Massive Stars and their Supernovae

Massive stars and their supernovae are prominent sources of radioactive isotopes, the observations of which thus can help to improve our astrophysical models of those. Our understanding of stellar evolution and the final explosive endpoints such as supernovae or hypernovae or gamma-ray bursts relies on the combination of magneto-hydrodynamics, energy generation due to nuclear reactions accompanying composition changes, radiation transport, and thermodynamic properties (such as the equation of state of stellar matter). Nuclear energy production includes all nuclear reactions triggered during stellar evolution and explosive end stages, also among unstable isotopes produced on the way. Radiation transport covers atomic physics (e.g. opacities) for photon transport, but also nuclear physics and neutrino nucleon/nucleus interactions in late phases and core collapse. Here we want to focus on the astrophysical aspects, i.e. a description of the evolution of massive stars and their endpoints, with a special emphasis on the composition of their ejecta (in form of stellar winds during the evolution or of explosive ejecta). Low and intermediate mass stars end their evolution as a white dwarf with an unburned C and O composition. Massive stars evolve beyond this point and experience all stellar burning stages from H over He, C, Ne, O and Si-burning up to core collapse and explosive endstages. In this chapter we discuss the nucleosynthesis processes involved and the production of radioactive nuclei in more detail.Comment: 79 pages; Chapter of "Astronomy with Radioactivities", a book in Springer's 'lecture notes in physics series, Vol. 812, Eds. Roland Diehl, Dieter H. Hartmann, and Nikos Prantzos, to appear in summer 201

Nüsse in der Ernährung. Ein Bericht über neuere Forschungsergebnisse

In den letzten Jahren haben mehrere epidemiologische Studien ein abnehmendes Risiko für Herz-Kreislauf-Erkrankungen bei zunehmendem Verzehr von Nüssen gezeigt. Wie aus klinischen Studien hervorgeht, beruht diese Wirkung teilweise oder vollständig auf einer durch den Nussverzehr bewirkten Senkung des Gesamtcholesterin- und des LDL-Cholesterinspiegels im Blut. Welche Inhaltsstoffe der Nüsse für diese Wirkung verantwortlich sind, ist noch unklar, obwohl vieles dafür spricht, dass vor allem das günstige Fettsäureprofil der Nussfette eine Rolle spielt (relativ hoher Gehalt an einfach und mehrfach ungesättigten Fettsäuren). Diese Untersuchungen sind vor allem in USA durchgeführt worden und haben dort bei Ernährungswissenschaftlern und -beratern einen starken Wandel in der Bewertung des Verzehrs von Nüssen bewirkt. Die früher eher negative Sicht ("Kalorienbomben") ist der eindeutigen Befürwortung eines höheren Verzehrs gewichen. In Europa ist dieser Wandel noch wenig zur Kenntnis genommen worden. Es werden Vorschläge zur Änderung dieser Situation gemacht

Young Adults with Immigrant Background and their Transition to the German System of Vocational Training. The Role of Preferences, Resources, and Opportunities

Anhand gepoolter Datensätze dreier Schulabgängerbefragungen des Bundesinstituts für Berufsbildung (BIBB) wird der Frage nach dem Grad und den Ursachen der Benachteiligung Jugendlicher ausländischer Herkunft beim Zugang zu Ausbildungsplätzen nachgegangen. Es wird untersucht, welche Rolle folgende Unterschiede zwischen Ausbildungsplatzsuchenden deutscher und ausländischer Herkunft spielen: ihre Präferenzen für eine bestimmte berufliche Ausbildung, ihre Ausstattung mit arbeitsmarktrelevanten Ressourcen sowie ihnen offen stehende Opportunitäten auf dem Ausbildungsstellenmarkt. Dabei zeigt sich erstens, dass vor allem männliche Jugendliche ausländischer Herkunft deutlich geringere Chancen haben, einen Ausbildungsplatz zu finden, als Jugendliche deutscher Herkunft. Dies gilt weitgehend unabhängig davon, welchen Wunschberuf sie verfolgen, welchen Schulabschluss sie besitzen und welche Erstsprache sie gelernt haben. Auch Unterschiede in ihren Suchstrategien nach einem Ausbildungsplatz scheinen wenig zur Erklärung dieses Phänomens beizutragen, zumal diese bei den Gruppen kaum differieren. Die Analysen belegen zweitens, dass selbst diejenigen Jugendlichen ausländischer Herkunft, die einen Ausbildungsplatz gefunden haben, nur halb so oft in ihrem "Wunschberuf" ausgebildet werden wie deutsche Jugendliche. Nicht zuletzt der starke Unterschied zwischen Mädchen und Jungen mit Migrationshintergrund spricht dafür, dass Diskriminierungsprozesse seitens der Arbeitgeber bei der Vergabe von Ausbildungsplätzen möglicherweise eine größere Rolle spielen als bei anderen Dimensionen der Arbeitsmarktintegration. Dies steht vermutlich im Zusammenhang mit Spezifika des Ausbildungsstellenmarktes, der durch eine vergleichsweise geringe Produktivität der Ausbildungsplatzsuchenden und eine Knappheit an Ausbildungsplätzen gekennzeichnet ist.In this article, we examine the extent and the causes of ethnic inequalities in access to apprenticeship training positions within the German system of vocational training. Analyses are based on pooled data from three surveys of high school graduates conducted at the German Federal Institute for Vocational Education and Training (BIBB). The role of the following differences between German and applicants with an immigrant background for vocational training positions is analyzed: their preferences for certain occupational fields, their endowment with resources relevant to the integration of the individual in the labor market, and the opportunities available in the vocational training market. We can show, first, that the chances of finding a vocational training position are substantially lower for young - especially male - adults with an immigrant background even if their occupational preferences, their human capital endowment, and their first language are taken into account. Furthermore, there is no evidence that German and immigrant background youths differ substantially in terms of their job-search strategies. Our analyses show, secondly, that even those immigrant background youths who did manage to find a vocational training position are only half as likely as young Germans to be trained in their preferred occupational field. The large gender differences within the immigrant background group in particular suggest that ethnic discrimination processes on the part of potential employers may play a more important role in explaining ethnic inequalities in the access to vocational training positions than in other dimensions of labor market integration. This is probably related to specificities in those vocational training sectors that are characterized by a comparatively low productivity of applicants and by a shortage of vocational training positions

