The coronal FeXXI lambda 1354.094 line in AB Doradus

Abstract

The active late-type star AB Doradus was observed in February 1996 with the Goddard High Resolution Spectrograph of the Hubble Space Telescope using the low resolution G140L grating. The observations covered one half of the star's rotation cycle (P = 0.514 d) with 11.5 min time resolution. The strong coronal FeXXI lambda 1354.094 line formed at 10⁷ K was analysed and its emission measure (EM) derived. This EM is much higher than that derived from recent XMM-Newton observations (Güdel et al. 2001), and earlier EXOSAT (Collier Cameron et al. 1988) and ASCA/EUVE (Mewe et al. 1996) data, as well, requiring a variability by a factor of 5. The physical reason for the variability remains unknown, since (outside flares) the observed broad band variability of AB Dor is much smaller. Based on observations 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 the NASA contract NAS 5-26555.