High-resolution spectroscopy of the R coronae borealis star V coronae australis

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 (CC)-C-12-C-13 bandhead indicating that C-13 is abundant: spectrum synthesis shows that C-12/C-13 is about 3-4. Absorption-line profiles are variable at maximum light with some lines showing evidence of splitting by about 10 km s(-1). A spectrum obtained as the star was recovering from a deep minimum shows the presence of cool C-2 molecules with a rotational temperature of about 1200 K, 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 Na I D and K I 7698 angstrom resonance lines.