WorldWideScience

Sample records for r-process enriched star

  1. r-Process Elements in EMP stars: Indicators of Inhomogeneous Early Halo Enrichment

    Science.gov (United States)

    Andersen, Johannes; Nordström, Birgitta; Thidemann Hansen, Terese

    2015-08-01

    Extremely metal-poor (EMP) halo stars with [Fe/H] below ~ -3 are considered to be fossil records of conditions in the early halo. In the simplest picture where iron is a proxy for overall metallicity and indirectly for time, EMP stars formed before the oldest and most metal-poor Galactic globular clusters. High-resolution spectroscopy with 8m-class telescopes has shown the detailed abundance pattern of these stars to be surprisingly uniform (e.g. Bonifacio+ 2012) and essentially Solar, apart from the α-enhancement typical of SN II nucleosynthesis. A small fraction (~3%) of EMP stars, however, is strongly enhanced in the heaviest (r-process) neutron-capture elements, highlighting that the periodic system of elements was fully populated already this early.These striking departures from the general chemical homogeneity could be produced by local or distant sources. The former case is simple - mass transfer from a binary companion that evolved to produce a highly neutron-rich environment (one or more NS). Alternatively, the r-process elements were formed in a site at interstellar distance and preferentially seeded into the natal clouds of the present-day EMP-r stars. Our long-term, precise monitoring of the radial velocities of a sample of such stars (Hansen+ 2011) disproved the binary hypothesis, which would in fact also fail to explain the existence of r-process poor stars, such as HD 122653. We thus conclude that the chemical enrichment of the early halo was far more complex, patchy and likely anisotropic than assumed in current models of Galactic chemical evolution: The EMP-r stars are not just peculiarities to be ignored, but indicate that a new level of complexity must be invoked. That r-process elements have not (yet) been observed in high-redshift DLA systems is readily explained by their low abundance relative to the lighter species and the rarity of strong enrichment events.

  2. Enrichment history of r-process elements shaped by a merger of neutron star pairs

    CERN Document Server

    Tsujimoto, Takuji

    2014-01-01

    The origin of r-process elements remains unidentified and still puzzles us. The recent discovery of evidence for the ejection of r-process elements from a short-duration gamma-ray burst singled out neutron star mergers (NSMs) as their origin. In contrast, core-collapse supernovae are ruled out as the main origin of heavy r-process elements (A>110) by recent numerical simulations. However, the properties characterizing NSM events - their rarity and high yield of r-process elements per event - have been claimed to be incompatible with the observed stellar records on r-process elements in the Galaxy. We add to this picture with our results, which show that the observed constant [r-process/H] ratio in faint dwarf galaxies and one star unusually rich in r-process in the Sculptor galaxy agree well with this rarity of NSM events. Furthermore, we found that a large scatter in the abundance ratios of r-process elements to iron in the Galactic halo can be reproduced by a scheme that incorporates an assembly of various ...

  3. Galactic r-process enrichment by neutron star mergers in cosmological simulations of a Milky Way-mass galaxy

    CERN Document Server

    van de Voort, Freeke; Hopkins, Philip F; Keres, Dusan; Faucher-Giguere, Claude-Andre

    2014-01-01

    We quantify the stellar abundances of neutron-rich r-process nuclei in cosmological zoom-in simulations of a Milky Way-mass galaxy from the Feedback In Realistic Environments project. The galaxy is enriched with r-process elements by binary neutron star (NS) mergers and with iron and other metals by supernovae. These calculations include key hydrodynamic mixing processes not present in standard semi-analytic chemical evolution models, such as galactic winds and hydrodynamic flows associated with structure formation. We explore a range of models for the rate and delay time of NS mergers, intended to roughly bracket the wide range of models consistent with current observational constraints. We show that NS mergers can produce [r-process/Fe] abundance ratios and scatter that appear reasonably consistent with observational constraints. At low metallicity, [Fe/H]<-2, we predict there is a wide range of stellar r-process abundance ratios, with both supersolar and subsolar abundances. Low-metallicity stars or sta...

  4. Puzzling Origin of CEMP-r/s Stars: An Interpretation of Abundance and Enrichment of s- and r-Process Elements from Asymptotic Giant Branch Supernovae

    Indian Academy of Sciences (India)

    Jiang Zhang; Fang Zhao; Yanping Chen; Wenyuan Cui; Bo Zhang

    2013-12-01

    CEMP-r/s stars at low metallicity are known as double-enhanced stars that show enhancements of both r-process and s-process elements. The chemical abundances of these very metal-poor stars provide us a lot of information for putting new restraints on models of neutron-capture processes. In this article, we put forward an accreted scenario in which the double enrichment of r-process and s-process elements is caused by a former intermediate-mass Asymptotic Giant Branch (AGB) companion in a detached binary system. As the AGB superwind is only present at the ultimate phase of AGB stars, there is thus a lot of potential that the degenerate-core mass of an intermediate-mass AGB star reaches the Chandrasekhar limit before the AGB superwind. In these circumstances, both s-process elements produced in the AGB shell and r-process elements synthesized in the subsequent explosion would be sprayed contemporaneously and accreted by its companion. Despite similarity to physical conditions of a core-collapse supernova, a major focus in this scenario is the degenerate C–O core surrounded by an envelope of a former intermediate-mass AGB donor that may collapse and explode. Due to the existence of an outer envelope, r-process nucleosynthesis is expected to occur. Hypothesizing the material-rich europium (Eu) accreted by the secondary via the wind from the supernova to be in proportion to the geometric fraction of the companion with respect to the exploding donor star, we find that the estimated yield of Eu (as representative of r-process elements) per AGB supernova event is about 1 × 10-9⊙ ∼ 5 × 10-9⊙. Using the yields of Eu, the overabundance of r-process elements in CEMP-r/s stars can be accounted for. The calculated results show that the value of parameter , standing for efficiency of wind pollution from the AGB supernova, will reach about 104, which means that the enhanced factor is much larger than unity due to the impact of gravity of the donor and the result of the

  5. On the R-Process Enrichment of Dwarf Spheroidal Galaxies

    CERN Document Server

    Bramante, Joseph

    2016-01-01

    Recent observations of Reticulum II have uncovered an overabundance of r-process elements, compared to similar ultra-faint dwarf spheroidal galaxies (UFDs). Because the metallicity and star formation history of Reticulum II appear consistent with all known UFDs, the high r-process abundance of Reticulum II suggests enrichment through a single, rare event, such as a double neutron star (NS) merger. However, we note that this scenario is extremely unlikely, as binary stellar evolution models require significant supernova natal kicks to produce NS-NS or NS-black hole mergers, and these kicks would efficiently remove compact binary systems from the weak gravitational potentials of UFDs. We examine alternative mechanisms for the production of r-process elements in UFDs, including a novel mechanism wherein NSs in regions of high dark matter density implode after accumulating a black-hole-forming mass of dark matter. We find that r-process proto-material ejection by tidal forces, when a single neutron star implodes ...

  6. r-Process Enhanced Halo Stars

    CERN Document Server

    Cowan, J J; Lawler, J E; Den Hartog, E A

    2006-01-01

    Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy -- the progenitors of the halo stars -- responsible for neutron-capture synthesis of the heavy elements. The large star-to-star scatter observed in the abundances of neutron-capture element/iron ratios at low metallicities -- which diminishes with increasing metallicity or [Fe/H] -- suggests the formation of these heavy elements (presumably from certain types of supernovae) was rare in the early Galaxy. The stellar abundances also indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution. Finally, the detection of thorium and uranium in halo and globular cluster stars offers an independent age-dating technique that can put lower limits on the age of t...

  7. The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

    CERN Document Server

    Hansen, T T; Nordstrøm, B; Beers, T C; Yoon, J; Buchhave, L A

    2015-01-01

    The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later mass transfer of processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. ...

  8. R-process enrichment from a single event in an ancient dwarf galaxy.

    Science.gov (United States)

    Ji, Alexander P; Frebel, Anna; Chiti, Anirudh; Simon, Joshua D

    2016-03-31

    Elements heavier than zinc are synthesized through the rapid (r) and slow (s) neutron-capture processes. The main site of production of the r-process elements (such as europium) has been debated for nearly 60 years. Initial studies of trends in chemical abundances in old Milky Way halo stars suggested that these elements are produced continually, in sites such as core-collapse supernovae. But evidence from the local Universe favours the idea that r-process production occurs mainly during rare events, such as neutron star mergers. The appearance of a plateau of europium abundance in some dwarf spheroidal galaxies has been suggested as evidence for rare r-process enrichment in the early Universe, but only under the assumption that no gas accretes into those dwarf galaxies; gas accretion favours continual r-process enrichment in these systems. Furthermore, the universal r-process pattern has not been cleanly identified in dwarf spheroidals. The smaller, chemically simpler, and more ancient ultrafaint dwarf galaxies assembled shortly after the first stars formed, and are ideal systems with which to study nucleosynthesis events such as the r-process. Reticulum II is one such galaxy. The abundances of non-neutron-capture elements in this galaxy (and others like it) are similar to those in other old stars. Here, we report that seven of the nine brightest stars in Reticulum II, observed with high-resolution spectroscopy, show strong enhancements in heavy neutron-capture elements, with abundances that follow the universal r-process pattern beyond barium. The enhancement seen in this 'r-process galaxy' is two to three orders of magnitude higher than that detected in any other ultrafaint dwarf galaxy. This implies that a single, rare event produced the r-process material in Reticulum II. The r-process yield and event rate are incompatible with the source being ordinary core-collapse supernovae, but consistent with other possible sources, such as neutron star mergers.

  9. An r-process Enhanced Star in the Dwarf Galaxy Tucana III

    Science.gov (United States)

    Hansen, T. T.; Simon, J. D.; Marshall, J. L.; Li, T. S.; Carollo, D.; DePoy, D. L.; Nagasawa, D. Q.; Bernstein, R. A.; Drlica-Wagner, A.; Abdalla, F. B.; Allam, S.; Annis, J.; Bechtol, K.; Benoit-Lévy, A.; Brooks, D.; Buckley-Geer, E.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Cunha, C. E.; da Costa, L. N.; Desai, S.; Eifler, T. F.; Fausti Neto, A.; Flaugher, B.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gschwend, J.; Gutierrez, G.; James, D. J.; Krause, E.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Miquel, R.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Santiago, B.; Scarpine, V.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Walker, A. R.; DES Collaboration

    2017-03-01

    Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate Tucana III. Because it is particularly bright for a star in an ultra-faint Milky Way (MW) satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. This star, DES J235532.66‑593114.9 (DES J235532), shows a mild enhancement in neutron-capture elements associated with the r-process and can be classified as an r-I star. DES J235532 is the first r-I star to be discovered in an ultra-faint satellite, and Tuc III is the second extremely low-luminosity system found to contain r-process enriched material, after Reticulum II. Comparison of the abundance pattern of DES J235532 with r-I and r-II stars found in other dwarf galaxies and in the MW halo suggests a common astrophysical origin for the neutron-capture elements seen in all r-process enhanced stars. We explore both internal and external scenarios for the r-process enrichment of Tuc III and show that with abundance patterns for additional stars, it should be possible to distinguish between them. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

  10. Enrichment of r-process elements in dwarf spheroidal galaxies in chemo-dynamical evolution model

    CERN Document Server

    Hirai, Yutaka; Saitoh, Takayuki R; Fujii, Michiko S; Hidaka, Jun; Kajino, Toshitaka

    2015-01-01

    The rapid neutron-capture process (r-process) is a major process to synthesize elements heavier than iron, but the astrophysical site(s) of r-process is not identified yet. Neutron star mergers (NSMs) are suggested to be a major r-process site from nucleosynthesis studies. Previous chemical evolution studies however require unlikely short merger time of NSMs to reproduce the observed large star-to-star scatters in the abundance ratios of r-process elements relative to iron, [Eu/Fe], of extremely metal-poor stars in the Milky Way (MW) halo. This problem can be solved by considering chemical evolution in dwarf spheroidal galaxies (dSphs) which would be building blocks of the MW and have lower star formation efficiencies than the MW halo. We demonstrate that enrichment of r-process elements in dSphs by NSMs using an N-body/smoothed particle hydrodynamics code. Our high-resolution model reproduces the observed [Eu/Fe] by NSMs with a merger time of 100 Myr when the effect of metal mixing is taken into account. Thi...

  11. ENRICHMENT OF r-PROCESS ELEMENTS IN DWARF SPHEROIDAL GALAXIES IN CHEMO-DYNAMICAL EVOLUTION MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Hirai, Yutaka; Kajino, Toshitaka [Department of Astronomy, Graduate School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Ishimaru, Yuhri [Department of Material Science,International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585 (Japan); Saitoh, Takayuki R. [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); Fujii, Michiko S.; Hidaka, Jun, E-mail: yutaka.hirai@nao.ac.jp [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa Mitaka, Tokyo 181-8588 (Japan)

    2015-11-20

    The rapid neutron-capture process (r-process) is a major process for the synthesis of elements heavier than iron-peak elements, but the astrophysical site(s) of the r-process has not yet been identified. Neutron star mergers (NSMs) are suggested to be a major r-process site according to nucleosynthesis studies. Previous chemical evolution studies, however, required unlikely short merger times of NSMs to reproduce the observed large star-to-star scatters in the abundance ratios of r-process elements to iron: the [Eu/Fe] of extremely metal-poor stars in the Milky Way (MW) halo. This problem can be solved by considering chemical evolution in dwarf spheroidal galaxies (dSphs), which would be building blocks of the MW and have lower star formation efficiencies than the MW halo. We demonstrate the enrichment of r-process elements in dSphs by NSMs using an N-body/smoothed particle hydrodynamics code. Our high-resolution model reproduces the observed [Eu/Fe] due to NSMs with a merger time of 100 Myr when the effect of metal mixing is taken into account. This is because metallicity is not correlated with time ∼300 Myr from the start of the simulation due to the low star formation efficiency in dSphs. We also confirm that this model is consistent with observed properties of dSphs such as radial profiles and metallicity distribution. The merger time and the Galactic rate of NSMs are suggested to be ≲300 Myr and ∼10{sup −4} year{sup −1}, respectively, which are consistent with the values suggested by population synthesis and nucleosynthesis studies. This study supports the argument that NSMs are the major astrophysical site of the r-process.

  12. r-Process enrichment by magnetorotational core-collapse supernovae in the early dwarf spheroidal galaxies

    CERN Document Server

    Tsujimoto, Takuji

    2015-01-01

    One of the hottest open issues in chemical evolution of $r$-process elements is fast enrichment in the early Universe. Clear evidence for it is seen in stellar abundances of extremely metal-poor stars in the Galactic halo. On the other hand, small-mass galaxies are the ideal testbed to follow the evolutionary features of r-process enrichment, given the potential rarity of production events yielding heavy r-process elements. Their occurrences become countable and thus an enrichment path due to each event can be found in the stellar abundances. We examine the chemical feature of Eu abundance at an early stage of [Fe/H] $\\lesssim -2$ in the Draco and Sculptor dwarf spheroidal (dSph) galaxies. Accordingly we constrain the properties of the Eu production in the early dSphs. We find that the Draco dSph experienced a few Eu production events while Eu enrichment took place more continuously in the Sculptor dSph due to its larger stellar mass. The event rate of Eu production is estimated to be about one per $100-200$ ...

  13. Magnetic Protoneutron Star Winds and r-Process Nucleosynthesis

    CERN Document Server

    Thompson, T A

    2003-01-01

    Because of their neutron-richness and association with supernovae, post-explosion protoneutron star winds are thought to be a likely astrophysical site for rapid neutron capture nucleosynthesis (the r-process). However, the most recent models of spherical neutrino-driven protoneutron star winds do not produce robust r-process nucleosynthesis for `canonical' neutron stars with a gravitational mass of 1.4M_sun and coordinate radius of 10km. These models fail variously; either the flow entropy is too low, the electron fraction is too high, or the dynamical expansion timescale is too long. To date, no models have included the effects of an ordered dipole magnetic field. We show that a strong magnetic field can trap the outflow in the neutrino heating region, thus leading to much higher matter entropy. We estimate both the trapping timescale and the resulting entropy amplification. For sufficiently large energy deposition rates, the trapped matter emerges dynamically from the region of closed magnetic field lines ...

  14. Chemo-dynamical evolution model: Enrichment of r-process elements in the Local Group dwarf galaxies

    Science.gov (United States)

    Hirai, Yutaka; Ishimaru, Yuhri; Saitoh, Takayuki R.; Fujii, Michiko S.; Hidaka, Jun; Kajino, Toshitaka

    2016-08-01

    Neutron star mergers are one of the candidate astrophysical site(s) of r-process. Several chemical evolution studies however pointed out that the observed abundance of r-process is difficult to reproduce by neutron star mergers. In this study, we aim to clarify the enrichment of r-process elements in the Local Group dwarf galaxies. We carry out numerical simulations of galactic chemo-dynamical evolution using an N-body/smoothed particle hydrodynamics code, ASURA. We construct a chemo-dynamical evolution model for dwarf galaxies assuming that neutron star mergers are the major source of r-process elements. Our models reproduce the observed dispersion in [Eu/Fe] as a function of [Fe/H] with neutron star mergers with a merger time of 100 Myr. We find that star formation efficiency and metal mixing processes during the first <~ 300 Myr of galaxy evolution are important to reproduce the observations. This study supports that neutron star mergers are a major site of r-process.

  15. Contribution of Neutron Star Mergers to the r-Process Chemical Evolution in the Hierarchical Galaxy Formation

    Science.gov (United States)

    Komiya, Yutaka; Shigeyama, Toshikazu

    2016-10-01

    The main astronomical source of r-process elements has not yet been identified. One plausible site is neutron star mergers (NSMs), but from the perspective of the Galactic chemical evolution, it has been pointed out that NSMs cannot reproduce the observed r-process abundance distribution of metal-poor stars at [{Fe}/{{H}}]\\lt -3. Recently, Tsujimoto & Shigeyama pointed out that NSM ejecta can spread into a much larger volume than ejecta from a supernova. We re-examine the enrichment of r-process elements by NSMs considering this difference in propagation using the chemical evolution model under the hierarchical galaxy formation. The observed r-process enhanced stars around [{Fe}/{{H}}]∼ -3 are reproduced if the star formation efficiency is lower for low-mass galaxies under a realistic delay-time distribution for NSMs. We show that a significant fraction of NSM ejecta escape from its host proto-galaxy to pollute intergalactic matter and other proto-galaxies. The propagation of r-process elements over proto-galaxies changes the abundance distribution at [{Fe}/{{H}}]\\lt -3 and obtains distribution compatible with observations of the Milky Way halo stars. In particular, the pre-enrichment of intergalactic medium explains the observed scarcity of extremely metal-poor stars without Ba and abundance distribution of r-process elements at [{Fe}/{{H}}]≲ -3.5.

  16. The History of R-Process Enrichment in the Milky Way

    CERN Document Server

    Shen, Sijing; Ramirez-Ruiz, Enrico; Madau, Piero; Mayer, Lucio; Guedes, Javiera

    2014-01-01

    We investigate the production sites and the enrichment history of r-process elements in the Galaxy, as traced by the [Eu/Fe] ratio, using the high resolution, cosmological zoom-in simulation `Eris'. At z=0, Eris represents a close analog to the Milky Way, making it the ideal laboratory to understand the chemical evolution of our Galaxy. Eris formally traces the production of $\\alpha$-capture and Fe-peak elements due to Type Ia and Type II supernovae. We include in post-processing the production of r-process elements from either Type II supernovae or compact binary mergers. Unlike previous studies, we find that the nucleosynthetic products from compact binary mergers can be incorporated into stars of very low metallicity and at early times, even with a minimum delay time of 100 Myr. This conclusion is relatively insensitive to modest variations in the merger rate and delay time distribution. By implementing a first-order prescription for metal-mixing, we can further improve the agreement between our model and ...

  17. The Hamburg/ESO R-process Enhanced Star survey (HERES) VIII. The r+s star HE 1405 0822

    CERN Document Server

    Cui, W Y; Christlieb, N

    2013-01-01

    Aims.The aim of this study is a detailed abundance analysis of the newly discovered r-rich star HE 1405 0822, which has [Fe=H]=-2.40. This star shows enhancements of both r- and s-elements, [Ba/Fe]= +1.95 and [Eu/Fe]=1.54, for which reason it is called r+s star. Methods.Stellar parameters and element abundances were determined by analying high-quality VLT/UVES spectra. We used Fe I line excitation equilibria to derive the e?ective temperature. The surface gravity was calculated from the Fei/Feii and Ti I/Ti II equilibria. Results.We determined accurate abundances for 39 elements, including 19 neutron-capture elements. HE 1405-0822 is a red giant. Its strong enhancements of C, N, and s-elements are the consequence of enrichment by a former AGB companion with an initial mass of less than 3 M_Sun. The heavy n-capture element abundances (including Eu, Yb, and Hf) seen in HE 1405-0822 do not agree with the r-process pattern seen in strongly r-process-enhanced stars. We discuss possible enrichment scenarios for thi...

  18. Contribution of Neutron Star Mergers to the R-process Chemical Evolution in the Hierarchical Galaxy Formation

    CERN Document Server

    Komiya, Yutaka

    2016-01-01

    The main astronomical source of r-process elements has not yet been identified. One plausible site is neutron star mergers (NSMs), but from perspective of the Galactic chemical evolution, it has been pointed out that NSMs cannot reproduce the observed r-process abundance distribution of metal-poor stars at [Fe/H] $< -3$. Recently, Tsujimoto & Shigeyama (2014) pointed out that NSM ejecta can spread into much larger volume than ejecta from a supernova. We re-examine the enrichment of r-process elements by NSMs considering this difference in propagation using the chemical evolution model under the hierarchical galaxy formation. The observed r-process enhanced stars around [Fe/H] $\\sim -3$ are reproduced if the star formation efficiency is lower for low-mass galaxies under a realistic delay time distribution for NSMs. We show that a significant fraction of NSM ejecta escape from its host proto-galaxy to pollute intergalactic matter and other proto-galaxies. The propagation of r-process elements over proto-...

  19. Possible discovery of the r-process characteristics in the abundances of metal-rich barium stars

    CERN Document Server

    Cui, W Y; Shi, J R; Zhao, G; Wang, W J; Niu, P

    2014-01-01

    We study the abundance distributions of a sample of metal-rich barium stars provided by Pereira et al. (2011) to investigate the s- and r-process nucleosynthesis in the metal-rich environment. We compared the theoretical results predicted by a parametric model with the observed abundances of the metal-rich barium stars. We found that six barium stars have a significant r-process characteristic, and we divided the barium stars into two groups: the r-rich barium stars ($C_r>5.0$, [La/Nd]\\,$<0$) and normal barium stars. The behavior of the r-rich barium stars seems more like that of the metal-poor r-rich and CEMP-r/s stars. We suggest that the most possible formation mechanism for these stars is the s-process pollution, although their abundance patterns can be fitted very well when the pre-enrichment hypothesis is included. The fact that we can not explain them well using the s-process nucleosynthesis alone may be due to our incomplete knowledge on the production of Nd, Eu, and other relevant elements by the ...

  20. R-Process Nucleosynthesis in Dynamically Ejected Matter of Neutron Star Mergers

    CERN Document Server

    Goriely, Stephane; Janka, H -Thomas

    2011-01-01

    Although the rapid neutron-capture process, or r-process, is fundamentally important for explaining the origin of approximately half of the stable nuclei with A > 60, the astrophysical site of this process has not been identified yet. Here we study r-process nucleosynthesis in material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars (NSs) and within milliseconds afterwards. For the first time we make use of relativistic hydrodynamical simulations of such events, defining consistently the conditions that determine the nucleosynthesis, i.e., neutron enrichment, entropy, early density evolution and thus expansion timescale, and ejecta mass. We find that 10^{-3}-10^{-2} solar masses are ejected, which is enough for mergers to be the main source of heavy (A > 140) galactic r-nuclei for merger rates of some 10^{-5} per year. While asymmetric mergers eject 2-3 times more mass than symmetric ones, the exact amount depends weakly on whether the NSs have radii of ~15 ...

  1. The r-Process in Metal Poor Stars and Black Hole Formation

    Energy Technology Data Exchange (ETDEWEB)

    Boyd, R N; Famiano, M A; Meyer, B S; Motizuki, Y; Kajino, T; Roederer, I U

    2011-11-30

    Nucleosynthesis of heavy nuclei in metal-poor stars is generally ascribed to the r-process, as the abundance pattern in many such stars agrees with the inferred Solar r-process abundances. Nonetheless, a significant number of these stars do not share this r-process template. they suggest that many such stars have begun an r-process, but it was prevented from running to completion in more massive stars by collapse to black holes, creating a 'truncated r-process,' or 'tr-process'. The observed fraction of tr-process stars is found to be consistent with expectations from the initial mass function (IMF), and they suggest that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare earths. They test the tr-process hypothesis with calculations that are terminated before all r-process trajectories have been ejected. These produce qualitative agreement with observation when both black hole collapse and observational realities are taken into account.

  2. Complete element abundances of nine stars in the r-process galaxy Reticulum II

    CERN Document Server

    Ji, Alexander P; Simon, Joshua D; Chiti, Anirudh

    2016-01-01

    We present chemical abundances derived from high-resolution Magellan/MIKE spectra of the nine brightest known red giant members of the ultra-faint dwarf galaxy Reticulum II. These stars span the full metallicity range of Ret II (-3.5 < [Fe/H] < -2). Seven of the nine stars have extremely high levels of r-process material ([Eu/Fe]~1.7), in contrast to the extremely low neutron-capture element abundances found in every other ultra-faint dwarf galaxy studied to date. The other two stars are the most metal-poor stars in the system ([Fe/H] < -3), and they have neutron-capture element abundance limits similar to those in other ultra-faint dwarf galaxies. We confirm that the relative abundances of Sr, Y, and Zr in these stars are similar to those found in r-process halo stars but ~0.5 dex lower than the solar r-process pattern. If the universal r-process pattern extends to those elements, the stars in Ret II display the least contaminated known r-process pattern. The abundances of lighter elements up to the...

