Related papers: Do R Coronae Borealis Stars Form from Double White…
We have found that at least seven hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars, have 16O/18O ratios close to and in some cases less than unity, values that are orders of magnitude lower than measured in other stars…
We present the results of an investigation of the dredge-up and mixing during the merger of two white dwarfs with different chemical compositions by conducting hydrodynamic simulations of binary mergers for three representative mass ratios.…
The merger of a He white dwarf (WD) and a CO WD is the favored formation channel for R Coronae Borealis (RCB) stars. These stars exhibit ${^{16}}\mathrm{O}/{^{18}}\mathrm{O}$ ratios that are orders of magnitude lower than the solar value.…
We study the properties of double white dwarf (DWD) mergers by performing hydrodynamic simulations using the new and improved adaptive mesh refinement code Octo-Tiger. We follow the orbital evolution of DWD systems of mass ratio q=0.7 for…
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…
We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for five cool RCB stars. The 16O/18O ratios are derived by spectrum synthesis from…
Due to orbital decay by gravitational-wave radiation, some close-binary helium white dwarfs are expected to merge within a Hubble time. The immediate merger products are believed to be helium-rich sdO stars, essentially helium main-sequence…
The R Coronae Borealis (RCB) stars are hydrogen-deficient, variable stars that are most likely the result of He-CO WD mergers. They display extremely low oxygen isotopic ratios, 16O/18O ~ 1 - 10, 12C/13C>=100, and enhancements up to 2.6dex…
Orbital decay by gravitational-wave radiation will cause some close-binary white dwarfs (WDs) to merge within a Hubble time. The results from previous hydrodynamical WD-merger simulations have been used to guide calculations of the…
The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich, supergiants, best known for their spectacular declines in brightness at irregular intervals. Efforts to discover more RCB stars have more than doubled the number…
Many hydrogen deficient stars are characterised by surface abundance patterns that are hard to reconcile with conventional stellar evolution. Instead, it has been suggested that they may represent the result of a merger episode between a…
We present a nucleosynthesis study of the merger of a 0.4 solar masses helium white dwarf with a 0.8 solar masses carbon-oxygen white dwarf, coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a…
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…
We use Modules for Experiments in Stellar Astrophysics (MESA) to construct stellar evolution models that reach a hydrogen-deficient, carbon-rich giant phase like the R Coronae Borealis (R CrB) stars. These models use opacities from OPAL and…
The R Coronae Borealis (RCB) stars are rare hydrogen--deficient, carbon--rich supergiants. They undergo extreme, irregular declines in brightness of many magnitudes due to the formation of thick clouds of carbon dust. It is thought that RCB…
Hydrogen-deficient Carbon (HdC) stars are a class of supergiants with anomalous chemical compositions, suggesting that they are remnants of CO-He white dwarf (WD) mergers. This class comprises two spectroscopically similar subclasses -…
We present high-resolution (R~50,000) observations of near-IR transitions of CO and CN of the five known hydrogen-deficient carbon (HdC) stars and four R Coronae Borealis (RCB) stars. We perform an abundance analysis of these stars by using…
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…
The surface abundances of extreme helium (EHe) and R Coronae Borealis (RCB) stars are discussed in terms of the merger of a carbon-oxygen white dwarf with a helium white dwarf. The model is expressed as a linear mixture of the individual…
The origin of R Coronae Borealis stars has been elusive for over 200 years. Currently, two theories for their formation have been presented. These are the Final Flash scenario, in which a dying asymptotic giant branch (AGB) star throws off…