High-resolution optical spectra of the R Coronae Borealis ( RCB ) star V854 Centauri in the early stages of a decline show , in addition to the features reported for other RCBs in decline , narrow absorption lines from the C _ { 2 } Phillips system .
The low rotational temperature , T _ { rot } = 1150K , of the C _ { 2 } ground electronic state suggests the cold gas is associated with the developing shroud of carbon dust .
These absorption lines were not seen at a fainter magnitude on the rise from minimum light nor at maximum light .
This is the first detection of cold gas around a RCB star .