  3. The Hamburg/ESO R-process Enhanced Star survey (HERES) X. HE 2252-4225, one more r-process enhanced and actinide-boost halo star

    CERN Document Server

    Mashonkina, L; Eriksson, K

    2014-01-01

    We report on a detailed abundance analysis of the r-process enhanced giant star, HE 2252-4225 ([Fe/H] = -2.63, [r/Fe] = 0.80). Determination of stellar parameters and element abundances was based on analysis of high-quality VLT/UVES spectra. The surface gravity was calculated from the NLTE ionisation balance between Fe I and Fe II. Accurate abundances were determined for a total of 38 elements, including 22 neutron-capture elements beyond Sr and up to Th. This object is deficient in carbon, as expected for a giant star with Teff < 4800 K. The stellar Na-Zn abundances are well fitted by the yields of a single supernova of 14.4 Msun. For the neutron-capture elements in the Sr-Ru, Ba-Yb, and Os-Ir regions, the abundance pattern of HE 2252-4225 is in excellent agreement with the average abundance pattern of the strongly r-process enhanced stars CS 22892-052, CS 31082-001, HE 1219-0312, and HE 1523-091. This suggests a common origin of the first, second, and third r-process peak elements in HE 2252-4225 in the ...

  4. The Hamburg/ESO R-process Enhanced Star survey (HERES) XI. The highly $r$-process-enhanced star CS 29497-004

    CERN Document Server

    Hill, V; Beers, T C; Barklem, P S; Kratz, K -L; Nordström, B; Pfeiffer, B; Farouqi, K

    2016-01-01

    We report an abundance analysis for the highly r-process-enhanced (r-II) star CS 29497-004, a very metal-poor giant with Teff = 5013K and [Fe/H]=-2.85, whose nature was initially discovered in the course of the HERES project. Our analysis is based on high signal-to-noise, high-resolution (R~75000) VLT/UVES spectra and MARCS model atmospheres under the assumption of local thermodynamic equilibrium, and obtains abundance measurements for a total of 46 elements, 31 of which are neutron-capture elements. As is the case for the other 25 r-II stars currently known, the heavy-element abundance pattern of CS 29497-004 well-matches a scaled Solar System second peak r-process-element abundance pattern. We confirm our previous detection of Th, and demonstrate that this star does not exhibit an "actinide boost". Uranium is also detected (log e(U) =-2.20+/-0.30), albeit with a large measurement error that hampers its use as a precision cosmo-chronometer. Combining the various elemental chronometer pairs that are available...

  5. Opacities and Spectra of the r-process Ejecta from Neutron Star Mergers

    CERN Document Server

    Kasen, Daniel; Barnes, Jennifer

    2013-01-01

    Material ejected during (or immediately following) the merger of two neutron stars may assemble into heavy elements by the r-process. The subsequent radioactive decay of the nuclei can power electromagnetic emission similar to, but significantly dimmer than, an ordinary supernova. Identifying such events is an important goal of future transient surveys, offering new perspectives on the origin of r-process nuclei and the astrophysical sources of gravitational waves. Predictions of the transient light curves and spectra, however, have suffered from the uncertain optical properties of heavy ions. Here we consider the opacity of expanding r-process material and argue that it is dominated by line transitions from those ions with the most complex valence electron structure, namely the lanthanides. For a few representative ions, we run atomic structure models to calculate radiative data for tens of millions of lines. We find that the resulting r-process opacities are orders of magnitude larger than that of ordinary ...

  6. Searching for New Highly r-Process-Enhanced Stars in the Halo of the Milky Way

    Science.gov (United States)

    Beers, Timothy C.; Placco, Vinicius; Holmbeck, Erika M.; Hansen, Terese T.; Simon, Joshua D.; Thompson, Ian; Frebel, Anna

    2017-01-01

    Great progress has been made in recent years concerning understanding and constraining the nature of the astrophysical r-process, and on obtaining evidence for the likely astrophysical site(s) of its production. One of the keys to this progress was the identification, over 20 years ago, of a rare class of VMP stars ([Fe/H] Science Foundation.

  7. r-Process Elements as Tracers of Enrichment Processes in the Early Halo

    Science.gov (United States)

    Andersen, Johannes; Nordström, Birgitta; Hansen, Terese T.

    2016-08-01

    Significant minorities of extremely metal-poor (EMP) halo stars exhibit dramatic excesses of neutron capture elements. The standard scenario for their origin is mass transfer and dilution in binary systems, but requires them to be binaries. If not, these excesses must have been implanted in them from birth by processes that are not included in current models of SN II chemical enrichment. The binary population of such EMP subgroups is a test of this scenario.

  8. Complete Element Abundances of Nine Stars in the r-process Galaxy Reticulum II

    Science.gov (United States)

    Ji, Alexander P.; Frebel, Anna; Simon, Joshua D.; Chiti, Anirudh

    2016-10-01

    We present chemical abundances derived from high-resolution Magellan/Magellan Inamori Kyocera Echelle spectra of the nine brightest known red giant members of the ultra-faint dwarf galaxy Reticulum II (Ret II). These stars span the full metallicity range of Ret II (‑3.5 date. The other two stars are the most metal-poor stars in the system ([Fe/H] up to the iron peak are otherwise similar to abundances of stars in the halo and in other ultra-faint dwarf galaxies. However, the scatter in abundance ratios is large enough to suggest that inhomogeneous metal mixing is required to explain the chemical evolution of this galaxy. The presence of low amounts of neutron-capture elements in other ultra-faint dwarf galaxies may imply the existence of additional r-process sites besides the source of r-process elements in Ret II. Galaxies like Ret II may be the original birth sites of r-process enhanced stars now found in the halo. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  9. The r-process nucleosynthesis during the decompression of neutron star crust material

    Energy Technology Data Exchange (ETDEWEB)

    Goriely, S. [Institut d' Astronomie et d' Astrophysique, CP-226, Université Libre de Bruxelles, 1050 Brussels (Belgium); Bauswein, A. [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece and Max-Planck-Institut für Astrophysik, Postfach 1317, 85741 Garching (Germany); Janka, H.-T. [Max-Planck-Institut für Astrophysik, Postfach 1317, 85741 Garching (Germany); Sida, J.-L.; Lemaître, J.-F.; Panebianco, S. [C.E.A. Saclay, Irfu/Service de Physique Nucléaire, 91191 Gif-sur-Yvette (France); Dubray, N.; Hilaire, S. [CEA, DAM, DIF, F-91297 Arpajon (France)

    2014-05-02

    About half of the nuclei heavier than iron observed in nature are produced by the so-called rapid neutron capture process, or r-process, of nucleosynthesis. The identification of the astrophysics site and the specific conditions in which the r-process takes place remains, however, one of the still-unsolved mysteries of modern astrophysics. Another underlying difficulty associated with our understanding of the r-process concerns the uncertainties in the predictions of nuclear properties for the few thousands exotic neutron-rich nuclei involved, for which essentially no experimental data exist. The present paper emphasizes some important future challenges faced by nuclear physics in this problem, particularly in the determination of the nuclear structure properties of exotic neutron-rich nuclei as well as their radiative neutron capture rates and their fission probabilities. These quantities are particularly relevant to determine the composition of the matter resulting from the r-process. Both the astrophysics and the nuclear physics difficulties are critically reviewed with special attention paid to the r-process taking place during the decompression of neutron star matter following the merging of two neutron stars.

  10. s- and r-process elements in two very metal-poor stars

    CERN Document Server

    Ryan, S G; Blake, L A J; Norris, J E; Beers, T C; Gallino, R; Busso, M; Ando, H; Ryan, Sean G.; Aoki, Wako; Blake, Lisa A. J.; Norris, John E.; Beers, Timothy C.; Gallino, Roberto; Busso, Maurizio; Ando, Hiroyasu

    2000-01-01

    New measurements of neutron-capture elements are presented for two very metal-poor stars ([Fe/H] ~ -3). One (LP 625-44) has an s-process signature believed to be due to mass transfer from a now-extinct metal-poor AGB companion, and the second (CS 22897-008) is one of a number of very metal-poor stars having high [Sr/Ba] ratios which is not expected from the r-process. In the s-process star, many elements including lead have been detected, providing strong constraints on the 13C pocket in the now-extinct AGB star. In the Sr-rich star, Zn, Y, and Zr are also seen to be overabundant, and several possible nucleosynthesis mechanisms are discussed.

  11. Advanced LIGO Constraints on Neutron Star Mergers and r-process Sites

    Science.gov (United States)

    Côté, Benoit; Belczynski, Krzysztof; Fryer, Chris L.; Ritter, Christian; Paul, Adam; Wehmeyer, Benjamin; O’Shea, Brian W.

    2017-02-01

    The role of compact binary mergers as the main production site of r-process elements is investigated by combining stellar abundances of Eu observed in the Milky Way, galactic chemical evolution (GCE) simulations, and binary population synthesis models, and gravitational wave measurements from Advanced LIGO. We compiled and reviewed seven recent GCE studies to extract the frequency of neutron star–neutron star (NS–NS) mergers that is needed in order to reproduce the observed [Eu/Fe] versus [Fe/H] relationship. We used our simple chemical evolution code to explore the impact of different analytical delay-time distribution functions for NS–NS mergers. We then combined our metallicity-dependent population synthesis models with our chemical evolution code to bring their predictions, for both NS–NS mergers and black hole–neutron star mergers, into a GCE context. Finally, we convolved our results with the cosmic star formation history to provide a direct comparison with current and upcoming Advanced LIGO measurements. When assuming that NS–NS mergers are the exclusive r-process sites, and that the ejected r-process mass per merger event is 0.01 M {}ȯ , the number of NS–NS mergers needed in GCE studies is about 10 times larger than what is predicted by standard population synthesis models. These two distinct fields can only be consistent with each other when assuming optimistic rates, massive NS–NS merger ejecta, and low Fe yields for massive stars. For now, population synthesis models and GCE simulations are in agreement with the current upper limit (O1) established by Advanced LIGO during their first run of observations. Upcoming measurements will provide an important constraint on the actual local NS–NS merger rate, will provide valuable insights on the plausibility of the GCE requirement, and will help to define whether or not compact binary mergers can be the dominant source of r-process elements in the universe.

  12. The fundamental role of fission during r-process nucleosynthesis in neutron star mergers

    Energy Technology Data Exchange (ETDEWEB)

    Goriely, S. [Universite Libre de Bruxelles, Institut d' Astronomie et d' Astrophysique, CP-226, Brussels (Belgium)

    2015-02-01

    The rapid neutron-capture process, or r-process, is known to be of fundamental importance for explaining the origin of approximately half of the A > 60 stable nuclei observed in nature. Despite important efforts, the astrophysical site of the r-process remains unidentified. Here we study r-process nucleosynthesis in a material that is dynamically ejected by tidal and pressure forces during the merging of binary neutron stars. r-process nucleosynthesis during the decompression is known to be largely insensitive to the detailed astrophysical conditions because of efficient fission recycling, producing a composition that closely follows the solar r-abundance distribution for nuclei with mass numbers A > 140. Due to the important role played by fission in such a scenario, the impact of fission is carefully analyzed. We consider different state-of-the-art global models for the determination of the fission paths, nuclear level densities at the fission saddle points and fission fragment distributions. Based on such models, the sensitivity of the calculated r-process abundance distribution is studied. The fission path is found to strongly affect the region of heavy nuclei responsible for the fission recycling, while the fission fragment distribution of nuclei along the A ≅ 278 isobars defines the abundance pattern of nuclei produced in the 110 r-process peak around A ≅ 195. (orig.)

  13. On the robustness of the r-process in neutron-star mergers

    CERN Document Server

    Mendoza-Temis, Joel de Jesús; Langanke, K; Bauswein, A; Janka, H -T

    2014-01-01

    We have performed r-process simulations for a set of trajectories describing matter ejected in neutron star mergers. Our calculations consider an extended nuclear network, including spontaneous, $\\beta$- and neutron-induced fission and adopting fission yield distributions from the ABLA code. In particular we have studied the sensitivity of the r-process abundances on the nuclear mass models by using different models. We find that the general features of the observed r-process abundance distribution (the second and third peaks, the rare-earth peak and the lead peak) are reproduced by our simulations, independently of the merger trajectory, and for all mass models. We find distinct differences in the predictions of the mass models at and just above the third peak, which can be traced back to different predictions of neutron separation energies for r-process nuclei around neutron number N=130. In all simulations, we find that the second peak around $A\\sim 130$ is produced by the fission yields of the material th...

  14. R-process Nucleosynthesis during the Magnetohydrodynamics Explosions of a Massive Star

    CERN Document Server

    Saruwatari, Motoaki; Kotake, Kei; Yamada, Shoichi

    2012-01-01

    We investigate the possibility of the r-process during the magnetohydrohynamical explosion of supernova in a massive star of 13 solar mass with the effects of neutrinos induced. We adopt five kinds of initial models which include properties of rotation and the toroidal component of the magnetic field . The simulations which succeed the explosions are limitted to a concentrated magnetic field and strong differential rotation. Low $Y_{e}$ ejecta produce heavy elements and the third peak can be reprocuced. However, the second peak is low because $Y_{e}$ distribution as a function of radius is steep and ejecta corresponding to middle $Y_{e}$ is very few.

  15. Transport and mixing of r-process elements in neutron star binary merger blast waves

    CERN Document Server

    Montes, Gabriela; Naiman, Jill; Shen, Sijing; Lee, William H

    2016-01-01

    The r-process nuclei are robustly synthesized in the material ejected during a neutron star binary merger (NSBM), as tidal torques transport angular momentum and energy through the outer Lagrange point in the form of a vast tidal tail. If NSBM are indeed solely responsible for the solar system r- process abundances, a galaxy like our own would require to host a few NSBM per million years, with each event ejecting, on average, about 5x10^{-2} M_sun of r-process material. Because the ejecta velocities in the tidal tail are significantly larger than in ordinary supernovae, NSBM deposit a comparable amount of energy into the interstellar medium (ISM). In contrast to extensive efforts studying spherical models for supernova remnant evolution, calculations quantifying the impact of NSBM ejecta in the ISM have been lacking. To better understand their evolution in a cosmological context, we perform a suite of three-dimensional hydrodynamic simulations with optically-thin radiative cooling of isolated NSBM ejecta expa...

  16. The Hamburg/ESO R-process Enhanced Star survey (HERES)VII. Thorium abundances in metal-poor stars

    CERN Document Server

    Ren, Jin; Zhao, Gang

    2011-01-01

    We report thorium abundances for 77 metal-poor stars in the metallicity range of -3.5<[Fe/H]}<-1.0, based on "snapshot" spectra obtained with VLT-UT2/UVES during the HERES Survey. We were able to determine the thorium abundances with better than 1-sigma confidence for 17 stars, while for 60 stars we derived upper limits. For five stars common with previous studies, our results were in good agreement with the literature results. The thorium abundances span a wide range of about 4.0 dex, and scatter exists in the distribution of log(Th/Eu) ratios for lower metallicity stars, supporting previous studies suggesting the r-process is not universal. We derived ages from the log(Th/Eu) ratios for 12 stars, resulting in large scattered ages, and two stars with significant enhancement of Th relative to Eu are found, indicating the "actinide boost" does not seem to be a rare phenomenon and thus highlighting the risk in using log(Th/Eu) to derive stellar ages.

  17. Advanced LIGO Constraints on Neutron Star Mergers and R-Process Sites

    CERN Document Server

    Côté, Benoit; Fryer, Chris L; Ritter, Christian; Paul, Adam; Wehmeyer, Benjamin; O'Shea, Brian W

    2016-01-01

    The role of compact binary mergers as the main production site of r-process elements is investigated by combining stellar abundances of Eu observed in the Milky Way, galactic chemical evolution (GCE) simulations, binary population synthesis models, and Advanced LIGO gravitational wave measurements. We compiled and reviewed seven recent GCE studies to extract the frequency of neutron star - neutron star (NS-NS) mergers that is needed in order to reproduce the observed [Eu/Fe] vs [Fe/H] relationship. We used our simple chemical evolution code to explore the impact of different analytical delay-time distribution (DTD) functions for NS-NS mergers. We then combined our metallicity-dependent population synthesis models with our chemical evolution code to bring their predictions, for both NS-NS mergers and black hole - neutron star mergers, into a GCE context. Finally, we convolved our results with the cosmic star formation history to provide a direct comparison with current and upcoming Advanced LIGO measurements. ...

  18. Abundance of Weak r-Process Elements of Metal-Poor Stars ˜Universality or Diversity?˜

    Science.gov (United States)

    Aoki, Misa; Ishimaru, Yuhri; Aoki, Wako; Wanajo, Shinya

    The origin of the rapid neutron-capture process is a major question in astrophysics. The key to this question is the chemical abundance patterns of very metal-poor stars (VMP), which are believed to reflect the nucleosynthesis yields of single event. Recent observations of VMP indicate that there are at least two components to r-process; "main r-process" responsible for relatively heavy neutron-capture elements and "weak r-process" [1] responsible for relatively light neutron-capture elements. The VMP with heavier neutron-capture elements are known to have similar pattern to that of solar r-process, suggesting universality in main r-process nucleosynthesis [2]. A question is whether weak r-process also show such universality. We present the abundance analysis of neutron-capture elements in five stars (HD107752, HD110184, HD85773, HD23798, BD+6 648) in the Galactic halo observed by the Subaru Telescope High Dispersion Spectrograph. Their light neutron-capture elements (e.g., Sr, Y) show overabundance, inferring contribution of weak r-process, while heavy neutron-capture elements (e.g., Ba, Eu) are deficient. The overabundance of these stars, however, is not as significant as that found in HD122563 [3] known as the weak r-process star. These results suggests that there is diversity in the nucleosynthesis of the weak r-process. In addition, we compare our results with the latest nucleosynthesis models of electron capture supernova and core collapse supernova [4, 5].

  19. Production of the entire range of r-process nuclides by black hole accretion disc outflows from neutron star mergers

    Science.gov (United States)

    Wu, Meng-Ru; Fernández, Rodrigo; Martínez-Pinedo, Gabriel; Metzger, Brian D.

    2016-12-01

    We consider r-process nucleosynthesis in outflows from black hole accretion discs formed in double neutron star and neutron star-black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important - and in some cases dominant - contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disc outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second r-process peak (mass number A ˜ 130), independent of model parameters, with significant production of A dynamical ejecta with high electron fraction may not be required to explain the observed abundances of r-process elements in metal poor stars. Disc outflows reach the third peak (A ˜ 195) in most of our simulations, although the amounts produced depend sensitively on the disc viscosity, initial mass or entropy of the torus, and nuclear physics inputs. Some of our models produce an abundance spike at A = 132 that is absent in the Solar system r-process distribution. The spike arises from convection in the disc and depends on the treatment of nuclear heating in the simulations. We conclude that disc outflows provide an important - and perhaps dominant - contribution to the r-process yields of compact binary mergers, and hence must be included when assessing the contribution of these systems to the inventory of r-process elements in the Galaxy.

  20. Production of all $r$-process nuclides by black hole accretion disk outflows from neutron star mergers

    CERN Document Server

    Wu, Meng-Ru; Martínez-Pinedo, Gabriel; Metzger, Brian D

    2016-01-01

    We consider $r$-process nucleosynthesis in outflows from black hole accretion disks formed in double neutron star and neutron star - black hole mergers. These outflows, powered by angular momentum transport processes and nuclear recombination, represent an important -- and in some cases dominant -- contribution to the total mass ejected by the merger. Here we calculate the nucleosynthesis yields from disk outflows using thermodynamic trajectories from hydrodynamic simulations, coupled to a nuclear reaction network. We find that outflows produce a robust abundance pattern around the second $r$-process peak (mass number $A \\sim 130$), independent of model parameters, with significant production of $A < 130$ nuclei. This implies that dynamical ejecta with high electron fraction may not be required to explain the observed abundances of $r$-process elements in metal poor stars. Disk outflows reach the third peak ($ A \\sim 195$) in most of our simulations, although the amounts produced depend sensitively on the ...

  1. New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars

    CERN Document Server

    Sneden, Christopher; Cowan, John J; Ivans, Inese I; Hartog, Elizabeth A Den

    2009-01-01

    We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally-consistent Ba, rare-earth, and Hf (56<= Z <= 72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.

  2. The influence of neutrinos on r-process nucleosynthesis in the ejecta of black hole-neutron star mergers

    Science.gov (United States)

    Roberts, Luke F.; Lippuner, Jonas; Duez, Matthew D.; Faber, Joshua A.; Foucart, Francois; Lombardi, James C., Jr.; Ning, Sandra; Ott, Christian D.; Ponce, Marcelo

    2017-02-01

    During the merger of a black hole and a neutron star, baryonic mass can become unbound from the system. Because the ejected material is extremely neutron-rich, the r-process rapidly synthesizes heavy nuclides as the material expands and cools. In this work, we map general relativistic models of black hole-neutron star mergers into a Newtonian smoothed particle hydrodynamics (SPH) code and follow the evolution of the thermodynamics and morphology of the ejecta until the outflows become homologous. We investigate how the subsequent evolution depends on our mapping procedure and find that the results are robust. Using thermodynamic histories from the SPH particles, we then calculate the expected nucleosynthesis in these outflows while varying the level of neutrino irradiation coming from the post-merger accretion disc. We find that the ejected material robustly produces r-process nucleosynthesis even for unrealistically high neutrino luminosities, due to the rapid velocities of the outflow. None the less, we find that neutrinos can have an impact on the detailed pattern of the r-process nucleosynthesis. Electron neutrinos are captured by neutrons to produce protons while neutron capture is occurring. The produced protons rapidly form low-mass seed nuclei for the r-process. These low-mass seeds are eventually incorporated into the first r-process peak at A ˜ 78. We consider the mechanism of this process in detail and discuss if it can impact galactic chemical evolution of the first peak r-process nuclei.

  3. The Role of Fission in Neutron Star Mergers and the Position of the Third r-Process Peak

    CERN Document Server

    Eichler, Marius; Kelic, Alexandra; Korobkin, Oleg; Langanke, Karlheinz; Martinez-Pinedo, Gabriel; Panov, Igor V; Rauscher, Thomas; Rosswog, Stephan; Winteler, Christian; Zinner, Nikolaj T; Thielemann, Friedrich-Karl

    2014-01-01

    The comparison between observational abundance features and those obtained from nucleosynthesis predictions of stellar evolution and/or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. Here we test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model (FRDM), the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral (ETFSI-Q), and the Hartee-Fock-Bogoliubov (HFB) mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. Furthermore, we explore the origin of a shift in the third r-process peak position in comparison with the solar r-process abundances which have been noticed in a number of merger ...

  4. COMPACT STELLAR BINARY ASSEMBLY IN THE FIRST NUCLEAR STAR CLUSTERS AND r-PROCESS SYNTHESIS IN THE EARLY UNIVERSE

    Energy Technology Data Exchange (ETDEWEB)

    Ramirez-Ruiz, Enrico; MacLeod, Morgan [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Trenti, Michele [Kavli Institute for Cosmology and Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Roberts, Luke F. [TAPIR, California Institute of Technology, Pasadena, California 91125 (United States); Lee, William H.; Saladino-Rosas, Martha I. [Instituto de Astronomía, Universidad Nacional Autónoma de México, México DF 04510, México (Mexico)

    2015-04-01

    Investigations of elemental abundances in the ancient and most metal deficient stars are extremely important because they serve as tests of variable nucleosynthesis pathways and can provide critical inferences of the type of stars that lived and died before them. The presence of r-process elements in a handful of carbon-enhanced metal-poor (CEMP-r) stars, which are assumed to be closely connected to the chemical yield from the first stars, is hard to reconcile with standard neutron star mergers. Here we show that the production rate of dynamically assembled compact binaries in high-z nuclear star clusters can attain a sufficient high value to be a potential viable source of heavy r-process material in CEMP-r stars. The predicted frequency of such events in the early Galaxy, much lower than the frequency of Type II supernovae but with significantly higher mass ejected per event, can naturally lead to a high level of scatter of Eu as observed in CEMP-r stars.

  5. Spectroscopic Studies of Extremly Metal-Poor Stars with Subaru/HDS:II.The r-process Elements, Including Thorium

    CERN Document Server

    Honda, S; Kajino, T; Ando, H; Beers, T C; Izumiura, H; Sadakane, K; Takada-Hidai, M

    2004-01-01

    We present the abundance analyses for the neutron-capture elements, and discuss the observed abundance distributions in very metal-poor stars with excesses of r-process elements. As has been found by previous abundance studies, the star-to-star scatter in the abundances of neutron-capture elements are very large. The abundance patterns of the heavy neutron-capture elements (56 $\\leq$ Z $\\leq$ 70) in seven objects with moderate to large excesses of the neutron-capture elements are similar to that of the solar system r-process component. These results strongly suggest that the heavy neutron-capture elements in these objects are primarily synthesized by the r-process. On the other hand, the abundance ratios of the light neutron-capture elements (38 $\\leq$ Z $\\leq$ 46) exhibit a rather large dispersion. Our inspection of the correlation between Sr and Ba abundances in very metal-poor stars reveals that the dispersion of the Sr abundances clearly decreases with increasing Ba abundance. This results support previou...

  6. The Role of Fission in Neutron Star Mergers and its Impact on the r-Process Peaks

    DEFF Research Database (Denmark)

    Eichler, Marius; Arcones, Almudena; Kelic, Alexandra

    2015-01-01

    Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features...... of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model (FRDM), the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral (ETFSI-Q), and the Hartree......-Fock-Bogoliubov (HFB) mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub...

