Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000ap.....43..435r&link_type=abstract
Astrophysics (English translation of Astrofizika), v. 43, Issue 4, p. 435-445 (2000).
Astronomy and Astrophysics
Astrophysics
3
Scientific paper
The transformation of the line and molecular spectra of R CrB from absorption to emission at the 1985 minimum is traced from spectroscopic observations, and it is concluded for the first time, from a comparison with light curves and color indices, that the rapid variation of the color index U - B by -0m.6 during fading is due exclusively to this transformation. The transformation of the spectrum can result in an increase in the star's brightness in the UBV photometric bands by about 1m.4, 0m.75, and up to 0m.75, respectively. This removes one of the main objections to using the concept of a homogeneous spherical shell to interpret the R Coronae Borealis phenomenon. High-resolution spectroscopic observations of SV Sge, a star with variability of the R Coronae Borealis type, showed the presence of an intense circumstellar component in Na I D lines with a violet shift corresponding to 240 km/sec, which is unrelated to visible brightness minima. It is suggested that a stream of matter with such a velocity through the star's vicinity is the cause of the excitation not only of the broad emission features observed during brightness minima upon fading of the photospheric emission but also of the narrow ones. Assuming that a brightness minimum is associated with the temporary formation of another spherical screening shell, some characteristics of the permanent shell are determined. Its optical depth and geometrical thickness are 0.2-0.7 and at least 0.4 of its radius, respectively.
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