An age-activity calibration for old low-mass stars

Low-mass stars are highly interesting targets: we are able to detect planets in their habitable zones, and upcoming searches for biomarkers in exoplanet atmospheres will focus on low-mass star systems due to their ubiquity and proximity. We aim to develop an age-activity calibration for old low-mass stars, using wide binary systems consisting of an M or K dwarf and a white dwarf. The age of the system is determined by the WD cooling time plus its progenitor lifetime, yielding reliable ages in the regime >1 Gyr. For an exploratory sample of 7 systems where we have already derived ages, we propose to perform Chandra ACIS-S observations to determine the X-ray luminosities of the M dwarfs and correlate their stellar activity with age. We ask for a total observing time of 110 ks.