Old, quiet, and slow? A study of field M dwarf activity and rotation in the TESS Southern Continuous Viewing Zone.

Potentially habitable, Earth-like planets are most likely to be discovered orbiting M dwarfs. To constrain the evolution and current habitability of these planets, we need to understand the magnetic activity of their parent stars today and in the past. The origins and evolution of magnetism in M dwarfs remain murky, however, and we can only weakly predict levels of activity for M dwarfs of a given mass and age. This is particularly true at the old (few Gyr) ages that are typical of field stars. We report initial results from our spectroscopic survey of 122 nearby M dwarfs in the Southern Continuous Viewing Zone (CVZ) of the Transiting Exoplanet Survey Satellite (TESS). These stars have the benefit of high-precision, year-long optical light curves with which we can measure their (expected) long rotation periods. We have obtained at least one R ~ 2000 optical spectrum, which we use to characterize chromospheric Hα emission, a common proxy for the strength of the stellar magnetic field, for 120 of our targets. More than half of our stars have at least four spectra, allowing us to explore potential connections between Hα emission and photometric variability. With the rotational information we extract from TESS, these Hα data enhance our understanding of magnetic activity and its evolution in low-mass stars—and will eventually help us to characterize the past, present, and future habitability of nearby, Earth-like planets.