The Effects of Starspots on Spectroscopic Mass Estimates of Low-mass Young Stars

TL;DR

This study investigates how starspots affect spectroscopic mass estimates of young stars, finding that infrared temperature measurements yield more accurate stellar masses than optical ones, despite discrepancies.

Contribution

It provides a comparative analysis of optical and infrared temperature measurements and their impact on stellar mass estimates, highlighting the importance of infrared data for young star characterization.

Findings

Infrared temperatures are systematically different from optical temperatures.

Magnetic field strengths correlate positively with temperature differences.

Infrared-derived masses are more accurate and precise than optical-derived masses.

Abstract

Magnetic fields and mass accretion processes create dark and bright spots on the surface of young stars. These spots manifest as surface thermal inhomogeneities, which alter the global temperature measured on the stars. To understand the effects and implications of these starspots, we conducted a large iSHELL high-resolution infrared spectroscopic survey of T Tauri stars in Taurus-Auriga and Ophiuchus star-forming regions. From the K band spectra, we measured stellar temperatures and magnetic field strengths using a magnetic radiative transfer code. We compared our infrared-derived parameters against literature optical temperatures and found a) a systematic temperature difference between optical and infrared observations, and b) a positive correlation between the magnetic field strengths and the temperature differences. The discrepant temperature measurements imply significant differences in the inferred stellar masses from stellar evolutionary models. To discern which temperature better predicts the mass of the star, we compared our model-derived masses against dynamical masses measured from ALMA and PdBI for a sub-sample of our sources. From this comparison we conclude that, in the range of stellar masses from 0.3 to 1.3 $\rm M_\odot$, neither infrared nor optical temperatures perfectly reproduce the stellar dynamical masses. But, on average, infrared temperatures produce more precise and accurate stellar masses than optical ones.