365 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
Discovery of a Second L Subdwarf in the Two Micron All Sky Survey
I report the discovery of the second L subdwarf identified in the Two Micron
All Sky Survey, 2MASS J16262034+3925190. This high proper motion object (mu =
1.27+/-0.03 "/yr) exhibits near-infrared spectral features indicative of a
subsolar metallicity L dwarf, including strong metal hydride and H2O absorption
bands, pressure-broadened alkali lines, and blue near-infrared colors caused by
enhanced collision-induced H2 absorption. This object is of later type than any
of the known M subdwarfs, but does not appear to be as cool as the apparently
late-type sdL 2MASS 0532+8246. The radial velocity (Vrad = -260+/-35 km/s) and
estimated tangential velocity (Vtan ~ 90-210 km/s) of 2MASS 1626+3925 indicate
membership in the Galactic halo, and this source is likely near or below the
hydrogen burning minimum mass for a metal-poor star. L subdwarfs such as 2MASS
1626+3925 are useful probes of gas and condensate chemistry in low-temperature
stellar and brown dwarf atmospheres, but more examples are needed to study
these objects as a population as well as to define a rigorous classification
scheme.Comment: 11 pages, 3 figures, accepted for publication ApJ Letters, v. 614
October 200
- …