Vsini-s for late-type stars from spectral synthesis in K-band region

TL;DR

This study uses synthetic spectral templates to measure the rotational velocities of late-type stars in the K-band, demonstrating accuracy comparable to optical methods and highlighting the importance of spectral resolution.

Contribution

It introduces a method for determining vsini in late-type stars using synthetic spectra in the K-band, eliminating the need for observational templates.

Findings

Synthetic spectra accurately determine vsini for late-type stars.

Errors in vsini are typically less than 10% due to parameter inaccuracies.

Higher spectral resolution is needed to analyze slower rotators.

Abstract

We analyse medium-resolution spectra (R\sim 18000) of 19 late type dwarfs in order to determine vsini-s using synthetic rather than observational template spectra. For this purpose observational data around 2.2 $\mu$m of stars with spectral classes from G8V to M9.5V were modelled. We find that the Na I (2.2062 and 2.2090 $\mu$m) and $^{12}$CO 2-0 band features are modelled well enough to use for vsini determination without the need for a suitable observational template spectra. Within the limit of the resolution of our spectra, we use synthetic spectra templates to derive vsini values consistent with those derived in the optical regime using observed templates. We quantify the errors in our vsini determination due to incorrect choice of model parameters \Teff, log $g$, $v_{\rm micro}$, [Fe/H] or FWHM and show that they are typically less than 10 per cent. We note that the spectral resolution of our data(\sim 16 km/s) limited this study to relatively fast rotators and that resolutions of 60000 will required to access most late-type dwarfs.