Unidentified emission features in the R Coronae Borealis star V854 Centauri

TL;DR

This study analyzes unidentified emission features in the R Coronae Borealis star V854 Centauri during its 2012 decline, revealing new features and comparing them with other RCBs to understand their nature.

Contribution

It reports the detection of a new emission feature at 8692 Å and compares unidentified features across different RCB stars, suggesting possible chemical requirements.

Findings

Detection of a new emission feature at 8692 Å in V854 Cen.

Unidentified features are similar in V854 Cen and the Red Rectangle.

The 8692 Å feature is present in all RCBs studied.

Abstract

During its 2012 decline the R Coronae Borealis star (RCB) V854 Cen was spectroscopically monitored with X-shooter on the ESO Very Large Telescope. The obscured optical and near-infrared spectrum exhibits many narrow and several broad emission features, as previously observed. The envelope is spatially resolved along the slit and allows for a detailed study of the circumstellar material. In this Letter we report on the properties of a number of unidentified emission features (UFs), including the detection of a new one at 8692 {\AA}. These UFs have been observed in the Red Rectangle, but their chemical and physical nature is still a mystery. The previously known UFs behave similarly in the Red Rectangle and V854 Cen, but are not detected in six other observed RCBs. Possibly the presence of some hydrogen is required for the formation of their carrier(s). The $\lambda 8692$ UF is present in all RCBs. Its carrier is likely of a carbonaceous molecular nature, presumably different from that of the other UFs.