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We briefly discuss the influence of mass loss on the internal evolutionary properties of massive stars. In particular we show that the C abundance left by the central He burning depends significantly on the adopted mass loss rate after the H rich mantle has been completely ejected. [ABSTRACT FROM AUTHOR]

We review the main properties of solar metallicity massive stars in the range 11–120 M⊙. The influence of the mass loss on the hydrostatic burning stages as well as the final explosion is discussed in some detail. We find that the minimum masses that enter the WNL, WNE and WC stages are 30 M⊙, 35 M⊙ and 40 M⊙ respectively; the limiting mass between stars exploding as SNII and SNIb/c is between 30 and 35 M⊙; the limiting mass between stars forming neutron stars and black holes after the explosion is between 25–30 M⊙. We also discuss the properties of the chemical yields integrated over a Salpeter IMF and we find that stars with M >= 35 M⊙ contribute for ∼ 60% to the production of C, N and for ∼ 40% to the production Sc and s-process elements up to Zr, while they do not produce any intermediate mass element because of the large remnant masses. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The formation of massive C-O white dwarfs in the range 1.1 to 1.4 M... opens interesting channels for novae, supernovae and accretion induced collapse events. We will review the present situation concerning the maximum mass attained by the C-O core inside an AGB star, both following standard and non-standard evolution, and taking into account the observational constraints. We find that to form C-O cores with masses greater than 1.1 M..., the 2[sup nd] dredge-up should be delayed and that the only obvious mechanism for that is rotation. [ABSTRACT FROM AUTHOR]

Based on multi-dimensional neutrino-radiation hydrodynamic simulations, we report several cutting-edge issues about the long-veiled explosion mechanism of core-collapse supernovae (CCSNe). In this contribution, we pay particular attention to whether three-dimensional (3D) hydrodynamics and/or general relativity (GR) would or would not help the onset of explosions. By performing 3D simulations with spectral neutrino transport, we show that it is more difficult to obtain an explosion in 3D than in 2D. In addition, our results from the first generation of full general relativistic 3D simulations including approximate neutrino transport indicate that GR can foster the onset of neutrino-driven explosions. Based on our recent parametric studies using a light-bulb scheme, we discuss impacts of nuclear energy deposition behind the supernova shock and stellar rotation on the neutrino-driven mechanism, both of which have yet to be included in the self-consistent 3D supernova models. Finally we give an outlook with a summary of the most urgent tasks to extract the information about the explosion mechanisms from multi-messenger CCSN observables. [ABSTRACT FROM AUTHOR]

In this contribution, I will review the most recent developments that concern the transition from a primordial, predominantly massive mode of star formation - the Population III stars - to a mode of star formation characterized by the first low mass and long lived stars - the Population II stars. Although the recent observation of a star in the Galactic Halo with a total metallicity of only Z = 4.5×10-5Z⊙ has demonstrated that stars with masses of approximately ∼ 0.8M⊙ can form even at these extremely low metallicities, there are many aspects of the Pop III/II transition that are still poorly understood and that certainly require further investigation. For this reason, I have organized my contribution into three fundamental questions which I try to address based on the current theoretical and observational indications. [ABSTRACT FROM AUTHOR]

The diversity in brightness and explosion energy of supernovae (SNe) that have recently been observed is remarkable. Determining the origin of unusual SNe, such as extremely faint or extremely luminous ones, or the very energetic explosions associated with GRBs (hypernovae), is very challenging. We present a core-collapse hypernova model for the extremely luminous Type Ic SN 2007bi as an alternative to the pair-instability model. We discuss how nucleosynthesis from a variety of SNe is connected to the abundance patterns of extremely metal-poor stars. Such connections may impose important constraints on the properties of the first stars, such as their evolution with mass accretion, or the asphericity of their explosions. [ABSTRACT FROM AUTHOR]

