eROSITA detected cool stars TESS derived periods

Our results show that F-type stars do not reach the "classical" saturation limit of LX/Lbol~10^-3^, instead exhibiting significantly lower LX/Lbol values. We find that the convective turnover times derived from this sample closely agree with theoretical computations, supporting the idea that Rossby number-activity relations hold for all late-type main sequence stars. The lower level of activity in earlier spectral types (e.g., F-type and late A-type stars) is a physical consequence of their short convective turnover times, which prevent them from rotating rapidly enough to ever reach the saturation regime.

We demonstrate that a simple model incorporating our derived turnover times versus color can successfully reproduce he observed characteristics of the eROSITA X-ray activity distribution, as measured by the LX /Lbol ratio and Gaia BP-RP color.