PROCEEDINGS OF SPIE SPIEDigitalLibrary.org/conference-proceedings-of-spie The ExoGRAVITY project: using single mode interferometry to characterize exoplanets Lacour, S., Wang, J., Nowak, M., Pueyo, L., Eisenhauer, F., et al. S. Lacour, J. J. Wang, M. Nowak, L. Pueyo, F. Eisenhauer, A.-M. Lagrange, P. Mollière, R. Abuter, A. Amorin, R. Asensio-Torres, M. Bauböck, M. Benisty, J. P. Berger, H. Beust, S. Blunt, A. Boccaletti, A. Bohn, M. Bonnefoy, H. Bonnet, W. Brandner, F. Cantalloube, P. Caselli, B. Charnay, G. Chauvin, E. Choquet, V. Christiaens, Y. Clénet, A. Cridland, P. T. de Zeeuw, R. Dembet, J. Dexter, A. Drescher, G. Duvert, F. Gao, P. Garcia, R. Garcia-Lopez, T. Gardner, E. Gendron, R. Genzel, S. Gillessen, J. H. Girard, X. Haubois, G. Heißel, T. Henning, S. Hinkley, S. Hippler, M. Horrobin, M. Houllé, Z. Hubert, A. Jiménez-Rosales, L. Jocou, J. Kammerer, M. Keppler, P. Kervella, L. Kreidberg, V. Lapeyrere, J.-B. Le Bouquin, P. Léna, D. Lutz, A.-L. Maire, A. Mérand, J. D. Monnier, D. Mouillet, A. Muller, E. Nasedkin, T. Ott, G. P. P. L. Otten, C. Paladini, T. Paumard, K. Perraut, G. Perrin, O. Pfuhl, J. Rameau, L. Rodet, G. Rodriguez- Coira, G. Rousset, J. Shangguan, T. Shimizu, J. Stadler, O. Straub, C. Straubmeier, E. Sturm, T. Stolker, E. F. van Dishoeck, A. Vigan, F. Vincent, S. D. von Fellenberg, K. Ward Duong, F. Widmann, E. Wieprecht, E. Wiezorrek, J. Woillez, "The ExoGRAVITY project: using single mode interferometry to characterize exoplanets," Proc. SPIE 11446, Optical and Infrared Interferometry and Imaging VII, 114460O (16 December 2020); doi: 10.1117/12.2561667 Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 21 Dec 2020 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use Invited Paper The ExoGRAVITY project: using single mode interferometry to characterize exoplanets S. Lacoura,b, J. J. Wangc, M. Nowakd, L. Pueyoe, F. Eisenhauerf, A.-M. Lagrangeg,a, P. Molli`ereh, R. Abuterb, A. Amorimi,j, R. Asensio-Torresh, M. Baub¨ockf, M. Benistyg, J.P. Bergerg, H. Beustg, S. Bluntc, A. Boccalettia, A. Bohnl, M. Bonnefoyg, H. Bonnetb, W. Brandnerh, F. Cantalloubeh, P. Caselli f, B. Charnaya, G. Chauving, E. Choquetk, V. Christiaensm, Y. Cl´eneta, A. Cridlandl, P.T. de Zeeuwl,f, R. Dembetb, J. Dexterf, A. Drescherf, G. Duvertg, F. Gaof, P. Garciaj,p, R. Garcia Lopezq,h, T. Gardnerr, E. Gendrona, R. Genzelf, S. Gillessenf, J. H. Girarde, X. Hauboiss, G. Heißela, T. Henningh, S. Hinkleyt, S. Hipplerh, M. Horrobinn, M. Houll´ek, Z. Hubertg, A. Jim´enez-Rosalesf, L. Jocoug, J. Kammererb,u, M. Kepplerh, P. Kervellaa, L. Kreidbergh, V. Lapeyr`erea, J.-B. Le Bouquing, P. L´enaa, D. Lutzf, A.-L. Mairev,h, A. M´erandb, J.D. Monnierr, D. Mouilletg, A. Mullerh, E. Nasedkinh, T. Ottf, G. P. P. L. Ottenk, C. Paladinis, T. Paumarda, K. Perrautg, G. Perrina, O. Pfuhlb, J. Rameaug, L. Rodetw, G. Rodriguez-Coiraa, G. Rousseta, J. Shangguanf, T. Shimizu f, J. Stadlerf, O. Straubf, C. Straubmeiern, E. Sturmf, T. Stolkerl, E.F. van Dishoeckl,f, A. Vigank, F. Vincenta, S.D. von Fellenbergf, K. Ward-Duongy, F. Widmannf, E. Wieprechtf, E. Wiezorrekf, and J. Woillezb a LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Universit´e,92195 Meudon, France b European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany c Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA d Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK e Space Telescope Science Institute, Baltimore, MD 21218, USA f Max Planck Institute for extraterrestrial Physics, 85748 Garching, Germany g Universit´eGrenoble Alpes, CNRS, IPAG, 38000 Grenoble, France h Max Planck Institute for Astronomy, K¨onigstuhl17, 69117 Heidelberg, Germany i Universidade de Lisboa - Faculdade de Ci^encias, Campo Grande, 1749-016 Lisboa, Portugal j CENTRA - Centro de Astrof´ısicae Gravita¸c~ao,Universidade de Lisboa, Lisboa, Portugal k Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France l Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands m School of Physics and Astronomy, Monash University, Clayton, Melbourne, Australia n 1. Institute of Physics, University of Cologne, Z¨ulpicher Straße 77, 50937 Cologne, Germany o Max Planck Institute for Radio Astronomy, Auf dem H¨ugel69, 53121 Bonn, Germany p Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, Porto, Portugal q School of Physics, University College Dublin, Belfield, Dublin 4, Ireland r Astronomy Department, University of Michigan, Ann Arbor, MI 48109 USA s European Southern Observatory, Casilla 19001, Santiago 19, Chile t University of Exeter, Physics Building, Stocker Road, Exeter EX4 4QL, United Kingdom u Research School of Astronomy & Astrophysics, Australian National University, Australia v STAR Institute/Universit´ede Li`ege,Belgium wDepartment of Astronomy, Cornell University, Ithaca, NY 14853, USA y Five College Astronomy Department, Amherst College, Amherst, MA 01002, USA Optical and Infrared Interferometry and Imaging VII, edited by Peter G. Tuthill, Antoine