First VLTI/GRAVITY Observations of HIP 65426 b: Evidence for a Low or Moderate Orbital Eccentricity

Creators: Blunt, Sarah^{1, 2}; Balmer, W. O.^{3, 4}; Wang, J. J.¹; Lacour, S.^{5, 6}; Petrus, S.⁷; Bourdarot, G.⁸; Kammerer, J.⁴; Pourré, N.⁹; Rickman, E.⁴; Shangguan, J.⁸; Winterhalder, T.⁶; Abuter, R.⁶; Amorim, A.¹⁰; Asensio-Torres, R.¹¹; Benisty, M.⁹; Berger, J.-P.⁹; Beust, H.⁹; Boccaletti, A.⁵; Bohn, A.¹²; Bonnefoy, M.⁹; Bonnet, H.^{6, 9}; Brandner, W.¹¹; Cantalloube, F.¹³; Caselli, P.⁸; Charnay, B.⁵; Chauvin, G.⁹; Chavez, A.¹; Choquet, E.¹³; Christiaens, V.¹⁴; Clénet, Y.⁵; du Foresto, V. Coudé⁵; Cridland, A.¹²; Dembet, R.⁵; Drescher, A.⁸; Duvert, G.⁹; Eckart, A.^{15, 16}; Eisenhauer, F.⁸; Feuchtgruber, H.⁸; Garcia, P.^{10, 17}; Garcia Lopez, R.^{11, 18}; Gendron, E.⁵; Genzel, R.⁸; Gillessen, S.⁸; Girard, J. H.⁴; Haubois, X.⁶; Heißel, G.^{5, 19}; Henning, Th.¹¹; Hinkley, S.²⁰; Hippler, S.¹¹; Horrobin, M.¹⁵; Houllé, M.²¹; Hubert, Z.⁹; Jocou, L.⁹; Keppler, M.¹¹; Kervella, P.⁵; Kreidberg, L.¹¹; Lagrange, A.-M.^{5, 9}; Lapeyrère, V.⁵; Le Bouquin, J.-B.⁹; Léna, P.⁵; Lutz, D.⁸; Maire, A.-L.⁹; Mang, F.⁸; Marleau, G.-D.^{11, 22, 23, 24}; Mérand, A.⁶; Mollière, P.¹¹; Monnier, J. D.²⁵; Mordasini, C.²⁴; Mouillet, D.⁹; Nasedkin, E.¹¹; Nowak, M.²⁶; Ott, T.⁸; Otten, G. P. P. L.²⁷; Paladini, C.⁶; Paumard, T.⁵; Perraut, K.⁹; Perrin, G.⁵; Pfuhl, O.⁶; Pueyo, L.⁴; Rameau, J.⁹; Rodet, L.²⁸; Rustamkulov, Z.³; Shimizu, T.⁸; Sing, D.³; Stolker, T.¹²; Straubmeier, C.¹⁵; Sturm, E.⁸; Tacconi, L. J.⁸; van Dishoeck, E. F.^{8, 12}; Vigan, A.¹³; Vincent, F.⁵; Ward-Duong, K.²⁹; Widmann, F.⁸; Wieprecht, E.⁸; Wiezorrek, E.⁸; Woillez, J.⁶; Yazici, S.⁸; Young, A.⁸; The exoGRAVITY collaboration

1. Northwestern University
2. California Institute of Technology
3. Johns Hopkins University
4. Space Telescope Science Institute
5. Laboratory of Space Studies and Instrumentation in Astrophysics
6. European Southern Observatory
7. University of Valparaíso
8. Max Planck Institute for Extraterrestrial Physics
9. Institut de Planétologie et d'Astrophysique de Grenoble
10. University of Lisbon
11. Max Planck Institute for Astronomy
12. Leiden University
13. Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
14. Monash University
15. University of Cologne
16. Max Planck Institute for Radio Astronomy
17. University of Porto
18. University College Dublin
19. European Space Research and Technology Centre
20. University of Exeter
21. Lagrange Laboratory
22. University of Duisburg-Essen
23. University of Tübingen
24. University of Bern
25. University of Michigan–Ann Arbor
26. University of Cambridge
27. Institute of Astronomy and Astrophysics, Academia Sinica
28. Cornell University
29. Smith College

Abstract

Giant exoplanets have been directly imaged over orders of magnitude of orbital separations, prompting theoretical and observational investigations of their formation pathways. In this paper, we present new VLTI/GRAVITY astrometric data of HIP 65426 b, a cold, giant exoplanet which is a particular challenge for most formation theories at a projected separation of 92 au from its primary. Leveraging GRAVITY's astrometric precision, we present an updated eccentricity posterior that disfavors large eccentricities. The eccentricity posterior is still prior dependent, and we extensively interpret and discuss the limits of the posterior constraints presented here. We also perform updated spectral comparisons with self-consistent forward-modeled spectra, finding a best-fit ExoREM model with solar metallicity and C/O = 0.6. An important caveat is that it is difficult to estimate robust errors on these values, which are subject to interpolation errors as well as potentially missing model physics. Taken together, the orbital and atmospheric constraints paint a preliminary picture of formation inconsistent with scattering after disk dispersal. Further work is needed to validate this interpretation. Analysis code used to perform this work is available on GitHub: https://github.com/sblunt/hip65426.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank Aldo Sepulveda and Dan Huber for collaborative and informative discussions. S.B. and J.J.W. are supported by NASA Grant 80NSSC23K0280. G.-D.M. acknowledges the support of the DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (MA 9185/1) and from the Swiss National Science Foundation under grant 200021_204847 "PlanetsInTime." Parts of this work have been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation. S.P. acknowledges the support of ANID, - Millennium Science Initiative Program—NCN19_171. S.L. acknowledges the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-21-CE31-0017 (project ExoVLTI). This work is based on observations collected at the European Southern Observatory under ESO program 1104.C-0651. It also made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. S.B. wishes to acknowledge her status as a settler on the ancestral lands of the Gabrielino/Tongva people.

Funding

S.B. and J.J.W. are supported by NASA Grant 80NSSC23K0280. G.-D.M. acknowledges the support of the DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (MA 9185/1) and from the Swiss National Science Foundation under grant 200021_204847 "PlanetsInTime." Parts of this work have been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation. S.P. acknowledges the support of ANID, - Millennium Science Initiative Program—NCN19_171. S.L. acknowledges the support of the French Agence Nationale de la Recherche (ANR), under grant ANR-21-CE31-0017 (project ExoVLTI).

Software References

tinygp (github.com/dfm/tinygp; Foreman-Mackey et al. 2022), jax (Bradbury et al. 2018), numpy (Harris et al. 2020), pandas (McKinney 2010), matplotlib (Hunter 2007), spectres (Carnall 2017), species (Stolker et al. 2020), corner (Foreman-Mackey 2016), scipy (Virtanen et al. 2020), astropy (Astropy Collaboration et al. 2013, 2018, 2022), and orbitize! (Blunt et al. 2020). Analysis code used to perform this work is available on GitHub with a copy deposited to Zenodo: 10.5281/zenodo.8429161 (Blunt & Balmer 2023).

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