|Ph.D Student||Sabach Efrat|
|Subject||Mass Transfer in Stellar Binary Systems Resulting in|
|Department||Department of Physics||Supervisor||Professor Noam Soker|
|Full Thesis text|
This Ph.D. research focuses on systems where stellar evolution is affected by an interaction with a companion leading to a peculiar outcome. As this research is not limited to a specific sort of peculiar objects we examine a wide range of peculiarities, from stars and stellar systems with peculiar properties to peculiar eruptions such as supernovae (SNe). With better sky coverage more and more rare peculiar objects and transient events are detected, yet the mechanism of many of these events is poorly understood. In this work we study the stellar evolution with different initial conditions, e.g., different mass range, while focusing on interaction, or possible interaction, with a companion as the main formation mechanism of the peculiarities. The interaction takes place through mass transfer via Roche Lobe Overflow (RLOF), common envelope evolution (CEE) and/or angular momentum transfer. Using numerical simulations of stellar evolution and population synthesis calculations, along with analytical estimations, we provide constraints on the final outcome of the systems studied.
An episode of mass transfer can occur when in a binary system the more massive star explodes as a core collapse SN and its outer layers are accreted on to the companion giant star that intercepts a large fraction of the ejecta. As a result the companion is "polluted" and its composition is enriched by the newly synthesized elements in the explosion. We term these SNPGs for SN polluted giants, such as the observed star H2112. A second intriguing scenario addressed in this research is the breaking of a binary inside a CE. We propose that the triple pulsar system PSR J0336? with two white dwarf companions was formed by this scenario. This scenario employs an efficient envelope removal by jets launched by a compact object that is immersed in the envelope of a giant star.
As binary interaction has many implications on stellar evolution it might also change the stellar mass-loss rate itself. Such events can arise from an interaction with even a substellar companion. We further suggest that stars whose angular momentum (J) does not increase by a companion, star or planet, along their post-main sequence evolution have much lower mass-loss rates along their giant branches than previously estimated. We find that solar-type J-isolated stars, or Jsolated stars in short, reach higher luminosities and radii on the upper asymptotic giant branch (AGB), and hence are more likely to swallow brown dwarfs and planets during the AGB than traditional calculations predict. This might lead to the formation of elliptical Planetary Nebulae (PNe) and account for bright PNe in old stellar populations.
Overall, this research proposes several new scenarios and perspectives as to the influence of binary interaction, or interaction with sub-stellar companions, on stellar evolution. The scenarios and treatments presented here account for peculiar astrophysical objects and eruptions.