Asymptotics of Clebsch-Gordan Coefficients

Asymptotic expressions for Clebsch-Gordan coefficients are derived from an exact integral representation. Both the classically allowed and forbidden regions are analyzed. Higher-order approximations are calculated. These give, for example, six digit accuracy when the quantum numbers are in the hundreds.Comment: 30 pages, two figures. New Appendix added. Accepted for publication in the Journal of Mathematical Physic

Supersoft X-ray sources in M31: II. ROSAT-detected supersoft sources in the ROSAT, Chandra and XMM eras

We have performed Chandra observations during the past 3 years of 5 of the M31 supersoft X-ray sources (SSS) discovered with ROSAT. Surprisingly, only one of these sources has been detected, despite a predicted detection of about 20-80 counts. This has motivated a thorough check of the ROSAT M31 survey I data, including a relaxation of the hardness ratio requirement used to select SSS. This increases the number of SSS identified in survey I by 7. We then carried out a comparison with the ROSAT M31 survey II dataset which had hitherto not been explicitly investigated for SSS. We find that most of the ROSAT survey I sources are not detected, and only two new SSS are identified. The low detection rate in the ROSAT survey II and our Chandra observations implies that the variability time scale of SSS is a few months. If the majority of these sources are close-binary SSS with shell hydrogen burning, it further implies that half of these sources predominantly experience large mass transfer rates.Comment: accepted for publ. in ApJ; 2 ps-figures; high-quality figures available at http://www.mpe.mpg.de/~jcg/publis.htm

A Flare of AE Aquarii Observed with XMM-Newton

We present the results of analyzing the XMM-Newton data obtained in 2001 November 7 - 8. A flare is observed simultaneously in X-ray and UV together with a quiescence. We find that during the flare event X-ray flux varies with UV with no significant time lag, indicating a close correlation of flux variation for X-ray and UV flares. An upper limit of the lag is estimated to be \~1 min. From a timing analysis for X-ray data, we find that both pulsed and unpulsed flux increase clearly as the flare advances in the entire energy band 0.15 - 10 keV. The net increase of pulsed flux to the quiescence is, however, small and corresponds to about 3 - 4% of the increase in unpulsed flux, confirming that a flux variation of flare in AE Aqr is dominated by unpulsed X-rays. A spectral analysis reveals that the energy spectrum is similar to that of the quiescence at the beginning of the flare, but the spectrum becomes harder as the flare advances. Based on these results, we discuss the current issues that need to be clarified, e.g., the possible flaring site and the mass accretion problem of the white dwarf. We also discuss the flare properties obtained in this study.Comment: 15 pages, 3 tables, 9 figures, accepted for publication in Ap

Herkunftsvergleiche von Legehennen in Station und Feld unter besonderer Berücksichtigung ökologischer Haltungsverfahren

Der Beitrag beschreibt die Bedingungen von Legeleistungsprüfungen in Deutschland mit Bezug auf Genotyp Umwelt-Interaktionen. Außerdem werden die Besonderheiten der Eierproduktion auf ökologischer Basis herausgestellt. Daraus werden Anregungen für ein Konzept einer zukünftigen Feldprüfung von Legehennen erarbeitet. In Deutschland werden keine offiziellen Legeleistungsprüfungen der Länder mehr durchgeführt. Unabhängige Leistungsinformationen aus Herkunftsvergleichen stehen daher nur aus einzelnen Prüfungen (LfL Bayern, 2006) zur Verfügung. Interaktionen zwischen Legehennenherkünften und unterschiedlichen Haltungssystemen sind nach Literaturangaben gut belegt. Für die Ökoproduktion von Eiern ist aufgrund der produktionstechnischen Unterschiede zur konventionellen Produktion ebenfalls mit solchen Wechselwirkungen zu rechnen. Deshalb braucht die ökologische Eierproduktion eine Leistungsprüfung, die auf die speziellen Produktionsbedingungen abgestimmt ist. Die Entwicklung eines Feldtests für Legehennen in ökologischer Haltung kann daher ein Weg sein, das gegenwärtige Informationsdefizit der Landwirte über die Leistung und das Verhalten erhältlicher Zuchtprodukte unter Öko-Bedingungen zu verringern. Das Konzept muss eine praktikable Datenerfassung gewährleisten. Ein geeignetes und kostengünstig durchführbares Versuchsdesign zur Ermittlung der durchschnittlichen Eignung von Legehennenherkünften für die ökologische Haltung muss dazu entwickelt werden

