution facilities, and that can be better addressed with the higher imaging performance of the instrument currently proposed, are:

• Sizes of asteroids: we are now involved in the ﬁrst interferometric observations of minor bodies of the Solar system ever attempted. Interferometric observations allow us to get direct size estimates for these objects and to derive their physical parameters taking advantage of the known orbits. • Young stellar objects: Properties of the close environment of young stars to address the dynamical interplay between the disk, the pre-main sequence star, and the emanated jet. • Mira variables: determination of the photospheric diameter of Mira-type stars so far prevented by their large asymmetries whose origin is still unknown. • AGN: i) existence and size of the dusty tori at the core of the Uniﬁed Model for Active Galactic Nuclei; ii) geometry and kinematics of the Broad Line Region in AGN; iii) determination of the IR counterpart to the VLBI mas radio observations in radio-loud AGN; iv) structure of galaxies at high redshift.

Additional information on the proposing Institutes can be derived from the Internet sites of INAF and the Astronomy Department of the Padova University:

• http://www.inaf.it • http://dipastro.pd.astro.it

A.6 Institut d’Astrophysique et de G´eophysique de Li`ege

Internet web pages:

– http://www.astro.ulg.ac.be/iagl.html – http://www.astro.ulg.ac.be/Rech/AEOS

Personnel

IAGL comprises some 80 employees, among which approximately 15 senior scientists, 15 post-docs and 25 PhD students. Within IAGL, several astronomers from the AEOS group (Astrophysique Extragalactique et Observations Spatiales) ought to contribute to the VLTi Spectro-Imager. These are :

• Jean Surdej,professor & FNRS honorary research director: interest in high angular resolution imaging and extragalactic astrophysics • Olivier Absil, PhD student: interferometry, Darwin, Genie, Pegase, extrasolar planets, exo-zodi, debris disks, massive stars Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 88 / 118

• Denis Defr`ere, PhD student: interferometry, Darwin, young stellar disks • Emilie Herwats, PhD student: interferometry, young stellar disks • Dimitri Mawet, PhD student: coronagraphy, interferometry, Darwin, Achromatic Phase Shifters, AGN, extrasolar planets • Pierre Riaud, post-doc, coronagraphy, interferometry, Achromatic Phase Shifters, adaptive optics, AGN, extrasolar planets, exo-zodi, circumstellar envelopes

Several members of the GAPHE group (Eric Gosset, FNRS Research Associate; Gr´egorRauw, FNRS Research Associate and Michael De Becker, post-doc) also wish to contribute to elaborate the scientiﬁc case of massive stars in the context of the phase-A studies of the VLTi Spectro-Imager.

Past instrumental realizations

• Construction of a pupil densifier with a sky experiment on the stars Castor and Altair (P. Riaud) • Microlens replication with NOA and Silicon on the AOA master for the pupil densifier device (P. Riaud) • Participation to brain-storming sessions for the interferometric optimization of a coronagraphic device for the TPF project (Team Boeing-SVS, P. Riaud) • Optimization of a coronagraphic instrument for JWST/MIRI (LESIA-CEA partnership). Building of one Lyot mask (Al) and three monochromatic Four Quadrant Phase Masks (FQPM) in Germanium substrates for the three wavelengths: 10.6 / 11.4 / 15.5 microns (P. Riaud & D. Mawet) • Upgrade proposition and realization of a monochromatic FQPM coronagraph for the VLT/NACO instrument in the Ks band. Commissioned and accessible to the scientific community since the P75 period (P. Riaud, D. Mawet) • Manufacturing and testing of a half-wave FQPM coronagraph in the visible (P. Riaud, D. Mawet) • Participation to high order adaptive optics test of achromatized FQPM coronagraph on the workbench BOA in ONERA (P. Riaud) • Partnership with LESIA and the CEA-LETI for the construction of 4QZOG and AGPM coronagraphs with a pi-phase shift achromatization provided by the Zero Order Grating (ZOG) technology (D. Mawet, P. Riaud, J. Surdej, J. Baudrand, S. Habraken, P. Baudoz, D. Rouan, + CSL) • ESA contract concerning the APS (Achromatic Phase-Shifter) for the DARWIN project in the thermal infrared (6-18 microns). This device is also using the ZOG technology (D. Mawet, P. Riaud, J. Surdej, S. Habraken, D. Vandormael + CSL) • Participation to the pre-phase A study of the GENIE nulling instrument with ESA/ESTEC (O. Absil) • Participation to the phase A study of the GENIE nulling instrument in collaboration with Alcatel Alenia Space (O. Absil) • Participation to the phase 0 of the Pegase space interferometer (O. Absil) • Contribution to the preliminary design of the Darwin mission (O. Absil) • Definition of the preliminary design of ALADDIN, the Antarctic nulling interferometer (O. Absil) • On-going construction of the International 4m Liquid Mirror Telescope (J. Surdej)

A.7 Institut f¨urAstronomie, Universit¨atWien

Web-page: http://www.univie.ac.at/astro Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 89 / 118

Scientiﬁc interests

One of the main topics of astronomical research at IfA is Stellar Astrophysics (AGB-stars, asteroseismology, magnetic stars). Thus there is a growing interest in interferometry at IfA and therefore the institute is also partner in the European Interferometry Initiative and in the corresponding part of OPTICON. Participation in a proposal for a 2nd generation VLTI instrument is a logical next step not only for increasing the scientiﬁc exploitation of interferometric instruments but also to gain more experience in interferometric instrumentation and data-processing.

