Projected Rotational Velocities and Fundamental Properties of Low-mass Pre-main-sequence Stars in the Taurus-Auriga Star-forming Region

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, as well as 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 similar to 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 similar to 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.