Rotational Velocities and Radii Estimates of Low-Mass Pre-Main Sequence Stars in NGC 2264

TL;DR

This study measures rotational velocities and estimates stellar radii of young stars in NGC 2264, revealing insights into angular momentum evolution, starspot effects, and binary influences during early stellar development.

Contribution

It provides new v sin i measurements for 254 PMS stars, compares observed radii with models including starspots, and introduces analysis methods for multiple clusters.

Findings

Weak-lined TTSs may rotate faster than Classical TTSs.

Stars in binary systems may have higher rotation rates.

Starspot-inclusive models better match observed stellar radii.

Abstract

Investigating the angular momentum evolution of pre-main sequence (PMS) stars provides important insight into the interactions between Sun-like stars and their protoplanetary disks, and the timescales that govern disk dissipation and planet formation. We present projected rotational velocities (v sin i values) of 254 T Tauri stars (TTSs) in the ~3 Myr-old open cluster NGC 2264, measured using high-dispersion spectra from the WIYN 3.5m telescope's Hydra instrument. We combine these with literature values of temperature, rotation period, luminosity, disk classification, and binarity. We find some evidence that Weak-lined TTSs may rotate faster than their Classical TTS counterparts and that stars in binary systems may rotate faster than single stars. We also combine our v sin i measurements with rotation period to estimate the projected stellar radii of our sample stars, and then use a maximum likelihood modeling technique to compare our radii estimates to predicted values from stellar evolution models. We find that starspot-free models tend to underestimate the radii of the PMS stars at the age of the cluster, while models that incorporate starspots are more successful. We also observe a mass dependence in the degree of radius inflation, which may be a result of differences in the birthline location on the HR diagram. Our study of NGC 2264 serves as a pilot study for analysis methods to be applied to four other clusters ranging in age from 1 to 14 Myr, which is the timescale over which protoplanetary disks dissipate and planetary systems begin to form.