期刊
ASTRONOMY & ASTROPHYSICS
卷 633, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201936898
关键词
planets and satellites: formation; planets and satellites: atmospheres; techniques: interferometric; stars: individual: beta Pictoris
资金
- ESO programme [0101.C-0912(A), 2101.C-5050(A)]
- European Research Council (ERC), under the European Union's Horizon 2020 research and innovation programme [639248]
- ERC under the European Union's Horizon 2020 research and innovation programme [694513, 832428]
- Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship
- Science Foundation Ireland [18/SIRG/5597]
- French CNRS
- Agence Nationale de la Recherche (ANR) [GIPSE ANR-14-CE33-0018]
- ERC under the Horizon 2020 Framework Program (ERC Advanced Grant) [Origins 832428]
- European Research Council (ERC) [639248] Funding Source: European Research Council (ERC)
Context. beta Pictoris is arguably one of the most studied stellar systems outside of our own. Some 30 yr of observations have revealed a highly-structured circumstellar disk, with rings, belts, and a giant planet: beta Pictoris b. However very little is known about how this system came into being. Aims. 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. Methods. 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 beta 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. Results. Our new astrometry disfavors a circular orbit for beta Pic b (e = 0.15(-0.04)(+0.05)). Combined with previous results and with HIPPARCOS/Gaia measurements, this astrometry points to a planet mass of M = 12.7 +/- 2.2 M-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 +/- 0.05 vs. 0.43(-0.03)(+0.04)). We argue that if the stellar C/O in beta 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.
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