New Magellanic Cloud R Coronae Borealis and DY Per type stars from the EROS-2 database: the connection between RCBs, DYPers and ordinary carbon stars
P. Tisserand, P. R. Wood, J. B. Marquette, C. Afonso, J. N. Albert, J. Andersen, R. Ansari, E. Aubourg, P. Bareyre, J. P. Beaulieu, X. Charlot, C. Coutures, R. … 展开作者
P. Tisserand, P. R. Wood, J. B. Marquette, C. Afonso, J. N. Albert, J. Andersen, R. Ansari, E. Aubourg, P. Bareyre, J. P. Beaulieu, X. Charlot, C. Coutures, R. Ferlet, P. Fouqué, J. F. Glicenstein, B. Goldman, A. Gould, M. Gros, J. de Kat, E. Lesquoy, C. Loup, C. Magneville, E. Maurice, A. Maury, A. Milsztajn, M. Moniez, N. Palanque-Delabrouille, O. Perdereau, J. Rich, P. Schwemling, M. Spiro, A. Vidal-Madjar
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22 pages, 38 figures, Accepted for publication in A&A
R Coronae Borealis stars (RCB) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs, called the Double degenerate scenario. This scenario is also studied as a source, at higher mass, of type Ia Supernovae (SnIa) explosions. Therefore a better understanding of RCBs composition would help to constrain simulations of such events. We searched for and studied RCB stars in the EROS Magellanic Clouds database. We also extended our research to DY Per type stars (DYPers) that are expected to be cooler RCBs (T~3500 K) and much more numerous than their hotter counterparts. The light curves of ~70 millions stars have been analysed to search for the main signature of RCBs and DYPers: a large drop in luminosity. Follow-up optical spectroscopy was used to confirm each photometric candidate found. We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers, but also listed new candidates: 3 RCBs and 14 DYPers. We estimated a range of Magellanic RCB shell temperatures between 360 and 600 K. We confirm the wide range of absolute luminosity known for RCB stars, M_V~-5.2 to -2.6. Our study further shows that mid-infrared surveys are ideal to search for RCB stars, since they have thinner and cooler circumstellar shells than classical post-AGB stars. In addition, by increasing the number of known DYPers by ~400%, we have been able to shed light on the similarities in the spectral energy distribution between DYPers and ordinary carbon stars. We also observed that DYPer circumstellar shells are fainter and hotter than those of RCBs. This suggests that DYPers may simply be ordinary carbon stars with ejection events, but more abundance analysis is necessary to give a status on a possible evolutionnary connexion between RCBs and DYPers.
Surface abundances of 14 (11 majority class and 3 minority class) R Coronae Borealis stars (RCBs) along with the final flash object, V4334 Sgr (Sakurai's object) are revised based on their carbon abundances measured from the observed C2 bands; note that the earlier reported abundances were derived using an assumed carbon abundance due to the well known ``carbon problem''. The hot RCB MV Sgr is not subject to a carbon problem; it is remarkable to note that MV Sgr's carbon abundance lies in the range that is measured for the majority and minority class RCBs. The revised iron abundances for the R…
R Coronae Borealis stars (RCBs) are the best candidates to be the products of white dwarf mergers in the intermediate mass range ($0.4<M_{tot}<1.1$ M$_{\odot}$). After a merger, a He envelope surrounds a CO core, and a short-lived supergiant phase starts. RCBs correspond to that phase. They are known to be hydrogen-deficient and carbon-rich supergiant stars. They are rare; They are also highly diverse in chemical abundances, brightness and photosphere temperature. To understand their evolutionary path, constrain their spatial distribution and test their formation rate, we aim to increase signi…
R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich variable supergiants thought to be the result of dynamically unstable white dwarf mergers. We attempt to model RCBs through all the relevant timescales by simulating a merger event in Octo-tiger, a 3D adaptive mesh refinement (AMR) hydrodynamics code and mapping the post-merger object into MESA, a 1D stellar evolution code. We then post-process the nucleosynthesis on a much larger nuclear reaction network to study the enhancement of s-process elements. We present models that match observations or previous studies in most su…
The R Coronae Borealis (RCB) stars are extremely hydrogen-deficient carbon stars which produce large amounts of dust, causing sudden deep declines in brightness. They are believed to be formed primarily through white dwarf mergers. In this paper, we use MESA to investigate how post-merger objects with a range of initial He-burning shell temperatures from 2.1 - 5.4 *10^8 K with solar and subsolar metallicities evolve into RCB stars. The most successful model of these has subsolar metallicity and an initial temperature near 3 *10^8 K. We find a strong dependence on initial He-burning shell tempe…
Context: R Coronae Borealis (RCB) variables and their non-variable counterparts, the dustless Hydrogen-Deficient Carbon (dLHdC) stars have been known to exhibit enhanced s-processed material on their surfaces, especially Sr, Y, and Ba. No comprehensive work has been done to explore the s-process in these types of stars, however one particular RCB star, U Aqr, has been under scrutiny for its extraordinary Sr enhancement. Aims: We aim to identify RCB and dLHdC stars that have significantly enhanced Sr abundances, such as U Aqr, and use stellar evolution models to begin to estimate the type of ne…
Light Curves For Ten R Coronae Borealis Stars For Longer Than a Century: Secular Evolution, Dip Statistics, and a General Model for the Shape of Isolated Light Curve Dips
