Paschen lines in M dwarfs chromospheres

This situation is mostly caused by a lack of observations, owing to their location in the near-infrared regime, which is covered by few high-resolution spectrographs. We study the Pa{beta} line, using a sample of 360 M dwarfs observed by the CARMENES spectrograph.

Descending the spectral sequence of inactive M stars in quiescence, we find the Pa{beta} line to get shallower until about spectral type M3.5 V, after which a slight re-deepening is observed. Looking at the whole sample, for stars with H{alpha} in absorption, we find a loose anti-correlation between the (median) pseudo-equivalent widths (pEWs) of H{alpha} and Pa{beta} for stars of similar effective temperature. Looking instead at time series of individual stars, we often find correlation between pEW(H{alpha}) and pEW(Pa{beta}) for stars with H{alpha} in emission and an anti-correlation for stars with H{alpha} in absorption.