Photometry of the low accretion rate polar HS 1023+3900

SIGLEAvailable from TIB Hannover: RR 7310(2001-26) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Zeeman lines and a single cyclotron line in the low-accretion rate polar 1RXS JO12851.9-233931(RBS0206)

We present a low-resolution discovery spectrum and CCD-photometry of the bright X-ray source 1RXS J012851.9-233931 found in the ROSAT All-Sky Survey. These first observations suggest that the source is an AM Herculis star (polar) accreting at a low rate. The optical specturm is dominated by Zeeman absorption features from the white dwarf, indicating a mean photospheric magnetic field of 36#+-#1 MG. Only weak Balmer line emission was observed. In the near infra-red, a single intense cyclotron hump was observed. The inferred magnetic field strength in the accretion plasma is 45#+-#1 MG, the temperature in the plasma is below 2 keV. Likely orbital periods are #propor to#90min or #propor to#146 min, the latter inside the cataclysmic variable period gap. The system is an ideal target for further detailed investigations of the field structure on a magnetic white dwarf by phase-resolved spectropolarimetry. (orig.)SIGLEAvailable from TIB Hannover: RR 7310(99-21) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

System parameters of the long-period polar V1309 Ori

SIGLEAvailable from TIB Hannover: RR 7310(2001-22) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The soft X-ray eclipses of HU Aqr

SIGLEAvailable from TIB Hannover: RR 7310(2001-24) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

The isolated neutron star candidate RBS1223 (1RXS J130848.6+212708)

In the ROSAT Bright Survey (RBS) we have almost completely optically identified the brightest #propor to#2000 high-galactic latitude sources from the ROSAT All-Sky Survey Bright Source Catalogue (1RXS). A small number of sources has empty X-ray error circles on optical images. ROSAT HRI follow-up observations of RBS 1223 (=1 RXS J 130848.6+212708), a soft object with extreme X-ray to optical flux ratio, have confirmed a relatively bright X-ray source, whose position could be determined to an accuracy of 1.6 arcsec (90%) due to the presence of a nearby, X-ray detected bright star. Deep Keck R- and B-band images of the field were taken, but the refined X-ray error circle remains empty to a limiting magnitude B#propor to#26"m. With an X-ray to optical flux ratio of log(f_x/f_o_p_t)>4.1 this object is almost certaily an isolated neutron star, similar to the two so far best-known examples RX J1856.4-3754 and RX J0720.4-3125. We discuss limits on the number of similar objects in the RBS catalogue. (orig.)SIGLEAvailable from TIB Hannover: RR 7310(98-35) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Structural studies of emission regions in polars

We report on structure in the emissions region encountered in polars. This will become a travel along the accretion stream, starting at the surface of the secondary star, moving along the horizontal and vertical parts of the stream and finishing in the accretion spots on the white dwarf. For the first time we establish a detailed picture of the origin of atomic emission lines in a polar by means of Doppler tomography. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Tomography of polars

We are reviewing the power of Doppler tomography for detailed investigations of polars (magnetic cataclysmic binaries without accretion disk). Using high-resolution spectroscopy in combination with tomography as analytic tool, the structure and extent of the accretion flows and accretion curtains in the binaries can be uncovered and the irradiated and non-irradiated parts of the mass-donating secondary stars can be made visible. In addition we show, how basic system parameters like the binary inclination and the mass ratio can be addressed by tomography. (orig.)Proceedings of the Annapolis workshop on magnetic cataclysmic variables (MCV2), 22 refs.Available from TIB Hannover: RR 7310(98-26) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Accretion and magnetism - AM Herculies stars. Polars in the ROSAT era

