HAZMAT. VII. The Evolution of Ultraviolet Emission with Age and Rotation for Early M Dwarf Stars

The ultraviolet (UV) emission from the most numerous stars in universe, M dwarfs, impacts formation, chemistry, atmospheric stability, and surface habitability of their planets. We have analyzed spectral evolution UV M0–M2.5 (0.3–0.6 M?) as a function age, rotation, Rossby number using Hubble Space Telescope observations Tucana-Horologium (40 Myr), Hyades (650 field (2–9 Gyr) objects. quiescent flux C ii, iii, iv, He N v, Si iv lines, formed stellar transition region, remains elevated at constant level for 240 ± 30 Myr before declining by 2.1 orders magnitude to an age 10 Gyr. Mg ii far-UV pseudocontinuum emission, chromosphere, exhibits more gradual with 1.3 1.7 magnitude, respectively. youngest exhibit scatter 0.1 dex line attributable only rotational modulation, long-term activity cycles, or unknown source variability. Saturation-decay fits these data can predict star's lines accuracy 0.2–0.3 dex, accurate means presently available. Predictions will be useful studying exoplanetary destruction abiotic production biologically relevant molecules interpreting infrared optical planetary spectra measured observatories like James Webb Telescope.