Astron. J., 121, 2173-2184 (2001/April-0)
AB Dor in '94. I. Hubble space telescope Goddard high resolution spectrogaph observations of the quiescent chromosphere of an active star.
BRANDT J.C., HEAP S.R., WALTER F.M., BEAVER E.A., BOGGESS A., CARPENTER K.G., EBBETS D.C., HUTCHINGS J.B., JURA M., LECKRONE D.S., LINSKY J.L., MARAN S.P., SAVAGE B.D., SMITH A.M., TRAFTON L.M., WEYMANN R.J., NORMAN D. and REDFIELD S.
Abstract (from CDS):
We analyze Hubble Space Telescope/Goddard High Resolution Spectrograph spectra of AB Doradus, the prototypical, ultrarapidly rotating K dwarf. We observed chromospheric (Mg II) and transition-region (C II, Si IV, C IV, and N V) lines periodically throughout the stellar rotation period and provide a low-dispersion stellar atlas of 78 emission lines. The quiescent line profiles of the chromospheric and transition-region lines show narrow cores superposed on very broad wings. The broad wings of the Mg II k and h lines and of the transition-region lines can be explained by emission from gas corotating with the star and extending out to near the Keplerian corotation radius (2.8 stellar radii). While this is not a unique solution, it is consistent with previous studies of Hα emission, which are naturally explained by large corotating prominences. We find no evidence for rotational modulation of the emission-line fluxes. The density diagnostics suggest that the transition region is formed at constant pressure, with an electron density of 2-3x1012 cm–3 at a temperature of 3x104 K. The electron pressure is about 100 times larger than that for the quiet Sun. The emission-measure distribution shows a minimum between logT=5 and 5.5. The Mg II line exhibits three interstellar absorption components along the 15 pc line of sight. We identify the lowest velocity component with the G Cloud, but the other components are not identified with any interstellar clouds previously detected from other lines of sight.
ISM: Kinematics and Dynamics - Stars: Activity - Stars: Chromospheres - Stars: Individual: Constellation Name: AB Doradus
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