Fast Spectroscopic Variations on Rapidly Rotating Cool Dwarfs - Part Three - Masses of Circumstellar Absorbing Clouds on Ab-Doradus

Details Fast Spectroscopic Variations on Rapidly Rotating Cool Dwarfs - Part Three - Masses of Circumstellar Absorbing Clouds on Ab-Doradus Fast Spectroscopic Variations on Rapidly Rotating Cool Dwarfs - Part Three - Masses of Circumstellar Absorbing Clouds on Ab-Doradus

Dec 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.247..415c&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 247, NO. 3/DEC1, P. 415, 1990

Astronomy and Astrophysics

Astronomy

52

Scientific paper

We present new time-resolved Hα, Ca II H and K and Mg II h and k spectra of the rapidly rotating KO dwarf star AB Doradus (= HD 36705). The transient absorption features seen in the Hα line are also present in the Ca II and Mg II resonance lines. New techniques are developed for measuring the average strength of the line absorption along lines-of-sight intersecting the cloud. These techniques also give a measure of the projected cloud area. The strength of the resonance-line absorption provides new constraints on the column densities, projected surface areas, temperatures and internal turbulent velocity dispersions of the circumstellar clouds producing the absorption features. At any given time the star appears to be surrounded by between S and 20 clouds with masses in the range 2-6 × 1017 g. The clouds appear to have turbulent internal velocity dispersions of order 3-20 km s-1, comparable with the random velocities of discrete filamentary structures in solar quiescent prominences. Night-to-night changes in the amount of Ca II resonance line absorption can be explained by changes in the amplitude of turbulent motions in the clouds. The corresponding changes in the total energy of the internal motions are of order 1029 erg per cloud. Changes of this magnitude could easily be activated by the frequent energetic (˜1034 erg) X-ray flares seen on this star.

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