SPHERE: the Exoplanet Imager for the Very Large Telescope J.-L
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Astronomy & Astrophysics manuscript no. paper c ESO 2019 October 4, 2019 SPHERE: the exoplanet imager for the Very Large Telescope J.-L. Beuzit1; 2, A. Vigan2, D. Mouillet1, K. Dohlen2, R. Gratton3, A. Boccaletti4, J.-F. Sauvage2; 7, H. M. Schmid5, M. Langlois2; 8, C. Petit7, A. Baruffolo3, M. Feldt6, J. Milli13, Z. Wahhaj13, L. Abe11, U. Anselmi3, J. Antichi3, R. Barette2, J. Baudrand4, P. Baudoz4, A. Bazzon5, P. Bernardi4, P. Blanchard2, R. Brast12, P. Bruno18, T. Buey4, M. Carbillet11, M. Carle2, E. Cascone17, F. Chapron4, J. Charton1, G. Chauvin1; 23, R. Claudi3, A. Costille2, V. De Caprio17, J. de Boer9, A. Delboulbé1, S. Desidera3, C. Dominik15, M. Downing12, O. Dupuis4, C. Fabron2, D. Fantinel3, G. Farisato3, P. Feautrier1, E. Fedrigo12, T. Fusco7; 2, P. Gigan4, C. Ginski15; 9, J. Girard1; 14, E. Giro19, D. Gisler5, L. Gluck1, C. Gry2, T. Henning6, N. Hubin12, E. Hugot2, S. Incorvaia19, M. Jaquet2, M. Kasper12, E. Lagadec11, A.-M. Lagrange1, H. Le Coroller2, D. Le Mignant2, B. Le Ruyet4, G. Lessio3, J.-L. Lizon12, M. Llored2, L. Lundin12, F. Madec2, Y. Magnard1, M. Marteaud4, P. Martinez11, D. Maurel1, F. Ménard1, D. Mesa3, O. Möller-Nilsson6, T. Moulin1, C. Moutou2, A. Origné2, J. Parisot4, A. Pavlov6, D. Perret4, J. Pragt16, P. Puget1, P. Rabou1, J. Ramos6, J.-M. Reess4, F. Rigal16, S. Rochat1, R. Roelfsema16, G. Rousset4, A. Roux1, M. Saisse2, B. Salasnich3, E. Santambrogio19, S. Scuderi18, D. Segransan10, A. Sevin4, R. Siebenmorgen12 C. Soenke12, E. Stadler1, M. Suarez12, D. Tiphène4, M. Turatto3, S. Udry10, F. Vakili11, L. B. F. M. Waters20; 15, L. Weber10, F. Wildi10, G. Zins13, and A. Zurlo21; 22; 2 (Affiliations can be found after the references) Received 11 February 2019 / Accepted 20 September 2019 ABSTRACT Observations of circumstellar environments that look for the direct signal of exoplanets and the scattered light from disks have significant instru- mental implications. In the past 15 years, major developments in adaptive optics, coronagraphy, optical manufacturing, wavefront sensing, and data processing, together with a consistent global system analysis have brought about a new generation of high-contrast imagers and spectrographs on large ground-based telescopes with much better performance. One of the most productive imagers is the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE), which was designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE includes an extreme adaptive optics system, a highly stable common path interface, several types of coronagraphs, and three science instruments. Two of them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager and Spectrograph (IRDIS), were designed to efficiently cover the near-infrared (NIR) range in a single observation for an efficient search of young planets. The third instrument, ZIMPOL, was designed for visible (VIS) polarimetric observation to look for the reflected light of exoplanets and the light scattered by debris disks. These three scientific instruments enable the study of circumstellar environments at unprecedented angular resolution, both in the visible and the near-infrared. In this work, we thoroughly present SPHERE and its on-sky performance after four years of operations at the VLT. Key words. instrumentation: adaptive optics – instrumentation: high angular resolution – instrumentation: polarimeters – instrumentation: spec- trographs – planets and satellites: detection 1. Introduction telescopes equipped with devices capable of suppressing or at- tenuating the starlight. The performance of the first generation of adaptive optics- Even before the discovery of the first exoplanet, the study of equipped, near-infrared (NIR) instruments on large ground- circumstellar environments was already an important driver for based telescopes like the VLT/NaCo (Lenzen et al. 2003; Rous- designing instrumentation capable of detecting faint structures in set et al. 2003) or Gemini/NIRI (Hodapp et al. 2003; Herriot the close vicinity of bright stars. It emphasized, from the begin- et al. 1998) was greatly improved as compared to previous sys- arXiv:1902.04080v2 [astro-ph.IM] 3 Oct 2019 ning, the need for new observational capabilities. An emblematic tems on smaller telescopes (e.g., Beuzit et al. 1997). This pro- example is that of the star β Pictoris, where the detection of an lific generation of instruments led to major discoveries from the infrared excess with IRAS (Aumann 1984) led to observations exoplanet imaging point-of-view, such as the first direct image with early prototypes of stellar coronagraphs that enabled the of a planetary-mass companion (Chauvin et al. 2004), to the first discovery of a debris disk (Smith & Terrile 1984), extending up direct image of a multi-planet system (Marois et al. 2008a), and to several 100 au from the star. Another important step in the pi- the detection of a giant exoplanet in the disk surrounding β Pic- oneering era