Experience and staﬀ involved

While the IfA has no direct experience in interferometric instrumentation, there is considerable experience in space and ground-based instruments with a strong emphasis in the development of control and data-processing software and in project management. This concerns the following projects:

• space: HERSCHEL/PACS, COROT • ground: DENIS, TIMMI2

The following staﬀ members are participating in Viennas contribution to the VLTi Spectro-Imager:

J. Hron: Co-I of DENIS, coordinator of Viennas involvement in TIMMI2, member of science board of the European Interferometry Initiative; working on atmospheres of late-type giants (model-atmospheres, IR-spectroscopy and IR-interferometry). F. Kerschbaum: Co-I of Herschel/PACS and coordinator of Vienna contribution; research on winds of late type giants (spectroscopy, mm-interferometry). W.W. Weiss: Co-I of COROT, coordinator of Viennas involvment in COROT and MOST; research on asteroseismology and magnetic stars (optical photometry and spectroscopy).

A.8 Astrophysikalisches Institut und Universit¨ats-Sternwarte

This description does not concern only AIU Jena, but also the Fraunhofer Institute for Applied Optics (IoF) in Jena directed by for Prof. Andreas T¨unnermann, who will fully participate in this Phase-A study.

Previous experience

At AIU Jena, the mid-infrared instruments TIMMI and TIMMI2 for the ESO 3.6m telescopes were built. The infrastructure with institute and faculty workshops are still available. The Institute of Applied Physics (IAP) at University Jena lead by Prof. Andreas Tünnermann, has a longstanding tradition and competence in design, fabrication and application of active and passive photonic elements for both, optic and opto-electronic devices. A total staff of 30 scientists and engineers are working presently in education and R & D. The institute has a floorspace of 1200 square meters with installed clean rooms and optical laboratories including microstructure technology (electron beam and photo lithography, reactive ion and reactive ion beam etching, diffusion and ion exchange ovens, coating facilities, scanning electron and atomic force microscopy) and optic / opto-electronic testing and measuring instrumentation. The Fraunhofer Institute for Applied Optics (IoF) in Jena, also led by Prof. Andreas Tünnermann, will participate as well in the VLTI phase-A study. Research and development at Fraunhofer IOF focuses on optical systems technology with a view to continually improving the control of light from generation via guiding and manipulation up to its application. Integrated Optical devices are one of the main fields of IoF: Integrated electro-optical controlled devices can be used for phase- and amplitude modulation in micro system technology. Optical waveguide structures are fabricated in electro-optical crystals like lithium niobate (LiNbO3) or potassium titanyl phosphate (KTiOPO4) by means of proton or ion exchange. Using an electrode system a phase information can be impressed on the guided wave. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 90 / 118

Intensity modulators are constructed by insertion of a phase modulator in a Mach-Zehnder interferometer structure. The modulation voltages are between 3 and 10 Volts, depending on the polarization and the wavelength of the guided light. Typical modulation depths are about 500:1 up to frequencies in the Gigahertz range. The central operation wavelengths can amount between 450 nm to the near infrared. It is possible to guide and modulate optical powers up to 500 mW. Application fields are the fields of communication, sensor technology, polygraphic technology, and beam combination of astrophysical sources. For the design of integrated-optical devices a broad variety of software tools and methods is used. Eigenmode calculation is done by mode solvers based on finite difference and finite element schemes, mode matching, and transfer matrix algorithm, respectively. Field evolution is modeled by beam propagation methods, by mode propagation, and by the finite difference time domain method. Ad hoc programs, macros and interfaces are used to optimize designs, to relate design and measurement, to combine optical modeling with e.g. thermal analysis, and to facilitate hybrid designs combining integrated-optical and micro-optical components. According to specific requirements of multimode applications ray-tracing methods are used as well.

Science interest

AIU scientists study the formation of stars, brown dwarfs, and planets, including circumstellar disks, both by observations and theory. Most recently, we perform high-angular resolution, high sensitive AO observations (e.g. with VLT/NACO) to detect young sub-stellar companions around young nearby stars, in order to study the formation of such companions empirically. We have contributed the detection of the first few brown dwarf companions to young stars (TWA-5, HR 7329, GSC 8047) and also the direct imaging detection of the first (or at least one of the first few) planets, ever imaged directly, namely GQ Lupi b. In addition, we are also working on theoretical models to understand planet formation, and to estimate the masses of companions from observables, like luminosity and temperature (or color). Most conventional models do not take into account the formation of the objects, so that they are not valid for young objects (below a few tens of Myrs), while our models (Wuchterl et al.) do take into the formation, so that they arte also valid for young objects. The advantage of observing young stars is the fact that their companions are also young and, due to contraction and accretion, they are self-luminous, i.e. much brighter than old planets.

