Changes in the 11 minute period of 4U 1820 - 30

Journal Article · Sat Jun 01 04:00:00 EDT 1991 · Astrophysical Journal; (United States)

DOI:https://doi.org/10.1086/170118· OSTI ID:5393563

Tan, J; Morgan, E; Lewin, W H.G.; Penninx, W; Van der klis, M ^[1]

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1. MIT, Cambridge, MA (USA) Amsterdam, University (USA) Center for High Energy Astrophysics (Netherlands)

Observations made in February and April 1989 with the Ginga satellite show that the times of maximum light for the 685 s X-ray intensity variations of 4U 1820 {minus} 30 occur 71 + or {minus} 21 and 94 + or {minus} 21 s earlier than would be expected for the constant-period ephemeris based on previous observations. The times of maximum light observed between 1976 and 1989 are consistent with a constant rate period decrease of 0.074 + or {minus} 0.013 ms/yr. The decrease is found to be significant at the 99.9 percent level. If this reflected a true change in the orbital period, this result would be inconsistent with the standard model in which the 685 s period is that of the orbit of a binary star consisting of a neutron star whose companion is a low-mass (0.07 solar mass) degenerate helium star, and mass transfer is driven by loss of orbital angular momentum through gravitational radiation. The apparent period change may be explained in two ways: either the standard model is incorrect, or 4U 1820 {minus} 30 is being accelerated toward the earth by the gravitational field of another body. Acceleration of the binary by a distant third companion in a hierarchical triple, or by the cluster potential, are both possibilities. 44 refs.

• OSTI ID: 5393563
• Journal Information: Astrophysical Journal; (United States), Journal Name: Astrophysical Journal; (United States) Vol. 374; ISSN ASJOA; ISSN 0004-637X
• 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
BRIGHTNESS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
GRAVITATION
GRAVITATIONAL RADIATION
IONIZING RADIATIONS
MASS
MASS TRANSFER
MATHEMATICAL MODELS
NEUTRON STARS
OPTICAL PROPERTIES
ORBITS
PHYSICAL PROPERTIES
RADIATIONS
STAR MODELS
STARS
X RADIATION