K. Reinsch

IDENTIFICATION OF SELECTED SOURCES FROM THE ROSAT GALACTIC PLANE SURVEY. I.

We report on optical searches in the error circles of 93u2000ROSAT survey sources located at low galactic latitudes ( H . This relatively good segregation offers the possibility to build source samples with enhanced probability of identification with a given class. Complete optical identification of such subsamples could eventually be used to compute meaningful probabilities of identification for all sources using as basis a restricted set of multi-wavelength information.

The isolated neutron star X-ray pulsars RX J0420.0-5022 and RX j0806.4-4123: New X-ray and optical observations

We report on the analysis of new X-ray data obtained with XMM-Newton and Chandra from two ROSAT-discovered X-ray dim isolated neutron stars (XDINs). RX J0806.4−4123 was observed with XMM-Newton in April 2003, 2.5 years after nthe first observation. The EPIC-pn data confirm that this object is an X-ray pulsar with 11.371 s neutron star spin period. The X-ray spectrum is consistent with absorbed black-body emission with a temperature kT = 96 eV and N H = 4 × 10 19 cm −2 without significant changes between the two observations. Four XMM-Newton observations of RX nJ0420.0−5022 between December 2002 and July 2003 did not confirm the 22.7 s pulsations originally indicated in ROSAT data, but clearly reveal a 3.453 s period. A fit to the X-ray spectrum using an absorbed black-body model yields kT = 45 eV, the lowest value found from the small group of XDINs and N H = 1.0 × 10 20 cm −2. Including a broad absorption line improves the quality of the spectral fits considerably for both objects and may indicate the presence of absorption features similar to those reported from RBS1223, RX J1605.3+3249 and RX J0720.4−3125. For both targets we derive accurate X-ray positions from the Chandra data and present an optical counterpart candidate for RX J0420.0−5022 with B = 26.6 ± 0.3 mag from VLT imaging.

Zeeman tomography of magnetic white dwarfs - IV. The complex field structure of the polars EF Eridani, BL Hydri and CP Tucanae

Context. The magnetic fields of the accreting white dwarfs in magnetic cataclysmic variables (mCVs) determine the accretion geometries, the emission properties, and the secular evolution of these objects. nAims. We determine the structure of the surface magnetic fields of the white dwarf primaries in magnetic CVs using Zeeman tomography. nMethods. Our study is based on orbital-phase resolved optical flux and circular polarization spectra of the polars EF Eri, BL Hyi, and CP Tuc obtained with FORS1 at the ESO VLT. An evolutionary algorithm is used to synthesize best fits to these spectra from an nextensive database of pre-computed Zeeman spectra. The general approach has been described in previous papers of this series. nResults. The results achieved with simple geometries as centered or offset dipoles are not satisfactory. Significantly improved fits are obtained for multipole expansions that are truncated at degree lmax = 3 or 5 and include all tesseral and sectoral components with n0 ≤ m ≤ l. The most frequent field strengths of 13, 18, and 10MG for EF Eri, BL Hyi, and CP Tuc, and the ranges of field strength covered are similar for the dipole and multipole models, but only the latter provide access to accreting matter at the right locations on the white dwarf. The results suggest that the field geometries of the white dwarfs in short-period mCVs are quite complex, with nstrong contributions from multipoles higher than the dipole in spite of a typical age of the white dwarfs in CVs in excess of 1 Gyr. nConclusions. It is feasible to derive the surface field structure of an accreting white dwarf from phase-resolved low-state circular spectropolarimetry of sufficiently high signal-to-noise ratio. The fact that independent information is available on the strength and ndirection of the field in the accretion spot from high-state observations helps in unraveling the global field structure.

The 1995–96 decline of R Coronae Borealis: high-resolution optical spectroscopy

A set of high-resolution optical spectra of R CrB acquired before, during and after its 1995–96 decline is discussed. All of the components reported from earlier declines are seen. This novel data set provides new information on these components including several aspects not previously seen in declines of R CrB and other R Coronae Borealis stars. In the latter category is the discovery that the onset of the decline is marked by distortions of absorption lines of high-excitation lines, and quickly followed by emission in these and in low-excitation lines. This ‘photospheric trigger’ implies that dust causing the decline is formed close to the star. These emission lines fade quickly. After 1995 November 2, low-excitation narrow (FWHM ∼12xa0kmxa0s−1) emission lines remain. These appear to be a permanent feature, slightly blueshifted from the systemic velocity, and unaffected by the decline except for a late and slight decrease of flux at minimum light. The location of the warm dense gas providing these lines is uncertain. Absorption lines unaffected by overlying sharp emission are greatly broadened, weakened and redshifted at the faintest magnitudes when scattered light from the star is a greater contributor than direct light transmitted through the fresh soot cloud. A few broad lines (FWHM ≃300xa0kmxa0s−1) are seen at and near minimum light with approximately constant flux: prominent among these are the Hexa0i triplet series, Naxa0i D and [Nxa0ii] lines. These lines are blueshifted by about 30xa0kmxa0s−1 relative to the systemic velocity, with no change in velocity over the several months for which the lines were seen. It is suggested that these lines, especially the Hexa0i lines, arise from an accretion disc around an unseen compact companion which may be a low-mass white dwarf. If so, R CrB is similar to the unusual post-asymptotic giant branch star 89 Her.

The IAG solar flux atlas: Accurate wavelengths and absolute convective blueshift in standard solar spectra

We present a new solar flux atlas with the aim to understand wavelength precision and accuracy in solar benchmark data. The atlas covers the wavelength range 405--2300 nm and was observed at the Institut fur Astrophysik, Gottingen (IAG) with a Fourier Transform Spectrograph. In contrast to other FTS atlases, the entire visible wavelength range was observed simultaneously using only one spectrograph setting. We compare the wavelength solution of the new atlas to the Kitt Peak solar flux atlases and to the HARPS frequency-comb calibrated solar atlas. Comparison reveals systematics in the two Kitt Peak FTS atlases resulting from their wavelength scale construction, and shows consistency between the IAG and the HARPS atlas. We conclude that the IAG atlas is precise and accurate on the order of

Zeeman tomography of magnetic white dwarfs. III, The 70–80 Megagauss magnetic field of PG 1015+014

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Zeeman tomography of magnetic white dwarfs: II. The quadrupole-dominated magnetic field of HE 1045-0908

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Multi-wavelength spectrophotometry of EX Hydrae

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XMM-Newton observation of the long-period polar V1309 Orionis: the case for pure blobby accretion

in the wavelength range 405--1065 nm while the Kitt Peak atlases show deviations as large as several ten to 100 m s

The high-field polar RX J1007.5–2017

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