N. Kameswara Rao, David L. Lambert
The star R Corona Borealis (R CrB) shows forbidden lines of [O II], [N II],
and [S II] during the deep minimum when the star is fainter by about 8 to 9
magnitudes from normal brightness, suggesting the presence of nebular material
around it. We present low and high spectral resolution observations of these
lines during the ongoing deep minimum of R CrB, which started in July 2007.
These emission lines show double peaks with a separation of about 170 km/s. The
line ratios of [S II] and [O II] suggest an electron density of about 100
cm$^{-3}$. We discuss the physical conditions and possible origins of this low
density gas. These forbidden lines have also been seen in other R Coronae
Borealis stars during their deep light minima and this is a general
characteristic of these stars, which might have some relevance to their
origins.
View original:
http://arxiv.org/abs/1112.6225
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