Intermediate Resolution Near-Infrared Spectroscopy of 36 late-M Dwarfs

TL;DR

This study uses intermediate-resolution near-infrared spectroscopy to measure rotational velocities, radial velocities, and atomic line strengths in 36 late-M dwarfs, confirming previous findings and identifying potential targets for radial velocity surveys.

Contribution

It provides new measurements for 12 late-M dwarfs and confirms previous data for 24, while analyzing atomic line behavior to aid metallicity estimation in late-M dwarfs.

Findings

13 stars have vsini below 12 km/s

4 stars are fast rotators with vsini > 30 km/s

p-EW of K I lines depends on spectral type

Abstract

We present observations of 36 late-M dwarfs obtained with the KeckII/NIRSPEC in the J-band at a resolution of \sim20,000. We have measured projected rotational velocities, absolute radial velocities, and pseudo-equivalent widths of atomic lines. 12 of our targets did not have previous measurements in the literature. For the other 24 targets, we confirm previously reported measurements. We find that 13 stars from our sample have vsini below our measurement threshold (12 km/s) whereas four of our targets are fast rotators (vsini > 30 km/s). As fast rotation causes spectral features to be washed out, stars with low projected rotational velocities are sought for radial velocity surveys. At our intermediate spectral resolution we have confirmed the identification of neutral atomic lines reported in Mclean et al. 2007. We also calculated pseudo-equivalent widths (p-EW) of 12 atomic lines. Our results confirm that the p-EW of K I lines are strongly dependent on spectral types. We observe that the p-EW of Fe I and Mn I lines remain fairly constant with later spectral type. We suggest that those lines are particularly suitable for deriving metallicities for late-M dwarfs.