List of scientists from Jena involved

Prof. Ralph Neuhäuser (director AIU, observer of sub-stellar companions, imaging), Prof. Dr. Alexander Krivov (AIU, theory of circumstellar disks), Dr. Katharina Schreyer (AIU, radio interferometry, disks), Dr. Günther Wuchterl (AIU, theory of formation, model tracks), Christopher Broeg (AIU, theory of formation, model tracks, finishing PhD in mid 2006, to stay at AIU as post-doc), Markus Mugrauer (AIU, observer of sub-stellar companions, astrometry, finishing PhD in mid 2006, to stay at AIU as post-doc), Walter Teuschel and/or NN (AIU, technician), Prof. Dr. Andreas Tünnermann (director IAP and IoF Jena) and his staff members and students, all working on integrated optics: Dr. Jens Limpert, Dr. JörgFuchs, Dr. E.-B. Kley, Dipl.-Phys. Markus Augustin, Dipl.-Phys. Bodo Martin, Dipl.- Phys. Bernd Schelle, and Mrs. Abbe, technician. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 91 / 118

Appendix B

Bibliography

The bibliography presented here comes from all members of the consortium. It has been sorted by methodology and in reverse chronology.

B.1 Astrophysical drivers

Absil, O., den Hartog, R., Gondoin, P., Fabry, P., Wilhelm, R., Gitton, F. and Puech, F.: 2006. Performance study of ground-based infrared Bracewell interferometers – Application to the detection of exozodiacal dust disks with GENIE. A&A , in press. Garcia, P., Berger, J. P., Corradi, R., Forveille, T., Harries, T., Henri, G., Malbet, F., Marconi, A., Perraut, K., Petrucci, P. O., Schrijver, K., Testi, L., Thiébaut, E. and Wolf, S.: VITRUV - Science Cases. In The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation VLTI Instrumentation”, Garching, (preprint astro-ph/0507580) (2005), in press. Hatzes, A. P. and Wuchterl, G.: 2005. Astronomy: Giant planet seeks nursery place. Nature 436, 182. Malbet, F., Berger, J. P., Garcia, P., Kern, P., Perraut, K., Benisty, M., Jocou, L., Herwats, E., Lebouquin, J. B., Labeye, P., Le Coarer, E., Preis, O., Tatulli, E. and Thiébaut, E.: VITRUV - Imaging close environments of stars and galaxies with the VLTI at milli-arcsec resolution. In ”The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation VLTI Instrumentation”, Allemagne (2005) (2005). Millour, F., Vannier, M., Petrov, R., Lopez, B. and Rantakiro, F.: 2005. Extrasolar Planets with AMBER/VLTI, What can we expect from current performances ? in IAU Syposium 200 , in press. Nowotny, W., Lebzelter, T., Hron, J. and Höfner, S.: 2005. Atmospheric dynamics in carbon-rich Miras. A&A 437, 285. Peˇcnik, B. and Wuchterl, G.: 2005. Giant planet formation. A first classification of isothermal protoplanetary equilibria. A&A 440, 1183. Smith, M. D. and Rosen, A.: 2005. Hydrodynamic simulations of molecular outflows driven by slow-precessing protostellar jets. MNRAS 357, 579. Vannier, M., Petrov, R., Millour, F. and Lopez, B.: Prospects for Direct Observation of ”Pegasi” Planets with Color- Differential Interferometry. In Protostars and Planets V, Proceedings of the Conference held October 24-28, 2005, in Hilton Waikoloa Village, Hawai’i. LPI Contribution No. 1286., p.8626 (2005), 8626–+. Wuchterl, G.: 2005a. Convective radiation fluid-dynamics: formation and early evolution at the substellar limit and beyond. Astronomische Nachrichten 326, 633. Wuchterl, G.: 2005b. Convective radiation fluid-dynamics: formation and early evolution of ultra low-mass objects. Astronomische Nachrichten 326, 905. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 92 / 118

