Pre-main-sequence isochrones. II. SFR

This result has wide-ranging implications, including that circumstellar discs survive longer (=~10-12Myr) and that the average Class I lifetime is greater (=~1Myr) than currently believed. For each star-forming region, we derived two ages from colour-magnitude diagrams.

First, we fitted models of the evolution between the zero-age main sequence and terminal-age main sequence to derive a homogeneous set of main-sequence ages, distances and reddenings with statistically meaningful uncertainties. Our second age for each star-forming region was derived by fitting pre-main-sequence stars to new semi-empirical model isochrones. For the first time (for a set of clusters younger than 50Myr), we find broad agreement between these two ages, and since these are derived from two distinct mass regimes that rely on different aspects of stellar physics, it gives us confidence in the new age scale.