SPH simulations of circumbinary accretion disks are verified with the help of a grid-based Eulerian code. The phenomenon of pulsed accretion flow through the central gap is confirmed.

We describe the ASCA observation of the eclipsing intermediate polar (IP) XY Ari (=H0253+19). This system was first discussed by Patterson & Halpern (1990, ApJ, 361, 173) as a possible IP based upon the HEAO-1 data. This system is impossible to study in the optical or ultraviolet because of the 12 mag of optical extinction associated with the molecular cloud Lynds 1457=MBM 12. The system has an orbital period of 0.2526 day and a pulse period of 208 sec. Our preliminary analysis of the ASCA data shows that the eclipse is nearly total (the precision of the background subtraction sets the limit). The eclipse ingress and egress occur very quickly, although we have not yet derived accurate numbers. There are sufficient photons that we can perform crude phase-resolved spectroscopy. The resulting spectra, each covering about 1/4 of the orbit, show that the Fe Kα line is not constant as a function of phase. A sample spectrum is reproduced below. We expect to submit a paper describing the results to the ApJ before the end of 1996.

We predict the quasar luminosity function (LF) from a population of sources with the activity driven by instabilities in an accretion disk. The ligth curve of a single source convolved with the mass distribution gives the quasar luminosity function at a given redshift. We model the observed LF at four different redshifts.

We present a full 3D model of galaxy formation, incorporating for the first time magnetohydrodynamical effects. By this means we hope to simulate the creation of active galactic nuclei, including jets. Preliminary results are encouraging.

We present the results from mid-infrared spectro-polarimetric observations of a number of bi-polar outflow sources. The specto-polarimetric data provides information on the polarization mechanism and the magnetic field direction. The field direction in the disks of the observed sources is most often normal to the ambient field direction and lies in the plane of the disk, indicating a toroidal rather than poloidal field configuration.

We present optical photometry of the eclipsing supersoft source, CAL 87. We find the eclipse structure to be stable over ~ 4 y, derive an improved ephemeris of To = HJD 2450111.5144(3)+0.442674(7)E, and see new structure in the light curve morphology.

The AM Herculis binaries (AM Hers) have high and low accretion states. A model is proposed in which the white dwarf’s rotation acts like an angular momentum storage battery for the binary orbit. The accreted material from the Roche lobe-overflowing secondary charges up this battery, whereas the magnetic torque of the white dwarf on the secondary discharges it back into the binary’s orbit. The Roche lobe’s volume becomes alternately larger and smaller than the secondary’s volume. This alternation causes the mass flow to vary between a high and low rate.

Soft X-ray spectra of many Active Galactic Nuclei (AGN) show structure which suggests excess emission at low energies, mostly below 1 keV. This was confirmed by the ROSAT spectra (0.1–2.4 keV) AGN in our samples which generally have steeper power law spectra than the canonical index of 0.7. The soft excess component may be the high energy tail of the big blue bump which in turn may be due to the integrated emission from an accretion disk around the central black hole.

We discuss results of our spectral analysis of two different samples of AGN: 1) QSO/Seyfert-I from the ROSAT All Sky Survey (RASS) and 2) radio-quiet QSO from ROSAT Pointed Observations. The ROSAT data are combined with UV Data from IUE and hard X-ray data from various hard X-ray missions.

Most likely produced as thermal emission by dust grains, infrared emission from young stars and active galaxies reveals information about the internal energy source, the spatial distribution of the surrounding matter and its dynamical evolution. In this way, radiative transfer works as a bridge between HD/MHD accretion disk theory and observations. For young stellar objects and active galactic nuclei, the source geometry is of crucial importance for the modelling the emerging radiation. Observations indicate rotationally symmetric accretion disks, tori, or more complicated density structures around multiple sources, making multidimensional calculations necessary.

We provide a kinematically-resolved analysis of 5000s QPOs found in the optical emission lines of GK Per during a dwarf nova outburst. These are consistent with models of reprocessing off blobs of gas orbiting within the inner accretion disc.