  7. The Hamburg/ESO R-process Enhanced Star survey (HERES) IV. Detailed abundance analysis and age dating of the strongly r-process enhanced stars CS 29491-069 and HE 1219-0312

    CERN Document Server

    Hayek, W; Christlieb, N; Eriksson, K; Korn, A J; Barklem, P S; Hill, V; Beers, T C; Farouqi, K; Pfeiffer, B; Kratz, K -L

    2009-01-01

    We report on a detailed abundance analysis of two strongly r-process enhanced, very metal-poor stars newly discovered in the HERES project, CS 29491-069 ([Fe/H]=-2.51, [r/Fe]=+1.1) and HE 1219-0312 ([Fe/H]=-2.96, [r/Fe]=+1.5). The analysis is based on high-quality VLT/UVES spectra and MARCS model atmospheres. We detect lines of 15 heavy elements in the spectrum of CS 29491-069, and 18 in HE 1219-0312; in both cases including the Th II 4019 {\\AA} line. The heavy-element abundance patterns of these two stars are mostly well-matched to scaled solar residual abundances not formed by the s-process. We also compare the observed pattern with recent high-entropy wind (HEW) calculations, which assume core-collapse supernovae of massive stars as the astrophysical environment for the r-process, and find good agreement for most lanthanides. The abundance ratios of the lighter elements strontium, yttrium, and zirconium, which are presumably not formed by the main r-process, are reproduced well by the model. Radioactive da...

  8. The Influence of Neutrinos on r-Process Nucleosynthesis in the Ejecta of Black Hole-Neutron Star Mergers

    CERN Document Server

    Roberts, Luke F; Duez, Matthew D; Faber, Joshua A; Foucart, Francois; Lombardi, James C; Ning, Sandra; Ott, Christian D; Ponce, Marcelo

    2016-01-01

    During the merger of a black hole and a neutron star, baryonic mass can become unbound from the system. Because the ejected material is extremely neutron-rich, the r-process rapidly synthesizes heavy nuclides as the material expands and cools. In this work, we map general relativistic models of black hole-neutron star (BHNS) mergers into a Newtonian smoothed particle hydrodynamics (SPH) code and follow the evolution of the thermodynamics and morphology of the ejecta until the outflows become homologous. We investigate how the subsequent evolution depends on our mapping procedure and find that the results are robust. Using thermodynamic histories from the SPH particles, we then calculate the expected nucleosynthesis in these outflows while varying the level of neutrino irradiation coming from the postmerger accretion disk. We find that the ejected material robustly produces r-process nucleosynthesis even for unrealistically high neutrino luminosities, due to the rapid velocities of the outflow. Nonetheless, we...

  9. Probing the Site for r-Process Nucleosyntheis with Abundances of Barium and Magnesium in Extremely Metal-Poor Stars

    CERN Document Server

    Tsujimoto, T; Yoshii, Y; Tsujimoto, Takuji; Shigeyama, Toshikazu; Yoshii, Yuzuru

    2000-01-01

    We suggest that if the astrophysical site for r-process nucleosynthesis in the early Galaxy is confined to a narrow mass range of Type II supernova (SN II) progenitors, with a lower mass limit of Mms = 20 Msun, a unique feature in the observed distribution of [Ba/Mg] vs.[Mg/H] for extremely metal-poor stars can be adequately reproduced. We associate this feature, a bifurcation of the observed elemental ratios into two branches in the Mg abundance interval -2.7 20 Msun. The second branch, which we call the ``i''-branch, is associated with the elemental abundance ratios of stars which were formed in the dense shells of the interstellar medium swept up by SNe II with Mms < 20 Msun that do not synthesize r-process elements, and applies to stars with observed Mg abundances in the range [Mg/H] < -2.7. The Ba abundances in these stars reflect those of the interstellar gas at the (later) time of their formation. The existence of a [Ba/Mg] i-branch strongly suggests that SNe II which are associated with stars o...

  10. Detection of Elements at All Three r-process Peaks in the Metal-Poor Star HD 160617

    CERN Document Server

    Roederer, Ian U; 10.1088/0004-637X/750/1/76

    2012-01-01

    We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selen...

  11. On the robustness of the r-process in neutron-star mergers against variations of nuclear masses

    Science.gov (United States)

    Mendoza-Temis, J. J.; Wu, M. R.; Martínez-Pinedo, G.; Langanke, K.; Bauswein, A.; Janka, H.-T.; Frank, A.

    2016-07-01

    r-process calculations have been performed for matter ejected dynamically in neutron star mergers (NSM), such calculations are based on a complete set of trajectories from a three-dimensional relativistic smoothed particle hydrodynamic (SPH) simulation. Our calculations consider an extended nuclear reaction network, including spontaneous, β- and neutron-induced fission and adopting fission yield distributions from the ABLA code. In this contribution we have studied the sensitivity of the r-process abundances to nuclear masses by using diferent mass models for the calculation of neutron capture cross sections via the statistical model. Most of the trajectories, corresponding to 90% of the ejected mass, follow a relatively slow expansion allowing for all neutrons to be captured. The resulting abundances are very similar to each other and reproduce the general features of the observed r-process abundance (the second and third peaks, the rare-earth peak and the lead peak) for all mass models as they are mainly determined by the fission yields. We find distinct differences in the predictions of the mass models at and just above the third peak, which can be traced back to different predictions of neutron separation energies for r-process nuclei around neutron number N = 130.

  12. Detection of low Eu abundances in extremely metal-poor stars and the origin of r-process elements

    CERN Document Server

    Ishimaru, Y; Aoki, W; Ryan, S G; Aoki, Wako; Ishimaru, Yuhri; Ryan, Sean G.; Wanajo, Shinya

    2003-01-01

    We report detailed abundance analyses for three extremely metal-poor stars with [Fe/H] lesssim -3 in the Galactic halo, using the Subaru High Dispersion Spectrograph (HDS). All these stars are found to have sub-solar relative abundances of [Eu/Fe], and exhibit the lowest [Eu/H] values at their metallicities. Comparison of these low Eu abundances with our chemical evolution model of the Galactic halo implies the dominant source of Eu to be the low-mass end of the Type II supernova mass range. This suggests that collapsing O-Ne-Mg cores resulting from 8-10 Msun stars are the major r-process site.

  13. Impact of weak interactions of free nucleons on the r-process in dynamical ejecta from neutron-star mergers

    CERN Document Server

    Goriely, Stephane; Just, Oliver; Pllumbi, Else; Janka, Hans-Thomas

    2015-01-01

    We investigate beta-interactions of free nucleons and their impact on the electron fraction (Y_e) and r-process nucleosynthesis in ejecta characteristic of binary neutron star mergers (BNSMs). For that we employ trajectories from a relativistic BNSM model to represent the density-temperature evolutions in our parametric study. In the high-density environment, positron captures decrease the neutron richness at the high temperatures predicted by the hydrodynamic simulation. Circumventing the complexities of modelling three-dimensional neutrino transport, (anti)neutrino captures are parameterized in terms of prescribed neutrino luminosities and mean energies, guided by published results and assumed as constant in time. Depending sensitively on the adopted neutrino-antineutrino luminosity ratio, neutrino processes increase Y_e to values between 0.25 and 0.40, still allowing for a successful r-process compatible with the observed solar abundance distribution and a significant fraction of the ejecta consisting of r...

  14. THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THE r-PROCESS PEAKS

    Energy Technology Data Exchange (ETDEWEB)

    Eichler, M.; Panov, I.; Rauscher, T.; Thielemann, F.-K. [Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland); Arcones, A.; Langanke, K.; Martinez-Pinedo, G. [Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstrasse 2, D-64289 Darmstadt (Germany); Kelic, A. [GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstrasse 1, D-64291 Darmstadt (Germany); Korobkin, O.; Rosswog, S. [The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden); Marketin, T. [Department of Physics, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia); Winteler, C. [Institut Energie am Bau, Fachhochschule Nordwestschweiz, St. Jakobs-Strasse 84, 4132 Muttenz (Switzerland); Zinner, N. T., E-mail: marius.eichler@unibas.ch [Department of Physics and Astronomy, Aarhus University, Ny Munkegade, bygn. 1520, DK-8000 Aarhus C (Denmark)

    2015-07-20

    Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree–Fock–Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)–(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  15. Impact of weak interactions of free nucleons on the r-process in dynamical ejecta from neutron star mergers

    Science.gov (United States)

    Goriely, S.; Bauswein, A.; Just, O.; Pllumbi, E.; Janka, H.-Th.

    2015-10-01

    We investigate β-interactions of free nucleons and their impact on the electron fraction (Ye) and r-process nucleosynthesis in ejecta characteristic of binary neutron star mergers (BNSMs). For that we employ trajectories from a relativistic BNSM model to represent the density-temperature evolutions in our parametric study. In the high-density environment, positron captures decrease the neutron richness at the high temperatures predicted by the hydrodynamic simulation. Circumventing the complexities of modelling three-dimensional neutrino transport, (anti)neutrino captures are parametrized in terms of prescribed neutrino luminosities and mean energies, guided by published results and assumed as constant in time. Depending sensitively on the adopted νe-bar{ν }_e luminosity ratio, neutrino processes increase Ye to values between 0.25 and 0.40, still allowing for a successful r-process compatible with the observed solar abundance distribution and a significant fraction of the ejecta consisting of r-process nuclei. If the νe luminosities and mean energies are relatively large compared to the bar{ν }_e properties, the mean Ye might reach values >0.40 so that neutrino captures seriously compromise the success of the r-process. In this case, the r-abundances remain compatible with the solar distribution, but the total amount of ejected r-material is reduced to a few per cent, because the production of iron-peak elements is favoured. Proper neutrino physics, in particular also neutrino absorption, have to be included in BNSM simulations before final conclusions can be drawn concerning r-processing in this environment and concerning observational consequences like kilonovae, whose peak brightness and colour temperature are sensitive to the composition-dependent opacity of the ejecta.

  16. RAVE J203843.2-002333: The First Highly R-process-enhanced Star Identified in the RAVE Survey

    Science.gov (United States)

    Placco, Vinicius M.; Holmbeck, Erika M.; Frebel, Anna; Beers, Timothy C.; Surman, Rebecca A.; Ji, Alexander P.; Ezzeddine, Rana; Points, Sean D.; Kaleida, Catherine C.; Hansen, Terese T.; Sakari, Charli M.; Casey, Andrew R.

    2017-07-01

    We report the discovery of RAVE J203843.2-002333, a bright (V = 12.73), very metal-poor ([{Fe}/{{H}}] = -2.91), r-process-enhanced ([{Eu}/{Fe}] = +1.64 and [{Ba}/{Eu}] = -0.81) star selected from the RAVE survey. This star was identified as a metal-poor candidate based on its medium-resolution (R ˜ 1600) spectrum obtained with the KPNO/Mayall Telescope, and followed up with high-resolution (R ˜ 66,000) spectroscopy with the Magellan/Clay Telescope, allowing for the determination of elemental abundances for 24 neutron-capture elements, including thorium and uranium. RAVE J2038-0023 is only the fourth metal-poor star with a clearly measured U abundance. The derived chemical abundance pattern exhibits good agreement with those of other known highly r-process-enhanced stars, and evidence suggests that it is not an actinide-boost star. Age estimates were calculated using U/X abundance ratios, yielding a mean age of 13.0 ± 1.1 Gyr. Based on observations gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile; Kitt Peak National Observatory, National Optical Astronomy Observatory (NOAO Prop. ID: 14B-0231; PI: Placco), which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. The authors are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham.

  17. MOLYBDENUM, RUTHENIUM, AND THE HEAVY r-PROCESS ELEMENTS IN MODERATELY METAL-POOR MAIN-SEQUENCE TURNOFF STARS

    Energy Technology Data Exchange (ETDEWEB)

    Peterson, Ruth C. [Astrophysical Advances, 607 Marion Place, Palo Alto, CA 94301 (United States)

    2013-05-01

    The ratios of elemental abundances observed in metal-poor stars of the Galactic halo provide a unique present-day record of the nucleosynthesis products of its earliest stars. While the heaviest elements were synthesized by the r- and s-processes, dominant production mechanisms of light trans-ironic elements were obscure until recently. This work investigates further our 2011 conclusion that the low-entropy regime of a high-entropy wind (HEW) produced molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed extreme overabundances of those elements with respect to iron. Only a few, rare nucleosynthesis events may have been involved. Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28 similar stars by matching spectral calculations to well-exposed near-UV Keck HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff stars with Mo or Ru line detections and no evidence for s-process production (therefore old), we find Mo and Ru to be three to six times overabundant. In contrast, the maximum overabundance is reduced to factors of three and two for the neighboring elements zirconium and palladium. Since the overproduction peaks sharply at Mo and Ru, a low-entropy HEW is confirmed as its origin. The overabundance level of the heavy r-process elements varies significantly, from none to a factor of four, but is uncorrelated with Mo and Ru overabundances. Despite their moderate metallicity, stars in this group trace the products of different nucleosynthetic events: possibly very few events, possibly events whose output depended on environment, metallicity, or time.

  18. Natal Kicks and Time Delays in Merging Neutron Star Binaries: Implications for r-process Nucleosynthesis in Ultra-faint Dwarfs and in the Milky Way

    Science.gov (United States)

    Beniamini, Paz; Hotokezaka, Kenta; Piran, Tsvi

    2016-09-01

    Merging neutron star binaries are prime candidate sources for heavy r-process nucleosynthesis. The amount of heavy r-process material is consistent with the mass ejection and rates of mergers, and abundances of relic radioactive materials suggest that heavy r-process material is produced in rare events. Observations of possible macronovae provide further support for this model. Still, some concerns remain. One is the observation of heavy r-process elements in ultra-faint dwarf (UFD) galaxies. The escape velocities from UFDs are so small that the natal kicks, taking place at neutron stars’ birth, might eject such binaries from UFDs. Furthermore, the old stellar populations of UFDs require that r-process nucleosynthesis must have taken place very early on, while it may take several Gyr for compact binaries to merge. This last problem arises also within the Milky Way where heavy r-process materials have been observed in some low-metallicity stars. We show here that ≳ 0.5 of neutron star binaries form with a sufficiently small proper motion to remain bound even in a UFD. Furthermore, approximately 90% of double neutron stars with an initial separation of 1011 cm merge within 300 Myr and ≈ 15 % merge in less than 100 Myr. This population of “rapid mergers” explains the appearance of heavy r-process material in both UFDs and in the early Milky Way.

  19. The Hamburg/ESO R-process Enhanced Star survey (HERES): Abundances

    Science.gov (United States)

    Barklem, P. S.; Christlieb, N.; Beers, T. C.; Hill, V.; Holmberg, J.; Marsteller, B.; Rossi, S.; Zickgraf, F.-J.; Bessell, M. S.

    We present the results of analysis of "snapshot" spectra (i.e., R=20,000 and S/N=50 per pixel) of 253 metal-poor halo stars -3.8[Fe/H] obtained in the HERES survey. The spectra are analysed using an automated line profile analysis method based on the Spectroscopy Made Easy (SME) codes of Valenti & Piskunov (1996). Elemental abundances of moderate precision (absolute r.m.s. errors of order 0.25 dex) have been obtained for 22 elements, C, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu, where detectable. The results are presented and discussed, particularly trends and scatter in the abundance distributions.

  20. Discovery of a strongly r-process enhanced extremely metal-poor star LAMOST J110901.22+075441.8

    CERN Document Server

    Li, Haining; Honda, Satoshi; Zhao, Gang; Christlieb, Norbert; Suda, Takuma

    2015-01-01

    We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits large excess of r-process elements with [Eu/Fe] ~ +1.16. The star is one of the newly discovered EMP stars identified from LAMOST low-resolution spectroscopic survey and the high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the "normal" population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy well...

  1. Natal Kicks and Time Delays in Merging Neutron Star Binaries - Implications for r-process nucleosynthesis in Ultra Faint Dwarfs and in the Milky Way

    CERN Document Server

    Beniamini, Paz; Piran, Tsvi

    2016-01-01

    Merging neutron star binaries are prime candidate sources for heavy r-process nucleosynthesis. The amount of heavy r-process material is consistent with the mass ejection and rates of mergers, and abundances of relic radioactive materials suggest that heavy r-process material is produced in rare events. Observations of possible macronovae provide further support for this model. Still, some concerns remain. One is the observation of heavy r-process elements in Ultra Faint Dwarf (UFD) galaxies. The escape velocities from UFDs are so small that the natal kicks, taking place at neutron stars birth, might eject such binaries from UFDs. Furthermore the old stellar populations of UFDs requires that r-process nucleosynthesis must have taken place very early on, while it may take several Gyr for compact binaries to merge. This last problem arises also within the Milky Way where heavy r-process materials has been observed in some low metallicity stars. We show here that since a significant fraction of neutron star bina...

  2. 贫金属星r过程核合成相关问题的研究进展%Progress of the Study About R-process Nucleosynthesis in Metal-poor Stars

    Institute of Scientific and Technical Information of China (English)

    张江; 崔文元; 张波

    2011-01-01

    快中子俘获过程(r过程)可以解释大约一半比铁重的稳定(和一些长寿命放射性的)富中子核素的产生,这已经被太阳系及各种金属丰度下恒星的观测结果所证实.为建立r过程模型,需要大量的核物理信息:涉及到β稳定谷与中子滴线之间的各种核素的稳定特性及β衰变分支等物理参数,实验和理论都面临巨大的挑战.综述了近年来贫金属星r过程核合成理论的研究情况,包括人们比较关注的主要r过程与弱r过程核合成、元素丰度分布规律及其产生场所等.%The rapid neutron-capture process (r-process) is traditionally believed to be responsible for the nucleosynthesis of approximately half of the heavy nuclei beyond the iron peak with long-decay half-lives in the solar material. In globular clusters and Galactic halo stars, the observed abundances show a nearly universal presence of r-process. With the rapid development of the abundance determinations, more elements (e.g., Lu, Z - 71) are firstly detected in metal-poor r-process-enriched halo stars, which can be used as the r-process indicators for the early Galaxy. Moreover, these r-rich stars provide a strong constraint on the models of the r-process nucleosynthesis, especially the early galaxy chemical evolution of neutron-capture elements.Based on new atomic lab data, recent neutron-capture abundance comparisons between six r-rich Galactic halo stars and the Solar System r-only abundance distribution indicate that the heavier stable neutron-capture elements beyond Ba (Z > 56) agree completely with a scaled solar system r-process abundance value. Nevertheless, the lighter neutron-capture elemental abundances in these stars are not in agreement with Solar-system r-only values. Although there is controversy over the origin of weak r-process, the neutron-capture elements are proposed to be formed possibly from multiple synthesis mechanisms, even if there exists little uncertainty. Whether the r-process

  3. New Observational Perspectives on r-process Nucleosynthesis

    Science.gov (United States)

    Roederer, Ian U.

    2012-10-01

    Elements heavier than the iron group can be found in nearly every star whose abundances have been studied in detail. More than 60 percent of the naturally-occurring elements between zinc and uranium have been detected in r-process enriched stars. Models of the r-process rely heavily on matching astronomical observations, so this is good news for studies of r-process nucleosynthesis. I will highlight some of what we've learned from three decades of studying r-process material in other stars, describe current efforts that use the Hubble Space Telescope to expand the chemical inventory in r-process environments beyond the Solar system, and note opportunities for complementary studies by the physics community.

  4. Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007: a New sand r-Process Paradigm

    Institute of Scientific and Technical Information of China (English)

    GUI Wen-Yuan; CUI Dong-Nuan; DU Yun-Shuang; ZHANG Bo

    2007-01-01

    The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity [Fe/H] = -2.0,which is just at the upper limit of the metallicity for the observed double-enhanced stars. Using a parametric model, we find that almost all s-elements were made in a single neutron exposure. This star should be a member of a post-common-envelope binary. After the s-process material has experienced only one neutron exposure in the nucleosynthesis region and is dredged-up to its envelope, he AGB evolution is terminated by the onset of common-envelope evolution. Based on the high radial-velocity of HE 1305-0007,we speculate that the star could be a runaway star from a binary system, in which the AIC event has occurred and produced the r-process elements.

  5. THE r-PROCESS IN MAGNETOROTATIONAL SUPERNOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Tsujimoto, Takuji [National Astronomical Observatory of Japan, Mitaka-shi, Tokyo 181-8588 (Japan); Nishimura, Nobuya, E-mail: taku.tsujimoto@nao.ac.jp [Astrophysics Group, Keele University, ST5 5BG Keele (United Kingdom)

    2015-09-20

    One of the hottest open issues involving the chemical evolution of r-process elements is fast enrichment in the early universe. Clear evidence for the chemical enrichement of r-process elements is seen in the stellar abundances of extremely metal poor stars in the Galactic halo. However, small-mass galaxies are the ideal testbed for studying the evolutionary features of r-process enrichment given the potential rarity of production events yielding heavy r-process elements. Their occurrences become countable and thus an enrichment path due to each event can be found in the stellar abundances. We examine the chemical feature of Eu abundance at an early stage of [Fe/H] ≲ −2 in the Draco and Sculptor dwarf spheroidal (dSph) galaxies. Accordingly, we constrain the properties of Eu production in the early dSphs. We find that the Draco dSph experienced a few Eu production events, whereas Eu enrichment took place more continuously in the Sculptor dSph due to its larger stellar mass. The event rate of Eu production is estimated to be about one per 100−200 core-collapse supernovae, and a Eu mass of ∼ (1–2) × 10{sup −5}M{sub ⊙} per single event is deduced by associating this frequency with the observed plateau value of [Eu/H] ∼ −1.3 for [Fe/H] ≳ −2. The observed plateau implies that early Eu enrichment ceases at [Fe/H] ≈ −2. Such a selective operation only in low-metallicity stars supports magnetorotational supernovae, which require very fast rotation, as the site of early Eu production. We show that the Eu yields deduced from chemical evolution agree well with the nucleosynthesis results from corresponding supernovae models.

  6. The Binary Frequency of r-Process-Element Enhanced Metal-Poor Stars and its Implications: Chemical Tagging in the Primitive Halo of the Milky Way

    CERN Document Server

    Hansen, Terese; Nordström, Birgitta; Buchhave, Lars A; Beers, Timothy C

    2011-01-01

    A few rare halo giants in the range [Fe/H] $\\simeq -2.9\\pm0.3$ exhibit {\\it r}-process element abundances that vary as a group by factors up to [$r$/Fe] $\\sim80$, relative to those of the iron peak and below. Yet, the astrophysical production site of these {\\it r}-process elements remains unclear. We report initial results from four years of monitoring the radial velocities of 17 {\\it r}-process-enhanced metal-poor giants to detect and characterise binaries in this sample. We find three (possibly four) spectroscopic binaries with orbital periods and eccentricities that are indistinguishable from those of Population I binaries with giant primaries, and which exhibit no signs that the secondary components have passed through the AGB stage of evolution or exploded as supernovae. The other 14 stars in our sample appear to be single -- including the prototypical $r$-process-element enhanced star CS 22892-052, which is also enhanced in carbon, but not in {\\it s}-process elements. We conclude that the {\\it r}-proces...

  7. The role of fission on neutron star mergers and its impact on the r-process peaks

    Science.gov (United States)

    Eichler, M.; Arcones, A.; Kelic, A.; Korobkin, O.; Langanke, K.; Marketin, T.; Martinez-Pinedo, G.; Panov, I.; Rauscher, T.; Rosswog, S.; Winteler, C.; Zinner, N. T.; Thielemann, F.-K.

    2016-06-01

    The comparison between observational abundance features and those obtained from nucleosynthesis predictions of stellar evolution and/or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. Here we test the abundance features of r-process nucleosynthesis calculations using four different fission fragment distribution models. Furthermore, we explore the origin of a shift in the third r-process peak position in comparison with the solar r-process abundances which has been noticed in a number of merger nucleosynthesis predictions. We show that this shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is not maintained anymore. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  8. Neutron Star Mergers as the Origin of r-Process Elements in the Galactic Halo Based on the Sub-halo Clustering Scenario

    CERN Document Server

    Ishimaru, Yuhri; Prantzos, Nikos

    2015-01-01

    Binary mergers (NSMs) of double neutron star (and black hole-neutron star) systems are suggested to be major sites of r-process elements in the Galaxy by recent hydrodynamical and nucleosynthesis studies. It has been pointed out, however, that the estimated long lifetimes of neutron star binaries are in conflict with the presence of r-process-enhanced halo stars at metallicities as low as [Fe/H] ~ -3. To resolve this problem, we examine the role of NSMs in the early Galactic chemical evolution on the assumption that the Galactic halo was formed from merging sub-halos. We present simple models for the chemical evolution of sub-halos with total final stellar masses between 10^4 M_solar and 2 x 10^8 M_solar. Typical lifetimes of compact binaries are assumed to be 100 Myr (for 95% of their population) and 1 Myr (for 5%), according to recent binary population synthesis studies. The resulting metallcities of sub-halos and their ensemble are consistent with the observed mass-metallicity relation of dwarf galaxies in...

  9. Molybdenum, Ruthenium, and the Heavy r-process Elements in Moderately Metal-Poor Main-Sequence Turnoff Stars

    CERN Document Server

    Peterson, Ruth C

    2013-01-01

    The ratios of elemental abundances observed in metal-poor stars of the Galactic halo provide a unique present-day record of the nucleosynthesis products of its earliest stars. While the heaviest elements were synthesized by the r- and s-processes, dominant production mechanisms of light trans-ironic elements were obscure until recently. This work investigates further our 2011 conclusion that the low-entropy regime of a high-entropy wind (HEW) produced molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed extreme overabundances of those elements with respect to iron. Only a few, rare nucleosynthesis events may have been involved. Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28 similar stars by matching spectral calculations to well-exposed near-UV Keck HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff stars with Mo or Ru line detections and no evidence for s-process production (therefore old), we find Mo and Ru to be three to six ti...

  10. Massive binary stars and self-enrichment of Massive binary stars and self-enrichment of

    NARCIS (Netherlands)

    R.G. Izzard; S.E. de Mink; O.R. Pols; N. Langer; H. Sana; A. de Koter

    2013-01-01

    Globular clusters contain many stars with surface abundance patterns indicating contributions from hydrogen burning products, as seen in the anti-correlated elemental abundances of e.g. sodium and oxygen, and magnesium and aluminium. Multiple generations of stars can explain this phenomenon, with th

  11. How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae

    Science.gov (United States)

    Chen, Ke-Jung; Whalen, Daniel J.; Wollenberg, Katharina M. J.; Glover, Simon C. O.; Klessen, Ralf S.

