  In a recent study, individual parallaxes were determined for many stars of
the Taurus-Auriga T association that are members of the same moving group. We
use these new parallaxes to re-address the issue of the relationship between
classical T Tauri stars (CTTSs) and weak-emission line T Tauri stars (WTTSs).
With the available spectroscopic and photometric information for 72 individual
stars or stellar systems among the Taurus-Auriga objects with known parallaxes,
we derived reliable photospheric luminosities, mainly from the Ic magnitude of
these objects. We then studied the mass and age distributions of the stellar
sample, using pre-main sequence evolutionary models to determine the basic
properties of the stellar sample. Statistical tests and Monte Carlo simulations
were then applied to studying the properties of the two T Tauri subclasses. We
find that the probability of CTTS and WTTS samples being drawn from the same
parental age and mass distributions is low; CTTSs are, on average, younger than
WTTSs. They are also less massive, but this is due to selection effects. The
observed mass and age distributions of both T Tauri subclasses can be
understood in the framework of a simple disk evolution model, assuming that the
CTTSs evolve into WTTSs when their disks are fully accreted by the stars.
According to this empirical model, the average disk lifetime in Taurus-Auriga
is 4 10**6 (Mstar/Msun)**0.75 yr.

Astrophysics