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Garcia, P., Glindemann, A., Henning, T. and Malbet, F. (Eds.): 2003. The Very Large Telescope Interferometer - Challenges for the Future (2003). Gil, C. S. C., Garcia, P. J. V., Foy, R. and Thiébaut, E.: Reaching the jet engine with AMBER/VLTI. In EAS Publications Series (2003), 261–+. Haniff, C.: 2003. Imaging stars and their environments with the VLTI. Astrophysics and Space Science 286, 163. Malbet, F.: 2003a. Probing the close environment of young stellar objects with interferometry. Ap&SS 286, 131. Malbet, F.: Young stellar objects science with interferometry. In Interferometry for Optical Astronomy II. Edited by Wesley A. Traub. Proceedings of the SPIE, Volume 4838, pp. 554-566 (2003). (2003b), 554–566. Marconi, A., Axon, D. J., Capetti, A., Maciejewski, W., Atkinson, J., Batcheldor, D., Binney, J., Carollo, M., Dressel, L., Ford, H., Gerssen, J., Hughes, M. A., Macchetto, D., Merrifield, M. R., Scarlata, C., Sparks, W., Stiavelli, M., Tsvetanov, Z. and van der Marel, R. P.: 2003. Is There Really a Black Hole at the Center of NGC 4041? Constraints from Gas Kinematics. ApJ 586, 868. Marconi, A. and Hunt, L. K.: 2003. The Relation between Black Hole Mass, Bulge Mass, and Near-Infrared Luminosity. ApJ 589, L21. Monnier, J. D., Millan-Gabet, R., Akeson, R. L., Berger, J.-P., Billmeier, R. R., Calvet, N., D’Alessio, P., Hart- mann, L., Hillenbrand, L. A., Kuchner, M., Traub, W. A., Tuthill, P. G. and Keck Interferometer (NASA-JPL, K. O. M. S. C. T.: 2003. Young Stellar Objects with the Keck Interferometer. American Astronomical Society Meeting Abstracts 203, . Pesenti, N., Dougados, C., Cabrit, S., O’Brien, D., Garcia, P. and Ferreira, J.: 2003. Near-IR [Fe II] emission diagnostics applied to cold disk winds in young stars. A&A 410, 155. Thiébaut, E., Garcia, P. J. V. and Foy, R.: 2003. Imaging with Amber/VLTI: the case of microjets. Ap&SS 286, 171. Vollmer, B. and Beckert, T.: 2003. Turbulent viscosity in clumpy accretion disks. II. Supernova driven turbulence in the Galaxy. A&A 404, 21. Wuchterl, G. and Tscharnuter, W. M.: 2003. From clouds to stars. Protostellar collapse and the evolution to the pre-main sequence I. Equations and evolution in the Hertzsprung-Russell diagram. A&A 398, 1081. Young, J. S.: From visibilities to science with simple models. In G. Perrin and F. Malbet (Eds.), Observing with the VLTI, volume 6 of EAS Publications Series (3–8 February 2002, Les Houches, France, 2003), 181. Beckert, T. and Duschl, W. J.: 2002. Where have all the black holes gone? A&A 387, 422. Beckert, T. and Falcke, H.: 2002. Circular polarization of radio emission from relativistic jets. A&A 388, 1106. Beckert, T., Krichbaum, T. P., Cimò,G., Fuhrmann, L., Kraus, A., Witzel, A. and Zensus, J. A.: 2002. The Size of IDV Jet Cores. Publications of the Astronomical Society of Australia 19, 55. Garcia, P. J. V., Foy, R. and Thiébaut, E.: Into the Twilight Zone [Claude Bertout, 1989]: Reaching the Jet Engine with AMBER/VLTI. In The Origins of Stars and Planets: The VLT View. Proceedings of the ESO Workshop held in Garching, Germany, 24-27 April 2001, p. 267. (2002), 267–+. Heiter, U., Kupka, F., van’t Veer-Menneret, C., Barban, C., Weiss, W. W., Goupil, M.-J., Schmidt, W., Katz, D. and Garrido, R.: 2002. New grids of ATLAS9 atmospheres I: Influence of convection treatments on model structure and on observable quantities. A&A 392, 619. Hron, J., Aringer, B., Gautschy-Loidl, R., Höfner,S. and Jørgensen, U. G.: Synthetic spectra for pulsating red giants: status, limitations and applications. In ASP Conf. Ser. 274: Observed HR Diagrams and Stellar Evolution (2002), 110–+. Ragland, S., Traub, W., Lacasse, M., Monnier, J., Millan-Gabet, R., Schloerb, P., Berger, J.-P., Pedretti, E. and Carleton, N.: 2002. Interferometric Investigations of Highly Evolved Stars. Bulletin of the American Astronomical Society 34, 1127. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 94 / 118

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B.2 Optical interferometry and related techniques

