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The Brown Dwarf Kinematics Project (BDKP). IV. Radial Velocities of 85 Late-M and L dwarfs with MagE | | Adam J. Burgasser
; Sarah E. Logsdon
; Jonathan Gagne
; John J. Bochanski
; Jaqueline K. Faherty
; Andrew A. West
; Eric E. Mamajek
; Sarah J. Schmidt
; Kelle L. Cruz
; | | Date: |
1 Jul 2015 | | Abstract: | Radial velocity measurements are presented for 85 late M- and L-type very low
mass stars and brown dwarfs obtained with the Magellan Echellette (MagE)
spectrograph. Targets primarily have distances within 20 pc of the Sun, with
more distant sources selected for their unusual spectral energy distributions.
We achieved precisions of 2--3 km/s, and combined these with astrometric and
spectrophotometric data to calculate $UVW$ velocities. Most are members of the
thin disk of the Galaxy, and velocity dispersions indicate a mean age of
5.2$pm$0.2 Gyr for sources within 20 pc. We find significantly different
kinematic ages between late-M dwarfs (4.0$pm$0.2 Gyr) and L dwarfs
(6.5$pm$0.4 Gyr) in our sample that are contrary to predictions from prior
simulations. This difference appears to be driven by a dispersed population of
unusually blue L dwarfs which may be more prevalent in our local volume-limited
sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an
asymmetric $U$ velocity distribution with a net inward flow, similar to
gradients recently detected in local stellar samples. Simulations incorporating
brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the
velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L
dwarf populations. We also find the L dwarfs to have a kinematic age-activity
correlation similar to more massive stars. We identify several sources with low
surface gravities, and two new substellar candidate members of nearby young
moving groups: the astrometric binary DENIS J08230313$-$4912012AB, a
low-probability member of the $eta$ Pictoris Moving Group; and 2MASS
J15104786-2818174, a moderate-probability member of the 30-50 Myr Argus
Association. | | Source: | arXiv, 1507.0057 | | Services: | Forum | Review | PDF | Favorites | |
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