Discovery of a 685 second orbital period from the X-ray source 4U 1820 - 30 in the globular cluster NGC 6624
The discovery of a coherent 685 s periodicity in the X-ray source 4U 1820 -30, which is located in the globular cluster NGC 6624, is reported. The modulation has a peak-to-peak amplitude of up to 3 percent and was independently detected in three observations by the EXOSAT Observatory. This period is unlikely to represent the rotation of a neutron star, because accretion torques should cause it to change by at least 10 s/yr, but observations constrain any change to less than 0.4 s/yr. The period is thus identified as the orbital period of 4U 1820 - 30, the first to be found for a globular cluster X-ray source and the shortest yet identified for any binary system. In this compact system the mass-losing star is probably a low-mass (0.055 solar mass) helium white dwarf. 37 references.
- Research Organization:
- EXOSAT Observatory, Darmstadt, West Germany; Los Alamos National Lab., NM; Max-Planck-Institut fuer extraterrestrische Physik, Garching, West Germany
- OSTI ID:
- 6581542
- Journal Information:
- Astrophys. J.; (United States), Vol. 312
- Country of Publication:
- United States
- Language:
- English
Similar Records
Evolution of tidal capture X-ray binaries - 4U 2127+12 (M15) to 4U 1820-30 (NGC 6624)
DISCOVERY OF A 693.5 s PERIOD IN THE X-RAY BINARY 4U 1820 - 30: A SUPERHUMP INTERPRETATION