The hydrogen Paschen lines are known activity indicators, but studies of them in M dwarfs during quiescence are as rare as their reports in flare studies. 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. Regarding flaring activity, we report the automatic detection of 35 Paschen line flares in 20 stars. Additionally we found visually six faint Paschen line flares in these stars plus 16 faint Paschen line flares in another 12 stars. In strong flares, Paschen lines can be observed up to Pa 14. Moreover, we find that Paschen line emission is almost always coupled to symmetric H{alpha} line broadening, which we ascribe to Stark broadening, indicating high pressure in the chromosphere. Finally we report a few Pa{beta} line asymmetries for flares that also exhibit strong H{alpha} line asymmetries.

The hydrogen Paschen beta, gamma, and delta lines are studied in a sample of 360 M dwarfs using CARMENES spectra by using pseudo equivalent width (pEW) measurements for a flare search. The Paschen lines are purely of chromospheric origin. We identified Pa{beta} in all stellar spectra and found, that the line gets more shallow for later spectral types with a slight re-deepening for types later than M3.5. For similar effective temperature and H{alpha} in absorption, pEW(H{alpha}) anti-correlates with pEW(Pa{beta}). We report the detection of 35 Paschen line flares in 20 stars following the thresholds for flares listed in the paper. We measure the pseudo-equivalent width (pEW) of the Pa lines in each stellar spectrum. The integration ranges for the lines and the reference bands are found in Table 1 of the paper. For comparison purposes we also measure pEW values of H{alpha}. From these measurements we compute the median pEW and the median absolute deviation (MAD) for the lines. We also list some basic stellar parameters.

Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033

No