    2017-08-01

    Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablative flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, so it might form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evaporation of the halo prior to the explosion is crucial to its later enrichment by the supernova.

  12. How the First Stars Regulated Star Formation: Enrichment by Nearby Supernovae

    CERN Document Server

    Chen, Ke-Jung; Wollenberg, Katharina M J; Glover, Simon C O; Klessen, Ralf S

    2016-01-01

    Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablative flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, and it can form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evapor...

  13. The First Galaxies: Chemical Enrichment, Mixing, and Star Formation

    CERN Document Server

    Greif, Thomas H; Bromm, Volker; Klessen, Ralf S

    2010-01-01

    Using three-dimensional cosmological simulations, we study the assembly process of one of the first galaxies, with a total mass of 10^8 M_sun, collapsing at z = 10. Our main goal is to trace the transport of the heavy chemical elements produced and dispersed by a pair-instability supernova exploding in one of the minihalo progenitors. To this extent, we incorporate an efficient algorithm into our smoothed particle hydrodynamics code which approximately models turbulent mixing as a diffusion process. We study this mixing with and without the radiative feedback from Pop III stars that subsequently form in neighboring minihalos. Our simulations allow us to constrain the initial conditions for second-generation star formation, within the first galaxy itself, and inside of minihalos that virialize after the supernova explosion. We find that most minihalos remain unscathed by ionizing radiation or the supernova remnant, while some are substantially photoheated and enriched to supercritical levels, likely resulting ...

  14. Star Formation and Chemical Enrichment for Globular Clusters

    Institute of Scientific and Technical Information of China (English)

    林清; 束成钢; 常瑞香; 赵君亮

    2001-01-01

    A model considering gas outflows due to supernova explosions is developed for the star formation and chemical enrichment for the globular clusters (GCs) in the Milky Way galaxy. Through Monte Carlo simulations, the observed global properties of GCs can be well reproduced, including the metallicity distribution, no-correlation between cluster masses and galactocentric distances, etc. The predicted mass function of the parent clouds for the observed GCs at present day can be well described as a power law with the index of-1.8, which is consistent with the current observations for the molecular clouds.

  15. Improved Laboratory Transition Probabilities for Er II and Applications to the Erbium Abundances of the Sun and Five r-Process Rich, Metal-Poor Stars

    CERN Document Server

    Lawler, J E; Cowan, J J; Wyart, J -F; Ivans, I I; Sobeck, J S; Stockett, M H; Hartog, E A Den

    2008-01-01

    Recent radiative lifetime measurements accurate to +/- 5% (Stockett et al. 2007, J. Phys. B 40, 4529) using laser-induced fluorescence (LIF) on 8 even-parity and 62 odd-parity levels of Er II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 418 lines of Er II. This work moves Er II onto the growing list of rare earth spectra with extensive and accurate modern transition probability measurements using LIF plus FTS data. This improved laboratory data set has been used to determine a new solar photospheric Er abundance, log epsilon = 0.96 +/- 0.03 (sigma = 0.06 from 8 lines), a value in excellent agreement with the recommended meteoric abundance, log epsilon = 0.95 +/- 0.03. Revised Er abundances have also been derived for the r-process-rich metal-poor giant stars CS 22892-052, BD+17 3248, HD 221170, HD 115444, and CS 31082-001. For these five stars the average Er/Eu abundance ratio, = 0.42, is in very good agreement ...

  16. Models of neutron star atmospheres enriched with nuclear burning ashes

    CERN Document Server

    Nättilä, Joonas; Kajava, Jari J E; Poutanen, Juri

    2015-01-01

    Low-mass X-ray binaries hosting neutron stars (NS) exhibit thermonuclear (type-I) X-ray bursts, which are powered by unstable nuclear burning of helium and/or hydrogen into heavier elements deep in the NS "ocean". In some cases the burning ashes may rise from the burning depths up to the NS photosphere by convection, leading to the appearance of the metal absorption edges in the spectra, which then force the emergent X-ray burst spectra to shift toward lower energies. These effects may have a substantial impact on the color correction factor $f_c$ and the dilution factor $w$, the parameters of the diluted blackbody model $F_E \\approx w B_E(f_c T_{eff})$ that is commonly used to describe the emergent spectra from NSs. The aim of this paper is to quantify how much the metal enrichment can change these factors. We have developed a new NS atmosphere modeling code, which has a few important improvements compared to our previous code required by inclusion of the metals. The opacities and the internal partition func...

  17. Where, oh where has the r-process gone?

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Y.-Z. [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)]. E-mail: qian@physics.umn.edu; Wasserburg, G.J. [Lunatic Asylum, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)]. E-mail: gjw@gps.caltech.edu

    2007-04-15

    We present a review of the possible sources for r-process nuclei (r-nuclei). It is known that there is as yet no self-consistent mechanism to provide abundant neutrons for a robust r-process in the neutrino-driven winds from nascent neutron stars. We consider that the heavy r-nuclei with mass numbers A>130 (Ba and above) cannot be produced in the neutrino-driven winds. Nonetheless, the r-process and the neutrino-driven winds may be directly or indirectly related by some unknown additional mechanism, which, for example, could provide ejecta with very short dynamic timescales of < or approx 0.004s. This undetermined mechanism must supply a neutron source within the same general stellar sites that undergo core collapse to produce the neutron star. Observational data on low-metallicity stars in the Galactic halo show that sites producing the heavy r-nuclei do not produce Fe or any other elements between N and Ge. Insofar as a forming neutron star is key to producing the heavy r-nuclei, then the only possible sources are supernovae resulting from collapse of O-Ne-Mg cores or accretion-induced collapse of white dwarfs, neither of which produce the elements of the Fe group or those of intermediate mass (above C and N). Observational evidence on s and r-nuclei in low-metallicity stars with high C and N abundances shows that the r-process is also active in binary systems. The nuclei with A{approx}90-110 produced by charged-particle reactions (CPR) in the neutrino-driven winds are in general present in metal-poor stars with high or low abundances of heavy r-nuclei. The CPR nuclei and the heavy r-nuclei are not strongly coupled. Some metal-poor stars show extremely high enrichments of heavy r-nuclei and have established that the abundance patterns of these nuclei are universally close to the solar abundance pattern of heavy r-nuclei. Using a template star with high enrichments of heavy r-nuclei and another with low enrichments we develop a two-component model based on the

  18. Supernova enrichment of planetary systems in low-mass star clusters

    Science.gov (United States)

    Nicholson, Rhana B.; Parker, Richard J.

    2017-02-01

    The presence and abundance of short-lived radioisotopes 26Al and 60Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe). Massive stars are more likely to form in massive star clusters (>1000 M⊙) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of ˜1 pc. We investigate whether low-mass (50-200 M⊙) star clusters containing one or two massive stars are a more likely avenue for early Solar system enrichment as they are more dynamically quiescent. We analyse N-body simulations of the evolution of these low-mass clusters and find that a similar fraction of stars experience SN enrichment than in high-mass clusters, despite their lower densities. This is due to two-body relaxation, which causes a significant expansion before the first SN even in clusters with relatively low (100 stars pc-3) initial densities. However, because of the high number of low-mass clusters containing one or two massive stars, the absolute number of enriched stars is the same, if not higher than for more populous clusters. Our results show that direct enrichment of protoplanetary discs from SNe occurs as frequently in low-mass clusters containing one or two massive stars (>20 M⊙) as in more populous star clusters (1000 M⊙). This relaxes the constraints on the direct enrichment scenario and therefore the birth environment of the Solar system.

  19. Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data

    CERN Document Server

    Lawler, J E; Cowan, J J; Ivans, I I; Hartog, E A Den

    2009-01-01

    Recent radiative lifetime measurements accurate to +/- 5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45 lines), a value in excellent agreement with the recommended meteoritic abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052, CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for determining the Ce abundance in these five stars, yielding a small statistical uncertainty of 0.01 dex similar to the Solar result. The relative abundances in the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun, matches r-process ...

  20. Massive binary stars and self-enrichment of globular clusters

    Science.gov (United States)

    Izzard, R. G.; de Mink, S. E.; Pols, O. R.; Langer, N.; Sana, H.; de Koter, A.

    ~Globular clusters contain many stars with surface abundance patterns indicating contributions from hydrogen burning products, as seen in the anti-correlated elemental abundances of e.g. sodium and oxygen, and magnesium and aluminium. Multiple generations of stars can explain this phenomenon, with the second generation forming from a mixture of pristine gas and ejecta from the first generation. We show that massive binary stars may be a source of much of the material that makes this second generation of stars. Mass transfer in binaries is often non-conservative and the ejected matter moves slowly enough that it can remain inside a globular cluster and remain available for subsequent star formation. Recent studies show that there are more short-period massive binaries than previously thought, hence also more stars that interact and eject nuclear-processed material.

  1. Massive Binary Stars and Self-Enrichment of Globular Clusters

    CERN Document Server

    Izzard, Robert G; Pols, Onno R; Langer, Norbert; Sana, Hugues; de Koter, Alex

    2013-01-01

    Globular clusters contain many stars with surface abundance patterns indicating contributions from hydrogen burning products, as seen in the anti-correlated elemental abundances of e.g. sodium and oxygen, and magnesium and aluminium. Multiple generations of stars can explain this phenomenon, with the second generation forming from a mixture of pristine gas and ejecta from the first generation. We show that massive binary stars may be a source of much of the material that makes this second generation of stars. Mass transfer in binaries is often non-conservative and the ejected matter moves slowly enough that it can remain inside a globular cluster and remain available for subsequent star formation. Recent studies show that there are more short-period massive binaries than previously thought, hence also more stars that interact and eject nuclear-processed material.

  2. A Comparative Study of Two 47 Tuc Giant Stars with Different s-process Enrichment

    Science.gov (United States)

    Cordero, M. J.; Hansen, C. J.; Johnson, C. I.; Pilachowski, C. A.

    2015-07-01

    Here we aim to understand the origin of 47 Tuc’s La-rich star Lee 4710. We report abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu and present a detailed abundance analysis of two 47 Tuc stars with similar stellar parameters but different slow neutron-capture (s-)process enrichment. Star Lee 4710 has the highest known La abundance ratio in this cluster ([La/Fe] = 1.14), and star Lee 4626 is known to have normal s-process abundances (e.g., [Ba/Eu] < 0). The nucleosynthetic pattern of elements with Z ≳ 56 for star Lee 4710 agrees with the predicted yields of a 1.3{M}⊙ asymptotic giant branch (AGB) star. Therefore, Lee 4710 may have been enriched by mass transfer from a more massive AGB companion, which is compatible with its location far away from the center of this relatively metal-rich ([Fe/H] ˜ -0.7) globular cluster. A further analysis comparing the abundance pattern of Lee 4710 with data available in the literature reveals that nine out of the ˜200 47 Tuc stars previously studied show strong s-process enhancements that point toward later enrichment by more massive AGB stars.

  3. Young alpha-enriched giant stars in the solar neighbourhood

    CERN Document Server

    Martig, Marie; Aguirre, Victor Silva; Hekker, Saskia; Mosser, Benoit; Elsworth, Yvonne; Bovy, Jo; Stello, Dennis; Anders, Friedrich; García, Rafael A; Tayar, Jamie; Rodrigues, Thaíse S; Basu, Sarbani; Carrera, Ricardo; Ceillier, Tugdual; Chaplin, William J; Chiappini, Cristina; Frinchaboy, Peter M; García-Hernández, D A; Hearty, Fred R; Holtzman, Jon; Johnson, Jennifer A; Mathur, Savita; Mészáros, Szabolcs; Miglio, Andrea; Nidever, David; Pinsonneault, Marc; Schiavon, Ricardo P; Schneider, Donald P; Serenelli, Aldo; Shetrone, Matthew; Zamora, Olga

    2014-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [{\\alpha}/Fe] values from APOGEE DR12 are available. We investigate the relation between age and chemical abundances for these stars, using a simple and robust approach to obtain ages. We first derive stellar masses using standard seismic scaling relations, then determine the maximum possible age for each star as function of its mass and metallicity, independently of its evolutionary stage. While the overall trend between maximum age and chemical abundances is a declining fraction of young stars with increasing [{\\alpha}/Fe], at least 14 out of 241 stars with [{\\alpha}/Fe]>0.13 are younger than 6 Gyr. Five stars with [{\\alpha}/Fe]>0.2 have ages below 4 Gyr. We examine the effect of modifications in the standard seismic scaling relations, as well as the effect of very low helium fractions, but these changes are not enough to make these stars as old a...

  4. CNO enrichment by rotating AGB stars in globular clusters

    CERN Document Server

    Decressin, T; Siess, L; Palacios, A; Meynet, G; Georgy, C

    2009-01-01

    AGB stars have long been held responsible for the important star-to-star variations in light elements observed in Galactic globular clusters. We analyse the main impacts of a first generation of rotating intermediate-mass stars on the chemical properties of second-generation globular cluster stars. The rotating models were computed without magnetic fields and without the effects of internal gravity waves. They account for the transports by meridional currents and turbulence. We computed the evolution of both standard and rotating stellar models with initial masses between 2.5 and 8 Msun within the metallicity range covered by Galactic globular clusters. During central He-burning, rotational mixing transports fresh CO-rich material from the core towards the hydrogen-burning shell, leading to the production of primary 14N. In stars more massive than M > 4 Msun, the convective envelope reaches this reservoir during the second dredge-up episode, resulting in a large increase in the total C+N+O content at the stel...

  5. Insights into Pre-Enrichment of Star Clusters and Self-Enrichment of Dwarf Galaxies from their Intrinsic Metallicity Dispersions

    CERN Document Server

    Leaman, Ryan

    2012-01-01

    Star clusters are known to have smaller intrinsic metallicity spreads than dwarf galaxies due to their shorter star formation timescales. Here we use individual spectroscopic [Fe/H] measurements of stars in 19 Local Group dwarf galaxies, 13 Galactic open clusters, and 49 globular clusters to show that star cluster and dwarf galaxy linear metallicity distributions are binomial in form, with all objects showing strong correlations between their mean linear metallicity $\\bar{Z}$ and intrinsic spread in metallicity $\\sigma(Z)^{2}$. A plot of $\\sigma(Z)^{2}$ versus $\\bar{Z}$ shows that the correlated relationships are offset for the dwarf galaxies from the star clusters. The common binomial nature of these linear metallicity distributions can be explained with a simple inhomogeneous chemical evolution model (e.g., Oey 2000), where the star cluster and dwarf galaxy behaviour in the $\\sigma(Z)^{2}-\\bar{Z}$ diagram is reproduced in terms of the number of enrichment events, covering fraction, and intrinsic size of the...

  6. Upper limit on star formation and metal enrichment in minihaloes

    Science.gov (United States)

    Cen, Renyue

    2017-02-01

    An analysis of negative radiative feedback from resident stars in minihaloes is performed. It is found that the most effective mechanism to suppress star formation is provided by infrared photons from resident stars via photodetachment of H-. It is shown that a stringent upper bound on (total stellar mass, metallicity) of (˜1000 M⊙, -3.3 ± 0.2) in any newly minted atomic cooling halo can be placed, with the actual values possibly significantly lower. This has both important physical ramifications on formation of stars and supermassive black seeds in atomic cooling haloes at high redshift, pertaining to processes of low-temperature metal cooling, dust formation and fragmentation, and direct consequences on the faint end galaxy luminosity function at high redshift and cosmological reionization. The luminosity function of galaxies at the epoch of reionization may be substantially affected due to the combined effect of a diminished role of minihaloes and an enhanced contribution from Population III stars in atomic cooling haloes. Upcoming results on reionization optical depth from Planck High-Frequency Instrument data may provide a significant constraint on and a unique probe of this star formation physical process in minihaloes. As a numerical example, in the absence of significant contributions from minihaloes with virial masses below 1.5 × 108 M⊙, the reionization optical depth is expected to be no greater than 0.065, whereas allowing for minihaloes of masses as low as (107 M⊙, 106.5 M⊙) to form stars unconstrained by this self-regulation physical process, the reionization optical depth is expected to exceed (0.075, 0.085), respectively.

  7. {beta}-decay studies of r-process nuclei at NSCL

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, J. [National Superconducting Cyclotron Laboratory, Michigan State University, E. Lansing, MI (United States); Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI (United States)], E-mail: pereira@nscl.msu.edu; Aprahamian, A. [Institute of Structure and Nuclear Astrophysics, University of Notre Dame, South Bend, IN (United States); Joint Institute for Nuclear Astrophysics, University of Notre Dame, South Bend, IN (United States); Arndt, O. [Institut fuer Kernchemie, Universitaet Mainz, Mainz (Germany); Virtuelles Institut fuer Struktur der Kerne and Nuklearer Astrophysik, Mainz (Germany); Becerril, A.; Elliot, T. [National Superconducting Cyclotron Laboratory, Michigan State University, E. Lansing, MI (United States); Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI (United States); Estrade, A. [National Superconducting Cyclotron Laboratory, Michigan State University, E. Lansing, MI (United States); Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI (United States); Department of Physics and Astronomy, Michigan State University, E. Lansing, MI (United States); Galaviz, D. [National Superconducting Cyclotron Laboratory, Michigan State University, E. Lansing, MI (United States); Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI (United States); Hennrich, S. [Institut fuer Kernchemie, Universitaet Mainz, Mainz (Germany); Virtuelles Institut fuer Struktur der Kerne and Nuklearer Astrophysik, Mainz (Germany); Hosmer, P. [National Superconducting Cyclotron Laboratory, Michigan State University, E. Lansing, MI (United States); Joint Institute for Nuclear Astrophysics, Michigan State University, E. Lansing, MI (United States); Department of Physics and Astronomy, Michigan State University, E. Lansing, MI (United States)] (and others)

    2008-06-01

    Observed neutron-capture elemental abundances in metal-poor stars, along with ongoing analysis of the extremely metal-poor Eu-enriched sub-class provide new guidance for astrophysical models aimed at finding the r-process sites. The present paper emphasizes the importance of nuclear physics parameters entering in these models, particularly {beta}-decay properties of neutron-rich nuclei. In this context, several r-process motivated {beta}-decay experiments performed at the National Superconducting Cyclotron Laboratory (NSCL) are presented, including a summary of results and impact on model calculations.

  8. β-decay studies of r-process nuclei at NSCL

    Science.gov (United States)

    Pereira, J.; Aprahamian, A.; Arndt, O.; Becerril, A.; Elliot, T.; Estrade, A.; Galaviz, D.; Hennrich, S.; Hosmer, P.; Schnorrenberger, L.; Kessler, R.; Kratz, K.-L.; Lorusso, G.; Mantica, P. F.; Matos, M.; Montes, F.; Pfeiffer, B.; Quinn, M.; Santi, P.; Schatz, H.; Schertz, F.; Smith, E.; Tomlin, B. E.; Walters, W. B.; Wöhr, A.

    2008-06-01

    Observed neutron-capture elemental abundances in metal-poor stars, along with ongoing analysis of the extremely metal-poor Eu-enriched sub-class provide new guidance for astrophysical models aimed at finding the r-process sites. The present paper emphasizes the importance of nuclear physics parameters entering in these models, particularly β-decay properties of neutron-rich nuclei. In this context, several r-process motivated β-decay experiments performed at the National Superconducting Cyclotron Laboratory (NSCL) are presented, including a summary of results and impact on model calculations.

  9. Upper Limit on Star Formation and Metal Enrichment in Minihalos

    CERN Document Server

    Cen, Renyue

    2016-01-01

    An analysis of negative radiative feedback from resident stars in minihalos is performed. It is found that the most effective mechanism to suppress star formation is provided by infrared photons from resident stars via photo-detachment of ${\\rm H^-}$. It is shown that a stringent upper bound on (total stellar mass, metallicity) of ($\\sim 1000{\\rm M_\\odot}$, $-3.3\\pm 0.2$) in any newly minted atomic cooling halo can be placed, with the actual values possibly significantly lower. This has both important physical ramifications on formation of stars and supermassive black seeds in atomic cooling halos at high redshift, pertaining to processes of low temperature metal cooling, dust formation and fragmentation, and direct consequences on the faint end galaxy luminosity function at high redshift and cosmological reionization. The luminosity function of galaxies at the epoch of reionization may be substantially affected due to the combined effect of a diminished role of minihalos and an enhanced contribution from Pop...

  10. Chemo-dynamical evolution of the Local Group dwarf galaxies: The origin of r-process elements

    Science.gov (United States)

    Hirai, Y.; Ishimaru, Y.; Saitoh, T. R.; Fujii, M. S.; Hidaka, J.; Kajino, T.

    2016-06-01

    The r-process elements such as Au, Eu, and U are observed in the extremely metal-poor stars in the Milky Way halo and the Local Group dwarf galaxies. However, the origin of r-process elements has not yet been identified. The abundance of r-process elements of stars in the Local Group galaxies provides clues to clarify early evolutionary history of galaxies. It is important to understand the chemical evolution of the Local Group dwarf galaxies which would be building blocks of the Milky Way. In this study, we perform a series of N-body/smoothed particle hydrodynamic simulations of dwarf galaxies. We show that neutron star mergers can reproduce the observation of r-process elements. We find that the effects of gas mixing processes including metals in the star-forming region of a typical scale of giant molecular clouds ¥sim 10-100 pc play significant roles in the early chemical enrichment of dwarf galaxies. We also find that the star formation rate of ˜ 10^{-3} M_{⊙}yr^{-1} in early epoch (<1 Gyr) of galactic halo evolution is necessary for these results. Our results suggest that neutron star mergers are a major site of r-process.

  11. Supernova enrichment of planetary systems in low-mass star clusters

    CERN Document Server

    Nicholson, Rhana B

    2016-01-01

    The presence and abundance of short lived radioisotopes (SLRs) $^{26}$Al and $^{60}$Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe). Massive stars are more likely to form in massive star clusters ($>$1000 M$_{\\odot}$) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of $\\sim$1 pc. We investigate whether low-mass (50 - 200 M$_{\\odot}$) star clusters containing one or two massive stars are a more likely avenue for early Solar system enrichment as they are more dynamically quiescent. We analyse $N$-body simulations of the evolution of these low-mass clusters and find that a similar fraction of stars experience supernova enrichment than in high mass clusters, despite their lower densities. This is due to two-body relaxation, which causes a significant expansion before the first supernov...

  12. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    Science.gov (United States)

    Loewenstein, Michael

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the buildup of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are fully consistent with observations in the field, cluster Fe enrichment immediately tracked a rapid, top-heavy phase of star formation - although transport of Fe into the ICM may have been more prolonged and star formation likely continued beyond redshift 1. The means of this prompt enrichment consisted of SNII yielding greater than or equal to 0.1 solar mass per explosion (if the SNIa rate normalization is scaled down from its value in the field according to the relative number of candidate progenitor stars in the 3 - 8 solar mass range) and/or SNIa with short delay times originating during the rapid star formation epoch. Star formation is greater than 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day stellar mass in the form of stellar remnants, are substantially greater in clusters than in the field.

  13. The New Model of Chemical Evolution of r-process Elements Based on The Hierarchical Galaxy Formation I: Ba and Eu

    CERN Document Server

    Komiya, Yutaka; Suda, Takuma; Fujimoto, Masayuki Y

    2014-01-01

    We investigate the chemical enrichment of r-process elements in the early evolutionary stages of the Milky Way halo within the framework of hierarchical galaxy formation using a semi-analytic merger tree. In this paper, we focus on heavy r-process elements, Ba and Eu, of extremely metal-poor (EMP) stars and give constraints on their astronomical sites. Our models take into account changes of the surface abundances of EMP stars by the accretion of interstellar matter (ISM). We also consider metal-enrichment of intergalactic medium (IGM) by galactic winds and the resultant pre-enrichment of proto-galaxies. The trend and scatter of the observed r-process abundances are well reproduced by our hierarchical model with $\\sim 10\\%$ of core-collapse supernovae in low-mass end ($\\sim 10M_{\\odot}$) as a dominant r-process source and the star formation efficiency of $\\sim 10^{-10} \\hbox{yr}^{-1}$. For neutron star mergers as an r-process source, their coalescence timescale has to be $ \\sim 10^7$yrs, and the event rates $...

  14. Supernova enrichment and dynamical histories of solar-type stars in clusters

    CERN Document Server

    Parker, Richard J; Davies, Melvyn B; Meyer, Michael R

    2013-01-01

    We use N-body simulations of star cluster evolution to explore the hypothesis that short-lived radioactive isotopes found in meteorites, such as 26-Al, were delivered to the Sun's protoplanetary disc from a supernova at the epoch of Solar System formation. We cover a range of star cluster formation parameter space and model both clusters with primordial substructure, and those with smooth profiles. We also adopt different initial virial ratios - from cool, collapsing clusters to warm, expanding associations. In each cluster we place the same stellar population; the clusters each have 2100 stars, and contain one massive 25M_Sun star which is expected to explode as a supernova at about 6.6Myr. We determine the number of Solar (G)-type stars that are within 0.1 - 0.3pc of the 25M_Sun star at the time of the supernova, which is the distance required to enrich the protoplanetary disc with the 26-Al abundances found in meteorites. We then determine how many of these G-dwarfs are unperturbed `singletons'; stars whic...

  15. Chemical evolution of 244Pu in the solar vicinity and its implications for the properties of r-process production

    Science.gov (United States)

    Tsujimoto, Takuji; Yokoyama, Tetsuya; Bekki, Kenji

    2017-01-01

    Meteoritic abundances of r-process elements are analyzed to deduce the history of chemical enrichment by the r-process, from the beginning of disk formation to the present time in the solar vicinity. Our analysis combines the abundance information from short-lived radioactive nuclei such as 244Pu with the abundance information from stable r-process nuclei such as Eu. These two types of nuclei can be associated with one r-process event and an accumulation of events until the formation of the solar system, respectively. With the help of the observed local star formation (SF) history, we deduce the chemical evolution of 244Pu and obtain three main results: (i) the last r-process event occurred 130–140 Myr before the formation of the solar system; (ii) the present-day low 244Pu abundance as measured in deep-sea reservoirs results from the low recent SF rate compared to ∼4.5‑5 Gyr ago; and (iii) there were ∼15 r-process events in the solar vicinity from the formation of the Galaxy to the time of solar system’s formation and ∼30 r-process events to the present time. Then, adopting the hypothesis that a neutron star (NS) merger is the r-process production site, we find that the ejected r-process elements are extensively spread out and mixed with interstellar matter, with a mass of ∼ 3.5× {10}6 M⊙, which is about 100 times larger than that for supernova ejecta. In addition, the event frequency of r-process production is estimated to be 1 per ~1400 core-collapse supernovae, which is identical to the frequency of NS mergers estimated from the analysis of stellar abundances.

