Long-term Chromospheric Activity in Southern M Dwarfs: Gl 229 a and Gl 752 A
Résumé
Several late-type stars present activity cycles similar to that of the Sun. However, these cycles have been mostly studied in F to K stars. Due to their small intrinsic brightness, M dwarfs are not usually the targets of long-term observational studies of stellar activity, and their long-term variability is generally not known. In this work, we study the long-term activity of two M dwarf stars: Gl 229 A (M1/2) and Gl 752 A (M2.5). We employ medium-resolution echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory CASLEO between 2000 and 2010, and photometric observations obtained from the ASAS database. We analyze Ca II K line-core fluxes and the mean V magnitude with the Lomb-Scargle periodogram, and we obtain possible activity cycles of ~4 yr for Gl 229 A and ~7 yr for Gl 752 A.