Recent observations have revealed remarkably large diversities of supernova properties. We present our challenge to explore the origin of unusual supernovae such as extremely faint and extremely luminous supernovae, and the extremely energetic explosions (hypernovae) associated with the Gamma-Ray Bursts. In particular, we present a core-collapse hypernova model for extremely luminous type Ic SN 2007bi as an alternative to the pair-instability model. We discuss how nucle-osynthetic properties resulted from unusual supernovae are connected with the unusual abundance patterns of extremely metal-poor stars. Such connections may provide important constraints on the properties of first stars. [ABSTRACT FROM AUTHOR]

Gamma-ray line observations with INTEGRAL measure decay of unstable isotopes which are ejected from sites of nucleosynthesis. Massive stars are believed to be producers of gamma-ray emitting isotopes 44Ti, 26Al, 60Fe. Measurements with the Ge spectrometer have shown that (1) inner core-collapse supernova ejecta from the Cas A supernova remnant appear to still travel at velocities beyond a few hundred km/sec; (2) 26Al synthesis occurs throughout the Galaxy corresponds to a supernova rate from core collapses of about one every 50 years; (3) 60Fe synthesis expected from massive stars is above the constraints from gamma-ray observations; 26Al synthesis in the Cygnus region appears on the high side of predictions from models; 26Al emission from the nearby Sco-Cen group of stars has been identified demonstrates massive-star activity close to the Sun. 26Al gamma-rays have been used to determine a longitude-velocity distribution of the presumably hot tenuous ISM which carries 26Al, which can be compared to molecular-gas star motions to help understand the Galaxy’s bar spiral-arm structure. Implications of the above nucleosynthesis constraints suggest that INTEGRAL’s observed positron annihilation gamma-rays need a contribution from another source located in the central regions of our Galaxy, and/or positrons may propagate kpc-distances away from their sources before annihilating. [ABSTRACT FROM AUTHOR]

We review the properties of supernovae (SNe) as a function of the progenitor’s mass M. (1) 8–10 M⊙ stars are super-AGB stars and resultant electron capture SNe may be Faint supernovae like Type IIn SN 2008S. (2) 10–13 M⊙ stars undergo Fe-core collapse to form neutron stars (NSs) and Faint supernovae. (3) 13 M⊙–MBN stars undergo Fe-core collapse to form NSs and normal core-collapse supernovae. (4) MBN–90 M⊙ stars undergo Fe-core collapse to form Black Holes. Resultant supernovae are bifurcate into Hypernovae and Faint supernovae. (5) 90–140 M⊙ stars produce Luminous SNe, like SNe 2007 bi and 2006 gy (6) 140–300 M⊙ stars become pair-instability supernovae which could be Luminous supernovae (SNe 2007 bi and 2006 gy). (7) Very massive stars with M>=300 M⊙ undergo core-collapse to form intermediate mass black holes. Some SNe could be more Luminous supernovae (like SN 2006 gy). [ABSTRACT FROM AUTHOR]

Isotopic ratios of C, N and O not in agreement with the canonical stellar evolutionary models are shown by spectra of evolved low mass stars and by presolar grains formed in their circumstellar origin. It has been shown in literature that partial mixing between the inner stellar regions and the base of the convective envelope can produce these chemical anomalies. We briefly describe how the evolution composition induced by such mixing episodes can be computed. [ABSTRACT FROM AUTHOR]

The primary scientific goal of the GRIPS mission is to study the early universe using γ-ray bursts. GRIPS, fully described in a paper by Greiner et al. (2008), is a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of γ-ray energies (200 keV—50 MeV) and of polarimetry (200–1000 keV). Scientific goals achievable by this mission are very broad, and include apart of the primary goal also direct measurements of supernova interiors through γ-ray lines from radioactive products of nucleosynthesis, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact objects, interstellar shocks, supernova remnants, superbubbles and clusters of galaxies. [ABSTRACT FROM AUTHOR]

