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 journalArticle

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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


Cite this

Pravdo, S. H., Shaklan, S. B., Wiktorowicz, S. J., Kulkarni, S., Lloyd, J. P., Martinache, F., ... Ireland, M. J. (2006). Masses of astrometrically discovered and imaged binaries: G78-28AB and GJ 231.1BC. Astrophysical Journal, 649(1 I), 389-398.