Beuermann, Klaus Peter

[["dc.bibliographiccitation.firstpage","671"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","681"],["dc.bibliographiccitation.volume","451"],["dc.contributor.author","Euchner, F."],["dc.contributor.author","Jordan, S."],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Reinsch, K."],["dc.contributor.author","Gansicke, B. T."],["dc.date.accessioned","2018-11-07T09:50:53Z"],["dc.date.available","2018-11-07T09:50:53Z"],["dc.date.issued","2006"],["dc.description.abstract","Aims. We analyse the magnetic field geometry of the magnetic DA white dwarf PG1015+014 with our Zeeman tomography method. Methods. This study is based on rotation-phase resolved optical flux and circular polarization spectra of PG1015+014 obtained with FORS1 at the ESO VLT. Our tomographic code makes use of an extensive database of pre-computed Zeeman spectra. The general approach has been described in Papers I and II of this series. Results. The surface field strength distributions for all rotational phases of PG1015+014 are characterised by a strong peak at 70 MG. A separate peak at 80MG is seen for about one third of the rotation cycle. Significant contributions to the Zeeman features arise from regions with field strengths between 50 and 90 MG. We obtain equally good simultaneous fits to the observations, collected in five phase bins, for two different field parametrizations: (i) a superposition of individually tilted and off-centred zonal multipole components; and (ii) a truncated multipole expansion up to degree l = 4 including all zonal and tesseral components. The magnetic fields generated by both parametrizations exhibit a similar global structure of the absolute surface field values, but differ considerably in the topology of the field lines. An effective photospheric temperature of T-eff = 10 000 +/- 1000 K was found. Conclusions. Remaining discrepancies between the observations and our best-fit models suggest that additional small-scale structure of the magnetic field exists which our field models are unable to cover due to the restricted number of free parameters."],["dc.identifier.doi","10.1051/0004-6361:20064840"],["dc.identifier.fs","45028"],["dc.identifier.isi","237272100027"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9385"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/35801"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Zeeman tomography of magnetic white dwarfs - III. The 70-80 Megagauss magnetic field of PG1015+014"],["dc.title.original","9385"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","651"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","660"],["dc.bibliographiccitation.volume","442"],["dc.contributor.author","Euchner, F."],["dc.contributor.author","Reinsch, K."],["dc.contributor.author","Jordan, S."],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Gansicke, B. T."],["dc.date.accessioned","2018-11-07T10:54:29Z"],["dc.date.available","2018-11-07T10:54:29Z"],["dc.date.issued","2005"],["dc.description.abstract","We report time-resolved optical flux and circular polarization spectroscopy of the magnetic DA white dwarf HE 1045- 0908 obtained with FORS1 at the ESO VLT. Considering published results, we estimate a likely rotational period of P-rot similar or equal to 2.7 h, but cannot exclude values as high as about 9 h. Our detailed Zeeman tomographic analysis reveals a field structure which is dominated by a quadrupole and contains additional dipole and octupole contributions, and which does not depend strongly on the assumed value of the period. A good fit to the Zeeman flux and polarization spectra is obtained if all field components are centred and inclinations of their magnetic axes with respect to each other are allowed for. The fit can be slightly improved if an offset from the centre of the star is included. The prevailing surface field strength is 16 MG, but values between 10 and similar to 75 MG do occur. We derive an effective photospheric temperature of HE 1045- 0908 of T-eff = 10 000 +/- 1000 K. The tomographic code makes use of an extensive database of pre-computed Zeeman spectra ( Paper I)."],["dc.identifier.doi","10.1051/0004-6361:20053038"],["dc.identifier.isi","232404400032"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9389"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/49572"],["dc.notes.intern","In goescholar not merged with http://resolver.sub.uni-goettingen.de/purl?gs-1/9853 but duplicate"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.rights","Goescholar"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.title","Zeeman tomography of magnetic white dwarfs - II. The quadrupole-dominated magnetic field of HE 1045-0908"],["dc.title.original","9389"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","821"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","827"],["dc.bibliographiccitation.volume","412"],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Harrison, Thomas E."],["dc.contributor.author","McArthur, Barbara E."],["dc.contributor.author","Benedict, G. Fritz"],["dc.contributor.author","Gansicke, B. T."],["dc.date.accessioned","2018-11-07T10:34:13Z"],["dc.date.available","2018-11-07T10:34:13Z"],["dc.date.issued","2003"],["dc.description.abstract","Using the HST Fine Guidance Sensor, we have measured a high precision astrometric parallax of the cataclysmic variable EX Hydrae, pi = 15.50 +/- 0.29 mas. From the wavelength-integrated accretion-induced energy flux, we derive a quiescent accretion luminosity for EX Hya of L-acc = (2.6 +/- 0.6) x 10(32) erg s(-1). The quiescent accretion rate then is. (M) over dot(av) = (6.2 +/- 1.5) x 10(-11)(M-1/0.5 M.)