The accretion processes in Am Herculis binaries are reigned by the strong magnetic field of a mass-accreting white dwarf. In the first part of this article I describe the methods applicable to infer the strength and structure of the magnetic fields in these systems. These are based on direct measurements of Zeeman split Balmer lines and/or harmonic cyclotron emission. All well-studied systems show signs of complex field structures or at least deviations from the most simple model of a centered dipole. The observed range of B-values is 10 -70 MG. The evolution of the systems is responsible for this range being much narrower than that measured in single white dwarfs, 100 kG - 1000 MG (see Schmidt 1995, this volume). The following parts of this article are devoted to other processes intimately interwoven with the presence of magnetic fields. These are the accretion streams (instead of accretion disks), the different ways of energy release in the accretion spots and the synchronous rotation of both stars. Considerable progress was reached in various fields after the launch of ROSAT which detected a lot of new and some very remarkable systems and which made detailed observational studies of individual systems possible. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The ROSAT Bright Survey. Pt. 2 Catalogue of all high-galactic latitude RASS sources with PSPC countrated CR > 0.2s"-"1

We present a summary of an identification program of the more than 2000 X-ray sources detected during the ROSAT All-Sky Survey (Voges et al. 1999) at high galactic latitude, vertical stroke b vertical stroke >30 , with countrate above 0.2 s"-"1. This program, termed the ROSAT Bright Survey RBS, is to more than 99.5% complete. A sub-sample of 931 sources with countrate above 0.2 s"-"1 in the hard spectral band between 0.5 and 2.0 keV is to 100% identified. The total survey area comprises 20391 deg"2 at a flux limit of 2.4 x 10"-"1 erg cm"-"2 s"-"1 in the 0.5-2.0 keV band. About 1500 sources of the complete sample could be identified by correlating the RBS with SIMBAD and the NED. The remaining #propor to#500 sources were identified by low-resolution optical spectroscopy and CCD imaging utilizing telescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apart from completely untouched sources, catalogued clusters and galaxies without published redshift as well as catalogued galaxies with unusual high X-ray luminosity were included in the spectroscopic identification program. Details of the observations with an on-line presentation of the finding charts and the optical spectra will be published separately. Here we summarize our identifications in a table which contains optical and X-ray information for each source. As a result we present the most massive complete sample of X-ray selected AGNs with a total of 669 members and a well populated X-ray selected sample of 302 clusters of galaxies with redshifts up to 0.70. Three fields studied by us remain without optical counterpart (RBS0378, RBS1223, RBS1556). While the first is a possible X-ray transient, the two latter are isolated neutron star candidates (Motch et al. 1999, Schwope et al. 1999). (orig.)Also published in Astronomische Nachrichten v. 321(1), 2000Available from TIB Hannover: RR 7310(2000-03) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The new long-period AM Herculis system RX J0203.8+2959

We present the first detailed multi-wavelength study of the ROSAT-discovered AM Herculis binary RX J0203.8+2959 comprising extended CCD and photoelectric photometry, phase-resolved spectroscopy with high and low spectral resolution and pointed ROSAT observations with the PSPC and the HRI. Between 1992 and 1997 the system displayed states of high and low accretion with mean brightness levels of V=15.5"m and 18"m, respectively. A timing analysis revealed that the binary is rotating synchronously with a period of 4.6 hr and is thus one of the longest-period polars known. The emission lines are structured showing narrow and broad components. We could distinguish between line emission arising from the heated side of the secondary star and the accretion stream. Velocity information derived for a narrow emission line with suspected origin on the heated side of the companion star allowed us to constrain its orbital velocity and to phase its inferior conjunction. In addition the photospheric spectrum of the secondary star could be detected in the near-infrared. The strength of the TiO-bands was used to determine its spectral type as dM 2.5, which is consistent with a Roche lobe filling main sequence star, and to estimate the distance of the system to be #propor to#600 pc. Definite confirmation of its magnetic nature is given by the detection of cyclotron harmonics implying a field strength of B=38#+-#2 MG. The accretion geometry could not be fixed unequivocally. The morphology of the optical light curves is suggestive of one active accretion region which undergoes no selfeclipse. A corresponding simple light curve pattern is not seen at X-ray wavelengths, it's time signature is dominated by instationary accretion of discrete blobs. We report on the occasional occurence of phase- and colour-dependent quasi-periodic oscillations at periods of #propor to#7 and #propor to#14 min. (orig.)Available from TIB Hannover: RR 7310(98-19) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman