Studies of optical pulsations from HZ Herculis/Hercules X-1: A determination of the mass of the neutron star

Journal Article · Wed Sep 01 04:00:00 EDT 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154638· OSTI ID:7337314

Middleditch, J; Nelson, J

In 500 hours of optical observations of this binary system we have repeatedly detected optical pulsations at the 0.1--0.3 percent level. These pulsations are present only for particular well-defined values of the binary and 35-day phases. Position of the pulsation-emitting regions, projected onto the orbital plane, have been measured, and three distinct regions have been resolved. A simple model is put forth which accounts for the observed binary behavior, which gives a direct determination of the mass ratio, M/sub HZHer//M/sub HerX-//sub 1/=1.68 +- 0.10 and which establishes that the spin of the pulsar is prograde. Additionally, it is shown that Hz Her fills its Roche lobe. Using the above, the known X-ray eclipse duration, and the mass function, we calculate the orbital inclination to be i=87degree +- 3degree and the masses to be M/sub HerX-//sub 1/=1.30 +- 0.14 M/sub sun/ and M/sub HZHer/=2.18 +- 0.11 M/sub sun/. (AIP)

• Research Organization: Lawrence Berkeley Laboratory, University of California, Berkeley
• OSTI ID: 7337314
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 208:2; 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 RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
ELECTROMAGNETIC RADIATION
MASS
MATHEMATICAL MODELS
NEUTRON STARS
PULSARS
PULSATIONS
RADIATIONS
ROCHE EQUIPOTENTIALS
SPECTRA
STAR MODELS
STARS
VISIBLE RADIATION