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

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

Research output: Contribution to journalArticlepeer-review


Using the Keck Planet Imager and Characterizer (KPIC), we obtained high-resolution (R35,000) 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
ux ratios. We developed a forward modeling framework that allows us to jointly t the spectra of the planets and the diracted starlight simultaneously in a likelihood-based approach and obtained posterior probabilities on their
eective temperatures, surface gravities, radial velocities, and spins. We measured v sin(i) values of 10.1+2.8-2.7 km/s for HR 8799 d and 15.0+2.3-2:6 km/s for HR 8799 e, and placed an upper limit of < 14 km/s of HR 8799 c. Under two dierent assumptions of their obliquities, we found tentative evidence that
rotation velocity is anti-correlated with companion mass, which could indicate that magnetic braking with a circumplanetary disk at early times is less ecient at spinning down lower mass planets.
Original languageEnglish
Article number148
Pages (from-to)1-24
Number of pages24
JournalAstronomical Journal
Issue number4
Publication statusPublished - 17 Sep 2021


  • astro-ph.EP


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