Context. The presence and strength of a stellar magnetic field and activity is rooted in a star's fundamental parameters such as mass and age. Can flares serve as an accurate stellar "clock"?
Aims: To explore if we can quantify an activity-age relation in the form of a flaring-age relation, we measured trends in the flaring rates and energies for stars with different masses and ages.
Methods: We investigated the time-domain photometry provided by Kepler's follow-up mission K2 and searched for flares in three solar metallicity open clusters with well-known ages, M 45 (0.125 Gyr), M 44 (0.63 Gyr), and M 67 (4.3 Gyr). We updated and employed the automated flare finding and analysis pipeline Appaloosa, originally designed for Kepler. We introduced a synthetic flare injection and recovery sub-routine to ascribe detection and energy recovery rates for flares in a broad energy range for each light curve.
Results: We collect a sample of 1761 stars, mostly late-K to mid-M dwarfs and found 751 flare candidates with energies ranging from 4 × 1032 erg to 6 × 1034 erg, of which 596 belong to M 45, 155 to M 44, and none to M 67. We find that flaring activity depends both on Teff, and age. But all flare frequency distributions have similar slopes with α ≈ 2.0-2.4, supporting a universal flare generation process. We discuss implications for the physical conditions under which flares occur, and how the sample's metallicity and multiplicity affect our results. The detected flare indices, the stellar parameters for M 44 and M 45, and a copy of Table 4 are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/A133. We also published all flares we validated, and stellar parameters used for M 44 and M 45 in the same location.
Astronomy and Astrophysics
- Pub Date:
- February 2019
- methods: data analysis;
- stars: activity;
- stars: flare;
- stars: low-mass;
- Astrophysics - Solar and Stellar Astrophysics
- 17 pages, 11 figures, appendix. Accepted to A&