Multiple origins for the DLA at zabs=0.313z_\mathrm{abs}=0.313 toward PKS 1127−-145 indicated by a complex dust depletion pattern of Ca, Ti, and Mn

We investigate the dust depletion properties of optically thick gas in and around galaxies and its origin we study in detail the dust depletion patterns of Ti, Mn, and Ca in the multi-component damped Lyman-$\alpha$ (DLA) absorber at $z_\mathrm{abs}=0.313$ toward the quasar PKS 1127$-$145.} We performed a detailed spectral analysis of the absorption profiles of CaII, MnII, TiII, and NaI associated with the DLA toward PKS 1127$-$145, based on optical high-resolution data obtained with the UVES instrument at the Very Large Telescope (VLT). We obtained column densities and Doppler-parameters for the ions listed above and determine their gas-phase abundances, from which we conclude on their dust depletion properties. We compared the Ca and Ti depletion properties of this DLA with that of other DLAs. One of the six analyzed absorption components shows a striking underabundance of Ti and Mn in the gas-phase, indicating the effect of dust depletion for these elements and a locally enhanced dust-to-gas ratio. In this DLA and in other similar absorbers, the MnII abundance follows that of TiII very closely, implying that both ions are equally sensitive to the dust depletion effects. Our analysis indicates that the DLA toward PKS 1127$-$145 has multiple origins. With its narrow line width and its strong dust depletion, component 3 points toward the presence of a neutral gas disk from a faint LSB galaxy in front of PKS 1127$-$145, while the other, more diffuse and dust-poor, absorption components possibly are related to tidal gas features from the interaction between the various, optically confirmed galaxy-group members. In general, the Mn/CaII ratio in sub-DLAs and DLAs possibly serves as an important indicator to discriminate between dust-rich and dust-poor in neutral gas in and around galaxies.Comment: 10 pages, 8 figures, accepted for A&

Non-Statistical Effects in Neutron Capture

There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at LANSCE. Measurements made with a 147Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the reduced-neutron-width distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,alpha) measurements had revealed that the alpha strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C6D6 gamma-ray detectors which we have employed for many years to measure neutron-capture cross sections at ORELA. Measurements with a 95Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.Comment: 8 pages, 3 figures, for proceedings of CGS1

Experimental opportunities at the pulsed neutron source ORELA

The authors have developed an improved C{sub 6}D{sub 6} detector system, a high-purity germanium n-type detector system, and a new BaF{sub 2} system for capture and fission measurements at ORELA. With their set of different detectors, they are able to measure high-precision data for total cross-section measurements, as well as fission, elastic scattering, {gamma}-ray, and neutron-production cross section data. Additional capabilities at ORELA include an intense, pulsed positron, source of {approximately} 10{sup 8}e{sup +}/sec

High-resolution neutron capture and transmission measurements and the stellar neutron capture cross sections of {sup 116,120}Sn

Improved astrophysical reaction rates for {sup 116,120}Sn(n, {gamma}) are of interest because nucleosynthesis models have not been able to reproduce the observed abundances in this mass region. For example, previous s-process calculations have consistently underproduced the s-only isotope {sup 116}Sn. Also, these studies have resulted in residual reprocess abundances for the tin isotopes which are systematically larger than predicted by reprocess calculations. It has been suggested that these problems could be solved by reducing the solar tin abundance by 10-20%, but there is no experimental evidence to justify this renormalization. Instead, it is possible that the problem lies in the (n,T) cross sections used in the reaction network calculations or in the s-process models. One reason to suspect the (n, {gamma}) data is that previous measurements did not extend to low enough energies to determine accurately the Maxwellian-averaged capture cross sections at the low temperatures (kT=6-8 keV) favored by the most recent stellar models of the s process. Also, the two most recent high-precision measurements of the {sup 120}Sn(n, {gamma}) cross section are in serious disagreement. Because of its small size, this cross section could affect (via the s-process branching at {sup 121}Sn) the relative abundances of the three s-only isotopes of Te

Hadron calorimeter with MAPD readout in the NA61/SHINE experiment

The modular hadron calorimeter with micro-pixel avalanche photodiodes readout for the NA61/SHINE experiment at the CERN SPS is presented. The calorimeter consists of 44 independent modules with lead-scintillator sandwich structure. The light from the scintillator tiles is captured by and transported with WLS-fibers embedded in scintillator grooves. The construction provides a longitudinal segmentation of the module in 10 sections with independent MAPD readout. MAPDs with pixel density of $~10^{4}$/mm$^2$ ensure good linearity of calorimeter response in a wide dynamical range. The performance of the calorimeter prototype in a beam test is reported

Heavy Element Abundances in Presolar Silicon Carbide Grains from Low-Metallicity AGB Stars

Primitive meteorites contain small amounts of presolar minerals that formed in the winds of evolved stars or in the ejecta of stellar explosions. Silicon carbide is the best studied presolar mineral. Based on its isotopic compositions it was divided into distinct populations that have different origins: Most abundant are the mainstream grains which are believed to come from 1.5-3 Msun AGB stars of roughly solar metallicitiy. The rare Y and Z grains are likely to come from 1.5-3 Msun AGB stars as well, but with subsolar metallicities (0.3-0.5x solar). Here we report on C and Si isotope and trace element (Zr, Ba) studies of individual, submicrometer-sized SiC grains. The most striking results are: (1) Zr and Ba concentrations are higher in Y and Z grains than in mainstream grains, with enrichments relative to Si and solar of up to 70x (Zr) and 170x (Ba), respectively. (2) For the Y and Z grains there is a positive correlation between Ba concentrations and amount of s-process Si. This correlation is well explained by predictions for 2-3 Msun AGB stars with metallicities of 0.3-0.5x solar. This confirms low-metallicity stars as most likely stellar sources for the Y and Z grains

The s Process: Nuclear Physics, Stellar Models, Observations

Nucleosynthesis in the s process takes place in the He burning layers of low mass AGB stars and during the He and C burning phases of massive stars. The s process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting s-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the s-process reaction network, current models are aiming at ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear and atomic physics, and stellar modeling is reviewed and the corresponding interplay is illustrated by the general abundance patterns of the elements beyond iron and by the effect of sensitive branching points along the s-process path. The strong variations of the s-process efficiency with metallicity bear also interesting consequences for Galactic chemical evolution.Comment: 53 pages, 20 figures, 3 tables; Reviews of Modern Physics, accepte