FUSE Observations of the Active Cool Star: AB Dor

Far ultraviolet spectra were obtained of the active cool star AB Doradus (HD 36705) during the calibration and checkout period of the FUSE satellite. Observations in this early phase of the mission were taken at a resolving power of 12000–15000 (∼20–25 km s −1 ) and covered the spectral range 905–1187u The integrated spectrum exhibits strong, rotationally broadened stellar emission from C iii (�977, �1175) and O vi (�1032, �1037), and many weaker lines. Strong emission lines of C iii and O vi exhibit broad wings. The C iii �977 profile shows blue-shifted absorption at ∼30 km s −1 and C ii �1036 absorption appears superposed on emission in the wing of O vi �1037. Rotational modulation of C iii and O vi is present, in harmony with its photometric variability. Flares were detected in the brightest lines and subexposures were analyzed to examine flux and profile variations. Downflows that extend to 600 km s −1 during a flare are found in the O vi profiles. These early observations demonstrate that FUSE will be an exceptional instrument for studying chromospheres in cool stars. Subject headings: stars:chromospheres – stars:flare – stars:individual(AB Dor) – stars:pre-main-sequence – ultraviolet:stars 1. OBSERVATIONS AND DATA ANALYSIS