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| Paper: |
What can we Learn about the Evolutionary History of Progenitors of EHBs and Related Binary Systems from their Observed Properties? |
| Volume: |
372, 15th European Workshop on White Dwarfs |
| Page: |
23 |
| Authors: |
Pustynski, V.-V.; Pustylnik, I. |
| Abstract: |
It has been shown quite recently with high probability (Morales- Rueda et al. 2003) that all subdwarf B (sdB) stars, extreme horizontal branch (EHB) objects, belong to binary systems. Assuming that the progenitors of EHB objects belong to the binaries with initial separations of roughly a hundred solar radii and fill in their critical Roche lobes when being close to the tip of the red giant branch, we have found earlier (Pustynski & Pustylnik 2006) that considerable shrinkage of the orbit can be achieved due to a combined effect of angular momentum loss from the red giant and appreciable on its low mass companion on the hydrodynamical timescale of the donor resulting in formation of helium WD with masses roughly equal to half a solar mass and thus evading the common envelope stage. Here we briefly discuss the outcome of evolution of orbit in terms of hydrodynamical time scale and the time scale of angular momentum loss. |
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