Placing Protostars on the H-R Diagram using Infrared Spectroscopy

Greg Doppmann

Accurate measurements of mass and age in young stars are fundamental to our understanding of protostellar formation timescales and the current evolutionary state of these objects. The primary means of estimating masses and ages for young stars is by measuring their stellar properties (e.g. temperature and luminosity/gravity) and then comparing these properties to the predictions of pre-main sequence (PMS) evolutionary models. Unfortunately, these theoretical models are compromised by uncertainties in the input physics and need to be tested against objects of known mass. From the observation side, reliable measurments of a star's effective temperature, and especially, its luminosity or gravity are critical for accurate placement in the H-R diagram. Accurate measurments these properties in young stars using photometry is limited by (e.g.) uncertainties in the distance, the amount of extinction and accretion luminosity. Using spectroscopy to measure these same properties offers the promise of more reliable measurements that are independent of the limitations that hamper photometric techniques.