M dwarf planetary systems: an observational study to look for prolonged activity in host stars

M dwarf stars begin their lives rapidly rotating and with high levels of activity, but as time goes on, they slow down via magnetically channelled winds, whilst their activity decreases. We aim to investigate the possibility of prolonged rotation and activity in M dwarfs due to tidal interaction with close-in planets, an effect previously observed for Sun-like stars with hot Jupiters by Poppenhaeger and Wolk (2014). As a prelude to our main programme, we are conducting a pilot survey of M dwarfs + white dwarf wide binary systems to study the age-activity relationship for M dwarfs by using the white dwarf as an age calibrator, a method that still remains biased against cool white dwarf components. We aim to identify an age-comprehensive population of common proper-motion/distance binaries using Gaia DR2 and our previously constructed SDSS/2MASS/WISE M dwarf catalogue (Cook et al. 2016). With this method we can also look for over-active M dwarf in our oldest systems. Preliminary results include a sample of common proper motion white dwarf + M dwarf pairs, some of them consisting in cool white dwarfs whose companion M-type stars need to be confirmed.