The unusual ultraviolet chromospheric spectrum of the R coronae borealis star, V854 centauri (NSV 6708), at minimum light

Geoffrey C. Clayton, University of Colorado Boulder
Barbara A. Whitney, Harvard-Smithsonian Center for Astrophysics
S. Adam Stanford, University of California, Berkeley
John S. Drilling, Louisiana State University
P. G. Judge, The Earth and Sun Systems Laboratory


The first IUE observations of a decline of the recently discovered R CrB star, V854 Cen, are reported. These observations are of particular interest because they include spectra taken at 7 mag below maximum light This is the deepest minimum ever observed in an R CrB star with the IUE. The "chromospheric" emission spectra show striking differences from UV spectra of other R CrB stars in decline. In fact, the emission spectrum of V854 Cen at minimum light does not seem to have an analogue in any known emission-line object Strong emission appears in several lines not normally seen in R CrB emission-line spectra, in particular at C II] λ2326, Mg I λ2852, and C i λλ2965, 2967. Spectral evolution similar to that seen in visible spectra of R CrB stars is clearly seen in the ultraviolet for the first time. The differences between V854 Cen and other R CrB stars may be related to known abundance differences or to different temperature and density conditions in the emission-line regions of the various R CrB stars. The emission may also be significantly affected by the presence of dust in or near the emitting region.