Lupus DANCe. Census of stars and 6D structure with Gaia-DR2 data
  Context: Lupus is recognised as one of the closest star-forming regions, but
the lack of trigonometric parallaxes in the pre-Gaia era hampered many studies
on the kinematic properties of this region and led to incomplete censuses of
its stellar population. Aims: We use the second data release of the Gaia space
mission combined with published ancillary radial velocity data to revise the
census of stars and investigate the 6D structure of the Lupus complex. Methods:
We performed a new membership analysis of the Lupus association based on
astrometric and photometric data over a field of 160 deg2 around the main
molecular clouds of the complex and compared the properties of the various
subgroups in this region. Results: We identified 137 high-probability members
of the Lupus association of young stars, including 47 stars that had never been
reported as members before. Many of the historically known stars associated
with the Lupus region identified in previous studies are more likely to be
field stars or members of the adjacent Scorpius-Centaurus association. Our new
sample of members covers the magnitude and mass range from G=8 to G=18 mag and
from 0.03 to 2.4Msun, respectively. We compared the kinematic properties of the
stars projected towards the molecular clouds Lupus 1 to 6 and showed that these
subgroups are located at roughly the same distance (about 160~pc) and move with
the same spatial velocity. Our age estimates inferred from stellar models show
that the Lupus subgroups are coeval (with median ages ranging from about 1 to 3
Myr). The Lupus association appears to be younger than the population of young
stars in the Corona-Australis star-forming region recently investigated by our
team using a similar methodology. The initial mass function of the Lupus
association inferred from the distribution of spectral types shows little
variation compared to other star-forming regions.