  16. ALMA Reveals Potential Localized Dust Enrichment from Massive Star Clusters in II Zw 40

    Science.gov (United States)

    Consiglio, S. Michelle; Turner, Jean L.; Beck, Sara; Meier, David S.

    2016-12-01

    We present subarcsecond images of submillimeter CO and continuum emission from a local galaxy forming massive star clusters: the blue compact dwarf galaxy II Zw 40. At ˜0.″4 resolution (20 pc), the CO(3-2), CO(1-0), 3 mm, and 870 μm continuum maps illustrate star formation on the scales of individual molecular clouds. Dust contributes about one-third of the 870 μm continuum emission, with free-free accounting for the rest. On these scales, there is not a good correspondence between gas, dust, and free-free emission. Dust continuum is enhanced toward the star-forming region as compared to the CO emission. We suggest that an unexpectedly low and spatially variable gas-to-dust ratio is the result of rapid and localized dust enrichment of clouds by the massive clusters of the starburst.

  17. Investigation for the enrichment pattern of the element abundances in r+s star HE 0338-3945: a special r-II star?

    CERN Document Server

    Cui, Wenyuan; Zhu, Zizhong; Zhang, Bo; 10.1088/0004-637X/708/1/51

    2010-01-01

    The very metal-poor star HE 0338-3945 shows a double-enhanced pattern of the neutron-capture elements. The study to this sample could make people gain a better understanding of s- and r-process nucleosynthesis at low metallicity. Using a parametric model,we find that the abundance pattern of the neutron-capture elements could be best explained by a binary system formed in a molecular cloud, which had been polluted by r-process material. The observed abundance pattern of C and N can be explained by an AGB model(Karakas & Lattanzio 2007), . Combing with the parameters obtained from Cui & Zhang (2006), we suggest that the initial mass of the AGB companion is most likely to be about 2.5Msun, which excludes the possibility of forming a type-1.5 supernova. By comparing with the observational abundance pattern of CS 22892-052, we find that the dominating production of O should accompany with the production of the heavy r-process elements of r+s stars. Similar to r-II stars, the heavy r-process elements are n...

  18. Helium enrichment and Carbon-star Production in Metal-rich Populations

    CERN Document Server

    Karakas, Amanda I

    2014-01-01

    We present new theoretical stellar evolutionary models of metal-rich asymptotic giant branch (AGB) stars. Stellar models are evolved with initial masses between 1Msun and 7Msun at Z=0.007, and 1Msun and 8Msun at Z=0.014 (solar) and at Z=0.03. We evolve models with a canonical helium abundance and with helium enriched compositions (Y=0.30, 0.35, 0.40) at Z=0.014 and Z=0.03. The efficiency of third dredge-up and the mass range of carbon stars decreases with an increase in metallicity. We predict carbon stars form from initial masses between 1.75-7Msun at Z=0.007 and between 2-4.5Msun at solar metallicity. At Z=0.03 the mass range for C-star production is narrowed to 3.25-4Msun. The third dredge-up is reduced when the helium content of the model increases owing to the reduced number of thermal pulses on the AGB. A small increase of Delta Y = 0.05 is enough to prevent the formation of C stars at Z=0.03, depending on the mass-loss rate, whereas at Z=0.014, an increase of Delta Y = 0.1 is required to prevent the fo...

  19. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    CERN Document Server

    Loewenstein, M

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the build-up of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are consistent with observations in the field, cluster Fe enrichment immediately tracks a rapid, top-heavy phase of star formation -- although transport of Fe into the ICM may be more prolonged and star formation likely continues to redshifts 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day st...

  20. The First Population II Stars Formed in Externally Enriched Mini-halos

    CERN Document Server

    Smith, Britton; O'Shea, Brian; Norman, Michael; Khochfar, Sadegh

    2015-01-01

    We present a simulation of the formation of the earliest Population II stars, starting from cosmological initial conditions and ending when metals created in the first supernovae are incorporated into a collapsing gas-cloud. This occurs after a supernova blast-wave collides with a nearby mini-halo, inducing further turbulence that efficiently mixes metals into the dense gas in the center of the halo. The gas that first collapses has been enriched to a metallicity of Z ~ 2e-5 Zsun. Due to the extremely low metallicity, collapse proceeds similarly to metal-free gas until dust cooling becomes efficient at high densities, causing the cloud to fragment into a large number of low mass objects. This external enrichment mechanism provides a plausible origin for the most metal-poor stars observed, such as SMSS J031300.36-670839.3, that appear to have formed out of gas enriched by a single supernova. This mechanism operates on shorter timescales than the time for low-mass mini-halos (M < 5e5 Msun) to recover their g...

  1. Galactic r-process production: The inhomogeneous approach

    CERN Document Server

    Wehmeyer, B; Thielemann, F -K

    2015-01-01

    The origin of elements made by the rapid neutron-capture process (r-process) is not fully understood. Different sources have been proposed, e.g., core-collapse supernovae and neutron star mergers. Old metal-poor stars carry the signature of the astrophysical r-process source(s). Europium is the most indicative element to trace the r-process production, since it is mostly made by the r-process and it is easy to observe compared to other heavy r-process elements. In this work we simulate the evolution of europium in our Galaxy with the inhomogeneous chemical evolution model ICE, and we compare our results with spectroscopic observations. We test the most important parameters affecting the chemical evolution of the r-process element Eu: (a) for neutron star mergers the coalescence time scale of the merger and the probability to experience a neutron star merger event after two supernova explosions occurred and formed a double neutron star system ) and (b) for the sub-class of magneto-rotationally driven Supernova...

  2. New Neutron-Capture Measurements in 23 Open Clusters. I. The R-Process

    CERN Document Server

    Overbeek, Jamie C; Jacobson, Heather R

    2016-01-01

    Neutron-capture elements, those with Z > 35, are the least well-understood in terms of nucleosynthesis and formation environments. The rapid neutron-capture, or r-process, elements are formed in the environments and/or remnants of massive stars, while the slow neutron-capture, or s-process, elements are primarily formed in low-mass AGB stars. These elements can provide much information about Galactic star formation and enrichment, but observational data is limited. We have assembled a sample of 68 stars in 23 open clusters that we use to probe abundance trends for six neutron-capture elements (Eu, Gd, Dy, Mo, Pr, and Nd) with cluster age and location in the disk of the Galaxy. In order to keep our analysis as homogenous as possible, we use an automated synthesis fitting program, which also enables us to measure multiple (3-10) lines for each element. We find that the pure r-process elements (Eu, Gd, and Dy) have positive trends with increasing cluster age, while the mixed r- and s- process elements (Mo, Pr, a...

  3. Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

    Science.gov (United States)

    Elmegreen, Bruce G.

    2017-02-01

    The self-enrichment of massive star clusters by p-processed elements is shown to increase significantly with increasing gas density as a result of enhanced star formation rates and stellar scatterings compared to the lifetime of a massive star. Considering the type of cloud core where a globular cluster (GC) might have formed, we follow the evolution and enrichment of the gas and the time dependence of stellar mass. A key assumption is that interactions between massive stars are important at high density, including interactions between massive stars and massive-star binaries that can shred stellar envelopes. Massive-star interactions should also scatter low-mass stars out of the cluster. Reasonable agreement with the observations is obtained for a cloud-core mass of ∼4 × 106 M ⊙ and a density of ∼2 × 106 cm‑3. The results depend primarily on a few dimensionless parameters, including, most importantly, the ratio of the gas consumption time to the lifetime of a massive star, which has to be low, ∼10%, and the efficiency of scattering low-mass stars per unit dynamical time, which has to be relatively large, such as a few percent. Also for these conditions, the velocity dispersions of embedded GCs should be comparable to the high gas dispersions of galaxies at that time, so that stellar ejection by multistar interactions could cause low-mass stars to leave a dwarf galaxy host altogether. This could solve the problem of missing first-generation stars in the halos of Fornax and WLM.

  4. Astronomical Oxygen Isotopic Evidence for Supernova Enrichment of the Solar System Birth Environment by Propagating Star Formation

    CERN Document Server

    Young, Edward D; Smith, Rachel L; Morris, Mark R; Pontoppidan, Klaus M

    2010-01-01

    New infrared absorption measurements of oxygen isotope ratios in CO gas from individual young stellar objects confirm that the solar system is anomalously high in its 18O/17O ratio compared with extra-solar oxygen in the Galaxy. We show that this difference in oxygen isotope ratios is best explained by 1 per cent enrichment of the proto-solar molecular cloud by ejecta from type II supernovae from a cluster having of order a few hundred stars that predated the Sun by at least 10 to 20 Myr. The likely source of exogenous oxygen was the explosion of one or more B stars during a process of propagating star formation.

  5. Ultra-faint dwarf galaxies as a test of early enrichment and metallicity-dependent star formation

    CERN Document Server

    Tassis, Konstantinos; Kravtsov, Andrey V

    2011-01-01

    The tight relation of star formation with molecular gas indicated by observations and assumed in recent models implies that the efficiency with which galaxies convert their gas into stars depends on gas metallicity. This is because the abundance of molecular hydrogen is sensitive to the abundance of dust, which catalyzes the formation of H_2 and helps to shield it from dissociating radiation. In this study we point out that in the absence of significant pre-enrichment by Population III stars forming out of zero metallicity gas, such H_2-based star formation is expected to leave an imprint in the form of bi-modality in the metallicity distribution among dwarf galaxies and in the metallicity distribution of stars within individual galaxies. The bi-modality arises because when gas metallicity (and dust abundance) is low, formation of molecular gas is inefficient, the gas consumption time scale is long, and star formation and metal enrichment proceed slowly. When metallicity reaches a critical threshold value sta...

  6. Primordial Black Holes and r -Process Nucleosynthesis

    Science.gov (United States)

    Fuller, George M.; Kusenko, Alexander; Takhistov, Volodymyr

    2017-08-01

    We show that some or all of the inventory of r -process nucleosynthesis can be produced in interactions of primordial black holes (PBHs) with neutron stars (NSs) if PBHs with masses 10-14 M⊙r -process content and evolution histories in these sites. Ejected matter is heated by beta decay, which leads to emission of positrons in an amount consistent with the observed 511-keV line from the Galactic center.

  7. Chemical enrichment of Damped Lyman Alpha systems as a direct constraint on Population III star formation

    CERN Document Server

    Kulkarni, Girish; Hennawi, Joseph F; Vangioni, Elisabeth

    2013-01-01

    Damped Ly-alpha absorbers (DLAs) can be used to measure gas-phase metallicities at large cosmological lookback times with high precision. Relative abundances can still be measured accurately deep into the reionization epoch (z > 6) using transitions redward of Ly-alpha. Here we study chemical evolution of DLAs using a constrained model for evolution of galaxies and IGM to determine the degree to which DLA abundance measurements can probe Population III enrichment. We find that if the critical metallicity of Population III to II transition is 5. Thus, a sample of DLA abundance measurements at high redshift holds the promise to constrain Population III IMF. A sample of just 10 DLAs with relative abundances measured to an accuracy of 0.1 dex is sufficient to constrain the Population III IMF at 4-sigma. These constraints may prove stronger than other probes such as metal-poor stars and individual DLAs. Our results provide a global picture of the cosmic thermal, ionization, and chemical evolution, and can rule ou...

  8. Impact of nuclear fission on r-process nucleosynthesis and origin of solar r-process elements

    Energy Technology Data Exchange (ETDEWEB)

    Shibagaki, Shota, E-mail: shota.shibagaki@nao.ac.jp [Department of Astronomy, Graduate School of Science, University of Tokyo, 2 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan and National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Kajino, Toshitaka [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan and Department of Astronomy, Graduate School of Science, University of Tokyo, 2 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Mathews, Grant J. [Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Chiba, Satoshi [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, 152-8850 (Japan)

    2015-02-24

    Binary neutron star mergers (NSMs) are expected to be main production sites of r-process elements. Their ejecta are extremely neutron-rich (Y{sub e}<0.1), and the r-process path proceeds along the neutron drip line and enters the region of fissile nuclei. In this situation, although superheavy nuclei may be synthesized and the r-process path may reach the island of stability, those are sensitive to theoretical models of nuclear masses and nuclear fission. In this study, we carry out r-process nucleosynthesis simulations in the NSMs. Our new nuclear reaction network code include new theoretical models of nuclear masses and nuclear fission. Our r-process simulation of a binary NSM shows that the final r-process elemental abundances exhibit flat pattern for A∼110-160, and several fission cycling operate in extremely neutron-rich conditions of the NSM. We find that the combination of the NSMs and the magnetorotational supernovae can reproduce the solar r-process elements. We discuss the validity of this interpretation.

  9. Detailed homogeneous abundance studies of 14 Galactic s-process enriched post-AGB stars: In search of lead (Pb)

    CERN Document Server

    De Smedt, Kenneth; Kamath, Devika; Siess, Lionel; Goriely, Stephane; Karakas, Amanda I; Manick, Rajeev

    2015-01-01

    This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. Lead (Pb) is the final product of the s-process nucleosynthesis and is predicted to have large overabundances with respect to other s-process elements in AGB stars of low metallicities. However, Pb abundance studies of enriched post-AGB stars in the Magellanic Clouds show the Pb overabundance is not observed. We used high-resolution UVES and HERMES spectra for detailed spectral abundance studies of our sample of 14 Galactic post-AGB stars. We do not find any clear evidence of Pb overabundances in our sample. Stars with T(eff) > 7500 K do not provide strong constraints on the Pb abundance. We conclude that the discrepancy between theory and observation increases towards lower metallicities. All objects, except IRAS 17279-1119, confirm the relation between neutron exposure [hs/ls] and third dredge-up efficiency [s/Fe], whereas no relation be...

  10. Recent Progress in the Understanding of the r-Process

    CERN Document Server

    Qian, Yong-Zhong

    2008-01-01

    A brief overview of the r-process is given with an emphasis on the observational implications for this process. The conditions required for the major production of the heavy r-process elements (r-elements) with mass numbers A >130 are discussed based on a generic astrophysical model where matter adiabatically expands from a hot and dense initial state. Nucleosynthesis in the neutrino-driven winds from nascent neutron stars is discussed as a specific example. Such winds readily produce the elements from Sr to Ag with A ~ 88 to 110 through charged-particle reactions in the alpha-process but appear incapable of making the heavy r-elements. Observations of elemental abundances in metal-poor stars have provided many valuable insights into the r-process. They have demonstrated that the production of the heavy r-elements must be associated with massive stars evolving on short timescales, provided evidence strongly favoring core-collapse supernovae over neutron star mergers as the major source for these elements, and...

  11. Radiative levitation in carbon-enhanced metal-poor stars with s-process enrichment

    CERN Document Server

    Matrozis, E

    2016-01-01

    A significant fraction of all metal-poor stars are carbon-rich. Most of these carbon-enhanced metal-poor (CEMP) stars also show enhancement in elements produced mainly by the s-process (CEMP-s stars) and evidence suggests that the origin of these non-standard abundances can be traced to mass transfer from a binary asymptotic giant branch (AGB) companion. Thus, observations of CEMP-s stars are commonly used to infer the nucleosynthesis output of low-metallicity AGB stars. A crucial step in this exercise is understanding what happens to the accreted material after mass transfer ceases. Here we present models of the post-mass-transfer evolution of CEMP-s stars considering the physics of thermohaline mixing and atomic diffusion, including radiative levitation. We find that stars with typical CEMP-s star masses (M ~ 0.85 Msun) have very shallow convective envelopes (Menv +4). We are therefore unable to reproduce the spread in the observed abundances with these models and conclude that some other physical process m...

  12. Metal-Poor Stars and the Chemical Enrichment of the Universe

    CERN Document Server

    Frebel, Anna

    2011-01-01

    Metal-poor stars hold the key to our understanding of the origin of the elements and the chemical evolution of the Universe. This chapter describes the process of discovery of these rare stars, the manner in which their surface abundances (produced in supernovae and other evolved stars) are determined from the analysis of their spectra, and the interpretation of their abundance patterns to elucidate questions of origin and evolution. More generally, studies of these stars contribute to other fundamental areas that include nuclear astrophysics, conditions at the earliest times, the nature of the first stars, and the formation and evolution of galaxies -- including our own Milky Way. We illustrate this with results from studies of lithium formed during the Big Bang; of stars dated to within ~1 Gyr of that event; of the most metal-poor stars, with abundance signatures very different from all other stars; and of the build-up of the elements over the first several Gyr. The combination of abundance and kinematic si...

  13. Detailed homogeneous abundance studies of 14 Galactic s-process enriched post-AGB stars: In search of lead (Pb)

    Science.gov (United States)

    De Smedt, K.; Van Winckel, H.; Kamath, D.; Siess, L.; Goriely, S.; Karakas, A. I.; Manick, R.

    2016-03-01

    Context. This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. The goal at large is to provide improved observational constraints to the models of the complex interplay between the AGB s-process nucleosynthesis and the associated mixing processes. Aims: Lead (Pb) is the final product of the s-process nucleosynthesis and is predicted to have large overabundances with respect to other s-process elements in AGB stars of low metallicities. However, Pb abundance studies of s-process enriched post-AGB stars in the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. The determined upper limits based on spectral studies are much lower than what is predicted. In this paper, we focus specifically on the Pb abundance of 14 Galactic s-process enhanced post-AGB stars to check whether the same discrepancy is present in the Galaxy as well. Among these 14 objects, two were not yet subject to a detailed abundance study in the literature. We apply the same method to obtain accurate abundances for the 12 others. Our homogeneous abundance results provide the input of detailed spectral synthesis computations in the spectral regions where Pb lines are located. Methods: We used high-resolution UVES and HERMES spectra for detailed spectral abundance studies of our sample of Galactic post-AGB stars. None of the sample stars display clear Pb lines, and we only deduced upper limits of the Pb abundance by using spectrum synthesis in the spectral ranges of the strongest Pb lines. Results: We do not find any clear evidence of Pb overabundances in our sample. The derived upper limits are strongly correlated with the effective temperature of the stars with increasing upper limits for increasing effective temperatures. We obtain stronger Pb constraints on the cooler objects. Moreover, we confirm the s-process enrichment and carbon enhancement of two

  14. Radiative levitation in carbon-enhanced metal-poor stars with s-process enrichment

    Science.gov (United States)

    Matrozis, E.; Stancliffe, R. J.

    2016-07-01

    A significant fraction of all metal-poor stars are carbon-rich. Most of these carbon-enhanced metal-poor (CEMP) stars also show enhancement in elements produced mainly by the s-process (CEMP-s stars), and evidence suggests that the origin of these non-standard abundances can be traced to mass transfer from a binary asymptotic giant branch (AGB) companion. Thus, observations of CEMP-s stars are commonly used to infer the nucleosynthesis output of low-metallicity AGB stars. A crucial step in this exercise is understanding what happens to the accreted material after mass transfer ceases. Here we present models of the post-mass-transfer evolution of CEMP-s stars considering the physics of thermohaline mixing and atomic diffusion, including radiative levitation. We find that stars with typical CEMP-s star masses, M ≈ 0.85 M⊙, have very shallow convective envelopes (Menv ≲ 10-7 M⊙). Hence, the surface abundance variations arising from the competition between gravitational settling and radiative levitation should be orders of magnitude larger than observed (e.g. [C/Fe] +4). Lower-mass stars (M ≈ 0.80 M⊙) retain thicker convective envelopes and thus show variations more in line with observations, but are generally too unevolved (log g > 4) when they reach the age of the Universe. We are therefore unable to reproduce the spread in the observed abundances with these models and conclude that some other physical process must largely suppress atomic diffusion in the outer layers of CEMP-s stars. We demonstrate that this could be achieved by some additional (turbulent) mixing process operating at the base of the convective envelope, as found by other authors. Alternatively, mass-loss rates around 10-13 M⊙yr-1 could also negate most of the abundance variations by eroding the surface layers and forcing the base of the convective envelope to move inwards in mass. Since atomic diffusion cannot have a substantial effect on the surface abundances of CEMP-s stars, the

  15. R-process and alpha-elements in the Galactic disk: Kinematic correlations

    CERN Document Server

    Koch, A

    2004-01-01

    Recent studies of elemental abundances in the Galactic halo and in the Galactic disk have underscored the possibility to kinematically separate different Galactic subcomponents. Correlations between the galactocentric rotation velocity and various element ratios were found, providing an important means to link different tracers of star formation and metal enrichment to the Galactic components of different origin (collapse vs. accretion). In the present work we determine stellar kinematics for a sample of 124 disk stars, which we derive from their orbits based on radial velocities and proper motions from the the literature. Our stars form a subsample of the Edvardsson et al. (1993) sample and we concentrate on three main tracers: (i) Europium as an r-process element is predominantly produced in Supernovae of type II. (ii) Likewise, alpha-elements, such as Ca, Si, Mg, are synthesised in SNe II, contrary to iron, which is being produced preferentially in SNe Ia. (iii) The s-process element Barium is a measure of...

  16. Weak magnetic field, solid-envelope rotation, and wave-induced N-enrichment in the SPB star ζ Cassiopeiae

    Science.gov (United States)

    Briquet, M.; Neiner, C.; Petit, P.; Leroy, B.; de Batz, B.

    2016-03-01

    Aims: The main-sequence B-type star ζ Cassiopeiae is known as a N-rich star with a magnetic field discovered with the Musicos spectropolarimeter. We model the magnetic field of the star by means of 82 new spectropolarimetric observations of higher precision to investigate the field strength, topology, and effect. Methods: We gathered data with the Narval spectropolarimeter installed at Télescope Bernard Lyot (TBL; Pic du Midi, France) and applied the least-squares deconvolution technique to measure the circular polarisation of the light emitted from ζ Cas. We used a dipole oblique rotator model to determine the field configuration by fitting the longitudinal field measurements and by synthesizing the measured Stokes V profiles. We also made use of the Zeeman-Doppler imaging technique to map the stellar surface and to deduce the difference in rotation rate between the pole and equator. Results: ζ Cas exhibits a polar field strength Bpol of 100-150 G, which is the weakest polar field observed so far in a massive main-sequence star. Surface differential rotation is ruled out by our observations and the field of ζ Cas is strong enough to enforce rigid internal rotation in the radiative zone according to theory. Thus, the star rotates as a solid body in the envelope. Conclusions: We therefore exclude rotationally induced mixing as the cause of the surface N-enrichment. We discuss that the transport of chemicals from the core to the surface by internal gravity waves is the most plausible explanation for the nitrogen overabundance at the surface of ζ Cas. Based on observations obtained at the Télescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique (CNRS) of France.

  17. ALMA Reveals Potential Localized Dust Enrichment from Massive Star Clusters in II Zw 40

    CERN Document Server

    Consiglio, S Michelle; Beck, Sara; Meier, David S

    2016-01-01

    We present subarcsecond images of submillimeter CO and continuum emission from a local galaxy forming massive star clusters: the blue compact dwarf galaxy II Zw 40. At $\\sim$0.4" resolution (20 pc), the CO(3-2), CO(1-0), 3mm and 870${\\mu}$m continuum maps illustrate star formation on the scales of individual molecular clouds. Dust contributes about a third of the 870${\\mu}$m continuum emission, with free-free accounting for the rest. On these scales, there is not a good correspondence between gas, dust, and free-free emission. Dust continuum is enhanced toward the star-forming region as compared to the CO emission. We suggest that an unexpectedly low and spatially variable gas-to-dust ratio is the result of massive clusters of the starburst.

  18. Solar r-process-constrained actinide production in neutrino-driven winds of supernovae

    Science.gov (United States)

    Goriely, S.; Janka, H.-Th.

    2016-07-01

    Long-lived radioactive nuclei play an important role as nucleo-cosmochronometers and as cosmic tracers of nucleosynthetic source activity. In particular, nuclei in the actinide region like thorium, uranium, and plutonium can testify to the enrichment of an environment by the still enigmatic astrophysical sources that are responsible for the production of neutron-rich nuclei by the rapid neutron-capture process (r-process). Supernovae and merging neutron-star (NS) or NS-black hole binaries are considered as most likely sources of the r-nuclei. But arguments in favour of one or the other or both are indirect and make use of assumptions; they are based on theoretical models with remaining simplifications and shortcomings. An unambiguous observational determination of a production event is still missing. In order to facilitate searches in this direction, e.g. by looking for radioactive tracers in stellar envelopes, the interstellar medium or terrestrial reservoirs, we provide improved theoretical estimates and corresponding uncertainty ranges for the actinide production (232Th, 235, 236, 238U, 237Np, 244Pu, and 247Cm) in neutrino-driven winds of core-collapse supernovae. Since state-of-the-art supernova models do not yield r-process viable conditions - but still lack, for example, the effects of strong magnetic fields - we base our investigation on a simple analytical, Newtonian, adiabatic and steady-state wind model and consider the superposition of a large number of contributing components, whose nucleosynthesis-relevant parameters (mass weight, entropy, expansion time-scale, and neutron excess) are constrained by the assumption that the integrated wind nucleosynthesis closely reproduces the Solar system distribution of r-process elements. We also test the influence of uncertain nuclear physics.

