Peering into the formation history of beta Pictoris b with VLTI/GRAVITY long baseline interferometry
Creators: name: GRAVITY Collaboration
name: Nowak, M.
name: Lacour, S.
name: Mollière, P.
name: Wang, J.
name: Charnay, B.
name: van Dishoeck, E. F.
name: Abuter, R.
name: Amorim, A.
name: Berger, J. P.
name: Beust, H.
name: Bonnefoy, M.
name: Bonnet, H.
name: Brandner, W.
name: Buron, A.
name: Cantalloube, F.
name: Collin, C.
name: Chapron, F.
name: Clenet, Y.
name: Foresto, V. Coude du
name: de Zeeuw, P. T.
name: Dembet, R.
name: Dexter, J.
name: Duvert, G.
name: Eckart, A.
name: Eisenhauer, F.
name: Schreiber, N. M. Forster
name: Fédou, P.
name: Lopez, R. Garcia
name: Gao, F.
name: Gendron, E.
name: Genzel, R.
name: Gillessen, S.
name: Haußmann, F.
name: Henning, T.
name: Hippler, S.
name: Hubert, Z.
name: Jocou, L.
name: Kervella, P.
name: Lagrange, A. -M.
name: Lapeyrere, V.
name: Bouquin, J. -B. Le
name: Lena, P.
name: Maire, A. -L.
name: Ott, T.
name: Paumard, T.
name: Paladini, C.
name: Perraut, K.
name: Perrin, G.
name: Pueyo, L.
name: Pfuhl, O.
name: Rabien, S.
name: Rau, C.
name: Rodriguez-Coira, G.
name: Rousset, G.
name: Scheithauer, S.
name: Shangguan, J.
name: Straub, O.
name: Straubmeier, C.
name: Sturm, E.
name: Tacconi, L. J.
name: Vincent, F.
name: Widmann, F.
name: Wieprecht, E.
name: Wiezorrek, E.
name: Woillez, J.
name: Yazici, S.
name: Ziegler, D.
Publisher: name: arXiv
Year: 2019
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Our objective is to estimate the C/O ratio in the atmosphere of beta Pictoris b and obtain an estimate of the dynamical mass of the planet, as well as to refine its orbital parameters using high-precision astrometry. We used the GRAVITY instrument with the four 8.2 m telescopes of the Very Large Telescope Interferometer to obtain K-band spectro-interferometric data on $β$ Pic b. We extracted a medium resolution (R=500) K-band spectrum of the planet and a high-precision astrometric position. We estimated the planetary C/O ratio using two different approaches (forward modeling and free retrieval) from two different codes (ExoREM and petitRADTRANS, respectively). Finally, we used a simplified model of two formation scenarios (gravitational collapse and core-accretion) to determine which can best explain the measured C/O ratio. Our new astrometry disfavors a circular orbit for $β$ Pic b ($e=0.15^{+0.05}_{-0.04}$). Combined with previous results and with Hipparcos/GAIA measurements, this astrometry points to a planet mass of $M = 12.7\pm{}2.2\,M_\mathrm{Jup}$. This value is compatible with the mass derived with the free-retrieval code petitRADTRANS using spectral data only. The forward modeling and free-retrieval approches yield very similar results regarding the atmosphere of beta Pic b. In particular, the C/O ratios derived with the two codes are identical ($0.43\pm{}0.05$ vs $0.43^{+0.04}_{-0.03}$). We argue that if the stellar C/O in $β$ Pic is Solar, then this combination of a very high mass and a low C/O ratio for the planet suggests a formation through core-accretion, with strong planetesimal enrichment.
description: 14 pages + 7 page appendix, 7 figures, accepted for pulication