The McDonald Accelerating Stars Survey (MASS): Discovery of a Long-Period Substellar Companion Orbiting the Old Solar Analog HD 47127

Brendan P. Bowler, Michael Endl, William D. Cochran, Phillip J. MacQueen, Justin R. Crepp, Greg W. Doppmann, Shannon Dulz, Timothy D. Brandt, G. Mirek Brandt, Yiting Li, Trent J. Dupuy, Kyle Franson, Kaitlin M. Kratter, Caroline V. Morley, Yifan Zhou

Research output: Contribution to journalArticlepeer-review


Brown dwarfs with well-determined ages, luminosities, and masses provide rare but valuable tests of low-temperature atmospheric and evolutionary models. We present the discovery and dynamical mass measurement of a substellar companion to HD 47127, an old (≈7-10 Gyr) G5 main sequence star with a mass similar to the Sun. Radial velocities of the host star with the Harlan J. Smith Telescope uncovered a low-amplitude acceleration of 1.93 ± 0.08 m s−1 yr−1 based on 20 years of monitoring. We subsequently recovered a faint (ΔH=13.14 ± 0.15 mag) co-moving companion at 1.95′′ (52 AU) with follow-up Keck/NIRC2 adaptive optics imaging. The radial acceleration of HD 47127 together with its tangential acceleration from Hipparcos and Gaia EDR3 astrometry provide a direct measurement of the three-dimensional acceleration vector of the host star, enabling a dynamical mass constraint for HD 47127 B (67.5-177 MJup at 95% confidence) despite the small fractional orbital coverage of the observations. The absolute H-band magnitude of HD 47127 B is fainter than the benchmark T dwarfs HD 19467 B and Gl 229 B but brighter than Gl 758 B and HD 4113 C, suggesting a late-T spectral type. Altogether the mass limits for HD 47127 B from its dynamical mass and the substellar boundary imply a range of 67-78 MJup assuming it is single, although a preference for high masses of ≈100 MJup from dynamical constraints hints at the possibility that HD 47127 B could itself be a binary pair of brown dwarfs or that another massive companion resides closer in. Regardless, HD 47127 B will be an excellent target for more refined orbital and atmospheric characterization in the future.
Original languageEnglish
Article numberL26
Pages (from-to)1-8
Number of pages8
JournalAstrophysical Journal Letters
Issue number2
Publication statusPublished - 31 May 2021


  • astro-ph.SR
  • astro-ph.EP


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