In:
The Astronomical Journal, American Astronomical Society, Vol. 162, No. 4 ( 2021-10-01), p. 148-
Abstract:
Using the Keck Planet Imager and Characterizer, we obtained high-resolution ( R ∼ 35,000) K -band spectra of the four planets orbiting HR 8799. We clearly detected H 2 O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H 2 O in b. These are the most challenging directly imaged exoplanets that have been observed at high spectral resolution to date when considering both their angular separations and flux ratios. We developed a forward-modeling framework that allows us to jointly fit the spectra of the planets and the diffracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their effective temperatures, surface gravities, radial velocities, and spins. We measured v sin ( i ) values of 10.1 − 2.7 + 2.8 km s − 1 for HR 8799 d and 15.0 − 2.6 + 2.3 km s − 1 for HR 8799 e, and placed an upper limit of 〈 14 km s −1 of HR 8799 c. Under two different assumptions of their obliquities, we found tentative evidence that rotation velocity is anticorrelated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less efficient at spinning down lower-mass planets.
Type of Medium:
Online Resource
ISSN:
0004-6256
,
1538-3881
DOI:
10.3847/1538-3881/ac1349
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2021
detail.hit.zdb_id:
2207625-6
detail.hit.zdb_id:
2003104-X
SSG:
16,12
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