The White Dwarf Opportunity: Constraining Stellar Winds from the Galaxys most Common Stars using a White Dwarf Companion

Abstract

The winds of M dwarf stars are poorly constrained and poorly understood. Literature values of M dwarf wind mass-loss rates span several orders of magnitude and suffer from poor number statistics, with fewer than 30 systems having well-constrained values. Stellar winds are especially important to how young planetary systems evolve, with consequences for expected exoplanet atmosphere loss, atmospheric chemistry, surface habitability, and more. While several methodologies exist for constraining stellar winds, only four have produced detections of wind mass-loss rates for M dwarf stars. One of these methodologies involves constraining the M dwarf mass-loss rate using atmospheric metal pollution of a close companion white dwarf star. In this work, I calculate wind mass-loss rates for two M dwarf stars using this methodology. Additionally, I expand the range of systems to which this methodology can be applied. Previous studies have noted that M dwarfs in close binary systems with white dwarfs are often magnetically active. This magnetic activity produces emission lines for magnetically sensitive elements, such as calcium. Calcium is also the metal pollutant that produces the deepest optical light absorption signals in white dwarfs. In this work, I develop methodology for recovering calcium absorption equivalent widths from white dwarf stars in unresolved binaries with magnetically active M dwarfs. I apply this methodology to 56 systems, recovering 19 white dwarf calcium equivalent widths which remain in absorption within their 1 sigma uncertainty. While it is left to a future work to calculate wind rates for these systems, this methodology does significantly expand the number of close white dwarf-M dwarf binary systems for which M dwarf wind rates can be recovered.