Radial velocity measurements of HR 8799 b and c with medium resolution spectroscopy

Jean-Baptiste Ruffio*, Bruce Macintosh, Quinn M. Konopacky, Travis Barman, Robert J. De Rosa, Jason J. Wang, Kielan K. Wilcomb, Ian Czekala, Christian Marois

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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High-contrast medium resolution spectroscopy has been used to detect molecules such as water and carbon monoxide in the atmospheres of gas giant exoplanets. In this work, we show how it can be used to derive radial velocity (RV) measurements of directly imaged exoplanets. Improving upon the traditional cross-correlation technique, we develop a new likelihood based on joint forward modeling of the planetary signal and the starlight background (i.e., speckles). After marginalizing over the starlight model, we infer the barycentric RV of HR 8799 b and c in 2010 yielding -9.2 ± 0.5 km s-1 and -11.6 ± 0.5 km s-1, respectively. These RV measurements help to constrain the 3D orientation of the orbit of the planet by resolving the degeneracy in the longitude of an ascending node. Assuming coplanar orbits for HR 8799 b and c, but not including d and e, we estimate Ω = 89 º -17 +27 and i = 20 º. 8 -3.7 +4.5.
Original languageEnglish
Article number200
Number of pages21
JournalAstronomical Journal
Issue number5
Early online date24 Oct 2019
Publication statusPublished - Nov 2019


  • Astrometry
  • Radial velocity
  • Bayesian statistics
  • Extrasolar gas giants
  • Direct imaging
  • High resolution spectroscopy


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