X-Ray Off States and Optical Variability in CAL 83

CAL 83 was one of the first supersoft X-ray binaries to be discovered and is considered to be the prototype of its class. In 15 X-ray observations between 1983-1997 it was observed to have nearly constant X-ray luminosity and temperature, with the exception of one off-state in 1996. We report on a second X-ray off-state, discovered with a Chandra ACIS-S observation in November 1999. Comparing the long-term X-ray and MACHO optical light curves, we find that, CAL 83 has exhibited distinct and well-defined low, intermediate, and high optical states. Transitions between states are not accompanied by color variations. Both X-ray off states were observed during optical high states and were followed by optical low states within ~50 days. We discuss possible explanations for the observed optical and X-ray variations.Comment: 12 pages A&A style with 5 figures; accepted for publication in A&A Main Journa

Temperature dependent characterization of optical fibres for distributed temperature sensing in hot geothermal wells

This study was performed in order to select a proper fibre for the application of a distributed temperature sensing system within a hot geothermal well in Iceland. Commercially available high temperature graded index fibres have been tested under in-situ temperature conditions. Experiments have been performed with four different polyimide coated fibres, a fibre with an aluminum coating and a fibre with a gold coating. To select a fibre, the relationship between attenuation, temperature, and time has been analyzed together with SEM micrographs. On the basis of these experiments, polyimide fibres have been chosen for utilisation. Further tests in ambient and inert atmosphere have been conducted with two polyimide coated fibres to set an operating temperature limit for these fibres. SEM micrographs, together with coating colour changes have been used to characterize the high temperature performance of the fibres. A novel cable design has been developed, a deployment strategy has been worked out and a suitable well for deployment has been selected.Comment: PACS: 42.81.Pa, 93.85.Fg, 47.80.Fg, 91.35.Dc, 07.20.Dt, 07.60.V

VLT observations of GRB 990510 and its environment

We present BVRI photometry and spectrophotometry of GRB990510 obtained with the ESO VLT/Antu telescope during the late decline phase. Between days 8 and 29 after the burst, the afterglow faded from R=24.2 to ~26.4. The spectral flux distribution and the light curve support the interpretation of the afterglow as synchrotron emission from a jet. The light curve is consistent with the optical transient alone but an underlying SN with maximum brightness R>27.4 or a galaxy with R>27.6 (3-sigma upper limits) cannot be ruled out. To a 5-sigma detection threshold of R=26.1, no galaxy is found within 6'' of the transient. A very blue V~24.5 extended object which may qualify as a starburst galaxy is located 12'' SE, but at unknown redshift.Comment: 5 pages A&A Latex, accepted for publication in A&A Letter

Thermal Timescale Mass Transfer and the Evolution of White Dwarf Binaries

The evolution of binaries consisting of evolved main sequence stars (1 < M_d/Msun < 3.5) with white dwarf companions (0.7 < M_wd/Msun < 1.2) is investigated through the thermal mass transfer phase. Taking into account the stabilizing effect of a strong, optically thick wind from the accreting white dwarf surface, we have explored the formation of several evolutionary groups of systems for progenitors with initial orbital periods of 1 and 2 days. The numerical results show that CO white dwarfs can accrete sufficient mass to evolve to a Type Ia supernova and ONeMg white dwarfs can be built up to undergo accretion induced collapse for donors more massive than about 2 Msun. For donors less massive than ~2 Msun the system can evolve to form a He and CO or ONeMg white dwarf pair. In addition, sufficient helium can be accumulated (~0.1 Msun) in systems characterized by 1.6 < M_d/Msun < 1.9 and 0.8 < M_wd/Msun < 1 such that sub Chandrasekhar mass models for Type Ia supernovae, involving off center helium ignition, are possible for progenitor systems evolving via the Case A mass transfer phase. For systems characterized by mass ratios > 3 the system likely merges as a result of the occurrence of a delayed dynamical mass transfer instability. A semi-analytical model is developed to delineate these phases which can be easily incorporated in population synthesis studies of these systems.Comment: 9 pages, 6 figures, Latex, emulateapj style, ApJ accepte