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 Duch ne, 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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


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+2.8km 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.

Original languageEnglish (US)
Article number148
JournalAstronomical Journal
Issue number4
StatePublished - Oct 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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