  19. History of Star Formation and Chemical Enrichment in the Milky Way Disk

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Based on a physical treatment of the star formation law similar to thatgiven by Efstathiou, we have improved our two-component chemical evolution modelfor the Milky Way disk. Two gas infall rates are compared, one exponential, oneGaussian. It is shown that the star formation law adopted in this paper dependsmore strongly on the gas surface density than that in Chang et al. It has large effectson the history of star formation and gas evolution of the whole disk. In the solarneighborhood, the history of chemical evolution and star formation is not sensitiveto whether the infall rate is Gaussian or exponential. For the same infall time scale,both forms predict the same behavior for the current properties of the Galactic disk.The model predictions do depend on whether or not the infall time scale varies withthe radius, but current available observations cannot decide which case is the morerealistic. Our results also show that it would be inadequate to describe the gradientevolution along the Galactic disk by only one word "flatter" or "steeper", as wassuggested by Hou et al. and Chiapinni et al. We point out that both the absolutevalue and the evolution of the abundance gradient may be different in the inner andouter regions.

  20. The yields of r-process elements and chemical evolution of the Galaxy

    CERN Document Server

    Chen, Z; Chen, Y P; Cui, W Y; Zhang, B; Chen, Zhe; Zhang, Jiang; Chen, YanPing; Cui, WenYuan; Zhang, Bo

    2006-01-01

    The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metal-poor stars on the left-side [Ba/Mg]-[Mg/H] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass $M_{ms}\\leq18M_{\\odot}$ are infertile sources and the SNe II with 20$M_{\\odot}\\leq M_{ms}\\leq 40M_{\\odot}$are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20$M_{\\odot}\\leq M_{ms}\\leq40M_{\\odot}$ with compared to the all massive stars is about $\\sim$18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced

  1. Star Formation, Quenching And Chemical Enrichment In Local Galaxies From Integral Field Spectroscopy

    Science.gov (United States)

    Belfiore, Francesco

    2017-08-01

    Within the currently well-established ΛCDM cosmological framework we still lack a satisfactory understanding of the processes that trigger, regulate and eventually quench star formation on galactic scales. Gas flows (including inflows from the cosmic web and supernovae-driven outflows) are considered to act as self-regulatory mechanisms, generating the scaling relations between stellar mass, star formation rate and metallicity observed in the local Universe by large spectroscopic surveys. These surveys, however, have so far been limited by the availability of only one spectrum per galaxy. The aim of this dissertation is to expand the study of star formation and chemical abundances to resolved scales within galaxies by using integral field spectroscopy (IFS) data, mostly from the ongoing SDSS-IV MaNGA survey. In the first part of this thesis I demonstrate the ubiquitous presence of extended low ionisation emission-line regions (LIERs) in both late- and early-type galaxies. By studying the Hα equivalent width and diagnostic line ratios radial profiles, together with tracers of the underlying stellar population, I show that LIERs are not due to a central point source but to hot evolved (post-asymptotic giant branch) stars. In light of this, I suggest a new classification scheme for galaxies based on their line emission. By analysing the colours, star formation rates, morphologies, gas and stellar kinematics and environmental properties of galaxies with substantial LIER emission, I identify two distinct populations. Galaxies where the central regions are LIER-like, but show star formation at larger radii are late types in which star formation is slowly quenched inside-out. This transformation is associated with massive bulges. Galaxies dominated by LIER emission at all radii, on the other hand, are red-sequence galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Quiescent galaxies devoid of line emission reside in denser

  2. Star Clusters in M31. V. Evidence for Self-Enrichment in Old M31 Clusters from Integrated Spectroscopy

    CERN Document Server

    Schiavon, Ricardo P; Conroy, Charlie; Graves, Genevieve J; Strader, Jay; MacArthur, Lauren A; Courteau, Stephane; Harding, Paul

    2013-01-01

    In the past decade, the notion that globular clusters (GCs) are composed of coeval stars with homogeneous initial chemical compositions has been challenged by growing evidence that they host an intricate stellar population mix, likely indicative of a complex history of star formation and chemical enrichment. Several models have been proposed to explain the existence of multiple stellar populations in GCs, but no single model provides a fully satisfactory match to existing data. Correlations between chemistry and global parameters such as cluster mass or luminosity are fundamental clues to the physics of GC formation. In this Letter, we present an analysis of the mean abundances of Fe, Mg, C, N, and Ca for 72 old GCs from the Andromeda galaxy. We show for the first time that there is a correlation between the masses of GCs and the mean stellar abundances of nitrogen, spanning almost two decades in mass. This result sheds new light on the formation of GCs, providing important constraints on their internal chemi...

  3. A spectral atlas of post-main-sequence stars in omega Centauri: kinematics, evolution, enrichment and interstellar medium

    CERN Document Server

    van Loon, Jacco Th; Smalley, Barry; Smith, Andrew W; Lyons, Nicola A; McDonald, Iain; Boyer, Martha L

    2007-01-01

    We present a spectral atlas of the post-main-sequence population of the most massive Galactic globular cluster, omega Centauri. Spectra were obtained of more than 1500 stars selected as uniformly as possible from across the (B, B-V) colour-magnitude diagram of the proper motion cluster member candidates of van Leeuwen et al. (2000). The spectra were obtained with the 2dF multi-fibre spectrograph at the Anglo Australian Telescope, and cover the approximate range lambda~3840-4940 Angstroem. We measure the radial velocities, effective temperatures, metallicities and surface gravities by fitting ATLAS9 stellar atmosphere models. We analyse the cluster membership and stellar kinematics, interstellar absorption in the Ca II K line at 3933 Angstroem, the RR Lyrae instability strip and the extreme horizontal branch, the metallicity spread and bimodal CN abundance distribution of red giants, nitrogen and s-process enrichment, carbon stars, pulsation-induced Balmer line emission on the asymptotic giant branch (AGB), an...

  4. Probing the Large Magellanic Cloud's recent chemical enrichment history through its star clusters

    CERN Document Server

    Palma, Tali; Geisler, Doug; Gramajo, Luciana V; Ahumada, Andrea V

    2015-01-01

    We present Washington system colour-magnitude diagrams (CMDs) for 17 practically unstudied star clusters located in the bar as well as in the inner disc and outer regions of the Large Magellanic Cloud (LMC). Cluster sizes were estimated from star counts distributed throughout the entire observed fields. Based on the best fits of theoretical isochrones to the cleaned $(C-T_1,T_1)$ CMDs, as well as on the $\\delta T_1$ parameter and the standard giant branch method, we derive ages and metallicities for the cluster sample. Four objects are found to be intermediate-age clusters (1.8-2.5 Gyr), with [Fe/H] ranging from -0.66 to -0.84. With the exception of SL263, a very young cluster ($\\sim$ 16 Myr), the remaining 12 objects are aged between 0.32 and 0.89 Gyr, with their [Fe/H] values ranging from -0.19 to -0.50. We combined our results with those for other 231 clusters studied in a similar way using the Washington system. The resulting age-metallicity relationship shows a significant dispersion in metallicities, wh...

  5. Enriched haloes at redshift z = 2 with no star formation: implications for accretion and wind scenarios

    Science.gov (United States)

    Bouché, N.; Murphy, M. T.; Péroux, C.; Contini, T.; Martin, C. L.; Forster Schreiber, N. M.; Genzel, R.; Lutz, D.; Gillessen, S.; Tacconi, L.; Davies, R.; Eisenhauer, F.

    2012-01-01

    In order to understand which process (e.g. galactic winds, cold accretion) is responsible for the cool (T ˜ 104 K) halo gas around galaxies, we embarked on a programme to study the star formation properties of galaxies selected by their Mg II absorption signature in quasar spectra. Specifically, we searched for the Hα line emission from galaxies near very strong z ≃ 2 Mg II absorbers (with rest-frame equivalent width ? Å) because these could be the signposts of outflows or inflows. Surprisingly, we detect Hα from only four hosts out of 20 sightlines (and two out of the 19 H I-selected sightlines), despite reaching a star formation rate (SFR) sensitivity limit of 2.9 M⊙ yr-1 (5σ) for a Chabrier initial mass function. This low success rate (4/20) is in contrast with our z ≃ 1 survey where we detected 66 per cent (14/21) of the Mg II hosts (down to 0.6 M⊙ yr-1; 5σ). Taking into account the difference in sensitivity between the two surveys, we should have been able to detect ≥11.4 (≥7.6) of the 20 z ≃ 2 hosts - assuming that SFR evolves as ∝(1 + z)γ with γ= 2.5 (or γ= 0) respectively - whereas we found only four galaxies. Interestingly, all the z = 2 detected hosts have observed SFRs ≳ 9 M⊙ yr-1, well above our sensitivity limit, while at z = 1 they all have SFR Prochaska et al. (2005); (4) from Ledoux et al. (2006) (5) from Ryabinkov, Kaminker & Varshalovich (2003); (6) from Srianand et al. (2008)]; (6) FWHM of the seeing PSF; (7) exposure time; (8) observing run ID; (9) dates of observations. 1Source common to both samples.

  6. The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries

    Science.gov (United States)

    Arnould, M.; Goriely, S.; Takahashi, K.

    2007-09-01

    The r-process, or the rapid neutron-capture process, of stellar nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system. A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. Fission probabilities of very neutron-rich actinides have also to be known in order to determine the most massive nuclei that have a chance to be involved in the r-process. Even the properties of asymmetric nuclear matter may enter the problem. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented. Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. The ultimate goal of r-process studies is clearly to identify realistic sites for the development of the r-process. Here too, the challenge is enormous, and the solution still eludes us. For long, the core collapse supernova of massive stars has been envisioned as the privileged r-process location. We present a brief summary of the one- or multidimensional spherical or non-spherical explosion simulations available to-date. Their predictions are confronted with the requirements imposed to obtain an r-process. The possibility of r-nuclide synthesis during the decompression of the matter of neutron stars following their merging is also discussed. Given the uncertainties remaining on the astrophysical r-process site and on the involved nuclear physics, any confrontation between predicted r-process

  7. The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries

    Energy Technology Data Exchange (ETDEWEB)

    Arnould, M. [Institut d' Astronomie et d' Astrophysique, Universite Libre de Bruxelles, CP226, B-1050 Brussels (Belgium)], E-mail: marnould@astro.ulb.ac.be; Goriely, S.; Takahashi, K. [Institut d' Astronomie et d' Astrophysique, Universite Libre de Bruxelles, CP226, B-1050 Brussels (Belgium)

    2007-09-15

    The r-process, or the rapid neutron-capture process, of stellar nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system. A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. Fission probabilities of very neutron-rich actinides have also to be known in order to determine the most massive nuclei that have a chance to be involved in the r-process. Even the properties of asymmetric nuclear matter may enter the problem. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented. Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. The ultimate goal of r-process studies is clearly to identify realistic sites for the development of the r-process. Here too, the challenge is enormous, and the solution still eludes us. For long, the core collapse supernova of massive stars has been envisioned as the privileged r-process location. We present a brief summary of the one- or multidimensional spherical or non-spherical explosion simulations available to-date. Their predictions are confronted with the requirements imposed to obtain an r-process. The possibility of r-nuclide synthesis during the decompression of the matter of neutron stars following their merging is also discussed. Given the uncertainties remaining on the astrophysical r-process site and on the involved nuclear physics, any confrontation between predicted r-process

  8. The impact of global nuclear mass model uncertainties on r-process abundance predictions

    Directory of Open Access Journals (Sweden)

    Mumpower M.

    2015-01-01

    Full Text Available Rapid neutron capture or ‘r-process’ nucleosynthesis may be responsible for half the production of heavy elements above iron on the periodic table. Masses are one of the most important nuclear physics ingredients that go into calculations of r-process nucleosynthesis as they enter into the calculations of reaction rates, decay rates, branching ratios and Q-values. We explore the impact of uncertainties in three nuclear mass models on r-process abundances by performing global monte carlo simulations. We show that root-mean-square (rms errors of current mass models are large so that current r-process predictions are insufficient in predicting features found in solar residuals and in r-process enhanced metal poor stars. We conclude that the reduction of global rms errors below 100 keV will allow for more robust r-process predictions.

  9. RELATIVE CONTRIBUTIONS OF THE WEAK, MAIN, AND FISSION-RECYCLING r-PROCESS

    Energy Technology Data Exchange (ETDEWEB)

    Shibagaki, S.; Kajino, T. [Department of Astronomy, The University of Tokyo, 113-033 Tokyo (Japan); Mathews, G. J.; Nishimura, S. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 (Japan); Chiba, S. [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550 (Japan); Lorusso, G. [RIKEN Nishina Center, 2-1 Hirosawa, Wako-shi, Saitama 351-0198 (Japan)

    2016-01-10

    There has been a persistent conundrum in attempts to model the nucleosynthesis of heavy elements by rapid neutron capture (the r-process). Although the locations of the abundance peaks near nuclear mass numbers 130 and 195 identify an environment of rapid neutron capture near closed nuclear shells, the abundances of elements just above and below those peaks are often underproduced by more than an order of magnitude in model calculations. At the same time, there is a debate in the literature as to what degree the r-process elements are produced in supernovae or the mergers of binary neutron stars. In this paper we propose a novel solution to both problems. We demonstrate that the underproduction of nuclides above and below the r-process peaks in main or weak r-process models (like magnetohydrodynamic jets or neutrino-driven winds in core-collapse supernovae) can be supplemented via fission fragment distributions from the recycling of material in a neutron-rich environment such as that encountered in neutron star mergers (NSMs). In this paradigm, the abundance peaks themselves are well reproduced by a moderately neutron-rich, main r-process environment such as that encountered in the magnetohydrodynamical jets in supernovae supplemented with a high-entropy, weakly neutron-rich environment such as that encountered in the neutrino-driven-wind model to produce the lighter r-process isotopes. Moreover, we show that the relative contributions to the r-process abundances in both the solar system and metal-poor stars from the weak, main, and fission-recycling environments required by this proposal are consistent with estimates of the relative Galactic event rates of core-collapse supernovae for the weak and main r-process and NSMs for the fission-recycling r-process.

  10. Star formation in the first galaxies - III. Formation, evolution, and characteristics of the first metal-enriched stellar cluster

    Science.gov (United States)

    Safranek-Shrader, Chalence; Montgomery, Michael H.; Milosavljević, Miloš; Bromm, Volker

    2016-01-01

    We simulate the formation of a low-metallicity (10-2 Z⊙) stellar cluster at redshift z ˜ 14. Beginning with cosmological initial conditions, the simulation utilizes adaptive mesh refinement and sink particles to follow the collapse and evolution of gas past the opacity limit for fragmentation, thus resolving the formation of individual protostellar cores. A time- and location-dependent protostellar radiation field, which heats the gas by absorption on dust, is computed by integration of protostellar evolutionary tracks. The simulation also includes a robust non-equilibrium chemical network that self-consistently treats gas thermodynamics and dust-gas coupling. The system is evolved for 18 kyr after the first protostellar source has formed. In this time span, 30 sink particles representing protostellar cores form with a total mass of 81 M⊙. Their masses range from ˜0.1 to 14.4 M⊙ with a median mass ˜0.5-1 M⊙. Massive protostars grow by competitive accretion while lower mass protostars are stunted in growth by close encounters and many-body ejections. In the regime explored here, the characteristic mass scale is determined by the cosmic microwave background temperature floor and the onset of efficient dust-gas coupling. It seems unlikely that host galaxies of the first bursts of metal-enriched star formation will be detectable with the James Webb Space Telescope or other next-generation infrared observatories. Instead, the most promising access route to the dawn of cosmic star formation may lie in the scrutiny of metal-poor, ancient stellar populations in the Galactic neighbourhood. The observable targets corresponding to the system simulated here are ultra-faint dwarf satellite galaxies such as Boötes II and Willman I.

  11. The alpha -Process and the r-Process

    Science.gov (United States)

    Woosley, S. E.; Hoffman, R. D.

    1992-12-01

    If material initially in nuclear statistical equilibrium (NSE) at high temperature and containing a large fraction of alpha -particles (or nucleons) is expanded and cooled so rapidly that not all the alpha -particles have time to reassemble, its final composition will differ substantially from what is traditionally calculated for particle-deficient freeze-outs. It has long been known that this phenomenon, the ``alpha -rich freeze-out," can lead to the production of elements heavier than the iron group, but only up to about zinc (A ~ 66). Here we explore the alpha -rich freeze-out for values of neutron excess larger than previously treated and discover nuclear systematics that, for neutron excesses greater than about 0.05, allow the creation of heavier elements all the way up to A ~ 100, even when most of the ejecta is in the form of heavy elements. In the limit of a very large fraction of unassembled alpha -particles and a large neutron excess, the alpha -rich freeze-out merges smoothly into the classical r-process. In contrast to previous studies, we find that a large part of the nuclear flow in the r-process may be carried by charged particle reactions up to about A = 100. We speculate that the site of these processes is the high entropy ``wind'' of a young (age 1-10 s) neutron star in which neutrino energy deposition is driving mass loss. The appropriate conditions exist in the delayed supernova explosion mechanism of Mayle & Wilson, but they may occur in other models as well. The mass of r-process ejected per supernova is expected to be ~ 10(-4) M\\sun \\ per Type II or Type Ib supernova, but this will be sensitive to details of the presupernova structure, the explosion mechanism, and the amount of material that falls back onto the neutron star when the reverse shock arrives there.

  12. Detailed Chemical Abundances in the r-Process-Rich Ultra-Faint Dwarf Galaxy Reticulum 2

    CERN Document Server

    Roederer, Ian U; Bailey, John I; Song, Yingyi; Bell, Eric F; Crane, Jeffrey D; Loebman, Sarah; Nidever, David L; Olszewski, Edward W; Shectman, Stephen A; Thompson, Ian B; Valluri, Monica; Walker, Matthew G

    2016-01-01

    The ultra-faint dwarf galaxy Reticulum 2 (Ret 2) was recently discovered in images obtained by the Dark Energy Survey. We have observed the four brightest red giants in Ret 2 at high spectral resolution using the Michigan/Magellan Fiber System. We present detailed abundances for as many as 20 elements per star, including 12 elements heavier than the Fe group. We confirm previous detection of high levels of r-process material in Ret 2 (mean [Eu/Fe]=+1.69+/-0.05) found in three of these stars (mean [Fe/H]=-2.88+/-0.10). The abundances closely match the r-process pattern found in the well-studied metal-poor halo star CS22892-052. Such r-process-enhanced stars have not been found in any other ultra-faint dwarf galaxy, though their existence has been predicted by at least one model. The fourth star in Ret 2 ([Fe/H]=-3.42+/-0.20) contains only trace amounts of Sr ([Sr/Fe]=-1.73+/-0.43) and no detectable heavier elements. One r-process enhanced star is also enhanced in C (natal [C/Fe]=+1.1). This is only the third s...

  13. Reaction Sensitivity of r-Process Nucleosynthesis

    CERN Document Server

    Sasaqui, T; Mathews, G J; Otsuki, K; Nakamura, K; Sasaqui, Taka.

    2005-01-01

    We study the efficiency and sensitivity of r-process nucleosynthesis to a number of light nuclear reaction rates. We adopt empirical power-law relations to parameterize the reaction sensitivities. We utilize two different hydrodynamic models for the neutrino-driven winds in order to study the dependence of our result on supernova wind models. We also utilize an exponential model to approximate a wide variety of other plausible conditions for the r-process. We identify several specific nuclear reactions among light neutron-rich nuclei that play a critical role in determining the final r-process nucleosynthesis yields. As an illustration, we examine ``semi-waing'' points among the carbon isotopes. We show that not only neutron capture and $\\beta$-decay, but also $(\\alpha, \\mathrm{n})$ reactions are important in determining waiting points along the r-process path. Our numerical results from this sensitivity analysis serve foremost to clarify which light nuclear reactions are most influential in determining the f...

  14. Astrophysical site(s of r-process elements in galactic chemodynamical evolution model

    Directory of Open Access Journals (Sweden)

    Hirai Yutaka

    2016-01-01

    Full Text Available Astrophysical site(s of rapid neutron-capture process (r-process is (are not identified yet. Although core-collapse supernovae have been regarded as one of the possible candidates of the astrophysical site of r-process, nucleosynthesis studies suggest that serious difficulties in core-collapse supernovae to produce heavy elements with mass number of ≳110. Recent studies show that neutron star mergers (NSMs can synthesize these elements due to their neutron rich environment. Some chemical evolution studies of the Milky Way halo, however, hardly reproduce the observed star-to-star scatters of the abundance ratios of r-process elements (e.g., Eu in extremely metal-poor stars. This is because of their low rate (∼ 10−4 yr−1 for a Milky Way size galaxy and long merger time (≳ 100 Myr. This problem might be solved if the stars in the Galactic halo are consisted of the stars formed in dwarf galaxies where the star formation efficiencies were very low. In this study, we carry out numerical simulations of galactic chemo-dynamical evolution using an N-body/smoothed particle hydrodynamics code. We construct detailed chemo-dynamical evolution model for the Local Group dwarf spheroidal galaxies (dSphs assuming that the NSMs are the major source of r-process elements. Our models successfully reproduce the observed dispersion in [Eu/Fe] as a function of [Fe/H] if we set merger time of NSMs, ≲ 300 Myr with the Galactic NSM rate of ∼ 10−4 yr−1. In addition, our results are consistent with the observed metallicity distribution of dSphs. In the early phase (≲1 Gyr of galaxy evolution is constant due to low star formation efficiency of dSphs. This study supports the idea that NSMs are the major site of r-process nucleosynthesis.

  15. Solar r-process-constrained actinide production in neutrino-driven winds of supernovae

    CERN Document Server

    Goriely, S

    2016-01-01

    Long-lived radioactive nuclei play an important role as nucleo-cosmochronometers and as cosmic tracers of nucleosynthetic source activity. In particular nuclei in the actinide region like thorium, uranium, and plutonium can testify to the enrichment of an environment by the still enigmatic astrophysical sources that are responsible for the production of neutron-rich nuclei by the rapid neutron-capture process (r-process). Supernovae and merging neutron-star (NS) or NS-black hole binaries are considered as most likely sources of the r-nuclei. But arguments in favour of one or the other or both are indirect and make use of assumptions; they are based on theoretical models with remaining simplifications and shortcomings. An unambiguous observational determination of a production event is still missing. In order to facilitate searches in this direction, e.g.\\ by looking for radioactive tracers in stellar envelopes, the interstellar medium or terrestrial reservoirs, we provide improved theoretical estimates and co...

  16. The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars -- CEMP-s stars

    CERN Document Server

    Hansen, T T; Nordström, B; Beers, T C; Placco, V M; Yoon, J; Buchhave, L A

    2016-01-01

    Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high- and low-C bands, mostly populated by binary and single stars, respectively. Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit strong enhancements of neutron-capture elements associated with the s-process. This allows us to test whether local mass transfer from a binary companion is necessary and sufficient to explain their dramatic carbon excesses. Eighteen of the 22 stars exhibit clear orbital motion, yielding a binary frequency of 82+-10%, while four stars appear to be single (18+-10%). We thus confirm that the binary frequency of CEMP-s stars...

  17. A search for metal-poor stars pre-enriched by pair-instability supernovae I.A pilot study for target selection from Sloan Digital Sky Survey

    Institute of Scientific and Technical Information of China (English)

    Jing Ren; Norbert Christlieb; Gang Zhao

    2012-01-01

    We report on a pilot study on identifying metal-poor stars pre-enriched by Pair-Instability Supernovae (PISNe).Very massive,first generation (Population Ⅲ) stars (140 M⊙ ≤ M ≤ 260 M⊙) end their lives as PISNe,which have been predicted by theories,but no relics of PISNe have been observed yet.Among the distinct characteristics of the yields of PISNe,as predicted by theoretical calculations,are a strong odd-even effect,and a strong overabundance of Ca with respect to iron and the solar ratio.We use the latter characteristic to identify metal-poor stars in the Galactic halo that have been pre-enriched by PISNe,by comparing metallicites derived from strong,co-added Fe lines detected in low-resolution (i.e.,R = λ/Δλ ~ 2000) spectra of the Sloan Digital Sky Survey (SDSS),with metallicities determined by the SDSS Stellar Parameters Pipeline (SSPP).The latter are based on the strength of the Ca Ⅱ K line and assumptions on the Ca/Fe abundance ratio.Stars are selected as candidates if their metallicity derived from Fe lines is significantly lower than the SSPP metallicities.In a sample of 12 300 stars for which SDSS spectroscopy is available,we have identified 18 candidate stars.Higher resolution and signal-to-noise ratio spectra of these candidates are being obtained with the Very Large Telescope of the European Southern Observatory and the XSHOOTER spectrograph,to determine their abundance patterns,and to verify our selection method.We plan to apply our method to the database of several million stellar spectra to be acquired with the Guo Shou Jing Telescope (LAMOST) in the next five years.

  18. r-Process Lanthanide Production and Heating Rates in Kilonovae

    CERN Document Server

    Lippuner, Jonas

    2015-01-01

    r-Process nucleosynthesis in material ejected during neutron star mergers may lead to radioactively powered transients called kilonovae. The timescale and peak luminosity of these transients depend on the composition of the material after nuclear burning ceases, which determines the local heating rate from nuclear decays and the opacity. Kasen et al. (2013, ApJ, 774, 25) and Tanaka & Hotokezaka (2013, ApJ, 775, 113) pointed out that lanthanides can drastically increase the opacity in these outflows. We use the new general-purpose nuclear reaction network SkyNet to carry out a parameter study of r-process nucleosynthesis for a range of initial electron fractions $Y_e$, initial specific entropies $s$, and expansion timescales $\\tau$. We find that the ejecta is lanthanide-free for $Y_e \\gtrsim 0.22 - 0.30$, depending on $s$ and $\\tau$. The heating rate is insensitive to $s$ and $\\tau$, but certain, larger values of $Y_e$ lead to reduced heating rates, due to individual nuclides dominating the heating. With a...

  19. New fission fragment distributions and r-process origin of the rare-earth elements

    CERN Document Server

    Goriely, S; Lemaitre, J -F; Panebianco, S; Dubray, N; Hilaire, S; Bauswein, A; Janka, H -Thomas

    2013-01-01

    Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A > 140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties, but calculations sensitively depend on nuclear physics. In particular the fission fragment yields determine the creation of 110 140.

