VizieR Online Data Catalog: Sample of 45 HαEW outliers (Kiman+, 2021)

In this work, we calibrate the relationship between Hα emission and M-dwarf ages. We compile a sample of 892 M-dwarfs with Hα equivalent width (HαEW) measurements from the literature that are either comoving with a white dwarf of known age (21 stars) or in a known young association (871 stars). In this sample we identify 7 M-dwarfs that are new candidate members of known associations. By dividing the stars into active and inactive categories according to their HαEW and spectral type (SpT), we find that the fraction of active dwarfs decreases with increasing age, and the form of the decline depends on SpT. Using the compiled sample of age calibrators, we find that Hα EW and fractional Hα luminosity (L_Hα/L_bol) decrease with increasing age. HαEW for SpT<~M7 decreases gradually up until ~1Gyr. For older ages, we found only two early M dwarfs that are both inactive and seem to continue the gradual decrease. We also found 14 mid-type M-dwarfs, out of which 11 are inactive and present a significant decrease in HαEW, suggesting that the magnetic activity decreases rapidly after ~1Gyr. We fit L_Hα/L_bol versus age with a broken power law and find an index of -0.11_-0.01^+0.02 for ages <~776Myr. The index becomes much steeper at older ages, but a lack of field age-calibrators (>>1Gyr) leaves this part of the relation far less constrained. Finally, from repeated independent measurements for the same stars, we find that 94% of them have a level of HαEW variability <~5Å at young ages (<1Gyr).

(1 data file).