The CARMENES search for exoplanets around M dwarfs. Variability of the He I line at 10830 Å

Abstract

The He I infrared (IR) triplet at 10830 Åis known as an activity indicator in solar-type stars and has become a primary diagnostic in exoplanetary transmission spectroscopy. He I lines are a tracer of the stellar extreme-ultraviolet irradiation from the transition region and corona. We study the variability of the He I IR triplet lines in a spectral time series of 319 M~dwarf stars that was obtained with the CARMENES high-resolution optical and near-infrared spectrograph at Calar Alto. We detect He I IR line variability in 18% of our sample stars, all of which show H$\alpha$ in emission. Therefore, we find detectable He I IR variability in 78% of the sub-sample of stars with H$\alpha$ emission. Detectable variability is strongly concentrated in the latest spectral sub-types, where the He I IR lines during quiescence are typically weak. The fraction of stars with detectable He I IR variation remains lower than 10% for stars earlier than M3.0 V, while it exceeds 30% for the later spectral sub-types. Flares are accompanied by particularly pronounced line variations, including strongly broadened lines with red and blue asymmetries. However, we also find evidence for enhanced He I IR absorption, which is potentially associated with increased high-energy irradiation levels at flare onset. Generally, He I IR and H$\alpha$ line variations tend to be correlated, with H$\alpha$ being the most sensitive indicator in terms of pseudo-equivalent width variation. This makes the He I IR triplet a favourable target for planetary transmission spectroscopy.

14 pages, 12 figures, accepted by A&A, full Table 2 only available electronically at CDS

References in corpus (9)

• Kepler Flares I. Active and Inactive M dwarfs
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• Hydrogen Balmer Line Broadening in Solar and Stellar Flares
• The Ca II infrared triplet's performance as an activity indicator compared to Ca II H and K
• Surprisingly different starspot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB
• Active cool stars and He I 10830 Å: the coronal connection
• The CARMENES search for exoplanets around M dwarfs. Period search in H$\alpha$, Na I D, and Ca II IRT lines
• Stellar atmospheric parameters of FGK-type stars from high-resolution optical and near-infrared CARMENES spectra
• The CARMENES search for exoplanets around M dwarfs. The He I triplet at 10830 $\mathring{\mathrm{A}}$ across the M dwarf sequence

Cited by in corpus (2)

• Zodiacal Exoplanets in Time (ZEIT) XIII: Planet Orbits and Atmospheres in the V1298 Tau System, a Keystone in Studies of Early Planetary Evolution
• High resolution near-infrared spectroscopy of a flare around the ultracool dwarf vB 10