An HRD-like Diagram for Pre-main Sequence Stars

Abstract When Pre-Main Sequence stars have two spectral types, an earlier one measured in the optical and a later one in the IR, the hotter one implies a greater Hertzsprung–Russell Diagram (HRD) mass than the cooler one. The mass discrepancy may be removed by plotting the stars on a modified HRD showing log (Luminosity) versus log (surface gravity). Placing two Pre-Main Sequence stars in Taurus, BP Tau and T Tau N, on such a HRD-like diagram shows that the hotter effective temperature represents the stars’ intrinsic parameter determined by their luminosity and radius and resolves the mass discrepancy in favor of the larger mass.