Astrophys. J., Suppl. Ser., 219, 33 (2015/August-0)
BANYAN. VII. A new population of young substellar candidate members of nearby moving groups from the BASS survey.
GAGNE J., FAHERTY J.K., CRUZ K.L., LAFRENIERE D., DOYON R., MALO L., BURGASSER A.J., NAUD M.-E., ARTIGAU E., BOUCHARD S., GIZIS J.E. and ALBERT L.
Abstract (from CDS):
We present the results of a near-infrared (NIR) spectroscopic follow-up survey of 182 M4-L7 low-mass stars and brown dwarfs (BDs) from the BANYAN All-Sky Survey (BASS) for candidate members of nearby, young moving groups (YMGs). We confirm signs of low gravity for 42 new BD discoveries with estimated masses between 8 and 75 MJup and identify previously unrecognized signs of low gravity for 24 known BDs. We refine the fraction of low-gravity dwarfs in the high-probability BASS sample to ∼82%. We use this unique sample of 66 young BDs, supplemented with 22 young BDs from the literature, to construct new empirical NIR absolute magnitude and color sequences for low-gravity BDs. We show that low-resolution NIR spectroscopy alone cannot differentiate between the ages of YMGs younger than ∼120 Myr, and that the BT-Settl atmosphere models do not reproduce well the dust clouds in field or low-gravity L-type dwarfs. We obtain a spectroscopic confirmation of low gravity for 2MASS J14252798-3650229, which is a new ∼27 MJup, L4 γ bona fide member of AB Doradus. We identify a total of 19 new low-gravity candidate members of YMGs with estimated masses below 13 MJup, 7 of which have kinematically estimated distances within 40 pc. These objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments. We find 16 strong candidate members of the Tucana-Horologium association with estimated masses between 12.5 and 14 MJup, a regime where our study was particularly sensitive. This would indicate that for this association there is at least one isolated object in this mass range for every 17.5–5.0+6.6 main-sequence stellar member, a number significantly higher than expected based on standard log-normal initial mass function, however, in the absence of radial velocity and parallax measurements for all of them, it is likely that this over-density is caused by a number of young interlopers from other associations.
brown dwarfs - methods: data analysis - proper motions - stars: kinematics and dynamics - stars: low-mass
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<Available at CDS (J/ApJS/219/33): table1.dat table4.dat table5.dat table8.dat table9.dat refs.dat>
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