  20. The role of binaries in the enrichment of the early Galactic halo. II. Carbon-Enhanced Metal-Poor Stars - CEMP-no stars

    CERN Document Server

    Hansen, T T; Nordström, B; Beers, T C; Placco, V M; Yoon, J; Buchhave, L A

    2015-01-01

    The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon - the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds, or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Most programme stars exhibit no statistically significant radial-velocit variation...

  1. r-PROCESS LANTHANIDE PRODUCTION AND HEATING RATES IN KILONOVAE

    Energy Technology Data Exchange (ETDEWEB)

    Lippuner, Jonas; Roberts, Luke F., E-mail: jlippuner@tapir.caltech.edu [TAPIR, Walter Burke Institute for Theoretical Physics, California Institute of Technology, MC 350-17, 1200 E California Boulevard, Pasadena CA 91125 (United States)

    2015-12-20

    r-process nucleosynthesis in material ejected during neutron star mergers may lead to radioactively powered transients called kilonovae. The timescale and peak luminosity of these transients depend on the composition of the ejecta, which determines the local heating rate from nuclear decays and the opacity. Kasen et al. and Tanaka and Hotokezaka pointed out that lanthanides can drastically increase the opacity in these outflows. We use the new general-purpose nuclear reaction network SkyNet to carry out a parameter study of r-process nucleosynthesis for a range of initial electron fractions Y{sub e}, initial specific entropies s, and expansion timescales τ. We find that the ejecta is lanthanide-free for Y{sub e} ≳ 0.22−0.30, depending on s and τ. The heating rate is insensitive to s and τ, but certain, larger values of Y{sub e} lead to reduced heating rates, due to individual nuclides dominating the heating. We calculate approximate light curves with a simplified gray radiative transport scheme. The light curves peak at about a day (week) in the lanthanide-free (-rich) cases. The heating rate does not change much as the ejecta becomes lanthanide-free with increasing Y{sub e}, but the light-curve peak becomes about an order of magnitude brighter because it peaks much earlier when the heating rate is larger. We also provide parametric fits for the heating rates between 0.1 and 100 days, and we provide a simple fit in Y{sub e}, s, and τ to estimate whether or not the ejecta is lanthanide-rich.

  2. Constraints on the Nature of the s- and r-processes

    Science.gov (United States)

    Sneden, Christopher; Cowan, John J.; Gallino, Roberto

    2010-03-01

    Neutron-capture (Z > 30) elements are detected in many very metal-poor halo stars, and so they must have been manufactured by some of the earliest element donors in our Galaxy's history. The bulk amounts of neutron-capture elements with respect to the iron group vary by several orders of magnitude from star to star at low metallicities. Additionally, abundance distributions among these elements are often strikingly different from that of the solar system. Some stars exhibit abundances that must have been made purely in “rapid” neutron-capture events (the r-process), some in “slow” events (the s-process), and some have hybrid mixes. Here we summarize the major observed categories of the neutron-capture abundances in metal-poor stars, and discuss their implications for early Galactic nucleosynthesis.

  3. The complexity that the first stars brought to the Universe: Fragility of metal enriched gas in a radiation field

    CERN Document Server

    Aykutalp, Aycin

    2011-01-01

    The initial mass function of the first (Population III) stars and Population II (Pop II) stars is poorly known due to a lack of observations of the period between recombination and re-ionization. In simulations of the formation of the first stars, it has been shown that, due to the limited ability of metal-free primordial gas to cool, the IMF of the first stars is a few orders of magnitude more massive than the current IMF. The transition from a high-mass IMF of the first stars to a lower-mass current IMF is thus important to understand. To study the underlying physics of this transition, we performed several simulations using the cosmological hydrodynamical adaptive mesh refinement code Enzo for metallicities of 10^{-4}, 10^{-3}, 10^{-2}, 10^{-1} Z_{\\odot}. In our simulations we include a star formation prescription that is derived from a metallicity dependent multi-phase ISM structure, an external UV radiation field, and a mechanical feedback algorithm. We also implement cosmic ray heating, photoelectric he...

  4. THE C+N+O ABUNDANCE OF {omega} CENTAURI GIANT STARS: IMPLICATIONS FOR THE CHEMICAL-ENRICHMENT SCENARIO AND THE RELATIVE AGES OF DIFFERENT STELLAR POPULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Marino, A. F. [Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei Muenchen (Germany); Milone, A. P.; Aparicio, A. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands (Spain); Piotto, G. [Dipartimento di Astronomia, Universita di Padova, Vicolo dell' Osservatorio 3, Padova, I-35122 (Italy); Cassisi, S. [INAF-Osservatorio Astronomico di Teramo, Via M. Maggini, 64100 Teramo (Italy); D' Antona, F. [INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio (Italy); Anderson, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bedin, L. R.; Renzini, A. [INAF-Osservatorio Astronomico di Padova, Vicolo dellOsservatorio 5, 35122 Padova (Italy); Villanova, S., E-mail: amarino@MPA-Garching.MPG.DE, E-mail: milone@iac.es, E-mail: aparicio@iac.es, E-mail: giampaolo.piotto@unipd.it, E-mail: cassisi@oa-teramo.inaf.it, E-mail: dantona@oa-roma.inaf.it, E-mail: jayander@stsci.edu, E-mail: luigi.bedin@oapd.inaf.it, E-mail: alvio.renzini@oapd.inaf.it, E-mail: svillanova@astro-udec.cl [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)

    2012-02-10

    We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri. We have measured abundances for carbon and nitrogen, and combined our results with abundances of O, Na, La, and Fe that we determined in our previous work. Our aim is to better understand the peculiar chemical-enrichment history of this cluster by studying how the total C+N+O content varies among the different metallicity stellar groups, and among stars at different places along the Na-O anticorrelation. We find that the (anti)correlations among the light elements that would be expected on theoretical grounds for matter that has been nuclearly processed via high-temperature proton captures. The overall [(C+N+O)/Fe] increases by {approx}0.5 dex from [Fe/H] {approx}-2.0 to [Fe/H] {approx}-0.9. Our results provide insight into the chemical-enrichment history of the cluster, and the measured CNO variations provide important corrections for estimating the relative ages of the different stellar populations.

  5. The C+N+O abundance of Omega Centauri giant stars: implications on the chemical enrichment scenario and the relative ages of different stellar populations

    CERN Document Server

    Marino, A F; Piotto, G; Cassisi, S; D'Antona, F; Anderson, J; Aparicio, A; Bedin, L R; Renzini, A; Villanova, S

    2011-01-01

    We present a chemical-composition analysis of 77 red-giant stars in Omega Centauri. We have measured abundances for carbon and nitrogen, and combined our results with abundances of O, Na, La, and Fe that we determined in our previous work. Our aim is to better understand the peculiar chemical-enrichment history of this cluster, by studying how the total C+N+O content varies among the different-metallicity stellar groups, and among stars at different places along the Na-O anticorrelation. We find the (anti)correlations among the light elements that would be expected on theoretical ground for matter that has been nuclearly processed via high-temperature proton captures. The overall [(C+N+O)/Fe] increases by 0.5 dex from [Fe/H] -2.0 to [Fe/H] -0.9. Our results provide insight into the chemical-enrichment history of the cluster, and the measured CNO variations provide important corrections for estimating the relative ages of the different stellar populations.

  6. R-Process Nucleosynthesis in MHD Jet Explosions of Core-Collapse Supernovae

    Directory of Open Access Journals (Sweden)

    Motoaki Saruwatari

    2013-01-01

    Full Text Available We investigate the r-process nucleosynthesis during the magnetohydrodynamical (MHD explosion of a supernova in a helium star of 3.3 M⊙, where effects of neutrinos are taken into account using the leakage scheme in the two-dimensional (2D hydrodynamic code. Jet-like explosion due to the combined effects of differential rotation and magnetic field is able to erode the lower electron fraction matter from the inner layers. We find that the ejected material of low electron fraction responsible for the r-process comes out from just outside the neutrino sphere deep inside the Fe-core. It is found that heavy element nucleosynthesis depends on the initial conditions of rotational and magnetic fields. In particular, the third peak of the distribution is significantly overproduced relative to the solar system abundances, which would indicate a possible r-process site owing to MHD jets in supernovae.

  7. The FMOS-COSMOS survey of star-forming galaxies at z~1.6. IV: Excitation state and chemical enrichment of HII regions

    CERN Document Server

    Kashino, D; Sanders, D; Kartaltepe, J S; Daddi, E; Renzini, A; Valentino, F; Rodighiero, G; Juneau, S; Kewley, L J; Zahid, H J; Arimoto, N; Nagao, T; Chu, J; Sugiyama, N; Civano, F; Ilbert, O; Kajisawa, M; Fevre, O Le; Maier, C; Onodera, M; Puglisi, A; Taniguchi, Y; COSMOS,

    2016-01-01

    We present results on the physical conditions of the interstellar medium of star-forming galaxies at 1.410^11Msun being well sampled. The excitation state and chemical enrichment of the ionized gas are investigated using diagnostic diagrams based on the ratios of emission line strengths, including Alpha, [NII]6584, [SII]6717,6731, Hbeta, and [OIII]5007. Our data confirm an offset of the star-forming sequence on the BPT diagram ([OIII]/Hbeta vs. [NII]/Halpha), primarily towards higher [OIII]/Hbeta, compared with local star-forming galaxies. Based on the [SII] ratio, we measure an electron density (n_e=222^{+172}_{-128} cm^-3), higher than that of local galaxies. Overall, these changes in emission-line properties are due to a higher ionization parameter in high redshift galaxies as demonstrated by a lower than expected [SII]/Halpha ratio and a comparison to theoretical models. These results likely rule out an offset in the BPT diagram caused by a harder radiation field or AGN as assessed with Chandra. Finally, ...

  8. Evolution of intermediate mass and massive binary stars: physics, mass loss, and rotation

    CERN Document Server

    Vanbeveren, D

    2016-01-01

    In the present review we discuss the past and present status of the interacting OB-type binary frequency. We critically examine the popular idea that Be-stars and supergiant sgB[e] stars are binary evolutionary products. The effects of rotation on stellar evolution in general, stellar population studies in particular, and the link with binaries will be evaluated. Finally a discussion is presented of massive double compact star binary mergers as possible major sites of chemical enrichment of r-process elements and as the origin of recent aLIGO GW events.

  9. Neutron-Capture Elements in Low Metallicity Stars within the Inner Galactic Halo

    Science.gov (United States)

    Jumper, Kenneth A.; Burris, Debra L.

    2017-01-01

    The inner galactic halo is home to some of the oldest and low metallicity stars known. These stars are local enough to observe heavy element synthesis in the oldest stars in our galaxy. The purpose of this research is to analyze the distributions of neutron capture elements in low metallicity stars to help us understand the nature of first stars, which are responsible for the chemical enrichment of our galaxy, and consequently get man closer to an answer to some of the most fundamental questions about the universe.. The researchers will analyze and measure the stellar abundances of metal poor stars using MOOG’s spectral synthesis. Heavy element formation is connected to stellar evolution, thus by observing the chronometric ages of the distributions of Thorium/Europium, one can determine the age of the oldest stars. Analyzing the distribution of Uranium and Thorium as chronometers can set a lower limit on the age of the Universe. The chemical composition in our oldest observable stars resemble that of the earliest stars. This demonstrates that these stars were not synthesized internally but a result of previous deaths of stars generations before. This in turn provides useful information about the first star’s formation, evolution and nucleosynthesis of stars, and the arrangement of the structure of the early Universe. The most r-process rich halo stars abundances are consistent with a scaled solar system r-process abundance distribution. Also, there is symmetry in the rare earth elements in the stars within the Galactic halo. However the lighter n-capture abundances don’t conform to the solar pattern. This suggests the possibility of multiple synthesis mechanisms for the n capture elements. The combinations could include the main r-process, V-P process (core collapsed super- novae), charged particle reactions with Beta delayed fission, and the weak r-process. The weak r-process is sometimes called the incomplete r-process does not have enough neutrons to

  10. Dependence of the Sr-to-Ba and Sr-to-Eu Ratio on the Nuclear Equation of State in Metal Poor Halo Stars

    CERN Document Server

    Famiano, M A; Aoki, W; Suda, T

    2016-01-01

    A model is proposed in which the light r-process element enrichment in metal-poor stars is explained via enrichment from a truncated r-process, or "tr-process." The truncation of the r-process from a generic core-collapse event followed by a collapse into an accretion-induced black hole is examined in the framework of a galactic chemical evolution model. The constraints on this model imposed by observations of extremely metal-poor stars are explained, and the upper limits in the [Sr/Ba] distributions are found to be related to the nuclear equation of state in a collapse scenario. The scatter in [Sr/Ba] and [Sr/Eu] as a function of metallicity has been found to be consistent with turbulent ejection in core collapse supernovae. Adaptations of this model are evaluated to account for the scatter in isotopic observables. This is done by assuming mixing in ejecta in a supernova event.

  11. Evidence for a chemical enrichment coupling of globular clusters and field stars in the Fornax dSph

    CERN Document Server

    Hendricks, Benjamin; Johnson, Christian I; Frank, Matthias J; Koch, Andreas; Mateo, Mario; Bailey, John I

    2016-01-01

    The globular cluster H4, located in the center of the Fornax dwarf spheroidal galaxy, is crucial for understanding the formation and chemical evolution of star clusters in low-mass galactic environments. H4 is peculiar because the cluster is significantly more metal-rich than the galaxy's other clusters, is located near the galaxy center, and may also be the youngest cluster in the galaxy. In this study, we present detailed chemical abundances derived from high-resolution (R~28000) spectroscopy of an isolated H4 member star for comparison with a sample of 22 nearby Fornax field stars. We find the H4 member to be depleted in the alpha-elements Si, Ca, and Ti with [Si/Fe]=-0.35+-0.34, [Ca/Fe]=+0.05+-0.08, and [Ti/Fe]=-0.27+-0.23, resulting in an average [alpha/Fe]=-0.19+-0.14. If this result is representative of the average cluster properties, H4 is the only known system with a low [alpha/Fe] ratio and a moderately low metallicity embedded in an intact birth environment. For the field stars we find a clear sequ...

  12. Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

    Science.gov (United States)

    Vlasov, Andrey D.; Metzger, Brian D.; Lippuner, Jonas; Roberts, Luke F.; Thompson, Todd A.

    2017-06-01

    We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly rotating, strongly magnetized protoneutron stars ('millisecond protomagnetars') for which the magnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the protomagnetar wind trajectories calculated by Vlasov, Metzger & Thompson through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the protoneutron star cooling phase. Although we do not find a successful second or third-peak r-process for any rotation period P, we show that protomagnetars with P ˜ 1-5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of ≳100-1000). The heaviest elements are synthesized by outflows emerging along flux tubes that graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the protoneutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If protomagnetars are central engines for GRBs, their relativistic jets should contain a high-mass fraction of heavy nuclei of characteristic mass number \\bar{A}≈ 100, providing a possible source for ultrahigh energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal Grezin-Zatsepin-Kuzmin cut-off for protons or iron nuclei.

  13. High-resolution abundance analysis of very metal-poor r-I stars

    CERN Document Server

    Siqueira-Mello, C; Barbuy, B; Spite, M; Spite, F; Beers, T C; Caffau, E; Bonifacio, P; Cayrel, R; François, P; Schatz, H; Wanajo, S

    2014-01-01

    Moderately r-process-enriched stars (r-I) are at least four times as common as those that are greatly enriched in r-process elements (r-II), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is(are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph. The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. We have derived abundances of light elements Li, C, and N, alpha-elements, odd-Z elements, iron-...

  14. Weak magnetic field, solid-envelope rotation, and wave-induced N-enrichment in the SPB star $\\zeta$ Cassiopeiae

    CERN Document Server

    Briquet, M; Petit, P; Leroy, B; de Batz, B

    2016-01-01

    Aims. The main-sequence B-type star $\\zeta$ Cassiopeiae is known as a N-rich star with a magnetic field discovered with the Musicos spectropolarimeter. We model the magnetic field of the star by means of 82 new spectropolarimetric observations of higher precision to investigate the field strength, topology, and effect. Methods. We gathered data with the Narval spectropolarimeter installed at T\\'elescope Bernard Lyot (TBL, Pic du Midi, France) and applied the least-squares deconvolution technique to measure the circular polarisation of the light emitted from $\\zeta$ Cas. We used a dipole oblique rotator model to determine the field configuration by fitting the longitudinal field measurements and by synthesizing the measured Stokes V profiles. We also made use of the Zeeman-Doppler Imaging technique to map the stellar surface and to deduce the difference in rotation rate between the pole and equator. Results. $\\zeta$ Cas exhibits a polar field strength $B_{\\rm pol}$ of 100-150 G, which is the weakest polar fiel...

  15. The FMOS-COSMOS Survey of Star-forming Galaxies at z ≈ 1.6. IV. Excitation State and Chemical Enrichment of the Interstellar Medium

    Science.gov (United States)

    Kashino, D.; Silverman, J. D.; Sanders, D.; Kartaltepe, J. S.; Daddi, E.; Renzini, A.; Valentino, F.; Rodighiero, G.; Juneau, S.; Kewley, L. J.; Zahid, H. J.; Arimoto, N.; Nagao, T.; Chu, J.; Sugiyama, N.; Civano, F.; Ilbert, O.; Kajisawa, M.; Le Fèvre, O.; Maier, C.; Masters, D.; Miyaji, T.; Onodera, M.; Puglisi, A.; Taniguchi, Y.

    2017-01-01

    We investigate the physical conditions of ionized gas in high-z star-forming galaxies using diagnostic diagrams based on the rest-frame optical emission lines. The sample consists of 701 galaxies with an Hα detection at 1.4≲ z≲ 1.7, from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS survey, that represent the normal star-forming population over the stellar mass range {10}9.6≲ {M}* /{M}ȯ ≲ {10}11.6, with those at {M}* > {10}11 {M}ȯ being well sampled. We confirm an offset of the average location of star-forming galaxies in the Baldwin–Phillips–Terlevich (BPT) diagram ({{[O}} {{III}}]/{{H}}β versus {{[N}} {{II}}]/{{H}}α ), primarily toward higher {{[O}} {{III}}]/{{H}}β , compared with local galaxies. Based on the [S ii] ratio, we measure an electron density ({n}{{e}}={220}-130+170 {{cm}}-3), which is higher than that of local galaxies. Based on comparisons to theoretical models, we argue that changes in emission-line ratios, including the offset in the BPT diagram, are caused by a higher ionization parameter both at fixed stellar mass and at fixed metallicity, with additional contributions from a higher gas density and possibly a hardening of the ionizing radiation field. Ionization due to active galactic nuclei is ruled out as assessed with Chandra. As a consequence, we revisit the mass–metallicity relation using {{[N}}{{II}}]/{{H}}α and a new calibration including {{[N}} {{II}}]/{{[S}} {{II}}] as recently introduced by Dopita et al. Consistent with our previous results, the most massive galaxies ({M}* ≳ {10}11 {M}ȯ ) are fully enriched, while those at lower masses have metallicities lower than local galaxies. Finally, we demonstrate that the stellar masses, metallicities, and star formation rates of the FMOS sample are well fit with a physically motivated model for the chemical evolution of star-forming galaxies.

  16. Impact of new data for neutron-rich heavy nuclei on theoretical models for r-process nucleosynthesis

    Science.gov (United States)

    Kajino, Toshitaka; Mathews, Grant J.

    2017-08-01

    Current models for the r process are summarized with an emphasis on the key constraints from both nuclear physics measurements and astronomical observations. In particular, we analyze the importance of nuclear physics input such as beta-decay rates; nuclear masses; neutron-capture cross sections; beta-delayed neutron emission; probability of spontaneous fission, beta- and neutron-induced fission, fission fragment mass distributions; neutrino-induced reaction cross sections, etc. We highlight the effects on models for r-process nucleosynthesis of newly measured β-decay half-lives, masses, and spectroscopy of neutron-rich nuclei near the r-process path. We overview r-process nucleosynthesis in the neutrino driven wind above the proto-neutron star in core collapse supernovae along with the possibility of magneto-hydrodynamic jets from rotating supernova explosion models. We also consider the possibility of neutron star mergers as an r-process environment. A key outcome of newly measured nuclear properties far from stability is the degree of shell quenching for neutron rich isotopes near the closed neutron shells. This leads to important constraints on the sites for r-process nucleosynthesis in which freezeout occurs on a rapid timescale.

  17. A Stringent Limit on the Mass Production Rate of $r$-Process Elements in the Milky Way

    CERN Document Server

    Macias, Phillip

    2016-01-01

    We analyze data from several studies of metal-poor stars in the Milky Way, focusing on both strong (Eu) and weak (Sr) $r$-process elements. Because these elements were injected in an explosion, we calculate the mass swept up when the blast wave first becomes radiative, yielding a lower limit for the dilution of such elements and hence a lower limit on the ejecta mass which is incorporated into the next generation of stars. Our study demonstrates that in order to explain the largest enhancements in [Eu/Fe] observed in stars at low [Fe/H] metallicities, individual $r$-process production events must synthesize a minimum of $10^{-3.5} M_{\\odot}$ of $r$-process material. We also show that if the site of Mg production is the same as that of Eu, individual injection events must synthesize up to $ \\sim 10^{-3} M_{\\odot}$ of $r$-process material. On the other hand, demanding that Sr traces Mg production results in $r$-process masses per event of $\\sim 10^{-5} M_{\\odot}$. This suggests that the astrophysical sites resp...

  18. Neutron-capture nucleosynthesis in the first stars

    Energy Technology Data Exchange (ETDEWEB)

    Roederer, Ian U. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Preston, George W.; Thompson, Ian B.; Shectman, Stephen A. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Sneden, Christopher, E-mail: iur@umich.edu [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)

    2014-04-01

    Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon- or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars.

  19. Enriched halos at redshift $z=2$ with no star-formation: Implications for accretion and wind scenarios

    CERN Document Server

    Bouche, N; Peroux, C; Contini, T; Martin, C L; Schreiber, N M Forster; Genzel, R; Lutz, D; Gillessen, S; Tacconi, L; Davies, R; Eisenhauer, F

    2011-01-01

    [Abridged] In order to understand which process (e.g. galactic winds, cold accretion) is responsible for the cool (T~10^4 K) halo gas around galaxies, we embarked on a program to study the star-formation properties of galaxies selected by their MgII absorption signature in quasar spectra. Specifically, we searched for the H-alpha line emission from galaxies near very strong z=2 MgII absorbers (with rest-frame equivalent width EW>2 \\AA) because these could be the sign-posts of outflows or inflows. Surprisingly, we detect H-alpha from only 4 hosts out of 20 sight-lines (and 2 out of the 19 HI-selected sight-lines), despite reaching a star-formation rate (SFR) sensitivity limit of 2.9 M/yr (5-sigma) for a Chabrier initial mass function. This low success rate is in contrast with our z=1 survey where we detected 66%\\ (14/21) of the MgII hosts. Taking into account the difference in sensitivity between the two surveys, we should have been able to detect >11.4 of the 20 z=2 hosts whereas we found only 4 galaxies. Int...

  20. Star-forming Galactic Contrails at z=3.2 as a Source of Metal Enrichment and Ionizing Radiation

    CERN Document Server

    Rauch, Michael; Haehnelt, Martin G; Gauthier, Jean-Rene

    2013-01-01

    A spectroscopically detected Lyman alpha emitting halo at redshift 3.216 in the GOODS-N field is found to reside at the convergence of several Lyman alpha filaments. HST images show that some of the filaments are inhabited by galaxies. Several of the galaxies in the field have pronounced head-tail structures, which are partly aligned with each other. The blue colors of most tails suggest the presence of young stars, with the emission from at least one of the galaxies apparently dominated by high equivalent width Lyman alpha. Faint, more diffuse, and similarly elongated, apparently stellar features, can be seen over an area with a linear extent of at least 90 kpc. The region within several arcseconds of the brightest galaxy exhibits spatially extended emission by HeII, NV and various lower ionization metal lines. The gas-dynamical features present are strongly reminiscent of ram-pressure stripped galaxies, including evidence for recent star formation in the stripped contrails. Spatial gradients in the appearan...

  1. The Intermediate r-process in Core-collapse Supernovae Driven by the Magneto-rotational Instability

    Science.gov (United States)

    Nishimura, N.; Sawai, H.; Takiwaki, T.; Yamada, S.; Thielemann, F.-K.

    2017-02-01

    We investigated r-process nucleosynthesis in magneto-rotational supernovae, based on a new explosion mechanism induced by the magneto-rotational instability (MRI). A series of axisymmetric magneto-hydrodynamical simulations with detailed microphysics including neutrino heating is performed, numerically resolving the MRI. Neutrino-heating dominated explosions, enhanced by magnetic fields, showed mildly neutron-rich ejecta producing nuclei up to A∼ 130 (i.e., the weak r-process), while explosion models with stronger magnetic fields reproduce a solar-like r-process pattern. More commonly seen abundance patterns in our models are in between the weak and regular r-process, producing lighter and intermediate-mass nuclei. These intermediate r-processes exhibit a variety of abundance distributions, compatible with several abundance patterns in r-process-enhanced metal-poor stars. The amount of Eu ejecta ∼ {10}-5 {M}ȯ in magnetically driven jets agrees with predicted values in the chemical evolution of early galaxies. In contrast, neutrino-heating dominated explosions have a significant amount of Fe ({}56{{Ni}}) and Zn, comparable to regular supernovae and hypernovae, respectively. These results indicate magneto-rotational supernovae can produce a wide range of heavy nuclei from iron-group to r-process elements, depending on the explosion dynamics.

  2. The Link between Rare-Earth Peak Formation and the Astrophysical Site of the R Process

    Science.gov (United States)

    Mumpower, Matthew R.; McLaughlin, Gail C.; Surman, Rebecca; Steiner, Andrew W.