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Kern, P., Berger, J.-P., Haguenauer, P., Malbet, F. and Perraut, K.: 2001. Planar Integrated Optics and astronomical interferometry. Academie des Sciences Paris Comptes Rendus 2, 111. Riaud, P., Boccaletti, A., Rouan, D., Lemarquis, F. and Labeyrie, A.: 2001. The Four-Quadrant Phase-Mask Coron- agraph. II. Simulation. PASP 113, 1145. Berger, J.-P., Benech, P., Schanen-Duport, I., Maury, G., Malbet, F. and Reynaud, F.: Combining up to eight telescope beams in a single chip. In Proc. SPIE Vol. 4006, p. 986-995, Interferometry in Optical Astronomy, Pierre J. Lena; Andreas Quirrenbach; Eds. (2000), 986–995. Buscher, D. F., Rogers, J., Baldwin, J. E., Boysen, R. C., George, A. V., Haniff, C. A., Pearson, D., Rogers, J., Warner, P. J., Wilson, D. M. A. and Young, J. S.: Technologies for a cost-effective astronomical imaging array. In Interferometry in Optical Astronomy, volume 4006 of Proc. SPIE. 27–29 March 2000, Munich (SPIE Press, 2000), 1061. Ollivier, M., Mariotti, J.-M., Sekulic, P., Michel, G., Leger, A. M., Bouchareine, P., Brunaud, J., Coude du Foresto, V., Mennesson, B. P., Borde, P. J., Amy-Klein, A., Vanlerberghe, A., Lagage, P.-O., Artzner, G. E. and Malbet, F.: Nulling interferometry for the DARWIN mission: experimental demonstration of the concept in the thermal infrared with high levels of rejection. In Proc. SPIE Vol. 4006, p. 354-358, Interferometry in Optical Astronomy, Pierre J. Lena; Andreas Quirrenbach; Eds. (2000), 354–358. Berger, J. P., Rousselet-Perraut, K., Kern, P., Malbet, F., Schanen-Duport, I., Reynaud, F., Haguenauer, P. and Benech, P.: 1999. Integrated optics for astronomical interferometry. II. First laboratory white-light interferograms. A&AS 139, 173. Colavita, M. M., Wallace, J. K., Hines, B. E., Gursel, Y., Malbet, F., Palmer, D. L., Pan, X. P., Shao, M., Yu, J. W., Boden, A. F., Dumont, P. J., Gubler, J., Koresko, C. D., Kulkarni, S. R., Lane, B. F., Mobley, D. W. and van Belle, G. T.: 1999. The Palomar Testbed Interferometer. ApJ 510, 505. Haniff, C. A.: Practical considerations for imaging interferometry. In S. Unwin and R. Stachnik (Eds.), Optical and IR Interferometry from Ground and Space (NASA/JPL Conference, 24–27 May 1999, Dana Point, California, 1999), 230–240. Lawson, P. R., Scott, T. R. and Haniff, C. A.: 1999. Group-delay tracking and visibility fluctuations in long-baseline interferometry. MNRAS 304, 218. Malbet, F., Kern, P., Schanen-Duport, I., Berger, J.-P., Rousselet-Perraut, K. and Benech, P.: 1999. Integrated optics for astronomical interferometry. I. Concept and astronomical applications. A&AS 138, 135. Ollivier, M., Léger, A., Sekulic, C. A. P., Brunaud, J., Artzner, G., Mariotti, J.-M., Michel, G., CoudéDu Foresto, V., Mennesson, B., Bouchareine, P., Lépine, T. and Malbet, F.: Nulling Interferometry for the DARWIN Mission - Lab- oratory Demonstration Experiment. In ASP Conf. Ser. 194: Working on the Fringe: Optical and IR Interferometry from Ground and Space (1999), 443–+. Dejonghe, J., Arnold, L., Lardiere, O., Berger, J.-P., Cazale, C., Dutertre, S., Kohler, D. and Vernet, D.: Optical very large array (OVLA) prototype telescope: status report and perspective for large mosaic mirrors. In Proc. SPIE Vol. 3352, p. 603-613, Advanced Technology Optical/IR Telescopes VI, Larry M. Stepp; Ed. (1998), 603–613. Gai, M., Casertano, S., Carollo, D. and Lattanzi, M. G.: 1998. Location Estimators for Interferometric Fringes. PASP 110, 848. Wallace, J. K., Boden, A. F., Colavita, M. M., Dumont, P. J., Gursel, Y., Hines, B. E., Koresko, C., Kulkarni, S. R., Lane, B., Malbet, F., Palmer, D., Pan, X., Shao, M., Vasisht, G., van Belle, G. T. and Yu, J. W.: Palomar Testbed Interferometer. In Proc. SPIE Vol. 3350, p. 864-871, Astronomical Interferometry, Robert D. Reasenberg; Ed. (1998), 864–871. Kern, P. and Malbet, F.: Astrofib’96: Integrated optics for Astronomical interferometry (Integrated Optics for Astro- nomical Interferometry, 1997). Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 101 / 118

