Nebula around R Corona Borealis
N. Kameswara Rao (1, 2), David L. Lambert (1), ((1) The W. J., McDonald Observatory, The University of Texas, Austin, USA, (2) Instituto de, Astrof\'isica de Canarias, IAC. La Laguna, Tenerife, Spain)

TL;DR
This paper reports the detection of nebular emission lines around R Corona Borealis during its deep minimum, indicating the presence of low-density gas and discussing its physical conditions and possible origins.
Contribution
It provides detailed spectroscopic observations of forbidden lines during deep minima, revealing nebular material around R CrB and similar stars, which is a new insight into their environment.
Findings
Forbidden lines show double peaks with 170 km/s separation.
Electron density of the nebula is about 100 cm$^{-3}$.
Forbidden lines are common in R CrB stars during minima.
Abstract
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. 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.
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