Recent observational studies show considerable small dispersions for abundance ratios of C–Zn relative to iron in metal-poor halo stars. On the other hand, abundance ratios of neutron-capture elements show large scatters, suggesting incomplete mixing of the interstellar medium at the beginning of the Galaxy. We attempt to explain these contradictory observations, using an inhomogeneous chemical evolution model, which is shown to well reproduce large scatters in neutron-capture elements in our previous studies. In particular, taking into account of difference of observational trends among iron-peak elements, we discuss nucleosynthesis of the very first stars. [ABSTRACT FROM AUTHOR]

We review our recent progresses on the presupernova evolution of massive stars in the range 11–120 M⊙ of solar metallicity. Special attention will be devoted to the effect of the mass loss rate during the Wolf-Rayet stages in determining the structure and the physical properties of the star prior the supernova explosion. We also discuss the explosive yields and the initial mass-remnant mass relation in the framework of the kinetic bomb induced explosion and hence the contribution of these stars to the global chemical enrichment of the interstellar medium [ABSTRACT FROM AUTHOR]

During the AGB phase of low and intermediate mass stars heavy s-process elements are produced and dredged-up in the envelope. In the following Planetary Nebula phase part of the AGB envelope will form the nebula around the hot central star, carrying the s-process signature unchanged. Recently, heavy elements have been observed is many Planetary Nebulae, providing a new tool to analyze the s-process nucleosynthesis working in the AGB stars. In this paper we present s-process predictions for a large spread of stellar masses, metallicities and 13C-pocket efficiencies. Theoretical results are compared with the most recent observations in PNe, finding a general good agreement. [ABSTRACT FROM AUTHOR]

We present the first detailed abundance analysis of the metal-poor giant HK-II 17435-00532. This star was observed as part of the University of Texas Long-Term Chemical Abundances of Stars in the Halo (CASH) Project. A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R∼15000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = -2.2) star has an unusually high lithium abundance (log[variant_greek_epsilon](Li) = +2.1), mild carbon ([C/Fe] = +0.7) and sodium ([Na/Fe] = +0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = +0.8) and r-process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing mechanisms that connect the convective envelope with the outer regions of the H-burning shell. If so, HK-II 17435-00532 is the most metal-poor starin which this short-lived phase of Li enrichment has been observed. The r- and s-process material was not produced in this star but was either present in the gas from which HK-II 17435-00532 formed or was transferred to it from a more massive binary companion. Despite the current non-detection of radial velocity variations (over a time span of ∼180 days), it is possible that HK-II 17435-00532 is in a long-period binary system, similar to other stars with both r and s enrichment. [ABSTRACT FROM AUTHOR]

A recent survey of a large sample of massive Galactic asymptotic giant branch (AGB) stars shows that significant overabundances of rubidium (up to 100 times solar), but merely solar zirconium, are present in these stars. These observations can set constraints on our theoretical notion of the slow neutron capture process (the s process) in AGB stars, as well as on the rates of the neutron capture reactions involved in the production of Rb and Zr. We use the Monash nucleosynthesis code with a recently extended network to try to reproduce these observations. We present results for AGB stars of masses 5, 6, and 6.5 M⊙ and solar metallicity. We also show results for different available choices of the neutron capture rates, as well as for the possible inclusion of a partial mixing zone (PMZ), leading to the activation of the 13C neutron source. We find increasing Rb overabundances with increasing stellar mass, as observed, but we are far from matching the highest observed Rb enhancements. Inclusion of a PMZ increases the Rb abundance, but also produces an overabundance of Zr, contrary to what is observed. Only if the third dredge up efficiency remains as high as before the onset of the superwind phase during the final few pulses of a massive AGB star, can we match the highest [Rb/Fe] ratios observed by García-Hernández et al. [l]. A better understanding of the third dredge up efficiency with decreasing envelope mass for massive AGB stars is essential for further investigation of this issue. [ABSTRACT FROM AUTHOR]

