Orbital Period Change of the Low-Mass X-Ray Binary EXO0748-676
Abstract
The transient low-mass X-ray binary, EXO0748-676, discovered with EXOSAT, is known to exhibit eclipses of a 492-s duration with a 3.82-hr period, intensity dips at pre-eclipse phases and type-I X-ray bursts. We observed this source with Ginga in 1989 March, 1990 December, 1991 January, and 1991 August and determined nine eclipse center times. Combining these eclipse center times with the previous result of the EXOSAT observations, we find that the orbital period of this source is not decaying monotonously, contrary to the previously reported suggestion. Instead, it shows a more complex behavior. A quadratic fit to the eclipse data yields a positive rate of change in orbital period (i.e., a secular growth of orbit) with an approximate rate of dot {P}_orb/P_orb\ =~ 0.9 times 10(-7) yr(-1) , although the EXOSAT observations made in 1985 do not fit this trend. A sinusoidal function gives a better fit to the observed orbital period changes with a period of about 12 yr and an amplitude of about 44 lt-s, although the period is much longer than the observation interval of about 6.5 yr. Possible mechanisms for the orbital period change, such as radiation driven mass transfer or a hierarchical triple system, are discussed in the context of the present observations.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- December 1992
- Bibcode:
- 1992PASJ...44..633A
- Keywords:
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- Orbital Elements;
- Stellar Orbits;
- X Ray Binaries;
- X Ray Sources;
- Neutron Stars;
- Stellar Mass;
- Transient Response;
- Astrophysics;
- STARS: NEUTRON;
- X-RAYS: BINARIES;
- X-RAYS: SOURCES