Activity observed by the Kepler space telescope: The M dwarf LHS 6351 (KIC 2164791)

Abstract

Continuous 123.87-day observations with the “Kepler” space telescope are used to study the activity of the fully convective, low-mass M dwarf LHS 6351. The axial-rotation period of the star is 3.36 day. High-precision photometric observations of LHS 6351 enabled studies of its surfacetemperature inhomogeneities and their evolution. The difference in the longitudes of active regions increased from 120° at the beginning to 207° at the end of the observations, for i = 60° (and from 156° to 198° for i = 30°). This variation of the locations of the spots on the stellar surface provides evidence for differential rotation of the star. According to our estimates, the rate of displacement of the active regions is (0.006–0.014) ± 0.002 rad/day. Assuming i = 60°, the total area of spots S decreased, on average, from 1.2% to 0.92% of the total visible surface of the star; if i = 30°, this area decreased from 1.8% to 1.0%. We compared manifestations of the magnetic activity of LHS 6351 with the properties of the fully convective M dwarfs V374 Peg and GJ 1243, studied earlier. We derived the dependence of ΔΩ on the Rossby number for these M dwarfs, and identified two groups of stars with differing mass and differential rotation.