B.3 Instrumental projects

Mawet, D., Riaud, P., Baudrand, J., Dupuis, O., Baudoz, P., Boccaletti, A. and Rouan, D.: 2006. The Four-Quadrant Phase-Mask Coronagraph: White light laboratory results with an achromatic device. A&A , in press. Allsop, T., Floreani, F., Jedrzejewski, K. P., Romero, R., Marques, P. V. S., Webb, D. J. and Bennion, I.: Tapered fibre LPG device as a sensing element for refractive index. In Third International Conference on Experimental Mechanics and Third Conference of the Asian Committee on Experimental Mechanics. Edited by Quan, Chenggen; Chau, Fook Siong; Asundi, Anand; Wong, Brian Stephen; Lim, Chwee Teck. Proceedings of the SPIE, Volume 5855, pp. 443-446 (2005). (2005), 443–446. Barge, P., Baglin, A., Auvergne, M., Buey, J.-T., Catala, C., Michel, E., Weiss, W. W., Deleuil, M., Jorda, L., Moutou, C. and COROT Team: CoRoT: a first space mission to find terrestrial planets. In SF2A-2005: Semaine de l’Astrophysique Francaise (2005), 193–+. Buscher, D. F., Baron, F., Coyne, J., Haniff, C. A. and Young, J. S.: BOBCAT - a photon-efficient multi-way combiner for the VLTI. In F. Paresce, A. Richichi, A. Chelli and F. Delplancke (Eds.), Proc. ESO-EII workshop, The power of optical/IR interferometry: recent scientific results and 2nd generation VLTI instrumentation (ESO, 2005). In press. Coyne, J., Baron, F., Buscher, D. F., Haniff, C. A. and Young, J. S.: A photon-efficient imaging beam combiner for VLTI. In UK National Astronomy Meeting, 4–8 April 2005, Birmingham (UK National Astronomy Meeting, 4–8 April 2005, Birmingham, 2005). Frazão, O., Melo, M., Marques, P. V. S. and Santos, J. L.: 2005a. Chirped Bragg grating fabricated in fused fibre taper for strain temperature discrimination. Measurement Science and Technology 16, 984. Frazão, O., Melo, M., Romero, R., Marques, P. V. S., Araújo, F. M., Ferreira, L. A. and Santos, J. L.: Short in-fibre Bragg grating structure for simultaneous measurement of strain and temperature. In Third International Conference on Experimental Mechanics and Third Conference of the Asian Committee on Experimental Mechanics. Edited by Quan, Chenggen; Chau, Fook Siong; Asundi, Anand; Wong, Brian Stephen; Lim, Chwee Teck. Proceedings of the SPIE, Volume 5855, pp. 876-879 (2005). (2005b), 876–879. Neill, R. J. and Young, J. S.: A new infra-red camera for COAST. In UK National Astronomy Meeting, 4–8 April 2005, Birmingham (UK National Astronomy Meeting, 4–8 April 2005, Birmingham, 2005). Ollivier, M., Le Duigou, J. M., Mourard, D., Absil, O., Cassaing, F., Herwats, E., Escarrat, L., Allard, F., Clédassou, R., CoudéDu Foresto, V., Delpech, M., Duchon, P., Guidotti, P. Y., Léger, A., Leyre, X., Malbet, F., Rouan, D. and Udry, S.: PEGASE... towards DARWIN. In SF2A-2005: Semaine de l’Astrophysique Francaise (2005), 197–+. Pauls, T. A., Young, J. S., Cotton, W. D. and Monnier, J. D.: 2005. A data exchange standard for optical (visible/IR) interferometry. PASP In press. Poglitsch, A., Waelkens, C., Geis, N., Cepa, J., Henning, T., van Hoof, C., Kerschbaum, F., Lemke, D., Renotte, E., Royer, P., Rodriguez, L. and Saraceno, P.: 2005. The Herschel Photodetector Array Camera and Spectrometer PACS. Astronomische Nachrichten 326, 583. Rego, G., Carvalho, J. C. C., Marques, P. V. S., Fernandez Fernandez, A., Dürr, F. and Limberger, H. G.: Stress profiling of arc-induced long-period gratings written in pure-silica-core fibers. In Third International Conference on Experimental Mechanics and Third Conference of the Asian Committee on Experimental Mechanics. Edited by Quan, Chenggen; Chau, Fook Siong; Asundi, Anand; Wong, Brian Stephen; Lim, Chwee Teck. Proceedings of the SPIE, Volume 5855, pp. 884-887 (2005). (2005a), 884–887. Rego, G. M., Falate, R., Kalinowski, H. J., Fabris, J. L., Marques, P. V., Salgado, H. M. and Santos, J. L.: Simulta- neous temperature and strain measurement based on arc-induced long-period fiber gratings. In Third International Conference on Experimental Mechanics and Third Conference of the Asian Committee on Experimental Mechanics. Edited by Quan, Chenggen; Chau, Fook Siong; Asundi, Anand; Wong, Brian Stephen; Lim, Chwee Teck. Proceedings of the SPIE, Volume 5855, pp. 679-682 (2005). (2005b), 679–682. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 102 / 118

