Discovery of a 685 second orbital period from the X-ray source 4U 1820 - 30 in the globular cluster NGC 6624

Journal Article · Thu Jan 01 04:00:00 EST 1987 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/184811· OSTI ID:6581542

Stella, L; White, N E; Priedhorsky, W

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), Journal Name: Astrophys. J.; (United States) Vol. 312; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BINARY STARS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DWARF STARS
ORBITS
STAR ACCRETION
STAR CLUSTERS
STAR EVOLUTION
STARS
VARIATIONS
WHITE DWARF STARS