Dreizler, Stefan

[["dc.bibliographiccitation.firstpage","498"],["dc.bibliographiccitation.journal","Memorie della Societa Astronomica Italiana"],["dc.bibliographiccitation.lastpage","504"],["dc.bibliographiccitation.volume","83"],["dc.contributor.author","Dreizler, S."],["dc.contributor.author","Beuermann, K."],["dc.contributor.author","Hesman, F. V."],["dc.date.accessioned","2019-07-10T08:14:09Z"],["dc.date.available","2019-07-10T08:14:09Z"],["dc.date.issued","2012"],["dc.description.abstract","In the recent years, several circum-binary planets orbiting post-common envelope systems have been announced. Some of the derived planetary parameters have been questioned by others. We therefore present an investigation of the current status in this dynamically evolving field. False positive scenarios for the eclipse time variations are therefore discussed. We also present an update on new measurements on NNSer and shortly address the quest for the frequency of planets in post-common envelope systems."],["dc.identifier.fs","596642"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9580"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/61448"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","0037-8720"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights.access","openAccess"],["dc.subject.ddc","530"],["dc.title","Evidence for planets in post-common envelope binaries"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","012048"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Journal of Physics. Conference Series"],["dc.bibliographiccitation.volume","172"],["dc.contributor.affiliation","S D Hügelmeyer, ; 1Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany"],["dc.contributor.affiliation","S Dreizler, ; 1Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany"],["dc.contributor.author","Hügelmeyer, S. D."],["dc.contributor.author","Dreizler, S."],["dc.date.accessioned","2019-07-09T11:52:44Z"],["dc.date.available","2019-07-09T11:52:44Z"],["dc.date.issued","2009"],["dc.date.updated","2022-02-19T14:35:34Z"],["dc.description.abstract","For a long time, no hydrogen-deficient white dwarfs have been known that have effective temperature between 30 kK and < 45 kK, i. e. exceeding those of DB white dwarfs and having lower ones than DO white dwarfs. Therefore, this temperature range was long known as the DB-gap. Only recently, the SDSS provided spectra of several candidate DB-gap stars. First analyses based on model spectra calculated under the assumption of local thermodynamic equilibrium (LTE) confirmed that these stars had 30 kK < Teff < 45 kK (Eisenstein et al. 2006). It has been shown for DO white dwarfs that the relaxation of LTE is necessary to account for non local effects in the atmosphere caused by the intense radiation field. Therefore, we calculated a non-LTE model grid and re-analysed the aforementioned set of SDSS spectra. Our results confirm the existence of DB-gap white dwarfs."],["dc.identifier.doi","10.1088/1742-6596/172/1/012048"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/5873"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60258"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1742-6596"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject.ddc","530"],["dc.title","Non-LTE spectral analyses of the lately discovered DB-gap white dwarfs from the SDSS"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","012023"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Journal of Physics. Conference Series"],["dc.bibliographiccitation.volume","172"],["dc.contributor.affiliation","R Heller, ; 1Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany"],["dc.contributor.affiliation","R Østensen, ; 3Institute of Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium"],["dc.contributor.author","Heller, R."],["dc.contributor.author","Homeier, D."],["dc.contributor.author","Dreizler, S."],["dc.contributor.author","Østensen, R."],["dc.date.accessioned","2019-07-09T11:52:44Z"],["dc.date.available","2019-07-09T11:52:44Z"],["dc.date.issued","2009"],["dc.date.updated","2022-02-19T14:25:24Z"],["dc.description.abstract","We present a catalog of 857 WD (WD)-M star binaries from the sixth data release of the Sloan Digital Sky Survey (SDSS), most of them known before. For 636 of them, we give a spectral analysis and derive the basic parameters of the stellar constituents and their distances from Earth. Our purpose is to test the modeled spectra applied in the fitting procedure on the one hand and to confine the respective evolutionary scenarios on the other hand. We use a χ2 minimization technique in order to decompose each combined spectrum and yield independent parameter estimates for the components. 