The WSO-UV Project

On Synergies Between Ground-Based and Space-Based Observations: the WSO-UV Project B. Shustov, M. Sachkov, and A. Shugarov Institute of Astronomy, Russian Academy of Sciences, Moscow, Russia, bshustov@inasan.ru Abstract. Ground-based support is an essential condition for the suc- cess of almost any space astronomical project. Optical telescopes are widely used to support space-based projects. In the first part of the paper, the main areas of the support are briefly considered: cooperative observations – both synchronous and asynchronous, ground testing of service systems (for example, fine guidance systems), astrometric (ballistic) support, etc. Some examples are briefly considered. Special attention is paid to ground support for the WSO-UV (Spektr-UF) space observatory. Specific examples of both science and technical support (new spectrographs designed for cooperative observations, ground testing of the guide sensor system) as well as organizational issues are discussed. The call for applications that require preliminary ground-based observation has been announced. Seven applications were selected. Keywords: telescopes; space vehicles DOI:10.26119/978-5-6045062-0-2 2020 12 1 Ground-Based Observational Support for Space Astronomy We enter a new epoch in science on Universe, epoch of multi-channel astronomy. A comprehensive studies electromagnetic radiation, gravitational waves, and el- ementary particles, such as neutrinos and high-energy cosmic rays emitted by the same extraterrestrial sources, in order to obtain information about processes occurring in space, is an essence of multi-channel approach. The multi-channel astronomy paradigm is becoming firmly embedded in science. For example we can refer to (presumably) first professional book on the issue (Multichannel Astronomy, Ed: A. M. Cherepashchuk, Publisher: Vek-2, Moscow, ISBN: 978-5- 85099-198-2, appeared in December 2018). The multi-channel approach to observations of electromagnetic radiation also implies multi-wave (all-wave) approach, i.e. observations at all wavelengths of Ground-Based Observations to Support the WSO-UV Project the electromagnetic spectrum. Multi-wavelength concept inevitably means the involvement of space-based observation facilities, since the possibility of ground- based observations is strongly limited by the transparency of the Earth’s atmo- sphere. Ground-based and space-based observations of astronomical objects tend to be much more correlated than previously. Astronomers make joint observations all the time, but they did and still do so in a generally un-coordinated way. However, the understanding of the necessity and inevitability of coordinated observations is growing. We share the opinion expressed in O’Meara (2019): “Science..in many cases not only benefits from ground/space coordination, but requires it. Our current mode of siloed operations slows, hampers, and in some cases, halts scientific progress”. This position is supported by many authors of Decadal Survey on Astronomy and Astrophysics 2020 (Astro2020)1. The authors consider broad scope of issues: from Solar system (Kofman et al. 2020; Roth et al. 2020) to stars (Clementini et al. 2020) and cosmology (Cuby et al. 2019). In some projects, ground-based and space-based telescopes are inseparable components of the project. For example, in the “Spektr-R” project, which op- erated in the space-Earth interferometer mode. The new project of space interferometer “Millimetron” (Kardashev 2017) and the recently proposed radio space-ground interferometer for BH shadow observations (Mikheeva et al. 2020) will work in the same way. Optical ground-based telescopes are actively used to support space-based astronomical projects for various purposes. There are several types of the support: – cooperative observations; – ground testing of optical scientific and service instruments; – astrometric (ballistic) support. In this paper we discuss some examples the of support. Of course, cooperative observations are the most important part of the support. They could be synchronous or asynchronous. For synchronous observations (the concept makes sense for observations of transients) the following requirement must be met: the time interval for overlapping observations (with different tools) is shorter than the time scale of changes of the object. A good example of (almost) synchronous observations – optical observations of the gamma-ray burst sources on the optical MASTER network (see e.g. Troja et al. (2017)). Asynchronous observations with optical telescopes are most numerous. For example, the 6-m telescope BTA at SAO observatory, as it is reported by D.Kud- ryavtsev, is used for support for Spectrum-RG (SRG) space observatory, namely 1 See for details https://www.nationalacademies.org/our-work/ decadal-survey-on-astronomy-and-astrophysics-2020-astro2020 13 Shustov et al. for optical identification of distant galaxy clusters and X–ray quasars; observations of active galactic nuclei using RATAN-600 and Radioastron; monitoring of bright sources with RATAN-600 during the Planck mission. Few more examples follow. In Zaznobin et al. (2019) results