Romero, R., Frazao, O., Floreani, F., Zhang, L., Marques, P. V. S. and Salgado, H. M.: 2005. Chirped fibre Bragg grating based multiplexer and demultiplexer for DWDM applications. Optics and Lasers in Engineering 43, 987. Weigelt, G., Beckert, T., Beckmann, U., Driebe, T., Foy, R., Fraix-Burnet, D., Hofmann, K. H., Kraus, S., Malbet, F., Mathias, P., Marconi, A., Monin, J. L., Petrov, R., Schertl, D., Stee, P. and Testi, L.: Near-infrared Interferometry with the AMBER Instrument of the VLTI. In Astronomische Nachrichten, volume 326 (2005), 572–572. Young, J. S., Haniff, C. A. and Buscher, D. F.: UK science and technology participation in the Magdalena Ridge Observatory Interferometer. In UK National Astronomy Meeting, 4–8 April 2005, Birmingham (UK National Astronomy Meeting, 4–8 April 2005, Birmingham, 2005). Basden, A. G., Haniff, C. A., Mackay, C. D., Bridgeland, M., Wilson, D. M. A., Young, J. S. and Buscher, D. F.: A new photon counting spectrometer for the COAST. In W. Traub, J. D. Monnier and M. Schöller(Eds.), New Frontiers in Stellar Interferometry, volume 5491 of Proc. SPIE. 21–25 June 2004, Glasgow (SPIE Press, 2004), 677. Boccaletti, A., Riaud, P., Baudoz, P., Baudrand, J., Rouan, D., Gratadour, D., Lacombe, F. and Lagrange, A.- M.: 2004. The Four-Quadrant Phase Mask Coronagraph. IV. First Light at the Very Large Telescope. PASP 116, 1061. Claudi, R. U., Costa, J., Feldt, M., Gratton, R., Amorim, A., Henning, T., Hippler, S., Neuhäuser, R., Pernechele, C., Turatto, M., Schmid, H. M., Walters, R. and Zinnecker, H.: CHEOPS: a second generation VLT instrument for the direct detection of exo-planets. In ESA SP-538: Stellar Structure and Habitable Planet Finding (2004a), 301–304. Claudi, R. U., Turatto, M., Gratton, R., Antichi, J., Buson, S., Pernechele, C., Desidera, S., Baruffolo, A., Lima, J., Alcalà,J., Cascone, E., Piotto, G., Ortolani, S., Schmid, H. M., Feldt, M., Neuhauser, R., Waters, R., Berton, A. and Bagnara, P.: CHEOPS NIR IFS: exploring stars neighborhood spectroscopically. In Ground-based Instrumentation for Astronomy. Edited by Alan F. M. Moorwood and Iye Masanori. Proceedings of the SPIE, Volume 5492, pp. 1351-1361 (2004). (2004b), 1351–1361. Creech-Eakman, M. J., Buscher, D. F., Haniff, C. A., Romero, V. D. and the MROI Design Team: The Magdalena Ridge Observatory Interferometer: A fully optimized aperture synthesis array for imaging. In W. Traub, J. D. Monnier and M. Schöller(Eds.), New Frontiers in Stellar Interferometry, volume 5491 of Proc. SPIE. 21–25 June 2004, Glasgow (SPIE Press, 2004), 405. Dugue, M., Lopez, B., Przygodda, F., Graser, U., Gitton, P. B., Wolf, S., Mathias, P., Antonelli, P., Augereau, J. C., Berruyer, N., Bresson, Y., Chesneau, O., Dutrey, A., Flament, S., Glazenborg-Kluttig, A. W., Glindemann, A., Henning, T., Hofmann, K.-H., Lagarde, S., Hugues, Y., Leinert, C., Meisenheimer, K., Menut, J.-L., Rohloff, R.-R., Roussel, A., Thiebaut, E. M. and Weigelt, G. P.: Recombining light of the VLTI at 10 microns by densifying the images. In New Frontiers in Stellar Interferometry, Proceedings of SPIE Volume 5491. Edited by Wesley A. Traub. Bellingham, WA: The International Society for Optical Engineering, 2004., p.1536 (2004), 1536–+. Feautrier, P., Dorn, R. J., Rousset, G., Cavadore, C., Charton, J., Cumani, C., Fusco, T., Hubin, N., Kern, P., Lizon, J. L., Magnard, Y., Puget, P., Rabaud, D., Rabou, P. and Stadler, E.: Performance and Results of the NAOS Visible Wavefront Sensor. In Scientific Detectors for Astronomy, The Beginning of a New Era (2004), 325–333. Fusco, T., Ageorges, N., Rousset, G., Rabaud, D., Gendron, E., Mouillet, D., Lacombe, F., Zins, G., Charton, J., Lidman, C. and Hubin, N. 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B.4 Observations and Interpretation

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B.5 Other technical papers

Augustin, M., Iliew, R., Etrich, C., Schelle, D., Fuchs, H.-J., Peschel, U., Nolte, S., Kley, E.-B., Lederer, F. and T¨unnermann, A.: 2005. Self-guiding of infrared and visible light in photonic crystal slabs. Applied Physics B: Lasers and Optics 81, 313. Gerken, M., Boschert, R., Bornemann, R., Lemmer, U., Schelle, D., Augustin, M., Kley, E.-B. and T¨unnermann, A.: Transmission measurements for the optical characterization of 2D-photonic crystals. In Detectors and Associated Signal Processing II. Edited by Chatard, Jean-Pierre; Dennis, Peter N. J. Proceedings of the SPIE, Volume 5965, pp. 143-149 (2005). (2005), 143–149. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 117 / 118

