2008MNRAS.384..477R

Optical high-resolution spectra of the R Coronae Borealis star V CrA at light maximum and during minimum light are discussed. Abundance analysis confirms previous results showing that V CrA has the composition of the small subclass of R Coronae Borealis (RCB) stars know as `minority' RCBs, i.e. the Si/Fe and S/Fe ratios are 100 times their solar values. A notable novel result for RCBs is the detection of the 1-0 Swan system ¹²C¹³C bandhead indicating that ¹³C is abundant: spectrum synthesis shows that ¹²C/¹³C is about 3-4. Absorption-line profiles are variable at maximum light with some lines showing evidence of splitting by about 10 km/s. A spectrum obtained as the star was recovering from a deep minimum shows the presence of cool C₂ molecules with a rotational temperature of about 1200K, a temperature suggestive of gas in which carbon is condensing into soot. The presence of rapidly outflowing gas is shown by blueshifted absorption components of the Nai D and Ki 7698 Å resonance lines.