Are These Planets Or Brown Dwarfs?
Using Keck Planet Imager and Characterizer (KPIC) high-resolution (R~35000) spectroscopy from 2.29-2.49 μm, we present uniform atmospheric retrievals for eight young substellar companions with masses of ~10-30 MJup, orbital separations spanning ~50-360 au, and Teff between ~1500-2600 K.
We find that all companions have solar C/O ratios, and metallicities, to within the 1-2σ level, with the measurements clustered around solar composition. Stars in the same stellar associations as our systems have near-solar abundances, so these results indicate that this population of companions is consistent with formation via direct gravitational collapse.
Alternatively, core accretion outside the CO snowline would be compatible with our measurements, though the high mass ratios of most systems would require rapid core assembly and gas accretion in massive disks. On a population level, our findings can be contrasted with abundance measurements for directly imaged planets with m<10 MJup, which show tentative atmospheric metal enrichment.
In addition, the atmospheric compositions of our sample of companions are distinct from those of hot Jupiters, which most likely form via core accretion. For two companions with Teff~1700-2000 K (kap And b and GSC 6214-210 b), our best-fit models prefer a non-gray cloud model with >3σ significance. The cloudy models yield 2-3σ lower Teff for these companions, though the C/O and [C/H] still agree between cloudy and clear models at the 1σ level. Finally, we constrain 12CO/13CO for three companions with the highest S/N data (GQ Lup b, HIP 79098 b, and DH Tau b), and report vsin(i) and radial velocities for all companions.
Are these planets or brown dwarfs? Broadly solar compositions from high-resolution atmospheric retrievals of ~10-30 MJup companions
Jerry W. Xuan, Chih-Chun Hsu, Luke Finnerty, Jason J. Wang, Jean-Baptiste Ruffio, Yapeng Zhang, Heather A. Knutson, Dimitri Mawet, Eric E. Mamajek, Julie Inglis, Nicole L. Wallack, Marta L. Bryan, Geoffrey A. Blake, Paul Mollière, Neda Hejazi, Ashley Baker, Randall Bartos, Benjamin Calvin, Sylvain Cetre, Jacques-Robert Delorme, Greg Doppmann, Daniel Echeverri, Michael P. Fitzgerald, Nemanja Jovanovic, Joshua Liberman, Ronald A. López, Evan Morris, Jacklyn Pezzato, Ben Sappey, Tobias Schofield, Andrew Skemer, James K. Wallace, Ji Wang, Shubh Agrawal, Katelyn Horstman
Comments: Accepted to ApJ, 52 pages, 20 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2405.13128 [astro-ph.EP] (or arXiv:2405.13128v1 [astro-ph.EP] for this version)
Submission history
From: Wenhao Xuan
[v1] Tue, 21 May 2024 18:02:40 UTC (14,525 KB)
https://arxiv.org/abs/2405.13128
Astrobiology, Astrochemistry, Astrogeology,