was the detection of the cool brown dwarf Gl 229 B toris (Lagrange et al. 2009). thanks to high-angular resolution either from the ground with However, the high-contrast imaging limitations of these in- adaptive optics (Nakajima et al. 1995) or from space (Oppen- struments were already foreseen during their design and early heimer et al. 1995). From these early observations, it was al- exploitation phases due to the limited number of degrees-of- ready clear that the path that would lead to significant progress freedom and cadence of their adaptive optics (AO) systems, and in this field would be the combination of diffraction-limited large the limited contrast performance of their simple Lyot corona- Article number, page 1 of 37 A&A proofs: manuscript no. paper graphs at very small angular separations. Major developments specification that were done before or in parallel to SPHERE, in coronagraphy and its interaction with adaptive optics in the GPI, and SCExAO. This includes the Lyot project (Oppenheimer early 2000s (Rouan et al. 2000; Sivaramakrishnan et al. 2001, et al. 2004; Sivaramakrishnan et al. 2007), the TRIDENT camera 2002; Perrin et al. 2003; Soummer et al. 2003) as well as in- tested at the CFHT (Marois et al. 2005), Project P1640 for Palo- novative observing strategies (Racine et al. 1999; Marois et al. mar (Oppenheimer et al. 2012; Hinkley et al. 2008, 2011), the 2006) quickly paved the way toward a new generation of in- LBT first-light AO system (Esposito et al. 2003), the Keck AO struments entirely optimized for high-contrast observations. In system (Wizinowich et al. 2000; van Dam et al. 2004) combined particular, these studies highlighted the need for low wavefront with the NIRC2 or OSIRIS instruments, the NICI instrument for errors (WFE) to minimize the residual speckles in the final focal Gemini (Chun et al. 2008) or MagAO (Close et al. 2013). Each plane. of these instruments or experiments can be considered as pre- With the objective of proposing a fully dedicated instrument cursors in the maturation of technologies, concepts or process- for the ESO Very Large Telescope (VLT), two teams of Euro- ing algorithms that later demonstrated their full performance in pean institutes led competitive phase A studies. This eventually SPHERE, GPI, and SCExAO. resulted in a joint project, the Spectro-Polarimetic High contrast In this paper we provide a detailed overview of the SPHERE imager for Exoplanets REsearch (SPHERE). The instrument was instrument in its current state, following four years of operations 1 developed by a consortium of eleven institutes in collaboration at the ESO VLT. In Sect.2 we first present the main trade-o ffs with ESO. The development of SPHERE started in early 2006, and design choices that drove the definition of the main func- with a preliminary design phase ending in September 2007 and tionalities of the instrument, in particular for what concerns the a final design phase in December 2008. The assembly, integra- adaptive optics, the coronagraphs, and the science sub-systems. tion, and testing of sub-systems at the various integration sites Then in Sect.3 we present the global system architecture and took almost three years until the fall of 2011, which wa followed the performance of the common path interface (CPI), which is by the final validation of the fully assembled instrument at IPAG the heart of SPHERE and feeds all the science sub-systems. The until the end of 2013. SPHERE was finally shipped to the VLT two fundamental components required for high-angular resolu- in early 2014, saw its first light in May 2014, and was available tion and high-contrast observations, namely the adaptive optics to the ESO community in April 2015. system and the coronagraphs, are described in Sect.4 and5 re- In parallel with the development of SPHERE for the VLT, spectively. Then Sect.6 is dedicated to ZIMPOL, the visible po- two other important high-contrast imaging instruments were be- larimetric imager of SPHERE, and Sect.7 and8 are dedicated to ing developed for other eight meter-class telescopes: the Gem- IFS and IRDIS respectively, the two near-infrared instruments of ini planet imager (GPI; Macintosh et al. 2006) and SCExAO for SPHERE. Finally, the instrument control, the operations and the Subaru (Guyon et al. 2010). GPI is a facility instrument for Gem- data reduction and handling are detailed in Sect.9. We conclude ini South that was developed on a similar model as SPHERE, and propose some perspective for future upgrades in Sect. 10. with more or less the same scientific goals and technical spec- ifications for the AO and coronagraphy, but with different de- sign choices partly due to observatory constraints (Cassegrain focus) and partly due to the available technologies upon its de- 2. Main trade-offs and design choices sign and development phase. Both SPHERE and GPI followed a similar schedule, which ended in November 2013 with a first The whole motivation and rationale behind the SPHERE project light of GPI (Macintosh et al.