The NASA-UC-UH eta-earth program. IV. A low-mass planet orbiting an M dwarf 3.6 PC from earth

Andrew W. Howard, Geoffrey W. Marcy, Debra A. Fischer, Howard Isaacson, Philip S. Muirhead, Gregory W. Henry, Tabetha S. Boyajian, Kaspar Von Braun, Juliette C. Becker, Jason T. Wright, John Asher Johnson

Research output: Contribution to journalArticlepeer-review

67 Scopus citations


We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab is a planet with minimum mass Msin i = 5.35 ± 0.75 M, orbital period P = 11.4433 ± 0.0016 days, and an orbit that is consistent with circular. We characterize the host star using a variety of techniques. Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of ∼0.1 mmag, thus supporting the existence of the planet. We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features, as confirmed by optical photometry and the Ca II H & K activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we measure an M2 V spectral type and a sub-solar metallicity ([M/H] = -0.22, [Fe/H] = -0.32). We measure a stellar radius of 0.3863 ± 0.0021 R based on interferometry from CHARA.

Original languageEnglish (US)
Article number51
JournalAstrophysical Journal
Issue number1
StatePublished - Oct 10 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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