We use the COMA code to calculate radiative opacity coefficients for low temperature gas, where the abundances of C and N are enhanced up to a factor of 2000 with respect to a scaled solar composition. These opacities include the contributions of the most relevant atomic and molecular species. Then, by means of the FRANEC stellar evolutionary code, we compute low mass metal-poor ([Fe/H]<-2) AGB models by interpolating over the new opacity tables. In this way, we properly take into account the recurrent increase of the C abundance in the envelope caused by the third dredge up. We discuss changes induced by the use of these opacities on the physical and chemical properties of the models, with particular emphasis to the synthesis of carbon, nitrogen and s-process elements. We also consider the effects of a possible N enhancement, which may be caused by cool bottom process or by the engulfment of protons from the top of the convective zone generated by the first fully-developed thermal pulse. For a given metallicity, we find that it exists a lower mass limit for which normal AGB evolution occurs. On the contrary, stars with initial mass smaller than this limit, experience a proton engulfment during the first thermal pulse, which leads to a peculiar s-process nucleosynthesis, a low 12C/13C and to a significant synthesis of primary N. Finally, we compare our results with the observed chemical pattern of CEMP stars. [ABSTRACT FROM AUTHOR]

Rapidly rotating massive stars are currently one of the most promising ways of explaining the high N/O abundances measured in normal metal poor stars. Here we show the predicted impact of fast rotators on the 12C/13C ratio at very low metallicities. We show that upon the inclusion of fast rotating massive stars, low 12C/13C ratios are expected in extremely metal poor halo stars. Observations of 12C/13C ratios in metal poor dwarf and turnoff stars would offer a crucial test to the idea that fast rotating stars were a common phenomenona in the primordial Universe. [ABSTRACT FROM AUTHOR]

We present the results of a survey of GRB afterglows and DLA absorption line systems, in which we compare the abundances of elements from the absorbers with surveys of stars, and previous work. Our results detect high metallicity systems within GRB afterglow absorption, consistent with galactic disks having high rates of star formation and enrichment of heavy elements. We also detect some of the lowest metallicity systems yet found in DLA absorption lines, with many values of [X/H]<-2.8, including one system which has metallicity of [C/H] and [O/H} of approximately -3.5. The low metallicity DLA systems are useful for constraining nucleosynthesis from the first Pop III stars, and we compare our results with one nucleosynthesis model. Finally we describe some preliminary results from a survey of OVI absorbers within quasar Lyman alpha forest spectra, and the evidence within these spectra for low-metallicity IGM. [ABSTRACT FROM AUTHOR]

We summarize the status of art of the secular evolution of low mass X-ray binaries (LMXBs) and take a close look at the orbital period distribution of LMXBs and of binary millisecond pulsars (MSP), in the hypothesis that this latter results from the LMXB evolution. The deficiency of systems below the period gap, which in cataclysmic binaries occurs between ∼ 2 and 3 hr, points to a very different secular evolution of LMXBs with respect to their counterparts containing a white dwarf compact object. The presence of several ultrashort period LMXBs (some of which are also X-ray millisecond pulsars), the important fraction of binary MSPs at periods between 0.1 and 1 day, the periods (26 and 32hr) of two “interacting” MSPs in Globular Clusters are other pieces of the puzzle in the period distribution. We consider the possible explanations for these peculiarities, and point out that Grindlay’s old proposal that all (most of) LMXBs in the field were originally born in globular clusters must be carefully reconsidered. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The discovery and analysis of metal-poor stars lead to insight into conditions when the Universe and Galaxy were young. We present the rationale for studying such objects (which become progressively rarer at lowest abundance), with a description of their systematic discovery, culminating in the recent analysis of two objects having [Fe/H] < -5.0. We discuss the Metallicity Distribution Function of metal-poor stars and the abundance patterns of several elements, from Li through to the heavy-neutron-capture elements. Relatively few (∼50) stars with [Fe/H] < -3.0 have been analyzed at high spectral resolution and high signal-to-noise. As one proceeds to lowest abundance one finds astounding overabundances of some or all of the CNO group and the lighter elements. This diversity among the most metal-poor stars has yet to be fully understood. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Observed large scatters in abundance ratios of neutron-capture elements relative to iron in metal-poor stars may suggest incomplete mixing of the interstellar medium at the beginning of the Galaxy. On the other hand, recent studies of metal-poor stars show considerable small dispersions for abundance ratios of C-Zn. We discuss whether such variations of scatters in abundance ratios can be explained by a consistent chemical evolution model. We also attempt to constrain the origins of r-process elements, comparing predictions by an inhomogeneous chemical evolution model with new observational results with Subaru HDS. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Cosmic gamma-ray lines convey isotopic information from sites of nucleosynthesis and from their surrounding interstellar medium. With recent space-borne gamma-ray spectrometers of high resolution (INTEGRAL, RHESSI), new results have been obtained for 44Ti from the Cas A core-collapse supernova, from long-lived radioactive 26Al and 60Fe, and from positron annihilation in our Galaxy: 44Ti ejection from Cas A may be on the low side of previously-reported values, and/or at velocities >7000 km s-1. 26Al sources apparently share the Galactic rotation in the inner Galaxy, and thus allow to estimate a total mass of 26Al in the Galaxy of 2.8 M⊙ from the measured flux. The 60Fe production in massive stars appears lower than predicted by standard models, as constrained by the recent, though marginal, 60Fe detections. Positron annihilation in the Galaxy shows a remarkable bulge component, which is difficult to understand in terms of nucleosynthetic production of the positrons. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Globular Clusters are among the most interesting objects in our own Galaxy. They have played a major role in our understanding of stellar evolution and dynamics of stellar systems in past decades. In the last few years, it is becoming clear that they are not so simple as originally thought. Their chemical evolution, although not as complex as that of a galaxy, is however not negligible. In globular clusters it seems possible to observe peculiar chemical abundances, due to the contribution to nucleosynthesis of groups of stars that are not usually well separated from the general enrichment of the interstellar medium in galaxies. This is stimulating new interesting investigations on stellar evolution, nucleosynthesis, and star formation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

