WISE survey : R Coronae Borealis

Article : "Tracking down R Coronae Borealis Stars from their mid-Infrared WISE colours" (Article: Astro-ph, ADS)

Abstract :

Context: R Coronae Borealis stars (RCBs) are hydrogen-deficient and carbon-rich supergiant stars. They are very rare, as only $\sim$50 are actually known in our Galaxy. Interestingly, RCBs are strongly suspected to be the evolved merger product of two white dwarfs and could therefore be an important tool to understand Supernovae type Ia in the Double Degenerate scenario. Constraints on the spatial distribution and the formation rate of such stars are needed to picture their origin and test it in the context of actual population synthesis results. To do so, it is crucial to increase significantly the number of known RCBs.

Aims: With an absolute magnitude M$_V\sim$-5 and a bright/hot circumstellar shell made of amorphous carbon grains, RCBs are so distinctive that we should be able nowadays to find them everywhere in our Galaxy using publicly available catalogues. In the optical, the search is difficult if one does not possess well sampled lightcurves as RCBs are known to undergo unpredictable declines due to puffs of clouds that obscure their photosphere. However mono-epoch mid-infrared data can help us to discriminate RCBs among other dust-producing stars. The aim is to produce from the mid-infrared WISE and near-infrared 2MASS catalogues, a new catalogue of reasonable size, enriched with RCBs stars.

Methods: Colour-Colour cuts used on all stars detected in all four WISE and three 2MASS broadbands are the main selection criteria. The selection efficiency was monitored using the 52 known RCBs located in the sky area covered by the WISE first preliminary data release.

Results: It has been found that selection cuts in mid-infrared colour-colour diagrams are a very efficient method of discriminating RCBs from other stars. An RCB enriched catalogue made of only 1602 stars, with a high detection efficiency of about 77\%, was produced. Spectral energy distribution of 49 known RCBs observed by WISE and/or AKARI are also presented with an estimate of their photosphere and circumstellar shell temperatures.

Conclusions: The newly released WISE all sky catalogue has proven to be a valuable resource in finding RCB stars. Actual scenarios predict that between 500 and 1000 RCBs exist in our Galaxy. The newly created RCB enriched catalogue is an important step forward to increase drastically the number of known RCB stars and therefore better understand their origin.

Page Updated : 12/08/2011
Patrick Tisserand