PostT Tauri Stars: A False Problem

摘要

We consider the problem of the apparent lack of old T Tauri stars in nearby star-forming regions in the framework of the standard model of low-mass star formation. We argue that the similarity between molecular cloud lifetimes and the ambipolar diffusion timescale implies that star formation does not take place instantaneously, nor at a constant rate. Thus, models based on the assumption of a constant star formation rate overestimate the predicted number of stars of ages greater than 25 Myr. We argue that the probability of finding a large population of old stars in a star-forming region is intrinsically very small. It is therefore unlikely that the dispersed X-ray sources found by ROSAT at large distances from molecular cloud complexes can be identified with such a population. We conclude that the postT Tauri problem is by and large nonexistent.