The CARMENES search for exoplanets around M dwarfs. A homogeneous catalogue of projected rotational velocities accounting for limb-darkening

TL;DR

This paper introduces a new convolution-based method with limb-darkening for measuring stellar rotational velocities from high-resolution spectra, resulting in a large, precise catalogue for M dwarfs.

Contribution

It presents a novel, more accurate technique for determining vsini in M dwarfs, improving measurement precision and expanding the existing catalogue.

Findings

Median relative uncertainty of 6.8% in vsini measurements

Largest uniform catalogue of vsini for M dwarfs to date

Significantly improved vsini values for several targets and 36 new targets

Abstract

Stellar rotation is closely linked to both age and magnetic activity. Through gyrochronology, it provides a means to estimate stellar ages and trace the evolution of planetary systems, and it is also crucial to constrain and correct stellar activity effects for robust exoplanet detection and characterisation. CARMENES is a dual-channel, high-resolution (R > 80000) spectrograph that has been highly successful in detecting exoplanets around M-dwarf stars using the radial-velocity technique, and it also enables precise measurements of the projected rotational velocity (vsini) from spectral line broadening. We present an oversampled convolution method incorporating a realistic limb-darkening model to determine vsini from CARMENES spectra by comparing observed spectra with that of a template star. The advantages over existing methods in the literature have been assessed using high-resolution synthetic spectra spanning effective temperatures of 2500-4000 K and projected rotational velocities of up to 50 km/s. Applied to 392 M dwarfs observed with CARMENES, our method yields vsini measurements (or upper limits at 2 km/s) with a median relative uncertainty of 6.8%, substantially smaller than the 15.4% reported in the literature. This work provides the largest uniform catalogue of vsini measurements for M dwarfs, including significantly updated values for several targets, along with 36 new targets.