1. Peering into the Young Planetary System AB Pic. Atmosphere, Orbit, Obliquity & Second Planetary Candidate
- Author
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Palma-Bifani, P., Chauvin, G., Bonnefoy, M., Rojo, P. M., Petrus, S., Rodet, L., Langlois, M., Allard, F., Charnay, B., Desgrange, C., Homeier, D., Lagrange, A. -M., Beuzit, J. -L., Baudoz, P., Boccaletti, A., Chomez, A., Delorme, P., Desidera, S., Feldt, M., Ginski, C., Gratton, R., Maire, A. -L., Meyer, M., Samland, M., Snellen, I., Vigan, A., and Zhang, Y.
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Astrophysics - Earth and Planetary Astrophysics - Abstract
We aim to revisit the system AB Pic which has a known companion at the exoplanet/ brown-dwarf boundary. We based this study on a rich set of observations to investigate the companion's orbit and atmosphere. We composed a spectrum of AB Pic b merging archival VLT/SINFONI K-band data, with published spectra at J and H-band (SINFONI) and Lp-band (Magellan-AO), and photometric measurements (HST and Spitzer). We modeled the spectrum with ForMoSA, based on two atmospheric models: ExoREM and BT-SETTL13. We determined the orbital properties of b fitting the astrometric measurements from NaCo (2003 and 2004) and SPHERE (2015). The orbital solutions favor a semi-major axis of $\sim$190au viewed edge-on. With Exo-REM, we derive a T$_{eff}$ of 1700$\pm$50K and surface gravity of 4.5$\pm$0.3dex, consistent with previous works, and we report for the first time a C/O ratio of 0.58$\pm$0.08 ($\sim$solar). The posteriors are sensitive to the wavelength interval and the family of models used. Given the 2.1hr rotation period and our vsin(i) of $\sim$73km/s, we estimate for the first time the true obliquity to be $\sim$45 or $\sim$135deg, indicating a significant misalignment between the planet's spin and orbit orientations. Finally, a proper motion anomaly between the Hipparcos and Gaia eDR3 compared to our SPHERE detection limits and adapted radial velocity limits indicate the existence of a $\sim$6M$_{Jup}$ inner planet orbiting from 2 to 10au (40-200mas). The possible existence of an inner companion and the likely miss-alignment of the spin axis orientation strongly favor a formation path by gravitational instability or core accretion within a disk closer inside followed by dynamical interactions. Confirmation and characterization of planet c and access to a broader wavelength coverage for planet b will be essential to probe the uncertainties associated with the parameters., Comment: 17 pages, 13 Figures, 6 Tables
- Published
- 2022
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