The mechanism providing the 35-day period found in optical and X-ray light curves of the eclipsing low-mass X-ray binary Her X-l is considered to be the precession of a tilted and twisted accretion disc about the neutron star. We have obtained spectrophotometric observations of this system. The majority of line absorption and emission originates on or near the mass-losing primary, with distributions over the inner face of the star consistent with irradiation from the environs of the compact object. After suitable corrections for heating, the neutron star is found have a mass of 1.6±0.3M⊙, in contrast to the last radial velocity study which found a value less than 1.0 M⊙ . Rotational velocity measurements, while insufficiently precise to reject the older mass estimate, suggest that the rotational period of HZ Her differs from the synchronous rate by no more than 20%. Using a recently determined figure for the effective temperature of the unheated face, the distance to Her X-l is estimated at 6.7±0.4kpc, higher than prior estimates. The systemic velocity is found to be –69±6km s−1. In order to to determine the plausibility of the twisted disc model we reconstruct the expected shadow of the disc across the heated inner face of the donor star to compare with observation. Large scale emission structure is reproduced, but the model fails to synthesize finer observational details. HeII λ4686 Å emission is detected and found to be distributed closely about the neutron star, and is a likely tracer of the accretion flow.

Slim accretion disk models with high accretion rates provide a natural explanation for the strong soft X-ray emission observed in several narrow–line Seyfert 1 galaxies.

Time-resolved spectroscopic data of the cataclysmic variable WW Cet were taken during quiescence, outburst, and decline from outburst. The profile of the Hα emission line is studied by measuring radial velocities of different parts of the line.

The complete poster is available on the World Wide Web at http://www. astro, ruhr-uni-bochum.de/cta/paper.html.

We present a class of steady axisymmetric MHD solutions, self-similar in the meridional direction, that are suitable to model collimated winds accelerated in the potential well of a spherical object.

The analysis of dwarf nova SS Cyg light curves at quiescence is performed and some important are determined.

We present a new eclipse mapping technique, which is able to map distributions in physical parameters of accretion disks in ecliping cataclysmic variables.

In the framework of Euler flows, I present simulations of wind accretion in well separated binaries for three different cases: Cygnus X-3, a high mass X-ray binary (see e.g. Schmutz et al. 1996), ζ Aurigae, a system showing strong atmospheric eclipse effects (see e.g. Griffin et al. 1990), and the generic barium star model of Theuns and Jorissen (1993), which is recomputed here with a different numerical method (a MUSCL-type integrator, incorporated in our AMRCART code). These simulations represent a first, small sample out of the large parameter space of wind accretion in separated binaries (see Table 1).

On the orbital scale, the vorticity of the flow is due to the orbital motion of the stars. It is particularly large for the case where the wind velocity is comparable to the orbital speed of the stars (see Fig. 1). In the vicinity of the accreting star, the vorticity is determined by the accretion process. With two strong vortices above and below the accretor (with respect to the orbital plane), the flow resembles the flow out of a bath tub. On a smaller scale, one finds even more vorticity: The flow is highly turbulent. Such turbulence and the shear flows in the large scale vortices cannot be well captured by an Euler flow model. A next step of improvement would be the use of an appropriate MHD turbulence model.

The ~ 108−109 old neutron stars in the Galaxy may be undergoing low luminosity accretion from the interstellar medium (Ostriker et al. 1970; Shvartsman 1971). It was first recognized by Shvartsman (1971) that the accretion induced radiation from the stellar surface can heat the infalling material, which in turn inhibits further accretion. This preheating instability has been studied in detail in the high luminosity regime where equilibrium ionization and heating holds (e.g., Buff & McCray 1974; Ostriker et al. 1976; Cowie et al. 1978). In the low luminosity regime, however, dynamical timescales are typically much shorter than atomic timescales so the accretion flow dynamics is strongly coupled to non-equilibrium (NEQ) atomic processes (cf. Blaes et al. 1995).

We present results of 3-D self-gravitating hydrodynamical calculations of the encounter between two protostellar discs. We find that the interaction leads to fragmentation of the discs and the formation of new stars and multiple systems.

Considerations of donor star stability, age, and mass transfer rate show that low-mass X-ray binaries and binary millisecond pulsars with orbital periods longer than a few days must have survived an initial phase of super-Eddington mass transfer. We review the physical arguments leading to this conclusion, and examine its implications for the apparent discrepancy between the death rate for low-mass X-ray binaries and the birth rate of binary millisecond pulsars.