Letter to the Editor

The evolution of stars in the Taurus-Auriga T association^*

¹ Institut d'Astrophysique, 98bis Bd. Arago, 75014 Paris, France e-mail: claude.bertout@obspm.fr
² Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium
³ LERMA, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France

Received: 13 July 2007
Accepted: 20 August 2007

Abstract

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 I_c 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  yr.