41 of the stellar duets in our spectroscopic sample are optically resolved on the respective SDSS images. Despite various selection effects, the fraction of 6.4 % of WD-M star binaries with orbital separation around 500 AU and orbital perdiods of ~ 104 yr is a criterion for evolutionary models of stellar binary systems. We find 20 out of 636 WDs being fitted as DOs, with 16 of them indicating TefWD around 40000K. This excess of cool DOs is most likely due to additional WDs in the DB-DO Teff range, for which no detailed fitting was done. Furthermore, we identify 70 very low-mass objects, meaning secondaries with masses smaller than about 0.1 Modot, as candidate substellar companions. A trend of WD masses towards higher values in a binary constellation compared to those of field WDs is compatible with our results."],["dc.identifier.doi","10.1088/1742-6596/172/1/012023"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/5875"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60260"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1742-6596"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject.ddc","530"],["dc.title","Spectral analysis of 636 WD - M star binaries from the Sloan Digital Sky Survey (Data Release 6)"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","012060"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Journal of Physics. Conference Series"],["dc.bibliographiccitation.volume","172"],["dc.contributor.affiliation","S D Hügelmeyer, ; 1Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany"],["dc.contributor.affiliation","S Dreizler, ; 1Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany"],["dc.contributor.affiliation","D Homeier, ; 1Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany"],["dc.contributor.affiliation","P Hauschildt, ; 2Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany"],["dc.contributor.author","Hügelmeyer, S. D."],["dc.contributor.author","Dreizler, S."],["dc.contributor.author","Homeier, D."],["dc.contributor.author","Hauschildt, P."],["dc.date.accessioned","2019-07-09T11:52:44Z"],["dc.date.available","2019-07-09T11:52:44Z"],["dc.date.issued","2009"],["dc.date.updated","2022-02-19T14:40:41Z"],["dc.description.abstract","Gas and dust disks are common objects in the universe and can be found around various objects, e.g. young stars, cataclysmic variables, active galactic nuclei, or white dwarfs. The light that we receive from disks provides us with clues about their composition, temperature, and density. In order to better understand the physical and chemical dynamics of these disks, self-consistent radiative transfer simulations are inevitable. Therefore, we have developed a 1+1D radiative transfer code as an extension to the well-established model atmosphere code PHOENIX. We will show the potential of the application of our code to model the spectra of white dwarf debris disks."],["dc.identifier.doi","10.1088/1742-6596/172/1/012060"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/5874"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60259"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1742-6596"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject.ddc","530"],["dc.title","Spectral synthesis of circumstellar disks - application to white dwarf debris disks"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","012002"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Journal of Physics. Conference Series"],["dc.bibliographiccitation.volume","172"],["dc.contributor.affiliation","J Krzesinski, ; 1Mt. Suhora Observatory, Cracow Pedagogical University, ul. Podchorazych 2, 30-084 Cracow, Poland"],["dc.contributor.affiliation","A Nitta, ; 3Gemini Telescope, 670 N. A'Ohoku Place, Hilo, HI 96720, USA"],["dc.contributor.affiliation","S J Kleinman, ; 3Gemini Telescope, 670 N. A'Ohoku Place, Hilo, HI 96720, USA"],["dc.contributor.affiliation","S Hügelmeyer, ; 4Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany"],["dc.contributor.affiliation","S Dreizler, ; 4Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany"],["dc.contributor.affiliation","J Liebert, ; 5Steward Observatory, University of Arizona, Tucson, AZ 85726, USA"],["dc.contributor.affiliation","H Harris, ; 6U.S. Naval Observatory, PO Box 1149, Flagstaff, AZ 86002-1149, USA"],["dc.contributor.author","Krzesinski, J."],["dc.contributor.author","Nitta, A."],["dc.contributor.author","Kleinman, S. J."],["dc.contributor.author","Hügelmeyer, S."],["dc.contributor.author","Liebert, J."],["dc.contributor.author","Harris, H."],["dc.contributor.author","Dreizler, Stefan"],["dc.date.accessioned","2019-07-09T11:52:44Z"],["dc.date.available","2019-07-09T11:52:44Z"],["dc.date.issued","2009"],["dc.date.updated","2022-02-19T14:14:58Z"],["dc.description.abstract","A large collection of white dwarf (WD) spectra from Sloan Digital Sky Survey (SDSS) data release 4 (DR4) WD catalog data allowed us to obtain a luminosity function (LF) for the hottest WDs. The LF was calculated basing on spectra of the WDs from a special class of SDSS objects called hot standards (HS), for which the WD sample completeness can be estimated. WD distances were determined from the observed and absolute SDSS g filter magnitudes derived from WD stellar atmosphere model fits to the SDSS spectra. The result LF covers -0.5 up to 7 absolute bolometric magnitude range. It shows a slight disagreement at the cold end comparing to the literature LFs but it can be due to some problems with HS WD sample completeness estimations. It is clearly visible that the LF has unexpected plateau between 1.5 and 4 absolute bolometric magnitudes. There is nothing similar visible in a LF built only for non-DA WDs. The plateau might be real but we are concern that its existence can be connected to the problems with spectra calibration of the blue objects in SDSS DR4 data and lack of good stellar atmosphere models for the hottest DA white dwarfs."],["dc.identifier.doi","10.1088/1742-6596/172/1/012002"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/5876"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60261"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1742-6596"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject.ddc","530"],["dc.title","SDSS DR4: Progress on the hot white dwarf luminosity function"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]