News from the p-process: is the s-process a troublemaker?

The most detailed calculations of the p-process call for its development in the O/Ne layers of Type II supernovae. In spite of their overall success in reproducing the solar system content of p-nuclides, they suggest a significant underproduction of the light Mo and Ru isotopes. On grounds of a model for the explosion of a 25 solar mass star with solar metallicity, we demonstrate that this failure might just be related to the uncertainties left in the rate of the 22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed has a direct impact on the distribution of the s-process seeds for the p-process.Comment: 8 pages, 3 figures, Review talk at Nuclei in the Cosmos 2000, Aarhus, June 27 - July 1, 200

The synthesis of the light Mo and Ru isotopes: how now, no need for an exotic solution ?

The most detailed calculations of the p-process call for its development in the O/Ne layers of Type II supernovae. In spite of their overall success in reproducing the solar system content of p-nuclides, they suggest a significant underproduction of the light Mo and Ru isotopes. On grounds of a model for the explosion of a 25 solar mass star with solar metallicity, we demonstrate that this failure might just be related to the uncertainties left in the rate of the 22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed have a direct impact on the distribution of the s-process seeds for the p-process.Comment: 4 pages, 4 figures. LaTex2e with aa.cls. A&A Letters, in pres

Nucleosynthesis in Massive Stars With Improved Nuclear and Stellar Physics

We present the first calculations to follow the evolution of all stable nuclei and their radioactive progenitors in stellar models computed from the onset of central hydrogen burning through explosion as Type II supernovae. Calculations are performed for Pop I stars of 15, 19, 20, 21, and 25 M_sun using the most recently available experimental and theoretical nuclear data, revised opacity tables, neutrino losses, and weak interaction rates, and taking into account mass loss due to stellar winds. A novel ``adaptive'' reaction network is employed with a variable number of nuclei (adjusted each time step) ranging from about 700 on the main sequence to more than 2200 during the explosion. The network includes, at any given time, all relevant isotopes from hydrogen through polonium (Z=84). Even the limited grid of stellar masses studied suggests that overall good agreement can be achieved with the solar abundances of nuclei between 16O and 90Zr. Interesting discrepancies are seen in the 20 M_sun model and, so far, only in that model, that are a consequence of the merging of the oxygen, neon, and carbon shells about a day prior to core collapse. We find that, in some stars, most of the ``p-process'' nuclei can be produced in the convective oxygen burning shell moments prior to collapse; in others, they are made only in the explosion. Serious deficiencies still exist in all cases for the p-process isotopes of Ru and Mo.Comment: 53 pages, 17 color figures (3 as separate GIF images), slightly extended discussion and references, accepted by Ap

Spectroscopy of the heaviest nuclei (theory)

Recent progress in the applications of covariant density functional theory (CDFT) to the description of the spectroscopy of the heaviest nuclei is reviewed. The analysis of quasiparticle spectra in actinides and the heaviest A ~ 250 nuclei provides a measure of the accuracy of the description of single-particle energies in CDFT and an additional constraint for the choice of effective interactions for the description of superheavy nuclei. The response of these nuclei to the rotation is rather well described by cranked relativistic Hartree+Bogoliubov theory and it serves as a supplementary tool in configuration assignment in odd-mass nuclei. A systematic analysis of the fission barriers with allowance for triaxial deformation shows that covariant density functional theory is able to describe fission barriers on a level of accuracy comparable with the best phenomenological macroscopic+microscopic approaches.Comment: 10 pages, 7 figures, invited talk of A.V. Afanasjev at the International Nuclear Physics Conference (INPC 2010), Vancouver, Canada, July 4-9, 2010, to be published in Journal of Physics G: Conference Series (JPCS

Time-in-area represents foraging activity in a wide-ranging pelagic forager

Successful Marine Spatial Planning depends upon the identification of areas with high importance for particular species, ecosystems or processes. For seabirds, advancements in biologging devices have enabled us to identify these areas through the detailed study of at-sea behaviour. However, in many cases, only positional data are available and the presence of local biological productivity and hence seabird foraging behaviour is inferred from these data alone, under the untested assumption that foraging activity is more likely to occur in areas where seabirds spend more time. We fitted GPS devices and accelerometers to northern gannets Morus bassanus and categorised the behaviour of individuals outside the breeding colony as plunge diving, surface foraging, floating and flying. We then used the locations of foraging events to test the efficiency of 2 approaches: time-in-area and kernel density (KD) analyses, which are widely employed to detect highly-used areas and interpret foraging behaviour from positional data. For KD analyses, the smoothing parameter (h) was calculated using the ad hoc method (KDad hoc), and KDh=9.1, where h = 9.1 km, to designate core foraging areas from location data. A high proportion of foraging events occurred in core foraging areas designated using KDad hoc, KDh=9.1, and time-in-area. Our findings demonstrate that foraging activity occurs in areas where seabirds spend more time, and that both KD analysis and the time-in-area approach are equally efficient methods for this type of analysis. However, the time-in-area approach is advantageous in its simplicity, and in its ability to provide the shapes commonly used in planning. Therefore, the time-in-area approach can be used as a simple way of using seabirds to identify ecologically important locations from both tracking and survey data

Changes in behaviour drive inter-annual variability in the at-sea distribution of northern gannets

