Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...294l..49h&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 294, no. 3, p. L49-L52
Astronomy and Astrophysics
Astrophysics
8
Heat Flux, Mass Transfer, Stellar Mass Accretion, Stellar Rotation, X Ray Binaries, X Ray Irradiation, Companion Stars, Heat Transfer, Neutron Stars
Scientific paper
The cyclic external heating of a low-mass 0.4 solar mass star is studied in detail. The intermittent heating intervals simulate the irradiation of an asynchronously rotating star by the X-ray flux from an accreting companion neutron star in a binary system. Each point on the stellar surface resides for a certain time interval in the heated hemisphere of the star and a similar interval in the shadowed hemisphere. The question of whether a star in such a situation will expand, as is the case for a continuously and isotropically irradiated star, is relevant to the evolution of the secondary star in low-mass X-ray binaries (LMXBs). We study different periods for the heating cycle (100, 1000, and 2000 yr) as well as different heating fluxes ( 5 x 1010 and 5 x 1011 erg/(cu cm sec). Due to the computationally intensive nature of this problem, the evolution calculations were carried out for an interval of only approximately 4 x 106 yr, or approximately 2% of the Kelvin-Helmholtz timescale for a 0.4 solar mass star. We find that under these irradiation conditions, the secondary star is significantly affected and does indeed expand. We also find that the expansion rate with intermittent heating is only slightly lower than that found during an evolution with continuous heating. The total expansion of the star after 4 x 106 yr corresponds to approximately 2% and approximately 4% of its unperturbed radius for the lower and higher heating fluxes, respectively. These expansions are approximately 40% and approximately 13%, respectively, of the full expansions that a star continuously heated by these fluxes would experience. These results and others are discussed in the context of the evolution of LMXBs.
Harpaz Amos
Rappaport Saul
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