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New methods for determining the ages of PMS stars

Abstract We present three new methods for determining the age of groups of pre-main-sequence stars. The first, creating empirical isochrones allows us to create a robust age ordering, but not to derive actual ages. The second, using the width of the gap in colour-magnitude space between the pre-main-sequence and main-sequence (the radiative convective gap) has promise as a distance and extinction independent measure of age, but is as yet uncalibrated. Finally we discuss τ2 fitting of the main sequence as the stars approach the terminus of the main sequence. This method suggests that there is a factor two difference between these “nuclear” ages, and more conventional pre-main-sequence contraction ages.