Explosive hydrogen burning during type I X-ray bursts

Explosive hydrogen burning in type I X-ray bursts (XRBs) comprise charged particle reactions creating isotopes with masses up to A~100. Since charged particle reactions in a stellar environment are very temperature sensitive, we use a realistic time-dependent general relativistic and self-consistent model of type I x-ray bursts to provide accurate values of the burst temperatures and densities. This allows a detailed and accurate time-dependent identification of the reaction flow from the surface layers through the convective region and the ignition region to the neutron star ocean. Using this, we determine the relative importance of specific nuclear reactions in the X-ray burst.Comment: 53 pages, 24 figures, submitted to Astrophys.

Heating in the Accreted Neutron Star Ocean: Implications for Superburst Ignition

We perform a self-consistent calculation of the thermal structure in the crust of a superbursting neutron star. In particular, we follow the nucleosynthetic evolution of an accreted fluid element from its deposition into the atmosphere down to a depth where the electron Fermi energy is 20 MeV. We include temperature-dependent continuum electron capture rates and realistic sources of heat loss by thermal neutrino emission from the crust and core. We show that, in contrast to previous calculations, electron captures to excited states and subsequent gamma-emission significantly reduce the local heat loss due to weak-interaction neutrinos. Depending on the initial composition these reactions release up to a factor of 10 times more heat at densities < 10^{11} g/cc than obtained previously. This heating reduces the ignition depth of superbursts. In particular, it reduces the discrepancy noted by Cumming et al. between the temperatures needed for unstable 12C ignition on timescales consistent with observations and the reduction in crust temperature from Cooper pair neutrino emission.Comment: 10 pages, 11 figures, the Astrophysical Journal, in press (scheduled for v. 662). Revised from v1 in response to referee's comment

Mehr Arbeitsplätze durch Subventionsabbau

In der Bundesrepublik Deutschland werden weit mehr Subventionen vergeben, als die offizielle Berichterstattung erkennen läßt. Sie haben im Jahr 1985 eine Höhe von rund 120 Mrd. DM erreicht und sich damit in den vergangenen zehn Jahren verdoppelt. Trotz aller Bekenntnisse zum Abbau haben die Subventionen auch in jüngster Zeit weiter kräftig zugenommen. Vor allem die Steuervergünstigungen sind rasch angestiegen. Die Ziele der Subventionspolitik sind zumeist unklar und, sofern sie erkennbar sind, oft widersprüchlich. Mit gesamtwirtschaftlichen Erfordernissen lassen sich Subventionen nicht begründen. Sie verzerren das Wettbewerbsgefüge zwischen Branchen und Unternehmen und begünstigen insbesondere strukturschwache Bereiche. Darüber hinaus fördern sie einen übermäßigen Kapitaleinsatz. Modellrechnungen zeigen: Würden die Subventionen um die Hälfte gekürzt, dann nähme die Zahl der Arbeitsplätze mittelfristig um rund eine Million zu. Außerdem könnte die Bruttowertschöpfung um (real) fast 3 vH höher ausfallen. Dies sind die Untergrenzen für die vorteilhaften Wirkungen eines Subventionsabbaus. Voraussetzung wäre, daß im gleichen Ausmaß wie die Subventionen auch die Steuern gekürzt würden. Zudem müßten die Tarifvertragsparteien zulassen, daß die Steuersenkungen bei den Unternehmen zu entsprechenden Kostenentlastungen führen. Vorgeschlagen wird ein stufenweises Programm zur gleichmäßigen Kürzung aller Subventionen um insgesamt 50 vH über fünf Jahre, kombiniert mit einer Senkung der Lohn- und Einkommensteuer sowie der Körperschaftsteuer. Bei einer linearen Verringerung der Steuersätze würde der Eingangssteuersatz bei der Lohn- und Einkommensteuer von jetzt 22 vH auf 15 vH, der Spitzensteuersatz von 56 vH auf 39 vH und die durchschnittliche steuerliche Belastung von 25 vH auf 18 vH sinken. Neue Subventionen sollten nur gewährt werden, wenn im Gegenzug alte gestrichen werden. Eine Kommission aus unabhängigen Experten könnte sowohl den Subventionsabbau als auch die Neuvergabe überwachen. Diese Aufgabe könnte auch den Rechnungshöfen übertragen werden. Außerdem sollte die Konkurrentenklage bei Subventionsentscheidungen zugelassen werden. --

