Speaker
Dr
Jorge Horvath
(IAG-USP)
Description
We calculate the evolution of close binary systems (CBSs) formed by a neutron star (behaving as a radio pulsar) and a normal donor star, evolving either to a helium white dwarf (WD) or ultra short orbital period systems. Some of these systems are expected to evolve into so-called redback and black widow systems. The evolutionary tracks considered X-ray irradiation feedback and evaporation due to radio pulsar irradiation, usually dismissed in CBS evolution. We first show that irradiation feedback leads to cyclic mass transfer episodes, allowing CBSs to be observed in-between as radio pulsars with companions under conditions in which standard, non-irradiated models predict the occurrence of a LMXB. This behavior accounts for the existence of a family of binary systems known as redbacks. We found that, in general, CBSs with initial orbital periods ~ 1 day evolve into redback pulsars. Some of them produce low-mass helium WDs, and a subgroup withshorter Pi become black widows systems. Thus, some black widows may descent from redbacks, although not all redbacks evolve into black widows
We also predict redback companions should almost fill their Roche lobe, as it is the case of PSR J1723-2837. This state is also possible for systems evolving with larger orbital periods. Therefore, binary radio pulsars with companion star masses larger than expected to produce helium WDs may also result in such quasi-Roche Lobe Overflow states, rather than hosting a carbon-oxygen WDs. This swelling is a direct consequence of the irradiation feedback.
We finally present a calculation of the instability leading to the collapse/rebuilding of the accretion disc which depends heavily of the irradiation, showing that the timescale is a ~few years at most, in agreement with the recent observations. This shortening is only possible because of the incidence of X rays and complements the understanding of the evolution of these extreme systems.
Primary author
Dr
Jorge Horvath
(IAG-USP)
Co-authors
Dr
M.A. De Vito
(IALP-UNLP)
Prof.
O.G. Benvenuto
(IALP-UNLP)
