Stellar activity with LAMOST. III. Temporal variability pattern in Pleiades, Praesepe, and Hyades

Abstract

We present the results from a systematic study of temporal variation of stellar activity in young late-type stars. We used multi-epoch LAMOST low-resolution spectra of over 300 member candidates in three young open clusters: Pleiades, Praesepe, and Hyades. The spectral measurements of TiO band strength near 7050 Å (TiO2) and equivalent width of Hα line (EW Hα ) are used as the tracers of cool-spot coverage and chromospheric emission strength, respectively. The analysis of time-variation patterns of these two tracers suggested there exist detectable variabilities in TiO2 and EW Hα , and their time-scales are in the wide range from days to years. Results showed that more active stars, younger and fast rotators, tend to have larger activity variations. There is a tendency of anti-correlation between temporal variations in TiO2 and EW Hα . Also, appreciable anti-correlation in the rotational phase between Hα emission and K2 brightness is detected in some M dwarfs, indicating spatial co-location of the plages with cool starspots, however, cool stars do not always show such co-location features. Furthermore, spot coverage and Hα emission were evident at all rotational phases of several M dwarfs, indicating a basal level of activity, perhaps due to many small and randomly located active regions in the atmosphere.

19 pages, 15 figures

References in corpus (20)

• The NumPy array: a structure for efficient numerical computation
• The K2 Mission: Characterization and Early results
• Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics
• Kepler Flares I. Active and Inactive M dwarfs
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• Patterns of photometric and chromospheric variation among Sun-like stars: A 20-year perspective
• A Kepler Study of Starspot Lifetimes with Respect to Light Curve Amplitude and Spectral Type
• The Factory and The Beehive II. Activity and Rotation in Praesepe and the Hyades
• The Age and Age Spread of the Praesepe and Hyades Clusters: a Consistent, ~800 Myr Picture from Rotating Stellar Models
• Near and Mid-IR Photometry of the Pleiades, and a New List of Substellar Candidate Members
• Magnetic Activity Cycles in the Exoplanet Host Star epsilon Eridani
• K2 Variable Catalogue: Variable Stars and Eclipsing Binaries in K2 Campaigns 1 and 0
• The Seven Sisters DANCe. I. Empirical isochrones, Luminosity and Mass Functions of the Pleiades cluster
• Stellar activity with LAMOST - II. Chromospheric activity in open clusters
• The AstraLux Multiplicity Survey: Extension to Late M-dwarfs
• Stellar activity with LAMOST. I. Spot configuration in Pleiades
• Stellar rotational periods in the planet hosting open cluster Praesepe
• Association of Plages With Sunspots: A multi wavelength Study Using Kodaikanal Ca $\text{II}$ K and Greenwich sunspot area Data
• X-ray flares on the UV Ceti-type star CC Eridani: a "peculiar" time-evolution of spectral parameters