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

TL;DR

This study tracks the evolution of the nebula around the hot R Coronae Borealis star DY Cen, revealing rapid changes in nebular density and stellar temperature indicative of stellar evolution.

Contribution

It provides the first detailed analysis of nebular changes around DY Cen, linking spectral variations to stellar evolution in real time.

Findings

Nebular electron density increased from 290 to 3140 cm-3 between 1989 and 2010.

Stellar temperature increased from 19500 K to 25000 K over the same period.

The nebula's radius is approximately 0.02 parsecs, vastly larger than the binary's semimajor axis.

Abstract

Among the distinguishing characteristics of the remarkable hot R Coronae Borealis star DY Cen, which was recently found to be a spectroscopic binary, is the presence of nebular forbidden lines in its optical spectrum. A compilation of photometry from 1970 to the present suggests that the star has evolved to higher effective temperatures. Comparison of spectra from 2010 with earlier spectra 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 in the nebula's electron density of 290 cm-3 to 3140 cm-3 from 1989 to 2010 while the stellar temperature increased from 19500 K to 25000 K. The nebular radius is about 0.02 pc, 60000 times bigger than the semimajor axis of DY Cen binary system. Rapid changes of stellar temperature and its response by the nebula demonstrate stellar evolution in action.