R Coronae Borealis at the 2003 Light Minimum

Abstract

High-resolution optical spectra of R CrB obtained in 2003 March is discussed. The 2003 spectra are compared with the extensive collection of spectra from the 1995-1996 minimum. Spectroscopic features common to the two minima include sharp emission lines of neutral and singly-ionized atoms, broad emission lines including He {\sc i}, [N {\sc ii}] 6583 Å, Na D, and Ca {\sc ii} H & K lines, and blueshifted aborption lines of Na D, and K {\sc i} resonance lines. Prominent differences between the 2003 and 1995-96 spectra are seen. The 2003 profiles of Na D, Ca II H & K are fit by a single Gaussian but in 1995-1996 two Gaussians separated by about 200 km s$^{-1}$ were required. However, the He {\sc i} broad emission lines are fit by a single Gaussian at all times; the emitting He and Na-Ca atoms are probably not colocated. The C$_2$ Phillips 2-0 lines are detected as sharp absorption lines in 2003 indicating presence of gas at 1300 K.The 2003 spectra show C {\sc i} sharp emission lines at minimum light with a velocity changing in five days by about 20 km s$^{-1}$ when the velocity of `metal' sharp lines is unchanged; the C {\sc i} emission may arise from shock-heated gas. Spectra at maximum shows extended blue wings to strong lines with the extension dependent on a line's lower excitation potential a signature of stellar wind. Changes in the cores of the resonance lines of Al {\sc i} and Na D and the Ca {\sc ii} IR lines suggest complex flow patterns near the photosphere. The spectroscopic differences at the two mimima show the importance of continued scrutiny of the declines of R CrB.