arXiv subjects

H. Schatz

Publications and source records attributed to H. Schatz.

79 records · Page 5Linked to original sources

arXiv2002

Stellar Sources of the Interstellar Medium

With the exception of the Big Bang, responsible for 1,2H, 3,4He, and 7Li, stars act as sources for the composition of the interstellar medium. Cosmic rays are related to the latter and very probably due to acceleration of the mixed interstellar medium by shock waves from supernova remnants. Thus, the understanding of the abundance evolution in the interstellar medium and especially the enrichment of heavy elements, as a function of space and time, is essential. It reflects the history of star formation and the lifetimes of the diverse contributing stellar objects. Therefore, the understanding of the endpoints of stellar evolution is essential as well. These are mainly planetary nebulae and type II/Ib/Ic supernovae as evolutionary endpoints of single stars, but also events in binary systems can contribute, like e.g. supernovae of type Ia, novae and possibly X-ray bursts and neutron star or neutron star - black hole mergers. Despite many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies) is not existing, yet. Their fingerprints, however, seen either in spectra, lightcurves, radioactivities/decay gamma-rays or in galactic evolution, can help to constrain the composition of their ejecta and related model uncertainties.

astro-ph↗

arXiv2002

Proton Drip-Line Calculations and the Rp-process

One-proton and two-proton separation energies are calculated for proton-rich nuclei in the region $ A=41-75 $. The method is based on Skyrme Hartree-Fock calculations of Coulomb displacement energies of mirror nuclei in combination with the experimental masses of the neutron-rich nuclei. The implications for the proton drip line and the astrophysical rp-process are discussed. This is done within the framework of a detailed analysis of the sensitivity of rp process calculations in type I X-ray burst models on nuclear masses. We find that the remaining mass uncertainties, in particular for some nuclei with $N=Z$, still lead to large uncertainties in calculations of X-ray burst light curves. Further experimental or theoretical improvements of nuclear mass data are necessary before observed X-ray burst light curves can be used to obtain quantitative constraints on ignition conditions and neutron star properties. We identify a list of nuclei for which improved mass data would be most important.

nucl-th↗

arXiv2001

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.

astro-ph↗

arXiv2001

The endpoint of the rp process on accreting neutron stars

We calculate the rapid proton (rp) capture process of hydrogen burning on the surface of an accreting neutron star with an updated reaction network that extends up to Xe, far beyond previous work. In both steady-state nuclear burning appropriate for rapidly accreting neutron stars (such as the magnetic polar caps of accreting X-ray pulsars) and unstable burning of Type I X-ray bursts, we find that the rp process ends in a closed SnSbTe cycle. This prevents the synthesis of elements heavier than Te and has important consequences for X-ray burst profiles, the composition of accreting neutron stars, and potentially galactic nucleosynthesis of light p nuclei.

astro-ph↗

arXiv2001

Element Synthesis in Stars

Except for 1H, 2H, 3He, 4He, and 7Li, originating from the Big Bang, all heavier elements are made in stellar evolution and stellar explosions. Nuclear physics, and in many cases nuclear structure far from stability, enters in a crucial way. Therefore, we examine in this review the role of nuclear physics in astrophysics in general and in particular how it affects stellar events and the resulting nucleosynthesis. Stellar modeling addresses four major aspects: 1. energy generation and nucleosynthesis, 2. energy transport via conduction, radiation or possibly convection, 3. hydrodynamics/hydrostatics, and finally 4. thermodynamic properties of the matter involved. Nuclear Physics enters via nuclear reaction cross sections and nuclear structure (affecting the composition changes and nuclear energy generation), neutrino-nucleon and neutrino-nucleus cross sections (affecting neutrino opacities and transport), and e.g. the equation of state at and beyond nuclear densities which creates a relation between the nuclear many-body problem and the hydrodynamic response like pressure and entropy. In the following we review these four topics by highlighting the role and impact of nuclear physics in each of these aspects of stellar modeling. The main emphasis is put on the connection to element synthesis.

astro-ph↗

arXiv2000

X-Ray Bursts and Proton Captures Close to the Dripline

The hydrogen-rich accreted envelopes of neutron stars in binary systems are the site for the rapid proton capture nucleosynthethic process (rp-process), which involves nuclei close to the proton dripline. An overview of the relevant reactions and nuclear properties for rp-process studies is given, along with motivations for further experimental nuclear physics studies.

astro-ph↗

arXiv1997

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 $(p,γ)-(γ,p)$-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.

astro-ph↗