Masses of Astrometrically-Discovered and Imaged Binaries: G 78-28AB and GJ 231.1BC
نویسندگان
چکیده
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 1⁄4 0:370 0:034 M and MB 1⁄4 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 areMB 1⁄4 0:25 0:06M andMC 1⁄4 0:12 0:02M . 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. Subject headingg s: planetary systems — stars: individual (G78-28A)
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