A series of neutron-capture cross-section measurements on various krypton isotopes has been performed at the Geel Electron Linear Accelerator (GELINA). The total cross section of 84Kr and the capture cross section of 86Kr and 82Kr have been measured in the energy range from 0 up to 400 keV. Moreover, capture cross-section data for 80Kr and 83Kr have been obtained for a limited energy range, namely from 0 up to 5 keV, from a natural krypton sample. The main goal of the measurement campaign was to provide reliable nuclear data for s-process nucleosynthesis calculation. We performed a series of calculations for stars with mass from M = 1.5M⊙ to M = 3M⊙ and metallicity from solar down to 1/6 of solar with the aim to reproduce the krypton isotopic ratios found in silicon-carbide grains. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Gamma-ray lines from radioactive isotopes ejected into interstellar space by cosmic nucleosynthesis events can be observed with space telescopes. In the past decade, the Compton Observatory has provided a survey of the sky for the isotopes 56Co, ssNa, 44Ti, and 26Al, detecting supernova radioactivity and the diffuse glow of longlived radioactivity from massive stars in the Galaxy. Other experiments have demonstrated the additional capabilities of high-resolution spectroscopy with Ge detectors, identifying those isotopes, and measuring Doppler broadenings of the gamma-ray lines of SN1987A and 26Al. With ESA’s INTEGRAL satellite, since October 2002 a space-based Ge gamma-ray telescope is in operation. First year’s results include a detection of annihilation emission and 26Al emission from ther inner Galaxy, and 26Al emission from the Cygnus region. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The long term evolution of Carbon-Oxygen White Dwarfs accreting Hydrogen rich matter at a rate typical for a recurrent mild H-flashes regime is reviewed to determine the dependence of the various accretion regimes on both the accretion rate and the chemical composition of the accreted matter. On the basis of these results semi-analytical relations defining the steady state regime are provided for different values of the metallicity in the accreted matter. In addition it has been found that models accreting H-rich matter in a pulsating regime can undergo an explosive dynamical He-ignition in the He-buffer accreted as a by-product of the overlying H-burning shell. [ABSTRACT FROM AUTHOR]

