Masses of Astrometrically Discovered and Imaged Binaries: G78-28AB and GJ 231.1BC

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

Abstract

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 M_A = 0.370 ± 0.034 M_☉ and M_B = 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 M_B = 0.25 ± 0.06 M_☉ and M_C = 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.

Additional Information

© 2006 American Astronomical Society. Received 2006 April 12; accepted 2006 May 11. The research described in this paper was performed in part by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We performed observations at Caltech's Palomar Observatory and Keck Observatory and acknowledge the assistance of the staff. We thank I. Baraffe and G. Chabrier for their assistance. This research has made use of the NASA/ IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and of NASA's Astrophysics Data System Abstract Service. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. M. I. acknowledges Michelson Fellowship support from the Michelson Science Center and the NASA Navigator Program.

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