Detection and Bulk Properties of the HR 8799 Planets with High-resolution Spectroscopy

October 2021 • 2021AJ....162..148W

Authors • Wang, Jason J. • Ruffio, Jean-Baptiste • Morris, Evan • Delorme, Jacques-Robert • Jovanovic, Nemanja • Pezzato, Jacklyn • Echeverri, Daniel • Finnerty, Luke • Hood, Callie • Zanazzi, J. J. • Bryan, Marta L. • Bond, Charlotte Z. • Cetre, Sylvain • Martin, Emily C. • Mawet, Dimitri • Skemer, Andy • Baker, Ashley • Xuan, Jerry W. • Wallace, J. Kent • Wang, Ji • Bartos, Randall • Blake, Geoffrey A. • Boden, Andy • Buzard, Cam • Calvin, Benjamin • Chun, Mark • Doppmann, Greg • Dupuy, Trent J. • Duchêne, Gaspard • Feng, Y. Katherina • Fitzgerald, Michael P. • Fortney, Jonathan • Freedman, Richard S. • Knutson, Heather • Konopacky, Quinn • Lilley, Scott • Liu, Michael C. • Lopez, Ronald • Lupu, Roxana • Marley, Mark S. • Meshkat, Tiffany • Miles, Brittany • Millar-Blanchaer, Maxwell • Ragland, Sam • Roy, Arpita • Ruane, Garreth • Sappey, Ben • Schofield, Tobias • Weiss, Lauren • Wetherell, Edward • Wizinowich, Peter • Ygouf, Marie

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 H₂O and CO in the atmospheres of HR 8799 c, d, and e, and tentatively detected a combination of CO and H₂O 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 ${10.1}_{-2.7}^{+2.8}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ for HR 8799 d and ${15.0}_{-2.6}^{+2.3}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2021AJ....162..148W
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/ac1349/pdf
• PREPRINT http://arxiv.org/abs/2107.06949
• ELECTR https://iopscience.iop.org/article/10.3847/1538-3881/ac1349