In this paper we review the current ideas about the formation of our Galaxy. In particular, the main ingredients necessary to build chemical evolution models (star formation, initial mass function and stellar yields) are described and discussed. A critical discussion about the main observational constraints available is also presented. Finally, our model predictions concerning the evolution of the abundances of several chemical elements (H, D, He, C, N, O, Ne, Mg, Si, Ca and Fe) are compared with observations relative to the solar neighborhood and the whole disk. We show that from this comparison we can constrain the history of the formation and evolution of the Milky Way as well as the nucleosynthesis theories concerning the Big Bang and the stars. [ABSTRACT FROM AUTHOR]

Galactic abundances are neither constant in time nor do they evolve in a simple fashion, e.g. by an enrichment of heavy elements in constant relative proportions. Instead, their evolution in space and time reflects the history of star formation and the lifetimes of the diverse contributing stellar objects. Stellar winds from intermediate and massive stars, as well as supernovae of type Ia and type II/Ib/Ic are the main contributors to nucleosynthesis in galaxies. Despite many efforts, a full and self-consistent understanding of supernova explosion mechanisms is not existing, yet. However, they leave fingerprints, seen either in spectra, lightcurves, radioactivities/decay gamma-rays or in galactic evolution. The aim of the present paper is to highlight how model uncertainties can be constrained from abundance observations. [ABSTRACT FROM AUTHOR]

We present the first calculations to follow the evolution of all stable isotopes and their abundant radioactive progenitors in a finely zoned stellar model from the onset of central hydrogen burning through explosion as a Type II supernova. An extended adaptive nuclear reaction network is implemented that contains about 700 isotopes during hydrogen and helium burning and more than 2500 isotopes during the supernova explosion. The calculations were performed for 15, 20, and 25 M... Pop I stars using the most recently available set of experimental and theoretical nuclear data. We include revised opacity tables, take into account mass loss due to stellar winds, and implement revised weak interaction rates that significantly affect the properties of the presupernova core. An s-process is present, which, along with the usual nucleosynthesis from advanced burning stages and the explosion, produces nearly solar abundances for most nuclei up to A = 60 in the 25 M... star. Between A = 60 and A = 90 we find that the s-process leads to an over-production of key nuclei by a factor ∼ 2 - 3. Above A = 90 the s-process has makes little contribution, but we find the approximately solar production of many proton-rich isotopes above mass number A = 120 due to the γ-process. [ABSTRACT FROM AUTHOR]

Based on detailed models for the explosions, light curves and NLTE-spectra, evolutionary effects of Type Ia Supernovae (SNe Ia) with redshift have been studied to evaluate their size on cosmological time scales, how the effects can be recognized and how one may be able to correct for them. In the first part, we summarize the current status of scenarios for Type Ia Supernovae, including the explosion of a Chandrasekhar mass white dwarf (M[sub Ch]-WD), the merging scenario and the helium-triggered explosions of low-mass WDs. We show that delayed detonation models can account for the majority of observations of spectra and light curves. IR observations are a new and powerful tools to constrain explosion models and details of the flame propagation in the WD. A strong Mg II line at 1.05 µm shows that nuclear burning takes place at the outer, low density layers. This requires a transition from the deflagration to the detonation regime of the nuclear burning front, or a very fast deflagration close to the speed of sound. We put the models into context with the empirical brightness decline relation which is widely applied to use SNe Ia as yardsticks on cosmological distance scales. This relation can be well understood in the framework of M[sub Ch]-WDs as a consequence of the opacity effects in combination with the amount of [sup 56]Ni which determines the brightness. However, the amount of [sup 56]Ni actually produced depends on a combination of free parameters such as central density and the chemical composition of the WD, and the propagation of the burning front. We get a spread of ≈0.4[sup m] around the mean relation which is larger than currently favored by observations (≈0.12[sup m], [40]) which may hint of an underlying coupling of the progenitor, the accretion rates and the propagation of the burning front. In a second part, we investigate the possible evolutionary effects in SNe Ia both with respect to changes in the sample of SNe Ia and... [ABSTRACT FROM AUTHOR]

