Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21734106s&link_type=abstract
American Astronomical Society, AAS Meeting #217, #341.06; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astrophysics
Scientific paper
R Coronae Borealis (RCB) stars are hydrogen-deficient variable stars that suddenly fade by several magnitudes at irregular intervals whereafter they gradually return to their original brightness over a period of some months. The origin of RCBs remain a mystery. It is often thought that they are the result of the merger of a He and a CO white dwarf, while the fading is thought to be due to the formation of dust blocking light from the star. We are working on revealing the secrets behind the origin of RCBs. Here we present the results of 3 dimensional hydrodynamic simulations of the merger of a double white dwarf system where total mass is 0.9 M&sun; and initial mass ratio is q=0.7. We use a zero-temperature plus ideal gas equation of state that allows for heating through shocks. These simulations allow us to follow the evolution of the system for 10-20 initial orbital periods (1000-2000 seconds), from the onset of mass-transfer to a point after merger when the combined object has settled into a nearly axisymmetric, rotationally flattened configuration. The final merged object from the hydrodynamics simulation is then used as input for a stellar evolution code where the object's evolution can be followed over a much longer (thermal and/or nuclear) timescale. A preliminary post-merger stellar evolution simulation shows how an initial configuration of a 0.7 CO WD surrounded by 0.3 M&sun; of dynamically accreted He evolves on a time scale of 105 years to the location of the RCB stars in the H-R diagram at an effective temperature Teff<7000 K and log L 4.
We acknowledge support from NASA Astrophysics Theory Program grant number NNX10AC72G.
Clayton Geoffrey
Even Wesley
Fryer Chris
Geballe Theodore
Herwig Falk
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