A kinematically unbiased, all-sky search for nearby, young, low-mass stars

Kavli Affiliate: David A. Principe

| First 5 Authors: Alexander S. Binks, Matthieu Chalifour, Joel H. Kastner, David Rodriguez, Simon J. Murphy

| Summary:

The past two decades have seen dramatic progress in our knowledge of the
population of young stars of age $< 200,$Myr that lie within $150,$pc of the
Sun. These nearby, young stars, most of which are found in loose, comoving
groups, provide the opportunity to explore (among many other things) the
dissolution of stellar clusters and their diffusion into the field star
population. Here, we exploit the combination of astrometric and photometric
data from {it Gaia} and photometric data from GALEX (UV) and 2MASS (near-IR)
in an attempt to identify additional nearby, young, late-type stars.
Specifically, we present a sample of 146 GALEX UV-selected late-type
(predominantly K-type) field stars with {it Gaia}-based distances $< 125,$pc
(based on {it Gaia} Data Release 1) that have isochronal ages $< 80,$Myr even
if equal-components binaries. We investigate the spectroscopic and kinematic
properties of this sample. Despite their young isochronal ages, only $sim 10$
per cent) of stars among this sample can be confidently associated with
established nearby, young moving groups (MGs). These candidate MG members
include 5 stars newly identified in this study. The vast majority of our sample
of 146 nearby young star candidates have anomalous kinematics relative to the
known MGs. These stars may hence represent a previously unrecognised population
of young stars that has recently mixed into the older field star population. We
discuss the implications and caveats of such a hypothesis—including the
intriguing fact that, in addition to their non-young-star-like kinematics, the
majority of the UV-selected, isochronally young field stars within $50,$pc
appear surprisingly X-ray faint.

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