(-1.61) M. yr(-1). The time-averaged accretion rate, which includes a small correction for the rare outbursts, is 6% higher. We discuss the system parameters of EX Hya and deduce M-1 = 0.4-0.7 M., M-2 = 0.07-0.10 M., and i = 76.0degrees - 77.6degrees, using recent radial velocity measurements of both components and restrictions imposed by other observational and theoretical constraints. We conclude that the secondary is undermassive, overluminous, and expanded over a ZAMS star of the same mass. Near the upper limit to M-1, the accretion rate of the white dwarf coincides with that due to near-equilibrium angular momentum loss by gravitational radiation and angular momentum transfer from the orbit into the spin-up of the white dwarf. Near the lower mass limit, the correspondingly higher accretion rate requires that either an additional angular momentum loss process is acting besides gravitational radiation or that accretion occurs on a near-adiabatic time scale. The latter possibility would imply that EX Hya is in a transient phase of high mass transfer and the associated spin-up of the white dwarf."],["dc.identifier.doi","10.1051/0004-6361:20031498"],["dc.identifier.isi","000187075500023"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9807"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/44810"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","A precise HST parallax of the cataclysmic variable EX Hydrae, its system parameters, and accretion rate"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","984"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","998"],["dc.bibliographiccitation.volume","382"],["dc.contributor.author","Eisenbart, S."],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Reinsch, K."],["dc.contributor.author","Gansicke, B. T."],["dc.date.accessioned","2018-11-07T10:32:03Z"],["dc.date.available","2018-11-07T10:32:03Z"],["dc.date.issued","2002"],["dc.description.abstract","We present phase-resolved infrared and optical spectrophotometry of the intermediate polar EXHya supplemented by archival ultraviolet data. The spin-modulated emission from the accretion funnel and the emission from the accretion disk or ring contain substantial optically thin components. The white dwarf dominates the unmodulated flux in the ultraviolet and is identified by numerous absorption lines. Metal absorption in the accretion curtain may add to the observed spectral features. The secondary star is of spectral type M4 +/- 1 and is detected by its ellipsoidal modulation. We derive a distance of 65 +/- 11 pc which makes EX Hydrae one of the closest cataclysmic variables with a known distance. The luminosity derived from the integrated overall spectral energy distribution is 3 x 10(32) erg s(-1). The accretion rate of 3 x 10(15) g s(-1) (for an 0.6 M-. white dwarf) is in reasonable agreement with the rates expected from angular momentum loss by gravitational radiation and from the observed spin-up of the white dwarf."],["dc.identifier.doi","10.1051/0004-6361:20011655"],["dc.identifier.fs","19124"],["dc.identifier.isi","000174182900024"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9722"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/44255"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Multi-wavelength spectrophotometry of EX Hydrae"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1129"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","1137"],["dc.bibliographiccitation.volume","449"],["dc.contributor.author","Konig, M."],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Gansicke, B. T."],["dc.date.accessioned","2018-11-07T10:00:16Z"],["dc.date.available","2018-11-07T10:00:16Z"],["dc.date.issued","2006"],["dc.description.abstract","We present a pilot study of atmospheres of accreting magnetic white dwarfs irradiated by intense fluxes at ultraviolet to infrared wavelengths. The model uses a standard LTE stellar atmosphere code which is expanded by introducing an angle-dependent external radiation source. The present results are obtained for an external source with the spectral shape of a 10 000 K blackbody and a freely adjustable spectral flux. The model provides an explanation for the observed largely filled-up Lyman lines in the prototype polar AM Herculis during its high states. It also confirms the hypotheses (i) that irradiation by cyclotron radiation and other radiation sources is the principle cause for the large heated polar caps surrounding the accretion spots on white dwarfs in polars and (ii) that much of the reprocessed light appears in the far ultraviolet and not in the soft X-ray regime as suggested in the original simple theories. We also briefly discuss the role played by hard X-rays in heating the polar cap."],["dc.identifier.doi","10.1051/0004-6361:20054336"],["dc.identifier.fs","45033"],["dc.identifier.isi","000236248800025"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9393"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/37768"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Irradiated atmospheres of accreting magnetic white dwarfs with an application to the polar AM Herculis"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","633"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","647"],["dc.bibliographiccitation.volume","390"],["dc.contributor.author","Euchner, F."],["dc.contributor.author","Jordan, S."],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Gansicke, B. T."],["dc.contributor.author","Hessman, Frederic V."],["dc.date.accessioned","2018-11-07T10:11:47Z"],["dc.date.available","2018-11-07T10:11:47Z"],["dc.date.issued","2002"],["dc.description.abstract","We have computed optical Zeeman spectra of magnetic white dwarfs for field strengths between 10 and 