New observations and a slow rotator model of the X-ray binary AM Herculis

Journal Article · Tue Nov 01 04:00:00 EST 1977 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/155629· OSTI ID:5281002

Stockman, H S; Schmidt, G D; Angel, J R.P.; Liebert, J; Tapia, S; Beaver, E A

The soft X-ray binary AM Her/3U 1809+50 is known to have a common 3.09 hour period in its soft X-ray flux and in its optical flux, polarization, and spectral lines. Strong circular polarization which varies synchronously with the common period is confined. Blueward of 4100 A, the polarization is reduced dramatically. Spectroscopic observations varying from moderate-resolution spectrophotometry to high-resolution photographic spectra are presented. The energy distribution from 0.3 to 1 /sup +/m shows a smooth continuum, f (phi) proportional phi/sup -1/, with strong permitted emission lines and Balmer continuum superposed. The strong H I and He I lines are seen to have inverted line strengths relative to recombinational values. These are explained by invoking a collision-dominated, optically thick emission region. On the assumption that AM Her is at a distance of 100 pc, the total luminosity, approx.10/sup 33/ ergs s/sup -1/, is small compared to typical X-ray binaries. This fact, the unusually soft X-ray spectrum, and the unique strong circular polarization suggest that AM Her is a binary system in which material is accreting onto a magnetic white dwarf with a surface field of approx.10/sup 8/ gauss. A model is developed of a system in which the magnetic white dwarf's rotation is synchronized with the 3 hour binary period. In such a system the accreting material is dominated by the field shortly after it is gravitationally attracted to the white dwarf, and the accretion takes place down the field lines. No hot accretion disk is formed, but a hot, subsonic accretion funnel may be present in which a substantial fraction of the gravitational energy is converted into heating the infalling material. The resulting spectrum is in qualitative agreement with observations. The temperature, number density, and area of the emission region deduced from the spectrophotometry are consistent with the line emission originating near the secondary and the inner Lagrange point.

• Research Organization: Steward Observatory, University of Arizona
• OSTI ID: 5281002
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 217:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BINARY STARS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DWARF STARS
MAGNETIC FIELDS
MAGNETIC STARS
MATHEMATICAL MODELS
MOTION
NEUTRON STARS
POLARIZATION
ROTATION
SPECTRA
STAR ACCRETION
STAR EVOLUTION
STAR MODELS
STARS
WHITE DWARF STARS
X-RAY SPECTRA