The changing nebula around the hot R Coronae Borealis star DY Centauri

摘要

Among the distinguishing characteristics of the remarkable hot R CoronaeBorealis star DY Cen, which was recently found to be a spectroscopic binary, isthe presence of nebular forbidden lines in its optical spectrum. A compilationof photometry from 1970 to the present suggests that the star has evolved tohigher effective temperatures. Comparison of spectra from 2010 with earlierspectra show that between 2003 and 2010, the 6717 and 6730 A emission lines of[S II] underwent a dramatic change in their fluxes suggesting an increase inthe nebula's electron density of 290 cm-3 to 3140 cm-3 from 1989 to 2010 whilethe stellar temperature increased from 19500 K to 25000 K. The nebular radiusis about 0.02 pc, 60000 times bigger than the semimajor axis of DY Cen binarysystem. Rapid changes of stellar temperature and its response by the nebulademonstrate stellar evolution in action.