Ultraviolet emission lines and optical photometry of the flare star AT Microscopii

UV spectra of the dwarf flare star binary AT Mic were obtained with the IUE spacecraft over the course of three days in September 1985. A high-resolution short-wavelength spectrum was exposed for 25 h. Line wavelengths, widths, and fluxes were derived from the observed high-resolution spectra, and the effects of the binary structure of AT Mic on the spectral lines were evaluated. The data show that the UV emission-line spectrum is similar in nature to that of flare regions on the sun and other stars. The width of the Mg II k-line shows a good fit with the Wilson-Bappu relation, which thus seems to extend over a very large range of absolute magnitudes.