200 MG and effective temperatures between 8000 and 40 000 K. They form a database containing 20 628 sets of flux and circular polarization spectra. A least-squares optimization code based on an evolutionary strategy can recover relatively complex magnetic field topologies from phase-resolved synthetic Zeeman spectra of rotating magnetic white dwarfs. We consider dipole and quadrupole components which are non-aligned and shifted off-centre. The model geometries include stars with a single high-field spot and with two spots separated by similar to90degrees. The accuracy of the recovered field structure increases with the signal-to-noise ratio of the input spectra and is significantly improved if circular polarization spectra are included in addition to flux spectra. We discuss the strategies proposed so far to unravel the field geometries of magnetic white dwarfs."],["dc.identifier.doi","10.1051/0004-6361:20020726"],["dc.identifier.isi","177116700021"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9729"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/40109"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Zeeman tomography of magnetic white dwarfs - I. Reconstruction of the field geometry from synthetic spectra"],["dc.title.original","9729"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1071"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","1076"],["dc.bibliographiccitation.volume","401"],["dc.contributor.author","Mouchet, M."],["dc.contributor.author","Bonnet-Bidaud, J. M."],["dc.contributor.author","Roueff, E."],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","de Martino, Domitilla"],["dc.contributor.author","Desert, J. M."],["dc.contributor.author","Ferlet, R."],["dc.contributor.author","Fried, R. E."],["dc.contributor.author","Gansicke, B. T."],["dc.contributor.author","Howell, S. B."],["dc.contributor.author","Mukai, K."],["dc.contributor.author","Porquet, D."],["dc.contributor.author","Szkody, P."],["dc.date.accessioned","2018-11-07T10:39:38Z"],["dc.date.available","2018-11-07T10:39:38Z"],["dc.date.issued","2003"],["dc.description.abstract","We report on the first far-UV observations of the asynchronous polar BY Cam made by the Far-Ultraviolet Spectroscopic Explorer (FUSE). The source is known to exhibit the most extreme NV/CIV emission resonance line ratio observed among polars. The FUSE observations reveal a OVI resonance line weaker than in the prototype of polars, AM Her, with the absence of a detectable narrow component. The OVI broad line is detected with an equivalent width of the same order as in AM Her, the blueward doublet component is clearly present but the redward component is strongly affected by H(2) absorption. The presence of a strong NIII line and weak CIII lines also confirms the peculiar CNO line flux. We compare the resonance CNO line intensities with the predictions of the CLOUDY plasma code coupled to a geometrical model of the accretion column. Varying the temperature and/or intensity of the ionising spectrum is unable to reproduce the observed broad line ratios. A solution is obtained by significantly altering the element abundances with a strong depletion of C, overabundance of N and a weak underabundance of O. This confirms previous suggestions of non-solar abundances which may result from redistribution in the accreted material following nova outbursts and/or the secondary nuclear evolution. A very significant H(2) absorption is observed in front of the source, a possible indication for either the existence of a dense interstellar cloud or of circumstellar material."],["dc.identifier.doi","10.1051/0004-6361:20030176"],["dc.identifier.isi","000181929900026"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9810"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46095"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","The surprising Far-UV spectrum of the polar BY Camelopardalis"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","291"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","299"],["dc.bibliographiccitation.volume","419"],["dc.contributor.author","Beuermann, Klaus"],["dc.contributor.author","Harrison, Thomas E."],["dc.contributor.author","McArthur, Barbara E."],["dc.contributor.author","Benedict, G. Fritz"],["dc.contributor.author","Gansicke, B. T."],["dc.date.accessioned","2018-11-07T10:49:06Z"],["dc.date.available","2018-11-07T10:49:06Z"],["dc.date.issued","2004"],["dc.description.abstract","Using the Hubble space Telescope Fine Guidance Sensor. we have measured the trigonometric parallax of the bright cataclysmic variable 1223 Sgr. The absolute parallax is pi(abs) = 1.96 +/- 0.18 mas, making V 1223 Sur the most distant CV with a well-determined trigonometric parallax. This distance, a Lutz-Kelker correction, and the previously measured extinction yield an absolute visual high-state magnitude M(V) = 4.0 +/- 0.2. We outline a model, which is consistent with the observed spin-down of the white dwarf and provides for much Of the UV/optical emission by reverberation of X-rays. From previous X-ray and UV/optical data, we derive an accretion luminosity L(acc) = (2.6 +/- 0.8) x 10(34) erg s(-1), a white dwarf mass M(1) = 0.93 +/- 0.12 M(circle dot) and an accretion rate M = (1.4 +/- 0.3) x 10(17) g s(-1)."],["dc.identifier.doi","10.1051/0004-6361:20034424"],["dc.identifier.isi","000222213300028"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9832"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/48353"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","An HST parallax of the distant cataclysmic variable V1223 Sgr, its system parameters, and accretion rate"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]