On the origin of the cosmic elements and the nuclear history of the universe

The quest for the energy source of stars, capable of maintaining their long-lasting brightness, has puzzled physicists during centuries. Early suggestions, due to Julius R. von Mayer, John James Waterson, Hermann von Helmholtz, and William Thomson (Lord Kelvin), among others, relied on the conversion of gravitational potential energy into heat. However, the age of the Sun inferred in this framework was only a few million years, a value clearly at odds with estimates based on geological records

Overview of nucleon structure studies

A brief overview of the recent activity in the measurement of the elastic electromagnetic proton and neutron form factors is presented. It is discussed how the quality of the data has been greatly improved by performing double polarization experiments, and the role of two-photon exchange processes will be highlighted. The spatial information on the quark charge distribibutions in the nucleon resulting from the form factors measurements will be discussed, as well as the steady rate of improvements made in the lattice QCD calculations. It is discussed how generalized parton distributions have emerged as a unifying theme in hadron physics linking the spatial densities extracted from form factors with the quark momentum distribution information residing in quark structure functions. The recent progress in the electromagnetic excitation of the $\Delta(1232)$ resonance will also briefly be discussed.Comment: prepared for Proceedings of International Nuclear Physics Conference (INPC07), typos corrected + references adde

Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae

We perform multi-dimensional, time-dependent radiation transfer simulations for hard X-ray and γ -ray emissions, following radioactive decays of 56Ni and 56Co, for two-dimensional delayed-detonation models of Type Ia supernovae (SNe Ia). The synthetic spectra and light curves are compared with the sensitivities of current and future observatories for an exposure time of 106 s. The non-detection of the γ -ray signal from SN 2011fe at 6.4 Mpc by SPI on board INTEGRAL places an upper limit on the mass of 56Ni of 1.0 M, independently from observations in any other wavelengths. Signals from the newly formed radioactive species have not yet been convincingly measured from any SN Ia, but future X-ray and γ -ray missions are expected to deepen the observable horizon to provide high energy emission data for a significant SN Ia sample. We predict that the hard X-ray detectors on board NuStar (launched in 2012) or ASTRO-H (scheduled for launch in 2014) will reach to SNe Ia at ∼15 Mpc, i.e., one SN every few years. Furthermore, according to the present results, the soft γ -ray detector on board ASTRO-H will be able to detect the 158 keV line emission up to ∼25 Mpc, i.e., a few SNe Ia per year. Proposed next-generation γ -ray missions, e.g., GRIPS, could reach to SNe Ia at ∼20–35 Mpc by MeV observations. Those would provide new diagnostics and strong constraints on explosion models, detecting rather directly the main energy source of supernova light

