摘要：High-energy X-ray and ultraviolet (UV) radiation from young stars impacts planetary atmospheric chemistry andmass loss. The active ∼22 Myr M dwarf AU Mic hosts two exoplanets orbiting interior to its debris disk.Therefore, this system provides a unique opportunity to quantify the effects of stellar X-ray and UV irradiation onplanetary atmospheres as a function of both age and orbital separation. In this paper, we present over 5 hr of far-UV(FUV) observations of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Å) on the HubbleSpace Telescope (HST). We provide an itemization of 120 emission features in the HST/COS FUV spectrum andquantify the flux contributions from formation temperatures ranging from 104 to 107 K. We detect 13 flares in theFUV white-light curve with energies ranging from 1029 to 1031 erg s. The majority of the energy in each of theseflares is released from the transition region between the chromosphere and the corona. There is a 100× increase influx at continuum wavelengths λ < 1100 Å in each flare, which may be caused by thermal Bremsstrahlungemission. We calculate that the baseline atmospheric mass-loss rate for AU Mic b is ∼108 g s−1, although this ratecan be as high as ∼1014 g s−1 during flares with Lflare 1033 erg s−1. Finally, we model the transmission spectrafor AU Mic b and c with a new panchromatic spectrum of AU Mic and motivate future JWST observations of theseplanets.
