HST/STIS Echelle Spectra of the dM1e Star AU Microscopii Outside of Flares

We report on observations of the dM1e flare star AU Microscopii obtained with the Space Telescope Imaging Spectrograph (STIS) on 1998 September 6. A total of 10,105 s of observations were obtained with the medium-resolution E140M grating. We report here on the 9200 s of ``quiescent'' data when the star did not obviously flare. In this data set, we identify 142 emission lines from 28 species, including low-temperature chromospheric lines (e.g., C I, O I), transition-region lines (e.g., C II-IV, N IV, O III-V, Si II-IV), and the coronal line Fe XXI 1354 Å. There are a number of intersystem lines that are useful for measuring electron densities. We discuss line redshifts and the broad wings of transition-region lines that provide evidence of microflare heating. We derive the emission-measure distribution and compare it with the solar one. We also discuss the shape and formation mechanisms of the He II 1640 Å lines. The analysis of the flare data and of the interstellar absorption features seen in the H I, D I, C II, and O I resonance lines will be published elsewhere. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal ID 7556.