Masses of astrometrically discovered and imaged binaries: G78-28AB and GJ 231.1BC

Steven H. Pravdo*, Stuart B. Shaklan, Sloane J. Wiktorowicz, Shri Kulkarni, James P. Lloyd, Frantz Martinache, Peter G. Tuthill, Michael J. Ireland

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)


The Stellar Planet Survey (STEPS) is an ongoing astrometric search for giant planets and brown dwarfs around a sample of ∼30 M dwarfs. We have discovered several low-mass companions by measuring the motion of our target stars relative to their reference frames. The highest mass discovery thus far is G78-28B, a companion to the M dwarf G78-28A. The orbital period is 4.18 ± 0.03 yr, the system mass is 0.565 ± 0.055 M, and the semimajor axis is 2.19 ± 0.10 AU. Imaging observations with the Keck laser guide star adaptive optics (LGSAO) and the Palomar AO instruments resolved the system and also yielded JHK-band delta magnitudes. We use the orbital solution, light ratios, and mass-luminosity relationships to derive component masses of MA = 0.370 ± 0.034 M and MB = 0.195 ± 0.021 M. G78-28B is of type M4 V based on its colors and mass. We also discovered GJ 231.1C, a companion to GJ 231.1B, with STEPS and imaged the companion with LGSAO and Palomar AO, but the orbital period is longer than our observing baseline; thus, the system parameters are less constrained. In GJ 231.1BC the masses are MB = 0.25 ± 0.06 M and MC = 0.12 ± 0.02 M. The inferred spectral type of GJ 231.1C is M5 V. We demonstrate the results of the current state of mass estimation techniques with our data.

Original languageEnglish
Pages (from-to)389-398
Number of pages10
JournalAstrophysical Journal
Issue number1 I
Publication statusPublished - 20 Sep 2006
Externally publishedYes


Dive into the research topics of 'Masses of astrometrically discovered and imaged binaries: G78-28AB and GJ 231.1BC'. Together they form a unique fingerprint.

Cite this