High-resolution spectroscopy of two carbon stars with long-term obscuration events

Abstract

In this paper, we provide an analysis of the high-resolution optical spectra of two carbon variables, V1983 Cyg and V2074 Cyg, which are presumed to be cool R Corona Borealis (RCB) stars, according to their photometric behaviour. The stars show irregular long-term visual light variations of relatively large amplitude, similar to those exhibited by RCB variables. Based on the comparison of our high-resolution spectra with those of various carbon stars, we conclude that both variables have spectral properties typical for cool N-type carbon stars. However, two major differences from the spectra of normal carbon stars have been noted: the presence of high-velocity (∼−60 km s−1) components in the Na i D lines in both V1983 Cyg and V2074 Cyg and the unusually strong absorption in the Hα line in the spectrum of V1983 Cyg. The nature of these peculiarities is discussed. Although, according to their photometrical behaviour as well as their infrared properties, both V1983 Cyg and V2074 Cyg are ascribed to DY Persei (DY Per) type stars, we do not find any evidence that the two variables could be cool RCB stars similar to DY Per.