TY - JOUR
T1 - Masses of astrometrically discovered and imaged binaries
T2 - G78-28AB and GJ 231.1BC
AU - Pravdo, Steven H.
AU - Shaklan, Stuart B.
AU - Wiktorowicz, Sloane J.
AU - Kulkarni, Shri
AU - Lloyd, James P.
AU - Martinache, Frantz
AU - Tuthill, Peter G.
AU - Ireland, Michael J.
PY - 2006/9/20
Y1 - 2006/9/20
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=33749386156&partnerID=8YFLogxK
U2 - 10.1086/506192
DO - 10.1086/506192
M3 - Article
AN - SCOPUS:33749386156
VL - 649
SP - 389
EP - 398
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1 I
ER -