of optical iden- tifications and spectroscopic redshift measurements for galaxy clusters from the second Planck catalogue of Sunyaev-Zeldovich sources are presented. The observations were carried out with the 1.5-m Russian-Turkish telescope (RTT-150), the 1.6-m Sayan Observatory AZT-33IK telescope, the 3.5-m Calar Alto telescope, and the 6-m SAO RAS telescope (BTA). The 1.6-m AZT-33VM and AZT-33IK telescopes of the Sayan Observatory of the ISTP SB RAS are included in the ground-based optical support complex of the SRG Observatory. The first two spectra of distant quasars (z 4) that were detected by eROSITA were observed (Khorunzhev et al. 2020). ∼ As to examples of ground testing of optical scientific and service instruments we refer to Section 3 of this paper, where we describe some results of testing the WSO-UV Fine Guidance System with ground-based telescopes Both RTT-150 and AZT-33VM telescopes perform high-precision (accuracy of 0.1 and 0.3 arcsec correspondingly, difference is due to different focal length of the telescopes) astrometric monitoring of the SRG spacecraft. Next sections of this paper are devoted to space observatory WSO-UV. For many astrophysical tasks included in the Core program of the mission ground- based spectroscopic observations in spectral domain of 300 – 1000 nm with high resolution (R = 50000) are required. For these purposes existing facilities of the SAO RAS, including NES, ESPRI and CAES spectrographs are being upgrading or constructed (Panchuk et al. 2018). We consider this way - to prepare dedicated ground-based instruments well beforehand – as a very promising one. 2 WSO-UV Project: General Information and State of Art World Space Observatory - Ultraviolet (WSO-UV) aka “Spektr-UF” is a space astrophysical observatory for observations of astronomical objects in the far and near UV range (115–310 nm). Unlike the HST the space complex consists of unified platform (bus) “Navigator” and payload (P/L). Platform “Navigator” provides important service systems – attitude control (pointing and stabilisa- tion), radio link and power supply. Concept of the HST implies unique design of service subsystems integrated with the telescope. “Navigator” is a serial product. It was successfully used in space for five times, including astrophysical missions Spektr-R (Radioastron) and Spektr-RG. The latter at the moment is operating 14 Ground-Based Observations to Support the WSO-UV Project in space. P/L is essentially a complex of scientific equipments. We briefly remind major features of the project (see for more details Shustov et al. (2018)) 2.1 Complex of Scientific Equipment (CSE) The observatory has a complex of scientific equipment (CSE), which includes: – T-170M telescope (aperture 170 cm, focal ratio 10, field of view diameter 30’, diffraction image quality in the center of the field); – a block of spectrographs (WUVS), including three channels: vacuum ultraviolet echelle spectrograph VUVES (115–176 nm, R 50000), UV echelle spectrograph UVES (174–310 nm, R 50000) and a∼ spectrograph with a long slit LSS (115–305 nm, R 1000);∼ – field cameras unit (FCU), including∼ a far-UV channel (FUV) for obtaining direct images in the range of 115–175 nm and a near-UV channel (NUV) for obtaining direct images in the range of 174–305 nm; – scientific data management unit (SDMU); – scientific equipment “Konus-UV” that is a small gamma-ray detector devel- oped at the Ioffe Institute of Physics and Technology of the Russian Academy of Sciences and which has been successfully used in space in other projects. Fig. 1 shows the location of the fields of view (for spectrographs – that of slits) of scientific instruments and three guide sensors on the focal surface of the T-170M telescope. Work on the creation of the CSE continues as planned. Manutacturing of WUVES goes on. Current characteristics of FCU (see Tabl. 1) differ from those presented in Shustov et al. (2018). There is either a new pro- posal to include in the CSE an additional spectrograph for studying exospheres of Earth-like exoplanets. Space Research Institute and Institute of astronomy (both of the RAS) in cooperation with the Japanese aerospace Agency JAXA and a number of leading universities in Japan are working on creating a UV- spectrograph UVSPEX (Tavrov et al. 2018). Question about whether or not the UVSPEX spectrograph will be included in the CSE of the WSO-UV Observa- tory is discussed at the level of responsible persons in Roscosmos and JAXA. The main principle is – the inclusion of a new device in the CSE should not violate the project implementation schedule. 2.2 Cooperation Since Russia leads the major work on the creation of the WSO-UV Observatory, the project can be considered as national. According to preliminary estimates, up to 2 thousands of Russian scientists (astronomers, physicists, etc.) are eager to use the observatory in their research work. 15 Shustov et al. Fig. 1. Location of the fields of view of scientific instruments and three sensors of the Fine Guidance System (FGS S1, FGS S2 and FGS S3) on the focal surface of the T-170M telescope.

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