Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21443305b&link_type=abstract
American Astronomical Society, AAS Meeting #214, #433.05; Bulletin of the American Astronomical Society, Vol. 41, p.704
Astronomy and Astrophysics
Astronomy
Scientific paper
Ultracool subdwarfs are the metal-poor counterparts of the lowest luminosity, lowest-mass stars and brown dwarfs, encompassing sources classified sdM7/esdM7/usdM7 and later according to the schemes of Lepine et al. (2007) and Burgasser et al. (2007). Beside their peculiar spectral energy distributions and unusual near-infrared colors, ultracool subdwarfs exhibit space motions indicative of halo population kinematics, with highly inclined, eccentric, and occasionally retrograde orbits with respect to the Galactic thin disk. Drawing upon new absolute magnitude determinations for a handful of ultracool subdwarf benchmarks, we determine UVW space motions for the roughly 3 dozen known sources and examine the characteristics of their Galactic orbits. The currently known sample can be segregated into two fairly distinct subgroups: a majority population of "inner halo" sources with slightly prograde and highly eccentric orbits and apoapses near the Solar circle; and a very small number of "outer halo" subdwarfs whose extremely retrograde orbits take them far beyond the Solar circle. We examine integrals of motion for these two "kinematic subpopulations" using various Galactic potentials, and search for correlations in spectral properties and color discrepancies possibly indicative of metallicity differentiation.
Bochanski John J.
Burgasser Adam Jonathan
Cushing Michael
Faherty Jackie
Looper Dagny
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