Mass transfer from giant donors

Abstract

In this thesis we study MT from giant and subgiant donors in binary stars. We develop a MT simulation framework based on the MESA set of stellar libraries, which is suitable to study extremely high MT rates and predict the stability of MT. We find that the MT from giant donors is much more stable than previously thought: the currently used critical initial mass ratios are approximately two times lower than the ones predicted by our improved MT framework. We foresee that this improvement of stability will substantially affect the rate of double compact mergers in the Galaxy, which are the sources of gravitational radiation detectable by the gravitational observatories, such as the Advanced LIGO. We find that a non-degenerate He remnant obtained from an evolved main sequence star by rapid mass loss, as a donor to the three known ultra-compact X-ray binaries – 4U 1626-67, 4U 0614+09, and 4U 1916-053 can explain the anomalously high MT rates in them. We develop an improved magnetic braking prescription that can be used to study the evolution of low-mass X-ray binaries with a giant or subgiant donor. We find that this prescription can explain the extremely high MT rate observed in such binaries, for example in Sco X-1.