348 research outputs found
An Age Constraint for the Very Low-Mass Stellar/Brown Dwarf Binary 2MASS J03202839-0446358AB
2MASS J03202839-0446358AB is a recently identified, late-type M dwarf/T dwarf
spectroscopic binary system for which both the radial velocity orbit for the
primary and spectral types for both components have been determined. By
combining these measurements with predictions from four different sets of
evolutionary models, we determine a minimum age of 2.0+/-0.3 Gyr for this
system, corresponding to minimum primary and secondary masses of 0.080 Msun and
0.053 Msun, respectively. We find broad agreement in the inferred age and mass
constraints between the evolutionary models, including those that incorporate
atmospheric condensate grain opacity; however, we are not able to independently
assess their accuracy. The inferred minimum age agrees with the kinematics and
absence of magnetic activity in this system, but not the rapid rotation of its
primary, further evidence of a breakdown in angular momentum evolution trends
amongst the lowest luminosity stars. Assuming a maximum age of 10 Gyr, we
constrain the orbital inclination of this system to i >~ 53 degrees. More
precise constraints on the orbital inclination and/or component masses of 2MASS
J0320-0446AB, through either measurement of the secondary radial velocity orbit
(optimally in the 1.2-1.3 micron band) or detection of an eclipse (only 0.3%
probability based on geometric constraints), would yield a bounded age estimate
for this system, and the opportunity to use it as an empirical test for brown
dwarf evolutionary models at late ages.Comment: 8 pages, 2 figures, accepted for publication to Astonomical Journa
The Close Binary Fraction of Dwarf M Stars
We describe a search for close spectroscopic dwarf M star binaries using data from the Sloan Digital Sky Survey to address the question of the rate of occurrence of multiplicity in M dwarfs. We use a template-fitting technique to measure radial velocities from 145,888 individual spectra obtained for a magnitude-limited sample of 39,543 M dwarfs. Typically, the three or four spectra observed for each star are separated in time by less than four hours, but for ~17% of the stars, the individual observations span more than two days. In these cases we are sensitive to large-amplitude radial velocity variations on timescales comparable to the separation between the observations. We use a control sample of objects having observations taken within a four-hour period to make an empirical estimate of the underlying radial velocity error distribution and simulate our detection efficiency for a wide range of binary star systems. We find the frequency of binaries among the dwarf M stars with a < 0.4 AU to be 3%-4%. Comparison with other samples of binary stars demonstrates that the close binary fraction, like the total binary fraction, is an increasing function of primary mass
A New Low-Mass Eclipsing Binary from SDSS-II
We present observations of a new low-mass double-lined eclipsing binary
system discovered using repeat observations of the celestial equator from the
Sloan Digital Sky Survey II. Using near-infrared photometry and optical
spectroscopy we have measured the properties of this short-period
[P=0.407037(14) d] system and its two components. We find the following
parameters for the two components: M_1=0.272+/-0.020 M_sun, R_1=0.268+/-0.010
R_sun, M_2=0.240+/-0.022 M_sun, R_2=0.248+/-0.0090 R_sun, T_1=3320+/-130 K,
T_2=3300+/-130 K. The masses and radii of the two components of this system
agree well with theoretical expectations based on models of low-mass stars,
within the admittedly large errors. Future synoptic surveys like Pan-STARRS and
LSST will produce a wealth of information about low-mass eclipsing systems and
should make it possible, with an increased reliance on follow-up observations,
to detect many systems with low-mass and sub-stellar companions. With the large
numbers of objects for which these surveys will produce high-quality
photometry, we suggest that it becomes possible to identify such systems even
with sparse time sampling and a relatively small number of individual
observations.Comment: 15 Pages, 9 Figures, 6 Tables. Replaced with version accepted to Ap
Keck NIRSPEC Radial Velocity Observations of Late-M dwarfs
We present the results of an infrared spectroscopic survey of 23 late-M
dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using
telluric lines for wavelength calibration, we are able to achieve measurement
precisions of down to 45 m/s for our late-M dwarfs over a one to four year-long
baseline. Our sample contains two stars with RV variations of >1000 m/s. While
we require more measurements to determine whether these RV variations are due
to unseen planetary or stellar companions or are the result of starspots known
to plague the surface of M dwarfs, we can place upper limits of <40 MJsini on
the masses of any companions around those two M dwarfs with RV variations of
<160 m/s at orbital periods of 10-100 days. We have also measured the
rotational velocities for all the stars in our late-M dwarf sample and offer
our multi-order, high-resolution spectra over 2.0 to 2.4 micron to the
atmospheric modeling community to better understand the atmospheres of late-M
dwarfs.Comment: Accepted to Ap
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