Wide binaries as "mini clusters" to study the intrinsic scatter of activity in cool stars

The magnetic activity of cool stars is connected to the stellar age. The activity-rotation relations combined with Gyrochronology give us the big picture of the evolution of cool star activity. However, how similar could coeval Gyr-old stars of the same metallicity and similar mass be in terms of magnetic activity? Little is understood about this intrinsic scatter of activity in cool stars. It is, however, an essential piece of information required to understand the variability in the stellar environment over gigayears of stellar evolution, including having implications on the evaporation of exoplanetary atmospheres.

In my poster, we investigate this scatter by using wide binaries. We conducted Bayesian catalogue matching between Gaia eDR3 wide binaries and the XMM-Newton DR14 catalogue to find serendipitous wide binaries in the XMM-Newton catalogue. We then use the X-ray luminosity L_X, an indicator of activity, to compare the similar mass components of the binary to find the intrinsic scatter of activity. We also estimated upper limits for the counterpart in binaries where only one star was detected.

We find that the scatter of activity in partially and fully convective M-type binaries is much larger than that seen in more massive cool stars of spectral types F, G, and K. This high scatter comes from M-type stars that are found to be in the saturated regime due to their very long spindown timescales. The intrinsic scatter in the wide binaries of all spectral types, however, is much smaller than what is observed for randomly paired stars in the solar neighbourhood.

As the activity-rotation relations and Gyrochronology continue to be calibrated for field stars, X-ray studies of wide binaries like these can help determine the degree of deviation from coeval behaviour in the solar neighbourhood without the need to determine precise ages.