293 research outputs found
BANYAN. II. Very Low Mass and Substellar Candidate Members to Nearby, Young Kinematic Groups With Previously Known Signs of Youth
We present Bayesian Analysis for Nearby Young AssociatioNs II (BANYAN II), a
modified Bayesian analysis for assessing the membership of later-than-M5
objects to any of several Nearby Young Associations (NYAs). In addition to
using kinematic information (from sky position and proper motion), this
analysis exploits 2MASS-WISE color-magnitude diagrams in which old and young
objects follow distinct sequences. As an improvement over our earlier work, the
spatial and kinematic distributions for each association are now modelled as
ellipsoids whose axes need not be aligned with the Galactic coordinate axes,
and we use prior probabilities matching the expected populations of the NYAs
considered versus field stars. We present an extensive contamination analysis
to characterize the performance of our new method. We find that Bayesian
probabilities are generally representative of contamination rates, except when
a parallax measurement is considered. In this case contamination rates become
significantly smaller and hence Bayesian probabilities for NYA memberships are
pessimistic. We apply this new algorithm to a sample of 158 objects from the
literature that are either known to display spectroscopic signs of youth or
have unusually red near-infrared colors for their spectral type. Based on our
analysis, we identify 25 objects as new highly probable candidates to NYAs,
including a new M7.5 bona fide member to Tucana-Horologium, making it the
latest-type member. In addition, we reveal that a known L2{\gamma} dwarf is
co-moving with a bright M5 dwarf, and we show for the first time that two of
the currently known ultra red L dwarfs are strong candidates to the AB Doradus
moving group. Several objects identified here as highly probable members to
NYAs could be free-floating planetary-mass objects if their membership is
confirmed.Comment: 35 pages, 10 figures; accepted for publication in The Astrophysical
Journal (in press); Several typographic correction
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