Variability Timescales of H$\alpha$ on Active Mid-to-Late M dwarfs

Abstract

We present a study of the variation timescales of the chromospheric activity indicator H$\alpha$ on a sample of 13 fully-convective, active mid-to-late M stars with masses between 0.1--0.3 solar masses. Our goal was to determine the dominant variability timescale and, by inference, a possible mechanism responsible for the variation. We gathered 10 or more high-resolution spectra each of 10 stars using the TRES spectrograph at times chosen to span all phases of stellar rotation, as determined from photometric data from the MEarth Observatories. All stars varied in their H$\alpha$ emission. For 9 of these stars, we found no correlation between H$\alpha$ and rotational phase, indicating that constant emission from fixed magnetic structures, such as starspots and plage, are unlikely to be the dominant source of H$\alpha$ emission variability. In contrast, one star, G 7-34, shows a clear relationship between H$\alpha$ and stellar rotational phase. Intriguingly, we found that this star is a member of the AB Doradus moving group and hence has the young age of 149 Myr. High-cadence spectroscopic observations of three additional stars revealed that they are variable on timescales ranging from 20--45 minutes, which we posit may be due to flaring behavior. For one star, GJ 1111, simultaneous TESS photometry and spectroscopic monitoring show an increase in H$\alpha$ emission with increased photometric brightness. We conclude that low-energy flares are able to produce variation in H$\alpha$ on the timescales we observe and thus may be the dominant source of H$\alpha$ variability on active fully-convective M dwarfs.

arXiv commentAccepted for publication in The Astrophysical Journal

References in corpus (35)

• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Fast and scalable Gaussian process modeling with applications to astronomical time series
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• BANYAN. XI. The BANYAN $\Sigma$ multivariate Bayesian algorithm to identify members of young associations within 150 pc
• A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood
• Design Considerations for a Ground-based Transit Search for Habitable Planets Orbiting M dwarfs
• Kepler Flares I. Active and Inactive M dwarfs
• HAT-P-16b: A 4 Mj Planet Transiting A Bright Star On An Eccentric Orbit
• STARRY: Analytic Occultation Light Curves
• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• The rotation and Galactic kinematics of mid M dwarfs in the Solar Neighborhood
• Time-Resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra
• On the angular momentum evolution of fully-convective stars: rotation periods for field M-dwarfs from the MEarth transit survey
• Rotation in the Pleiades with K2: I. Data and First Results
• The Solar Neighborhood XXXVII: The Mass-Luminosity Relation for Main Sequence M Dwarfs
• Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series
• M Dwarfs in SDSS Stripe 82: Photometric Light Curves and Flare Rate Analysis
• The Solar Neighborhood. XXXIII. Parallax Results from the CTIOPI 0.9m Program: Trigonometric Parallaxes of Nearby Low-Mass Active and Young Systems
• Stellar activity mimics a habitable-zone planet around Kapteyn's star
• New rotation period measurements for M dwarfs in the southern hemisphere: an abundance of slowly rotating, fully convective stars
• The CARMENES search for exoplanets around M dwarfs. Activity indicators at visible and near-infrared wavelengths
• Disentangling Planets and Stellar Activity for Gliese 667C
• Autoregressive Times Series Methods for Time Domain Astronomy
• Flare Rates, Rotation Periods. and Spectroscopic Activity Indicators of a Volume-Complete Sample of Mid-to-Late M dwarfs within 15 Parsecs
• HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators
• Short-Term H-alpha Variability in M Dwarfs
• The Volume-Complete Sample of M Dwarfs with Masses 0.1 <= M/M_sol <= 0.3 within 15 Parsecs
• Chromospheric Variability in SDSS M Dwarfs. II. Short-Timescale H-alpha Variability
• Hα Emission Variability in Active M Dwarfs
• The CARMENES search for exoplanets around M dwarfs. Period search in H$\alpha$, Na I D, and Ca II IRT lines
• Spectroscopic Orbits of Eleven Nearby, Mid-to-Late M Dwarf Binaries
• The GAPS programme at TNG XXVI. Magnetic activity in M stars: spectroscopic monitoring of AD Leonis

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• The CARMENES search for exoplanets around M dwarfs. Variability on long timescales as seen in chromospheric indicators
• The CARMENES search for exoplanets around M dwarfs. Rotational variation in activity indicators of Ross 318, YZ CMi, TYC 3529-1437-1, and EV Lac
• Active Stars in the Spectroscopic Survey of Mid-to-Late M Dwarfs Within 15pc
• Correlation between activity indicators: H$\alpha$ and Ca II lines in M-dwarf stars
• FUMES III: Ultraviolet and Optical Variability of M Dwarf Chromospheres
• Exploring the short-term variability of H$\alpha$ and H$\beta$ emissions in a sample of M dwarfs
• Contemporaneous Observations of $H\alpha$ Luminosities and Photometric Amplitudes for M Dwarfs
• The Solar Neighborhood LII: M Dwarf Twin Binaries -- Presumed Identical Twins Appear Fraternal in Variability, Rotation, H$\alpha$, and X-rays
• Quantifying the Effect of Short-timescale Stellar Activity Upon Transit Detection in M Dwarfs
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