Andrew D. Silber

AR URSAE MAJORIS: THE FIRST HIGH-FIELD MAGNETIC CATACLYSMIC VARIABLE

We identify the luminous soft X-ray source AR UMa as a magnetic cataclysmic variable containing a white dwarf with the highest field yet detected in an accreting binary. IUE and optical spectroscopy, optical photometry, and circular polarimetry and spectropolarimetry define remarkably distinct accretion states of this binary. Circular polarization is nearly absent in the high state, but the low state exhibits values which vary between 2% and 5% on the orbital period of 1.932 hr. The UV continuum contains a broad absorption feature near 1300 A, while optical spectropolarimetry during the low state reveals a number of strongly polarized dips. These are interpreted as Zeeman components of hydrogen Lyα and another atmospheric species, possibly He I, in a photospheric magnetic field of ~ 230 MG.The radial velocity curve of the low-state optical emission lines shares the period of the optical photometry and polarimetry and is phased appropriately for an origin on the irradiated secondary star. While the high state exhibits prominent UV line emission typical of the magnetic variables, the strength of the UV continuum does not vary appreciably with a change in accretion state. This, combined with the high soft X-ray luminosity and lack of circular polarization, indicates that accretion occurs largely in the form of dense filaments which avoid a standoff shock and thermalize their kinetic energy below the white dwarf photosphere. We suggest that these phenomena may play a role in the apparent lack of high-field systems with easily detectable circular polarization during high-accretion states.

A gravitationally-lensed ring in MG 1549+3047

We report the discovery of a new gravitational lens in the radio source MG 1549+3047. The source has a compact core and two lobes, with a faint optical counterpart to the core. The brighter lobe is shaped like a ring, and centered on a foreground galaxy with known redshift. The radio structure of the ring can be reproduced by distorting a typical radio lobe through a simple elliptical gravitational lensing potential, which models the mass distribution in the foreground galaxy. From a preliminary lens model, we show that the mass distribution follows the observed luminosity, and we predict a central velocity dispersion of about 230 km s −1 . This corresponds to a blue mass-to-light ratio of about 18h solar units

H0538 + 608 (= BY Camelopardalis) - An asynchronously rotating AM Herculis binary?

Evidence from a concurrent X-ray/optical observing program is presented which indicates that the orbital period of the anomalous AM Her-type cataclysmic variable H0538 + 608 (BY Cam) differs from the rotational period by 1.3 +/- 0.1 percent. This finding would explain much of the unusual behavior previously exhibited in optical photometry and polarimetry. The model proposed by Ishida et al. (1991) is developed further using observations of accretion and the primary characteristics of optical and X-ray light curves and radial velocity measures of H-alpha. An optical QPO with a period of about 30 min was seen on two nights and possible causes of it are discussed.

Ginga observation of an AM Herculis type source H0538 + 608

Results from a Ginga observation of the AM Her type object H0538 + 608 are presented. During the first half of the observation (pulsing state) the source showed periodic modulations caused by the white dwarf rotation, and the modulation profile was characterized by a flat top and a flat bottom. During the second half, the source was in a remarkable flaring state and the periodic modulation disappeared. The dramatic change of the X-ray light curve is interpreted in terms of a change of accretion pattern between an eclipsing spot and a noneclipsing spot. The spectrum is well described throughout by a thin thermal model including an iron K-line with equivalent width of some hundred eV, supporting the standard model for the hard X-ray emission region. The temperature in the pulsing state was found to change with the spin phase of the white dwarf. In the flaring state, the temperature showed a positive correlation with the source luminosity. 32 refs.

The Lensing Galaxy in MG1549+3047

We have measured a velocity dispersion for the foreground galaxy in this gravitationally lensed system. Our dispersion confirms the prediction from lens models, provided that the source is distant enough (

The eclipsing AM Herculis variable H1907 + 690

z_{_S}>0.2

RXTE, ROSAT, EUVE, IUE, and Optical Observations through the 45 Day Supercycle of V1159 Orionis

). Current interpretations of lensing statistics depend sensitively on how the optical and mass dispersions are related. For

Identification of the soft X-ray source wga j1802.1+1804 with a new magnetic cataclysmic variable

z_{_S}>0.5

A New Magnetic Cataclysmic Variable: WGA J1047.1+6335

, our observations favor

Time Resolved Ultraviolet Spectroscopy of DQ Herculis: Eclipses and Pulsations

\sigma_{mass}/\sigma_{opt}\simeq1