Astrophys. J., 833, 96-96 (2016/December-2)
The Hawaii infrared parallax program. II. Young ultracool field dwarfs.
LIU M.C., DUPUY T.J. and ALLERS K.N.
Abstract (from CDS):
We present a large, uniform analysis of young (≃10-150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color-magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (>=100 km s–1) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.
© 2016. The American Astronomical Society. All rights reserved.
astrometry - brown dwarfs - parallaxes - planets and satellites: gaseous planets - stars: distances - stars: low-mass - stars: low-mass
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<Available at CDS (J/ApJ/833/96): table1.dat table2.dat table6.dat table7.dat refs.dat>
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