Core collapse supernovae (SN) are the final stages of stellar evolution in massive stars during which the central region collapses, forms a neutron star (NS), and the outer layers are ejected. Recent explosion scenarios assumed that the ejection is due to energy deposition by neutrinos into the envelope but detailed models do not produce powerful explosions. There is mounting evidence for an asphericity in the SN which is difficult to explain within this picture. This evidence includes the observed high polarization, pulsar kicks, high velocity iron-group and intermediate-mass elements material observed in remnants, etc. The discovery of highly magnetars revived the idea that the basic mechanism for the ejection of the envelope is related to a highly focused MHD-jet formed at the NS. Our 3-D hydro simulations of the jet propagation through the star confirmed that the mechanism can explain the asphericities. In this paper, detailed 3-D models for jet induced explosions of “classical” core collapse supernovae are presented. We demonstrate the influence of the jet properties and of the underlaying progenitor structure on the final density and chemical structure. Finally, we discuss the observational consequences, predictions and tests of this scenario. [ABSTRACT FROM AUTHOR]

We describe the evolution of dust within Population III supernova remnants (SNRs) and investigate the chemical compositions of the dust piled up in their dense shells. We show that the resulting abundance patterns of the major elements in the dense shells are in good agreement with that observed for a Galactic halo star, SDSS J102915+172927. This allows us to propose that SDSS J102915+172927 might be the second-generation star formed in the dust-enriched dense shell of a Population III SNR. We conclude that the segregation of dust from the metal-rich ejecta gas can be an important process in determining the abundance patterns of primitive low-mass stars. [ABSTRACT FROM AUTHOR]

WR 140 is one of the best known examples of a Wolf-Rayet stars. We executed the Suzaku X-ray observations at four different epochs around periastron passage in Jan. 2009 to understand the W-R stellar wind as well as the wind-wind collision shocks. The column density at periastron is about 30 times higher than that at pre-periastron, which can be explained as self-absorption by the Wolf-Rayet wind. The spectra are dominated by a line and continuum emission from a optically thin-thermal plasma. The strong Ne-K lines are evidence that the thermal plasma is shock-heated W-R wind materials by the interaction with the wind from the companion O star. We present the parameters of the wind, such as a mass-loss rate, which were calculated with the absorption and line emission in the spectra. [ABSTRACT FROM AUTHOR]

Barium stars (the classical Ba, and dwarf Ba) are formed in binary systems. When the primary star is on the Asymptotic Giant Branch, mass transfer by efficient stellar winds takes place, from the carbon and s-element rich primary onto the secondary star, which is observed on the main sequence or on the subgiant/redgiant phase. The envelope of the secondary star becomes thus enriched in barium and s-elements. Dilution of the s-elements within the envelope may occur due to mixing processes. We have made a comparison between theoretical predictions of AGB stellar models and high-resolution spectroscopic observations of a large sample of barium stars [1,2]. Good agreement between predicted and observed enhancements of s-elements was found for most stars, including Pb. Values of [Pb/Fe]>1 dex have indeed been observed for the first time in Barium stars by Allen & Barbuy [1], and can easily be explained by adopting a high efficiency of the main 13C neutron source in AGB models, making a direct link with the class of very-metal poor C-rich and s-process rich stars (CEMP-s). The physical mechanism, mass transfer of C-rich and s-process rich material from the primary companion while on the AGB in a binary system is the same. The much higher [Pb/Fe] values that can be achieved in CEMP-s stars is explained by the primary nature of the 13C neutron source and by the decreasing of Fe seeds with metallicity. [ABSTRACT FROM AUTHOR]

We have computed and analyzed the evolution of primordial stars of ZAMS masses between 5 and 10 M⊙, with and without overshooting, up to the early TP-(S) AGB. The initial mass limits for the formation of carbon-oxygen, oxygen-neon degenerate cores and core-collapse supernovae after the main central burning stages have been determined. The possible final fates of the considered stars have been explored in the frame of the existing uncertainties. [ABSTRACT FROM AUTHOR]