Kaempfe, T., Kley, E.-B. and Tuennermann, A.: Design and fabrication of refractive and diffractive micro optical elements used in holographic recording setups. In Detectors and Associated Signal Processing II. Edited by Chatard, Jean-Pierre; Dennis, Peter N. J. Proceedings of the SPIE, Volume 5965, pp. 17-28 (2005). (2005), 17–28. Käsebier, T., Hartung, H., Kley, E.-B. and Tünnermann, A.: Novel fabrication technique of continuous profiles for microoptics and integrated optics. In Detectors and Associated Signal Processing II. Edited by Chatard, Jean-Pierre; Dennis, Peter N. J. Proceedings of the SPIE, Volume 5965, pp. 29-39 (2005). (2005), 29–39. Nejadmalayeri, A. H., Herman, P. R., Burghoff, J., Will, M., Nolte, S. and Tünnermann, A.: 2005. Inscription of optical waveguides in crystalline silicon by mid-infrared femtosecond laser pulses. Optics Letters 30, 964. Augustin, M., Fuchs, H.-J., Schelle, D., Kley, E.-B., Nolte, S., Tünnermann, A., Iliew, R., Etrich, C., Peschel, U. and Lederer, F.: 2004a. High transmission and single-mode operation in low-index-contrast photonic crystal waveguide devices. Applied Physics Letters 84, 663. Augustin, M., Iliew, R., Fuchs, H.-J., Peschel, U., Kley, E.-B., Nolte, S., Lederer, F. L. and Tuennermann, A.: Highly efficient waveguide bends in low in-plane index contrast photonic crystals. In Quantum Sensing and Nanopho- tonic Devices. Edited by Razeghi, Manijeh; Brown, Gail J. Proceedings of the SPIE, Volume 5360, pp. 156-164 (2004). (2004b), 156–164. Schrempel, F., Opfermann, T., Ruske, J.-P., Grusemann, U. and Wesch, W.: 2004. Properties of buried waveguides produced by He-irradiation in KTP and Rb:KTP. Nuclear Instruments and Methods in Physics Research B 218, 209. Tünnermann, A., Schreiber, T., Augustin, M. and et al.: 2004. Photonic Crystal Structures in Ultrafast Optics. Advances in Solid State Physics 44, 117. Will, M., Burghoff, J., Limpert, J., Schreiber, T., Nolte, S. and Tuennermann, A.: High-speed fabrication of optical waveguides inside glasses using a high-repetition-rate fiber CPA system. In Free-Space Laser Communication Tech- nologies XVI. Edited by Mecherle, G. S.; Young, Cynthia Y.; Stryjewski, John S. Proceedings of the SPIE, Volume 5339, pp. 168-174 (2004). (2004), 168–174. Limpert, J., Schreiber, T., Liem, A., Nolte, S., Zellmer, H., Peschel, T., Guyenot, V. and Tünnermann, A.: 2003. Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation. Optics Express 11, 2982. Nolte, S., Will, M., Burghoff, J. and Tuennermann, A.: 2003. Femtosecond waveguide writing: a new avenue to three-dimensional integrated optics. Applied Physics A: Materials Science & Processing 77, 109. Schreiber, T., Limpert, J., Zellmer, H., Tünnermann, A. and Hansen, K. P.: 2003. High average power supercontinuum generation in photonic crystal fibers. Optics Communications 228, 71. Werner, E. A., Ruske, J.-P., Zeitner, B., Biehlig, W. and Tünnermann, A.: 2003. Integrated-optical amplitude modulator for high power applications. Optics Communications 221, 9. Will, M., Burghoff, J., Nolte, S. and Tuennermann, A.: Femtosecond-laser-induced refractive index modifications for fabrication of three-dimensional integrated optical devices. In Laser Micromachining for Optoelectronic Device Fabrication. Edited by Ostendorf, Andreas. Proceedings of the SPIE, Volume 4941, pp. 58-64 (2003). (2003), 58–64. Grusemann, U., Zeitner, B., Rottschalk, M., Ruske, J.-P., Tunnermann, A. and Rasch, A.: 2002. Integrated-optical wavelength sensor with self-compensation of thermally induced phase shifts by use of a LiNbO3 unbalanced Mach- Zehnder interferometer. Appl. Opt. 41, 6211. Schrempel, F., Höche, T., Ruske, J.-P., Grusemann, U. and Wesch, W.: 2002. Depth dependence of radiation damage + in Li -implanted KTiOPO4. Nuclear Instruments and Methods in Physics Research B 191, 202. Will, M., Nolte, S. and Tuennermann, A.: Single- and multimode waveguides in glasses manufactured with femtosecond laser pulses. In Proc. SPIE Vol. 4633, p. 99-106, Commercial and Biomedical Applications of Ultrafast and Free- Electron Lasers, Glenn S. Edwards; Joseph Neev; Andreas Ostendorf; John C. Sutherland; Eds. (2002), 99–106. Peterseim, M., Brozek, O. S., Danzmann, K., Tünnermann, A. and Freitag, I.: Earthbound and Deep Space Operation of Laser Metrology. In Second Edoardo Amaldi Conference on Gravitational Wave Experiments (1998), 391–+. Doc. No VSI-PRO-001 LAOG Cavendish VLTi Spectro-Imager Issue : 1.0 CAUP MPIfR INAF Date : 30/01/2006 IAGL IfA AIU Proposal for a second generation VLTI instrument Page : 118 / 118

Rottschalk, M., Ruske, J.-P., Untersch¨utz, B., Rasch, A. and Gr¨ober, V.: 1997. Single mode integrated-optical wide- band channel waveguides and junction splitters in KTiOPO4 for visible light. Journal of Applied Physics 81, 2504. Rottschalk, M., Ruske, J.-P. and Rasch, A.: 1995. Singlemode Channel Waveguides and Electrooptic Modulators in KTiOPO4 for the Short Visible Wavelength Region. Journal of Lightwave Technology 13, 2041. Ruske, J.-P., Rottschalk, M. and Steinberg, S.: 1995. Light-induced refractive index changes in singlemode channel waveguides in KTiOPO4. Optics Communications 120, 47. Rottschalk, M., Bachmann, T., Steinberg, S. and Ruske, J.-P.: 1994a. Annealed proton-implanted channel waveguides in LiNbO3 and their photorefractive properties. Optics Communications 106, 187. Rottschalk, M., Ruske, J.-P., Hornig, K. and Rasch, A.: Fabrication and characterization of singlemode channel waveguides and modulators in KTiOPO4 for the short visible wavelength region. In Proc. SPIE Vol. 2213, p. 152-163, Nanofabrication Technologies and Device Integration, Wolfgang Karthe; Ed. (1994b), 152–163.