SN2014J gamma rays from the 56^56Ni decay chain

R. Diehl, et al., “SN2014J gamma rays from the 56Ni decay chain”, Astronomy & Astrophysics, Vol. 574, January 2015. The version of record is available online at: https://www.aanda.org/articles/aa/abs/2015/02/aa24991-14/aa24991-14.html Reproduced with Permission from Astronomy and Astrophysics, © ESO 2015.Context. The detection and measurement of gamma-ray lines from the decay chain of 56Ni provides unique information about the explosion in supernovae. SN2014J at 3.3 Mpc is a sufficiently-nearby supernova of type Ia so that such measurements have been feasible with the gamma-ray spectrometer SPI on ESA’s INTEGRAL gamma-ray observatory. Aims. The 56Ni freshly produced in the supernova is understood to power the optical light curve, because it emits gamma rays upon its radioactive decay first to 56Co and then to 56Fe. Gamma-ray lines from 56Co decay are expected to become directly visible through the white dwarf material several weeks after the explosion, as they progressively penetrate the overlying material of the supernova envelope, which is diluted as it expands. The lines are expected to be Doppler-shifted or broadened from the kinematics of the 56Ni ejecta. We aim to exploit high-resolution gamma-ray spectroscopy with the SPI spectrometer on INTEGRAL toward constraining the 56Ni distribution and kinematics in this supernova. Methods. We use the observations with the SPI spectrometer on INTEGRAL, together with an improved instrumental background method. Results. We detect the two main lines from 56Co decay at 847 and 1238 keV, which are significantly Doppler-broadened, and at intensities (3.65 ± 1.21) × 10-4 and (2.27 ± 0.69) × 10-4 ph cm-2 s-1, respectively, at their brightness maximum. We measure their rise toward a maximum after about 60–100 days and a decline thereafter. The intensity ratio of the two lines is found to be consistent with expectations from 56Co decay (0.62 ± 0.28 at brightness maximum, the expected ratio is 0.68). We find that the broad lines seen in the late, gamma-ray transparent phase are not representative of the early gamma-ray emission, and notice instead that the emission spectrum is complex and irregular until the supernova is fully transparent to gamma rays, with progressive uncovering of the bulk of 56Ni. We infer that the explosion morphology is not spherically symmetric, both in the distribution of 56Ni and in the unburnt material which occults the 56Co emission. After we compare light curves from different plausible models, the resulting 56Ni mass is determined to be 0.49 ± 0.09 M⊙.Peer reviewe

Gamma-ray diagnostics of Type Ia supernovae Predictions of observables from three-dimensional modeling

Although the question of progenitor systems and detailed explosion mechanisms still remains a matter of discussion, it is commonly believed that Type Ia supernovae (SNe Ia) are production sites of large amounts of radioactive nuclei. Even though the gamma-ray emission due to radioactive decays is responsible for powering the light curves of SNe Ia, gamma rays themselves are of particular interest as a diagnostic tool because they directly lead to deeper insight into the nucleosynthesis and the kinematics of these explosion events

5.9-keV Mn K-shell X-ray luminosity from the decay of Fe-55 in Type Ia supernova models

We show that the X-ray line flux of the Mn Kα line at 5.9 keV from the decay of 55Fe is a promising diagnostic to distinguish between Type Ia supernova (SN Ia) explosion models. Using radiation transport calculations, we compute the line flux for two three-dimensional explosion models: a near-Chandrasekhar mass delayed detonation and a violent merger of two (1.1 and 0.9 M⊙) white dwarfs. Both models are based on solar metallicity zero-age main-sequence progenitors. Due to explosive nuclear burning at higher density, the delayeddetonation model synthesizes ∼3.5 times more radioactive 55Fe than the merger model. As a result, we find that the peak Mn Kα line flux of the delayed-detonation model exceeds that of the merger model by a factor of ∼4.5. Since in both models the 5.9-keV X-ray flux peaks five to six years after the explosion, a single measurement of the X-ray line emission at this time can place a constraint on the explosion physics that is complementary to those derived from earlier phase optical spectra or light curves. We perform detector simulations of current and future X-ray telescopes to investigate the possibilities of detecting the X-ray line at 5.9 keV. Of the currently existing telescopes, XMM–Newton/pn is the best instrument for close (!1–2 Mpc), non-background limited SNe Ia because of its large effective area. Due to its low instrumental background, Chandra/ACIS is currently the best choice for SNe Ia at distances above ∼2 Mpc. For the delayed-detonation scenario, a line detection is feasible with Chandra up to ∼3 Mpc for an exposure time of 106 s. We find that it should be possible with currently existing X-ray instruments (with exposure times !5 × 105 s) to detect both of our models at sufficiently high S/N to distinguish between them for hypothetical events within the Local Group. The prospects for detection will be better with future missions. For example, the proposed Athena/X-IFU instrument could detect our delayed-detonation model out to a distance of ∼5 Mpc. This would make it possible to study future events occurring during its operational life at distances comparable to those of the recent supernovae SN 2011fe (∼6.4 Mpc) and SN 2014J (∼3.5 Mpc)

pH‐dependent protonation of surface carboxylate groups in PsbO enables local buffering and triggers structural changes

Photosystem II (PSII) catalyzes the splitting of water, releasing protons and dioxygen. Its highly conserved subunit PsbO extends from the oxygen‐evolving center (OEC) into the thylakoid lumen and stabilizes the catalytic Mn4CaO5 cluster. The high degree of conservation of accessible negatively charged surface residues in PsbO suggests additional functions, as local pH buffer or by affecting the flow of protons. For this discussion, we provide an experimental basis, through the determination of pKa values of water‐accessible aspartate and glutamate side‐chain carboxylate groups by means of NMR. Their distribution is strikingly uneven, with high pKa values around 4.9 clustered on the luminal PsbO side and values below 3.5 on the side facing PSII. pH‐dependent changes in backbone chemical shifts in the area of the lumen‐exposed loops are observed, indicating conformational changes. In conclusion, we present a site‐specific analysis of carboxylate group proton affinities in PsbO, providing a basis for further understanding of proton transport in photosynthesis