Tuning the Clock: Uranium and Thorium Chronometers Applied to CS 31082-001

We obtain age estimates for the progenitor(s) of the extremely metal-poor ([Fe/H = -2.9) halo star CS 31082-001, based on the recently reported first observation of a Uranium abundance in this (or any other) star. Age estimates are derived by application of the classical r-process model with updated nuclear physics inputs. The [U/Th] ratio yields an age of 13+-4 Gyr or 8+-4 Gyr, based on the use of the ETFSI-Q or the new HFBCS-1 nuclear mass models, respectively. Implications for Thorium chronometers are discussed.Comment: 5 pages incl. 1 figure, a shorter 3 page version will be published in the proceedings of the "Astrophysical Ages and Timescales" conference held in Hilo, Hawaii, Feb 5-9, 200

An Approximation for the rp-Process

Hot (explosive) hydrogen burning or the Rapid Proton Capture Process (rp-process) occurs in a number of astrophysical environments. Novae and X-ray bursts are the most prominent ones, but accretion disks around black holes and other sites are candidates as well. The expensive and often multidimensional hydro calculations for such events require an accurate prediction of the thermonuclear energy generation, while avoiding full nucleosynthesis network calculations. In the present investigation we present an approximation scheme applicable in a temperature range which covers the whole range of all presently known astrophysical sites. It is based on the concept of slowly varying hydrogen and helium abundances and assumes a kind of local steady flow by requiring that all reactions entering and leaving a nucleus add up to a zero flux. This scheme can adapt itself automatically and covers situations at low temperatures, characterized by a steady flow of reactions, as well as high temperature regimes where a $(p,\gamma)-(\gamma,p)$-equilibrium is established. In addition to a gain of a factor of 15 in computational speed over a full network calculation, and an energy generation accurate to more than 15 %, this scheme also allows to predict correctly individual isotopic abundances. Thus, it delivers all features of a full network at a highly reduced cost and can easily be implemented in hydro calculations.Comment: 18 pages, LaTeX using astrobib and aas2pp4, includes PostScript figures; Astrophysical Journal, in press. PostScript source also available at http://quasar.physik.unibas.ch/preps.htm

Measurements of the Cosmic Ray Composition with Air Shower Experiments

In this paper we review air shower data related to the mass composition of cosmic rays above 10$^{15}$ eV. After explaining the basic relations between air shower observables and the primary mass and energy of cosmic rays, we present different approaches and results of composition studies with surface detectors. Furthermore, we discuss measurements of the longitudinal development of air showers from non-imaging Cherenkov detectors and fluorescence telescopes. The interpretation of these experimental results in terms of primary mass is highly susceptible to the theoretical uncertainties of hadronic interactions in air showers. We nevertheless attempt to calculate the logarithmic mass from the data using different hadronic interaction models and to study its energy dependence from 10$^{15}$ to 10$^{20}$ eV.Comment: 21 pages, invited review accepted for publication in Astroparticle Physics, Topical Issue on Cosmic Ray

Catching Element Formation In The Act

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV gamma-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by gamma-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at gamma-ray energies, and radioactivity provides a natural physical clock that adds unique information. New science will be driven by time-domain population studies at gamma-ray energies. This science is enabled by next-generation gamma-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous gamma-ray instruments. This transformative capability permits: (a) the accurate identification of the gamma-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new gamma-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new gamma-ray instruments to address a wide set of astrophysical questions.Comment: 14 pages including 3 figure

Author Correction: Non-local effect of impurity states on the exchange coupling mechanism in magnetic topological insulators

A Correction to this paper has been published: https://doi.org/10.1038/s41535-021-00314-