A kinematic study and membership analysis of the Lupus star-forming
  region
  This paper is dedicated to investigating the kinematic properties of the
Lupus moving group of young stars with the primary objective of deriving
individual parallaxes for each group member. We identify those stars in the
Lupus star-forming region that define the comoving association of young stars
by utilizing our new and improved convergent point search method that allows us
to derive the precise position of the convergent point of the comoving
association from the stars' proper motions. We used published proper motion
catalogs and searched the literature for radial velocities, which are needed to
compute individual parallaxes. We supplemented the radial velocity data with
new measurements from spectroscopic observations performed with the FEROS
spectrograph mounted on the MPG/ESO 2.2m telescope at La Silla. We identify a
comoving group with 109 pre-main sequence stars and candidates that define the
kinematic properties of the Lupus low-mass star-forming region. We derive
individual parallaxes for stars with known radial velocity and tentative
parallaxes for the remaining group members by assuming that all stars share the
same space motion. The convergent point method, combined with the k-NN
algorithm, makes it possible to distinguish the Lupus and Upper Centaurus Lupus
stars from the adjacent Scorpius-Centaurus association. We find significant
depth effects in this region and show that the classical T Tauri stars, located
in the close vicinity of the Lupus molecular clouds, form a background
population, while the weak-emission line T Tauri stars are dispersed not only
in angular extent but also in depth. The newly derived individual parallaxes
will be used in a forthcoming paper to refine the masses and ages of Lupus T
Tauri stars, with the aim of better constraining the lifetimes of their
circumstellar, protoplanetary disks.
