Geoffrey C Clayton | Searcharxiv

arXiv2026

The Historical Lightcurve of the R Coronae Borealis Star, V854 Cen, from 1890 to 2026

The R Coronae Borealis (RCB) Star, V854 Cen, was not discovered until the 1980's even though it is 7th magnitude at maximum light. This is because it was in a faint state due to the presence of thick circumstellar dust clouds for nearly a century. RCB stars are known for having deep declines of up to 9 magnitudes at irregular intervals. The declines are caused by dust clouds which block the light from the star. The historical lightcurve of V854 Cen before discovery was investigated by examining plates taken by Harvard College Observatory and other observatories beginning in 1889. These observations show that V854 Cen was well below 7th magnitude from 1890 to 1980, often as faint as 16th or 17th magnitude.

astro-ph.SR↗

arXiv2017

A Comparison of Grid-Based and SPH Binary Mass-Transfer and Merger Simulations

Currently there is great interest in the outcomes and astrophysical implications of mergers of double degenerate binaries. In a commonly adopted approximation, the components of such binaries are represented by polytropes with an index n=3/2. We present detailed comparisons of stellar mass-transfer and merger simulations of polytropic binaries that have been carried out using two very different numerical algorithms --- a finite-volume "grid" code and a smoothed-particle hydrodynamics (SPH) code. We find that there is agreement in both the ultimate outcomes of the evolutions and the intermediate stages if the initial conditions for each code are chosen to match as closely as possible. We find that even with closely matching initial setups, the time it takes to reach a concordant evolution differs between the two codes because the initial depth of contact cannot be matched exactly. There is a general tendency for SPH to yield higher mass transfer rates and faster evolution to the final outcome. We also present comparisons of simulations calculated from two different energy equations: in one series we assume a polytropic equation of state and in the other series an ideal gas equation of state. In the latter series of simulations an atmosphere forms around the accretor which can exchange angular momentum and cause a more rapid loss of orbital angular momentum. In the simulations presented here, the effect of the ideal equation of state is to de-stabilize the binary in both SPH and grid simulations, but the effect is more pronounced in the grid code.

astro-ph.SR↗