Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.246...20c&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 246, NO. 1/SEP1, P. 20, 1990
Astronomy and Astrophysics
Astronomy
7
Scientific paper
An MHD model has been built for the A2 IIIe star HD 190073 in order to account for the following observational facts.
(i) The star has a magnetic field. (ii) It has an expanding chromosphere. (iii) Shell lines of single ionized metals display large expansion velocities. (iv) The continuum spectrum displays an important IR excess. (v) The UV continuum spectrum exhibits an absorption band from 2600 Å towards shorter wavelengths. (vi) H nebular emissions are present in addition to the P Cyg III type of profile displayed by Hα and Hβ. (vii) Na I faint emissions yield low expansion velocities; shell lines bordered by faint emissions, corresponding to neutral metals, behave in a similar way.
From the theoretical point of view, the model is an application of Low & Tsinganos' MHD equations for a wind developed under the presence of a magnetic field.
The solution of these equations will provide us with a velocity law which will give, through the continuity relation, the density distribution. This density distribution is applied to Lamers & Waters' formalism for free-free and free-bound emission from a spherical extended atmosphere.
We reproduce (i) the observed velocity structure of the wind, (ii) the IR excess from 2 to 100 μm and (iii) the 2600 Å discontinuity in the UV spectrum.
Cuttela M.
Ringuelet Adela E.
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