Mérand, Stephanie Sallum, Proc. of SPIE Vol. 11446, 114460O · © 2020 SPIE CCC code: 0277-786X/20/$21 · doi: 10.1117/12.2561667 Proc. of SPIE Vol. 11446 114460O-1 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 21 Dec 2020 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use ABSTRACT Combining adaptive optics and interferometric observations results in a considerable contrast gain compared to single-telescope, extreme AO systems. Taking advantage of this, the ExoGRAVITY project is a survey of known young giant exoplanets located in the range of 0.1" to 2" from their stars. The observations provide astrometric data of unprecedented accuracy, being crucial for refining the orbital parameters of planets and illuminating their dynamical histories. Furthermore, GRAVITY will measure non-Keplerian perturbations due to planet-planet interactions in multi-planet systems and measure dynamical masses. Over time, repetitive observations of the exoplanets at medium resolution (R = 500) will provide a catalogue of K-band spectra of unprecedented quality, for a number of exoplanets. The K-band has the unique properties that it contains many molecular signatures (CO, H2O, CH4, CO2). This allows constraining precisely surface gravity, metallicity, and temperature, if used in conjunction with self-consistent models like Exo-REM. Further, we will use the parameter-retrieval algorithm petitRADTRANS to constrain the C/O ratio of the planets. Ultimately, we plan to produce the first C/O survey of exoplanets, kick-starting the difficult process of linking planetary formation with measured atomic abundances. Keywords: Exoplanets, optical interferometry, planet formation 1. INTRODUCTION With more than 4000 exoplanets discovered to date, the focus is rapidly shifting from census to characterization. The directly imaged exoplanets, seen through thermal emission, offer unique possibilities compared to transit spectroscopy: they are a distinct and young subset of exoplanets at large separations. We have started a program to observe young exoplanets by optical interferometry which objectives is to obtain high-resolution astrometry and K-band spectra of all known directly-imaged exoplanets, and more. We are using the GRAVITY instrument which offers the best astrometric accuracy and highest quality spectra. The scientific goal of this program is to answer the following two key scientific questions: • What are the dynamics of directly imaged planetary systems? We are monitoring the dynamical interactions between seen and unseen companions. We are also getting the best dynamical masses for directly-imaged planets either in combination with GAIA stellar astrometry or by directly measuring dynamical perturbations caused by planet-planet interactions in resonant multi-planet systems. • How does the carbon-to-oxygen ratio (C/O) vary for these young exoplanets? This ratio will allow us to establish, for the first time, correlations between atmospheric composition and formation. This ongoing program is already delivering to the community a catalogue of high quality spectra that will not be rivalled until the beginning of the ELT era. This catalogue will be used to test planetary atmosphere models for years to come. Astrometry will have an even longer lasting legacy, extending into the era of the ELTs. GRAVITY is an unpeered astrometric facility for imaged exoplanets for the next few decades, and the orbits it measures will be the foundation for understanding these planetary systems. 2. THE DYNAMICS OF EXOPLANETS A key diagnostic of planet formation and evolution is provided by analyzing planetary orbital parameters as trac- ers of their dynamical history. However, milliarcsecond-level astrometry as provided by single dish telescopes can only provide limited constraints on key orbital parameters without additional priors: for example, we currently cannot rule out eccentricities between 0 and 0.7 for 51 Eri b. GRAVITY has demonstrated 50-100 µas precision on directly-imaged planets3{6 with potential to reach 10 µas precision, as demonstrated on the Galactic Center. With a 10-100x refinement in the orbits (see Fig. 1, top), we will drastically improve our knowledge of several planetary systems. Here are a few examples. 51 Eridani b could be entering into its first Koazi-Lidov cycle as the timescale is too large for any cycles to have completed.7 Such dynamics are seen in a significant fraction of triple star systems and are thought to destabilize any interior planets.8 HD 95086 b cannot alone carve out the gap between two debris belts in this system. Detecting an eccentricity of ∼0.3 would allow HD 95086 b maintain the inner edge Proc. of SPIE Vol. 11446 114460O-2 Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 21 Dec 2020 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use Figure 1. Orbital and dynamical mass constraints with GRAVITY astrometry. Upper panels: Astrometry of HR 8799 e.