The at-sea distribution of seabirds primarily depends on the distance from their breeding colony, and the abundance, distribution and predictability of their prey, which are subject to strong spatial and temporal variation. Many seabirds have developed flexible foraging strategies to deal with this variation, such as increasing their foraging effort or switching to more predictable, less energy dense, prey, in poor conditions. These responses may vary both within and between individuals, and understanding this variability is vital to predict the population-level impacts of spatially explicit environmental disturbances, such as offshore windfarms. We conducted a multi-year tracking study in order to investigate the inter-annual variation in the foraging behaviour and location of a population of northern gannets breeding on Alderney in the English Channel. To do so, we investigated the link between individual-level behaviour and population-level behaviour. We found that a sample of gannets tracked in 2015 had longer trip durations, travelled further from the colony and had larger core foraging areas and home range areas than gannets tracked in previous years. This inter-annual variation may be associated with oceanographic conditions indexed by the North Atlantic Oscillation (NAO). Our findings suggest that this inter-annual variation was driven by individuals visiting larger areas in all of their trips rather than individuals diversifying to visit more, distinct areas. These findings suggest that, for gannets at least, if prey becomes less abundant or more widely distributed, more individuals may be required to forage further from the colony, thus increasing their likelihood of encountering pressures from spatially explicit anthropogenic disturbances

P-Process Nucleosynthesis inside Supernova-Driven Supercritical Accretion Disks

We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M_solar, using the self-similar solution of an optically thick advection dominated flow. Supercritical accretion is expected to occur in a supernova with fallback material accreting onto a new-born compact object. It is found that appreciable amounts of p-nuclei are synthesized via the p-process in supernova-driven supercritical accretion disks (SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs have similar feature to those of the oxygen/neon layers in Type II supernovae when the abundance of the fallback gas far from the compact object is that of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in the SSADs as in Type II supernovae. If the fallback gas is mixed with a small fraction of proton through Rayleigh-Taylor instability during the explosion, significant amounts of Mo92 are produced inside the SSADs. Ru96 and La138 are also produced when the fallback gas contains abundant proton though the overall abundance profile of p-nuclei is rather different from that of the solar system. The p-process nucleosynthesis in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if several percents of fallback matter are ejected via jets and/or winds.Comment: 15 pages, 7 figures included, 3 tables, LaTeX emulateapj5.sty, accepted for publication by the Astronomical Journal (March, 2003

The s-process weak component: uncertainties due to convective overshooting

Using a new s-nucleosynthesis code, coupled with the stellar evolution code Star2003, we performed simulations to study the impact of the convection treatment on the s-process during core He-burning of a 25 Msun star (ZAMS mass) with an initial metallicity of Z=0.02. Particular attention was devoted to the impact of the extent of overshooting on the s-process efficiency. The results show enhancements of about a factor 2-3 in s-process efficiency (measured as the average overproduction factor of the 6 s-only nuclear species with $60\lesssim A\lesssim 90$) with overshooting parameter values in the range 0.01-0.035, compared to results obtained with the same model but without overshooting. The impact of these results on the p-process model based on type II supernovae is discussed.Comment: 7 pages, 4 figures, accepted for publication in Astronomy & Astrophysic

On the Dynamics of Proto-Neutron Star Winds and r-Process Nucleosynthesis

We study here the formation of heavy r-process nuclei in the high-entropy environment of rapidly expanding neutrino-driven winds from compact objects. In particular, we explore the sensitivity of the element creation in the A>130 region to the low-temperature behavior of the outflows. For this purpose we employ a simplified model of the dynamics and thermodynamical evolution for radiation dominated, adiabatic outflows. It consists of a first stage of fast, exponential cooling, followed by a second phase of slower evolution, either assuming constant density and temperature or a power-law decay of these quantities. These cases are supposed to capture the most relevant effects of a strong deceleration or decreasing acceleration of the transsonic outflows, respectively, e.g. in a wind termination shock caused by the collision with the slower, preceding supernova ejecta. We find that not only the transition temperature between the two expansion phases can make a big difference in the formation of the platinum peak, but also the detailed cooling law during the later phase. Unless the transition temperature and corresponding (free neutron) density become too small (T < 2*10^8 K), a lower temperature or faster temperature decline during this phase allow for a stronger appearance of the third abundance peak. Since the nuclear photodisintegration rates between ~2*10^8 K and ~10^9 K are more sensitive to the temperature than the n-capture rates are to the free neutron density, a faster cooling in this temperature regime shifts the r-process path closer to the n-drip line. With low (gamma,n)- but high beta-decay rates, the r-processing then does not proceed through a (gamma,n)-(n,gamma) equilibrium but through a quasi-equilibrium of (n,gamma)-reactions and beta-decays, as recently also pointed out by Wanajo.Comment: 18 pages, 14 figures with 25 eps plots; referee comments included; accepted by Astronomy & Astrophysic

Aluminum abundances of multiple stellar generations in the globular cluster NGC 1851

We study the distribution of aluminum abundances among red giants in the peculiar globular cluster NGC 1851. Aluminum abundances were derived from the strong doublet Al I 8772-8773 A measured on intermediate resolution FLAMES spectra of 50 cluster stars acquired under the Gaia-ESO public survey. We coupled these abundances with previously derived abundance of O, Na, Mg to fully characterize the interplay of the NeNa and MgAl cycles of H-burning at high temperature in the early stellar generation in NGC 1851. The stars in our sample show well defined correlations between Al,Na and Si; Al is anticorrelated with O and Mg. The average value of the [Al/Fe] ratio steadily increases going from the first generation stars to the second generation populations with intermediate and extremely modified composition. We confirm on a larger database the results recently obtained by us (Carretta et al. 2011a): the pattern of abundances of proton-capture elements implies a moderate production of Al in NGC 1851. We find evidence of a statistically significant positive correlation between Al and Ba abundances in the more metal-rich component of red giants in NGC 1851.Comment: Astronomy and Astrophysics, in pres