Evidence that the directly imaged planet HD 131399 Ab Is a Background Star

Eric L. Nielsen, Robert J.De Rosa, Julien Rameau, Jason J. Wang, Thomas M. Esposito, Maxwell A. Millar-Blanchaer, Christian Marois, Arthur Vigan, S. Mark Ammons, Etienne Artigau, Vanessa P. Bailey, Sarah Blunt, Joanna Bulger, Jeffrey Chilcote, Tara Cotten, René Doyon, Gaspard Duchêne, Daniel Fabrycky, Michael P. Fitzgerald, Katherine B. FolletteBenjamin L. Gerard, Stephen J. Goodsell, James R. Graham, Alexandra Z. Greenbaum, Pascale Hibon, Sasha Hinkley, Li Wei Hung, Patrick Ingraham, Rebecca Jensen-Clem, Paul Kalas, Quinn Konopacky, James E. Larkin, Bruce MacIntosh, Jérôme Maire, Franck Marchis, Stanimir Metchev, Katie M. Morzinski, Ruth A. Murray-Clay, Rebecca Oppenheimer, David Palmer, Jennifer Patience, Marshall Perrin, Lisa Poyneer, Laurent Pueyo, Roman R. Rafikov, Abhijith Rajan, Fredrik T. Rantakyrö, Jean Baptiste Ruffio, Dmitry Savransky, Adam C. Schneider, Anand Sivaramakrishnan, Inseok Song, Remi Soummer, Sandrine Thomas, J. Kent Wallace, Kimberly Ward-Duong, Sloane Wiktorowicz, Schuyler Wolff

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


We present evidence that the recently discovered, directly imaged planet HD 131399 Ab is a background star with nonzero proper motion. From new JHK1L′ photometry and spectroscopy obtained with the Gemini Planet Imager, VLT/SPHERE, and Keck/NIRC2, and a reanalysis of the discovery data obtained with VLT/SPHERE, we derive colors, spectra, and astrometry for HD 131399 Ab. The broader wavelength coverage and higher data quality allow us to reinvestigate its status. Its near-infrared spectral energy distribution excludes spectral types later than L0 and is consistent with a K or M dwarf, which are the most likely candidates for a background object in this direction at the apparent magnitude observed. If it were a physically associated object, the projected velocity of HD 131399 Ab would exceed escape velocity given the mass and distance to HD 131399 A. We show that HD 131399 Ab is also not following the expected track for a stationary background star at infinite distance. Solving for the proper motion and parallax required to explain the relative motion of HD 131399 Ab, we find a proper motion of 12.3 mas yr-1. When compared to predicted background objects drawn from a galactic model, we find this proper motion to be high but consistent with the top 4% fastest-moving background stars. From our analysis, we conclude that HD 131399 Ab is a background K or M dwarf.

Original languageEnglish (US)
Article number218
JournalAstronomical Journal
Issue number6
StatePublished - Dec 2017
Externally publishedYes


  • adaptive optics - planets and satellites
  • astrometry - instrumentation
  • detection - stars
  • image processing - techniques
  • individual (HD 131399) - techniques
  • spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Evidence that the directly imaged planet HD 131399 Ab Is a Background Star'. Together they form a unique fingerprint.

Cite this