Towards the true number of flaring giant stars in the Kepler field. Are there flaring specialities associated with the giant nature?

Abstract

We aim to give a reliable estimate of the number of flaring giant stars in the Kepler field. By analyzing the flaring activity of these stars we explore their flare statistics and the released flare energies. The role of oscillation in suppressing magnetic activity is also investigated. On a sample of flaring giant stars we search for flaring specialities which may be associated with the giant nature. We search for flares using the full K1 data on a sample of 706 stars compiled from two lists of flaring giants found in the literature. In the end, we confirm only 61 stars as flaring giants. Among these 61 flaring giants we found only six which also show oscillations; we suggest that a large fraction of the 61 flaring giants are members of spectroscopic binaries which are proven already for 11. Tests are carried out to correct the detection bias at low flare energies for a subsample of 19 further studied, frequently flaring stars. For these 19 stars flare energy distributions and flare frequency diagrams (FFDs) are constructed. The number of detected flares on giant stars correlate only weakly with the rotational periods. The 61 confirmed flaring giant stars make up only about 0.3% of the entire giant star population in the Kepler database, in contrast with previous estimates of about an order higher percentage. No strong correlation was found between the stellar properties and the flaring characteristics. The wide scale of the flaring specialities are hardly related to the giant nature, if at all. This, together with the finding that the observed flare durations correlate with flare energies, regardless of the flare energy level and stellar luminosity class, suggest common background physics in flaring stars, or in other words, a general scaling effect behind.

23 pages with 24 figures and 5 tables; accepted for publication in Astronomy and Astrophysics

References in corpus (19)

• The Kepler Catalog of Stellar Flares
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• The connection between stellar granulation and oscillation as seen by the Kepler mission
• Mixed modes in red giants: a window on stellar evolution
• Testing the asteroseismic scaling relations for Red Giants with Eclipsing Binaries Observed by Kepler
• Activity indicators and stellar parameters of the Kepler targets. An application of the ROTFIT pipeline to LAMOST-Kepler stellar spectra
• The flare catalog and the flare activity in the Kepler mission
• The Magnetic Fields at the Surface of Active Single G-K Giants
• No Sun-like dynamo on the active star $\zeta$ Andromedae from starspot asymmetry
• The Evolution of Flare Activity with Stellar Age
• Time-resolved spectroscopy and photometry of an M dwarf flare star YZ Canis Minoris with OISTER and TESS: Blue asymmetry in H$\alpha$ line during the non-white light flare
• Stellar flares observed in long cadence data from the Kepler mission
• Active red giants: close binaries versus single rapid rotators
• A Search for Red Giant Solar-like Oscillations in All Kepler Data
• Spectroscopic and seismic analysis of red giants in eclipsing binaries discovered by Kepler
• Rotation--differential rotation relationships for late-type single and binary stars from Doppler imaging
• Superflares on the late-type giant KIC 2852961 -- Scaling effect behind flaring at different energy levels
• beta Cas: the first delta Scuti star with a dynamo magnetic field
• Observing dynamos in cool stars

Cited by in corpus (8)

• Finding flares in Kepler and TESS data with recurrent deep neural networks
• Stellar flare morphology with TESS across the main sequence
• Characterization of Kepler targets based on medium-resolution LAMOST spectra analyzed with ROTFIT
• Characteristics of flares on giant stars
• Magnetic activity of red giants: correlation between the amplitude of solar-like oscillations and chromospheric indicators
• EI Eridani: a star under the influence -- The effect of magnetic activity in the short and long term
• Starspots on eclipsing giant stars I.: The sample and eclipse mapping examples
• Inactive longitude and superflare in the active single-lined pre-main sequence binary V2279 Cyg