Probing activity and rotation of M dwarfs with X-rays and photometric timeseries

The activity-rotation relation of M dwarfs provides observational evidence of the stellar dynamo,

which is poorly understood for fully convective stars. It is known that the X-ray activity-rotation

relation has a two-regime behavior with saturation for faster rotating stars and with a Lx decrease

for slower rotation. However, the number of M dwarfs with sensitive X-ray and rotation measure-

ments has for a long time been very limited. New XMM-Newton, Chandra and eROSITA X-ray observations

with K2 mission and TESS rotation periods analyzed in my work have substantially increased the number

of low activity and fast/slow rotation stars that have been dicult to assess in the past. Combining

the new data with a systematic update and homogenization of the literature data has enabled

me to examine the activity-rotation relation in different mass bins within the M dwarf regime.

Several interesting findings emerged, including a non-constant Lx-level in the saturated regime and a

mass-dependence of the slope in the unsaturated regime.