Projected Rotational Velocities and Fundamental Properties of Low-Mass Pre-Main Sequence Stars in the Taurus-Auriga Star Forming Region

TL;DR

This study measures the rotational velocities and fundamental properties of 70 pre-main sequence stars in Taurus-Auriga, revealing insights into stellar rotation, binarity effects, and the lack of simple correlations with disks or evolutionary stage.

Contribution

It provides new high-resolution $v \, \sin i$ measurements, compares infrared and optical methods, and analyzes the effects of binarity and disks on stellar rotation in pre-main sequence stars.

Findings

Infrared $v \, \sin i$ measurements have a typical error floor of 1.8 km/s.

Binaries tend to have higher $v \, \sin i$, possibly due to contamination or tidal effects.

No significant difference between optical and infrared $v \, \sin i$ values regardless of disks.

Abstract

The projected stellar rotational velocity ($v \sin i$) is critical for our understanding of processes related to the evolution of angular momentum in pre-main sequence stars. We present $v \sin i$ measurements of high-resolution infrared and optical spectroscopy for 70 pre-main sequence stars in the Taurus-Auriga star-forming region, in addition to effective temperatures measured from line-depth ratios, and stellar rotation periods determined from optical photometry. From the literature, we identified the stars in our sample that show evidence of residing in circumstellar disks or multiple systems. The comparison of infrared $v \sin i$ measurements calculated using two techniques shows a residual scatter of $\sim$ 1.8 km s$^{-1}$, defining a typical error floor for the $v \sin i$ of pre-main sequence stars from infrared spectra. A comparison of the $v \sin i$ distributions of stars with and without companions shows that binaries/multiples typically have a higher measured $v \sin i$, which may be caused by contamination by companion lines, shorter disk lifetimes in binary systems, or tidal interactions in hierarchical triples. A comparison of optical and infrared $v \sin i$ values shows no significant difference regardless of whether the star has a disk or not, indicating that CO contamination from the disk does not impact $v \sin i$ measurements above the typical $\sim$ 1.8 km s$^{-1}$ error floor of our measurements. Finally, we observe a lack of a correlation between the $v \sin i$, presence of a disk, and H-R diagram position, which indicates a complex interplay between stellar rotation and evolution of pre-main sequence stars.