    2016-12-01

    The primary astrophysical source of the rare-earth elements is the rapid neutron capture process (r process). The rare-earth peak that is seen in the solar r-process residuals has been proposed to originate as a pile-up of nuclei during the end of the r process. We introduce a new method utilizing Monte Carlo studies of nuclear masses in the rare-earth region, that includes self-consistently adjusting β-decay rates and neutron capture rates, to find the mass surfaces necessary for the formation of the rare-earth peak. We demonstrate our method with two types of astrophysical scenario, one corresponding to conditions typical of hot winds from core-collapse supernovae and stellar-mass accretion disks, and one corresponding to conditions typical of the ejection of the material from the tidal tails of neutron star mergers. In each type of astrophysical condition, this method successfully locates a region of enhanced stability in the mass surface that is responsible for the rare-earth peak. For each scenario, we find that the change in the mass surface has qualitatively different features, thus future measurements can shed light on the type of environment in which the r process occurred.

  3. Relative contributions of the weak, main and fission-recycling r-process

    CERN Document Server

    Shibagaki, S; Mathews, G J; Chiba, S; Nishimura, S; Lorusso, G

    2015-01-01

    There has been a persistent conundrum in attempts to model the nucleosynthesis of heavy elements by rapid neutron capture (the $r$-process). Although the location of the abundance peaks near nuclear mass numbers 130 and 195 identify an environment of rapid neutron capture near closed nuclear shells, the abundances of elements just above and below those peaks are often underproduced by more than an order of magnitude in model calculations. At the same time there is a debate in the literature as to what degree the $r$-process elements are produced in supernovae or the mergers of binary neutron stars. In this paper we propose a novel solution to both problems. We demonstrate that the underproduction of elements above and below the $r$-process peaks characteristic in the main or weak $r$-process events (like magnetohydrodynamic jets or neutrino-driven winds in core-collapse supernovae) can be supplemented via fission fragment distributions from the recycling of material in a neutron-rich environment such as that ...

  4. The r-process of stellar nucleosynthesis: Astrophysics and nuclear physics achievements and mysteries

    CERN Document Server

    Arnould, M; Takahashi, K

    2007-01-01

    The r-process, or the rapid neutron-capture process, of stellar nucleosynthesis is called for to explain the production of the stable (and some long-lived radioactive) neutron-rich nuclides heavier than iron that are observed in stars of various metallicities, as well as in the solar system. A very large amount of nuclear information is necessary in order to model the r-process. This concerns the static characteristics of a large variety of light to heavy nuclei between the valley of stability and the vicinity of the neutron-drip line, as well as their beta-decay branches or their reactivity. The enormously challenging experimental and theoretical task imposed by all these requirements is reviewed, and the state-of-the-art development in the field is presented. Nuclear-physics-based and astrophysics-free r-process models of different levels of sophistication have been constructed over the years. We review their merits and their shortcomings. For long, the core collapse supernova of massive stars has been envi...

  5. Star-formation efficiency and metal enrichment of the intracluster medium in local massive clusters of galaxies

    CERN Document Server

    Zhang, Yu-Ying; Pierini, Daniele; Puchwein, Ewald; Schneider, Peter; Reiprich, Thomas H

    2011-01-01

    We have investigated the baryon-mass content in a subsample of 19 clusters of galaxies extracted from the X-ray flux-limited sample HIFLUGCS according to their positions in the sky. For these clusters, we have measured total masses and characteristic radii on the basis of a rich optical spectroscopic data set, physical properties of the intra-cluster medium (ICM) using XMM-Newton and ROSAT X-ray data, and total (galaxy) stellar masses utilizing the SDSS DR7 multi-band imaging. The observed (hot) gas-mass fractions are almost constant in this mass range. We confirm that the stellar mass fraction decreases as the total mass increases and shows (20+/-4)% scatter; in addition, we show that it decreases as the central entropy increases. The latter behavior supports a twofold interpretation: heating from merging quenches the star-formation activity of galaxies in massive systems and feedback from supernovae and/or radio galaxies drives a significant amount of gas to the regions beyond r_{500} or, alternatively, a s...

  6. Evidence for supernova injection into the solar nebula and the decoupling of r-process nucleosynthesis.

    Science.gov (United States)

    Brennecka, Gregory A; Borg, Lars E; Wadhwa, Meenakshi

    2013-10-22

    The isotopic composition of our Solar System reflects the blending of materials derived from numerous past nucleosynthetic events, each characterized by a distinct isotopic signature. We show that the isotopic compositions of elements spanning a large mass range in the earliest formed solids in our Solar System, calcium-aluminum-rich inclusions (CAIs), are uniform, and yet distinct from the average Solar System composition. Relative to younger objects in the Solar System, CAIs contain positive r-process anomalies in isotopes A 140. This fundamental difference in the isotopic character of CAIs around mass 140 necessitates (i) the existence of multiple sources for r-process nucleosynthesis and (ii) the injection of supernova material into a reservoir untapped by CAIs. A scenario of late supernova injection into the protoplanetary disk is consistent with formation of our Solar System in an active star-forming region of the galaxy.

  7. Are collapsars responsible for some r-process elements? How could we tell?

    Energy Technology Data Exchange (ETDEWEB)

    Pruet, J

    2004-04-05

    We consider the possibility that supernovae which form hyper-accreting black holes might be responsible for synthesis of r-process elements with mass A {approx}< 130. Calculations are presented which show that these elements are naturally synthesized in neutron-rich magnetically-dominated bubbles born in the inner regions of a black hole accretion disk. Simple considerations suggest that the total mass ejected in the form of these bubbles is about that needed to account for the entire galactic inventory of the 2nd-peak r-process elements. We also argue that if collapsars are responsible for, e.g., Ag synthesis, then Ag abundances should be correlated with Sc and/or Zn abundances in metal-poor stars.

  8. Supernova Neutrino-Effects on R-Process Nucleosynthesis in Black Hole Formation

    CERN Document Server

    Sasaqui, T; Balantekin, A B

    2005-01-01

    Stars with a wide range of masses provide a variety of production sites for intermediate-to-heavy mass elements. Very massive stars with mass $\\geq 8 M_{\\odot}$ culminate their evolution by supernova explosions which are presumed to be the most viable candidate astrophysical sites of r-process nucleosynthesis. If the models for the supernova r-process are correct, then nucleosynthesis results could also pose a significant constraint on the remnant of supernova explosions, $i.e.$ neutron star or black hole. In the case of very massive core collapse, a remnant stellar black hole is thought to be formed. Intense neutrino flux from the neutronized core and the neutrino sphere might suddenly cease during the Kelvin-Helmholtz cooling phase because of the black hole formation. It is interesting to explore observable consequences of such a neutrino flux truncation. Arguments have recently been given in the literature that even the neutrino mass may be determined from the time delay of deformed neutrino energy spectru...

  9. Impact of nuclear mass uncertainties on the $r$-process

    CERN Document Server

    Martin, Dirk; Nazarewicz, Witold; Olsen, Erik

    2015-01-01

    Nuclear masses play a fundamental role in understanding how the heaviest elements in the Universe are created in the $r$-process. We predict $r$-process nucleosynthesis yields using neutron capture and photodissociation rates that are based on nuclear density functional theory. Using six Skyrme energy density functionals based on different optimization protocols, we determine for the first time systematic uncertainty bands -- related to mass modeling -- for $r$-process abundances in realistic astrophysical scenarios. We find that features of the underlying microphysics make an imprint on abundances especially in the vicinity of neutron shell closures: abundance peaks and troughs are reflected in trends of neutron separation energy. Further advances in nuclear theory and experiments, when linked to observations, will help in the understanding of astrophysical conditions in extreme $r$-process sites.

  10. Monte Carlo calculations for r-process nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Mumpower, Matthew Ryan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-11-12

    A Monte Carlo framework is developed for exploring the impact of nuclear model uncertainties on the formation of the heavy elements. Mass measurements tightly constrain the macroscopic sector of FRDM2012. For r-process nucleosynthesis, it is necessary to understand the microscopic physics of the nuclear model employed. A combined approach of measurements and a deeper understanding of the microphysics is thus warranted to elucidate the site of the r-process.

  11. Impact of new data for neutron-rich heavy nuclei on theoretical models for $r$-process nucleosynthesis

    CERN Document Server

    Kajino, Toshitaka

    2016-01-01

    Current models for the $r$ process are summarized with an emphasis on the key constraints from both nuclear physics measurements and astronomical observations. In particular, we analyze the importance of nuclear physics input such as beta-decay rates; nuclear masses; neutron-capture cross sections; beta-delayed neutron emission; probability of spontaneous fission, beta- and neutron-induced fission, fission fragment mass distributions; neutrino-induced reaction cross sections, etc. We highlight the effects on models for $r$-process nucleosynthesis of newly measured $\\beta$-decay half-lives, masses, and spectroscopy of neutron-rich nuclei near the $r$-process path. We overview r-process nucleosynthesis in the neutrino driven wind above the proto-neutron star in core collapse supernovae along with the possibility of magneto-hydrodynamic jets from rotating supernova explosion models. We also consider the possibility of neutron star mergers as an r-process environment. A key outcome of newly measured nuclear prope...

  12. Detection of hot, metal-enriched outflowing gas around $z\\approx\\,$2.3 star-forming galaxies in the Keck Baryonic Structure Survey

    CERN Document Server

    Turner, Monica L; Steidel, Charles C; Rudie, Gwen C; Strom, Allison L

    2014-01-01

    We use quasar absorption lines to study the physical conditions in the circumgalactic medium of redshift $z\\approx 2.3$ star-forming galaxies taken from the Keck Baryonic Structure Survey (KBSS). In Turner et al. 2014 we used the pixel optical depth technique to show that absorption by HI and the metal ions OVI, NV, CIV, CIII and SiIV is strongly enhanced within $|\\Delta v|\\lesssim170$ km/s and projected distances $|d|\\lesssim180$ proper kpc from sightlines to the background quasars. Here we demonstrate that the OVI absorption is also strongly enhanced at fixed HI, CIV, and SiIV optical depths, and that this enhancement extends out to $\\sim350$ km/s. At fixed HI the increase in the median OVI optical depth near galaxies is 0.3-0.7 dex and is detected at 2--3-$\\sigma$ confidence for all seven HI bins that have $\\log_{10}\\tau_{\\rm HI}\\ge-1.5$. We use ionisation models to show that the observed strength of OVI as a function of HI is consistent with enriched, photoionised gas for pixels with $\\tau_{\\rm HI}\\gtrsim...

  13. A holistic approach to carbon-enhanced metal-poor stars

    CERN Document Server

    Masseron, T; Plez, B; Van Eck, S; Primas, F; Goriely, S; Jorissen, A

    2009-01-01

    Carbon-Enhanced Metal-Poor (CEMP) stars are known to be the direct witnesses of the nucleosynthesis of the first low- and intermediate-mass stars, because they have been polluted by a now-extinct AGB star. To put CEMP stars in a broad context, we collect abundances for about 180 stars of various metallicities (from solar down to [Fe/H]=-4), luminosity classes (dwarfs and giants), and abundance patterns (C-rich and poor, Ba-rich and poor, etc), from our own sample and from literature. First, we introduce a class of CEMP stars sharing the properties of CEMP-s stars and CEMP-no stars. We also show that there is a strong correlation between Ba and C in the s-only CEMP stars. This strongly points at the operation of the 13C neutron source in low-mass AGB stars. For the CEMP-rs stars (enriched with elements from both the s- and r-processes), the correlation of the N abundances with abundances of heavy elements from the 2nd and 3rd s-process peaks bears instead the signature of the 22Ne neutron source. Adding to the...

  14. Constraint on the cosmic age from the solar $r$-process abundances

    CERN Document Server

    Heng, T H; Niu, Z M; Sun, B H; Guo, J Y

    2014-01-01

    The cosmic age is an important physical quantity in cosmology. Based on the radiometric method, a reliable lower limit of the cosmic age is derived to be $15.68\\pm 1.95$ Gyr by using the $r$-process abundances inferred for the solar system and observations in metal-poor stars. This value is larger than the latest cosmic age $13.813\\pm 0.058$ Gyr from Planck 2013 results, while they still agree with each other within the uncertainties. The uncertainty of $1.95$ Gyr mainly originates from the error on thorium abundance observed in metal-poor star CS 22892-052, so future high-precision abundance observations on CS 22892-052 are needed to understand this age deviation.

  15. The link between rare earth peak formation and the astrophysical site of the $r$ process

    CERN Document Server

    Mumpower, M R; Surman, R; Steiner, A W

    2016-01-01

    The primary astrophysical source of the rare earth elements is the rapid neutron capture process ($r$ process). The rare earth peak that is seen in the solar $r$-process residuals has been proposed to originate as a pile-up of nuclei during the end of the $r$ process. We introduce a new method utilizing Monte Carlo studies of nuclear masses in the rare earth region, that includes self-consistently adjusting $\\beta$-decay rates and neutron capture rates, to find the mass surfaces necessary for the formation of the rare earth peak. We demonstrate our method with two types of astrophysical scenarios, one corresponding conditions typical of core-collapse supernova winds and one corresponding to conditions typical of the ejection of the material from the tidal tails of neutron star mergers. In each type of astrophysical conditions, this method successfully locates a region of enhanced stability in the mass surface that is responsible for the rare earth peak. For each scenario, we find that the change in the mass s...

  16. Nuclear structure studies for the astrophysical r-process

    CERN Document Server

    Pfeiffer, B; Thielemann, F K; Walters, W B

    2001-01-01

    The production of the heaviest elements in nature occurs via the r-process, i.e. a combination of rapid neutron captures, the inverse photodisintegrations, and slower beta sup - -decays, beta-delayed processes as well as fission and possibly interactions with intense neutrino fluxes. A correct understanding and modeling requires the knowledge of nuclear properties far from stability and a detailed prescription of the astrophysical environment. Experiments at radioactive ion beam facilities have played a pioneering role in exploring the characteristics of nuclear structure in terms of masses and beta-decay properties. Initial examinations paid attention to highly unstable nuclei with magic neutron numbers and their beta-decay properties, related to the location and height of r-process peaks, while recent activities focus on the evolution of shell effects at large distances from the valley of stability. We show in site-independent applications the effect of both types of nuclear properties on r-process abundanc...

  17. The r-process in the neutrino-driven wind from a black-hole torus

    CERN Document Server

    Wanajo, Shinya

    2011-01-01

    We examine r-process nucleosynthesis in the neutrino-driven wind from the thick accretion disk (or "torus") around a black hole. Such systems are expected as emnants of binary neutron star or neutron star -- black hole mergers. We consider a simplified, analytic, time-dependent evolution model of a 3M_sun central black hole surrounded by a neutrino emitting accretion torus with 90km radius, which serves as basis for computing spherically symmetric neutrino-driven wind solutions. We find that ejecta with modest entropies (~30 per nucleon in units of the Boltzmann constant) and moderate expansion timescales (~100ms) dominate in the mass outflow. The mass-integrated nucleosynthetic abundances are in good agreement with the solar system r-process abundance distribution if a minimal value of the electron fraction at the charged-particle freezeout, Ye,min~0.2, is achieved. In the case of Ye,min~0.3, the production of r-elements beyond A~130 does not reach to the third peak but could be still important for an explan...

  18. Colliding Neutron Stars as the Source of Heavy Elements

    Science.gov (United States)

    Kohler, Susanna

    2016-09-01

    Where do the heavy elements the chemical elements beyond iron in our universe come from? One of the primary candidate sources is the merger of two neutron stars, but recent observations have cast doubt on this model. Can neutron-star mergers really be responsible?Elements from Collisions?Periodic table showing the origin of each chemical element. Those produced by the r-process are shaded orange and attributed to supernovae in this image; though supernovae are one proposed source of r-process elements, an alternative source is the merger of two neutron stars. [Cmglee]When a binary-neutron-star system inspirals and the two neutron stars smash into each other, a shower of neutrons are released. These neutrons are thought to bombard the surrounding atoms, rapidly producing heavy elements in what is known as r-process nucleosynthesis.So could these mergers be responsible for producing the majority of the universes heavy r-process elements? Proponents of this model argue that its supported by observations. The overall amount of heavy r-process material in the Milky Way, for instance, is consistent with the expected ejection amounts from mergers, based both on predicted merger rates for neutron stars in the galaxy, and on the observed rates of soft gamma-ray bursts (which are thought to accompany double-neutron-star mergers).Challenges from Ultra-Faint DwarfsRecently, however, r-process elements have been observed in ultra-faint dwarf satellite galaxies. This discovery raises two major challenges to the merger model for heavy-element production:When neutron stars are born during a core-collapse supernova, mass is ejected, providing the stars with asymmetric natal kicks. During the second collapse in a double-neutron-star binary, wouldnt the kick exceed the low escape velocity of an ultra-faint dwarf, ejecting the binary before it could merge and enrich the galaxy?Ultra-faint dwarfs have very old stellar populations and the observation of r-process elements in these stars

  19. Hans A. Bethe Prize: Astrophysical, observational and nuclear-physics aspects of r-process nucleosynthesis

    Science.gov (United States)

    Kratz, Karl-Ludwig

    2014-03-01

    Guided by the Solar System (S.S.) abundance peaks at A ~= 130 and A ~= 195, the basic mechanisms for the rapid neutron-capture process (the r-process) have been known for over 50 years. However, even today, all proposed scenarios and sites face problems with astrophysical conditions as well as with the necessary nuclear-physics input. In my talk, I will describe efforts in experimental and theoretical nuclear-structure data for modeling today's three groups of r-process ``observables'', i.e. the bulk S.S. isotopic abundances, the elemental abundances in metal-poor halo stars, and peculiar isotopic patterns measured in certain cosmic stardust grains. To set a historical basis, I will briefly recall our site-independent ``waiting-point'' model, with superpositions of neutron-density components and the use of the first global, unified nuclear input based on the mass model FRDM(1992). This approach provided a considerable leap forward in the basic understanding of the required astrophysical conditions, as well as of specific shell-structure properties far from stability. Starting in the early millenium, the above simple model has been replaced by more realistic, dynamical parameter studies within the high-entropy wind scenario of core-collapse supernovae, now with superpositions of entropy (S) and electron-fraction (Ye) components. Furthermore, an improved, global set of nuclear-physics data is used today, based on the new mass model FRDM(2012). With this nuclear and astrophysics parameter combination, a new fit to the S.S. r-abundances will be shown, and its improvements and remaining deficiencies in terms of underlying shell structure will be discussed. Concerning the abundance patterns in metal-poor halo stars, an interpretation of the production of ``r-rich'' (e.g. CS 22892-052) and ``r-poor'' (e.g. HD 122563) stars in terms of different (Ye), S combinations will be presented. Finally, for the third group of ``r-observables'', a possible origin of the anomalous Xe

  20. The p- and r-processes reviews and other views

    CERN Document Server

    Arnould, M; Rayet, M

    2001-01-01

    A review is presented of the p-process in Type II supernovae, one of its goals being to enlighten the changes in views on this nucleosynthesis mechanism since the work of Jean and Jim on the subject in 1975. Specific discussions are also devoted to cases of particular interest, like the light Mo and Ru stable isotopes, the rare nuclide 138La or the radionuclide 146Sm. Some comments of diverse natures are also made on the r-process. These considerations do not aim at really providing an exhaustive review of the many nuclear physics and astrophysics intricacies of this process. In contrast, they are hoped to complement or to put in perspective other views that are often expressed in relation with this nucleosynthesis mechanism

  1. The p- and r- processes: reviews and other views

    Science.gov (United States)

    Arnould, M.; Goriely, S.; Rayet, M.

    A review is presented of the p-process in Type II supernovae, one of its goals being to enlighten the changes in views on this nucleosynthesis mechanism since the work of Jean and Jim on the subject in 1975. Specific discussions are also devoted to cases of particular interest, like the light Mo and Ru stable isotopes, the rare nuclide 138La or the radionuclide 146Sm. Some comments of diverse natures are also made on the r-process. These considerations do not aim at really providing an exhaustive review of the many nuclear physics and astrophysics intricacies of this process. In contrast, they are hoped to complement or to put in perspective other views that are often expressed in relation with this nucleosynthesis mechanism

  2. The intermediate neutron-capture process and carbon-enhanced metal-poor stars

    CERN Document Server

    Hampel, Melanie; Lugaro, Maria; Meyer, Bradley S

    2016-01-01

    Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) neutron-capture process (e.g., barium and europium respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP-s/r stars, which show both Ba and Eu enrichment, are particularly puzzling since the s and the r processes require neutron densities that are more than ten orders of magnitude apart, and hence are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patterns of CEMP-s/r stars can arise from the nucleosynthesis of the intermediate neutron-capture process (the i process), which is characterised by neutron densities between those of the s and the r processes. Using nuclear network calculations, we study neutron capture nucleosynthesis at different constant neutron densities n ranging from $10^7$ to $10^{15}$ cm$^{-3}$. With respect to the cl...

  3. Star formation history and chemical enrichment in the early Universe: clues from the rest-optical and rest-UV spectra of z~2-3 star-forming galaxies in the Keck Baryonic Structure Survey

    Science.gov (United States)

    Strom, Allison L.

    2017-01-01

    Galaxies at the peak of cosmic star formation (z~2-3) exhibit significantly higher star formation rates and gas fractions at fixed stellar mass than nearby galaxies. These z~2-3 galaxies are also distinct in terms of their nebular spectra, reflecting important differences not only in the physical conditions of their interstellar medium (e.g., electron density and gas-phase metallicity), but also in the details of their massive stellar populations, especially their ionizing radiation fields. Jointly observing galaxies' HII regions, at rest-UV and rest-optical wavelengths, and massive stars, at rest-UV wavelengths, is central to constructing a framework for understanding the differences between z~2-3 and z~0 star-forming galaxies and for self-consistently explaining the trends observed in the high-redshift population. My thesis is based on data from the Keck Baryonic Structure Survey (KBSS), which uniquely combines observations of individual galaxies in these two bandpasses. In total, the near-infrared component of the KBSS includes spectra of >700 z~2-3 galaxies obtained with Keck/MOSFIRE. I will present these results along with a detailed analysis of the full rest-optical (3600-7000 Ang) nebular spectra of ~400 galaxies, showing that high-redshift galaxies exhibit uniformly high degrees of ionization and excitation with respect to most z~0 galaxies. Combined with observations of the same galaxies' rest-UV spectra (obtained with Keck/LRIS) and photoionization model predictions, these results suggest that the disparity arises from differences in the shape of the ionizing radiation field at fixed gas-phase oxygen abundance, most likely due to the effects of Fe-poor massive binary stars. My comprehensive spectroscopic study of an unprecedentedly large sample of z~2-3 galaxies offers compelling evidence that the distinct chemical abundance patterns observed in these galaxies are the result of systematic differences in their star formation histories.

  4. NEUTRINO-DRIVEN WINDS IN THE AFTERMATH OF A NEUTRON STAR MERGER: NUCLEOSYNTHESIS AND ELECTROMAGNETIC TRANSIENTS

    Energy Technology Data Exchange (ETDEWEB)

    Martin, D.; Perego, A.; Arcones, A. [Institut für Kernphysik, Technische Universität Darmstadt, Schlossgartenstr. 2, Darmstadt D-64289 (Germany); Thielemann, F.-K. [Department of Physics, University of Basel, Klingelbergstraße 82, 4056, Basel (Switzerland); Korobkin, O.; Rosswog, S., E-mail: dirk.martin@physik.tu-darmstadt.de [The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden)

    2015-11-01

    We present a comprehensive nucleosynthesis study of the neutrino-driven wind in the aftermath of a binary neutron star merger. Our focus is the initial remnant phase when a massive central neutron star is present. Using tracers from a recent hydrodynamical simulation, we determine total masses and integrated abundances to characterize the composition of unbound matter. We find that the nucleosynthetic yields depend sensitively on both the life time of the massive neutron star and the polar angle. Matter in excess of up to 9 × 10{sup −3} M{sub ⊙} becomes unbound until ∼200 ms. Due to electron fractions of Y{sub e} ≈ 0.2–0.4, mainly nuclei with mass numbers A < 130 are synthesized, complementing the yields from the earlier dynamic ejecta. Mixing scenarios with these two types of ejecta can explain the abundance pattern in r-process enriched metal-poor stars. Additionally, we calculate heating rates for the decay of the freshly produced radioactive isotopes. The resulting light curve peaks in the blue band after about 4 hr. Furthermore, high opacities due to heavy r-process nuclei in the dynamic ejecta lead to a second peak in the infrared after 3–4 days.

  5. Formation of the Abundance Boundaries of the Heavier Neutron-capture Elements in Metal-poor Stars

    Science.gov (United States)

    Yang, Guochao; Li, Hongjie; Liu, Nian; Zhang, Lu; Cui, Wenyuan; Liang, Yanchun; Niu, Ping; Zhang, Bo

    2017-06-01

    The abundance scatter of heavier r-process elements (Z≥slant 56) relative to Fe ([r/Fe]) in metal-poor stars preserves excellent information of the star formation history and provides important insights into the various situations of the Galactic chemical enrichment. In this respect, the upper and lower boundaries of [r/Fe] could present useful clues for investigating the extreme situations of the star formation history and the early Galactic chemical evolution. In this paper, we investigate the formation of the upper and lower boundaries of [r/Fe] for the gas clouds. We find that, for a cloud from which metal-poor stars formed, the formation of the upper limits of [r/Fe] is mainly due to the pollution from a single main r-process event. For a cloud from which metal-poor stars formed, the formation of the lower limits of [r/Fe] is mainly due to the pollution from a single SN II event that ejects primary Fe.

  6. Chemistry of the Sagittarius dwarf galaxy: A top-light initial mass function, outflows, and the R-process

    Energy Technology Data Exchange (ETDEWEB)

    McWilliam, Andrew [The Observatories of the Carnegie Institute of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Wallerstein, George; Mottini, Marta, E-mail: andy@obs.carnegiescience.edu, E-mail: walleg@u.washington.edu [Astronomy Department, University of Washington, Seattle, WA 98195 (United States)

    2013-12-01

    From chemical abundance analysis of stars in the Sagittarius dwarf spheroidal galaxy (Sgr), we conclude that the α-element deficiencies cannot be due to the Type Ia supernova (SN Ia) time-delay scenario of Tinsley. Instead, the evidence points to low [α/Fe] ratios resulting from an initial mass function (IMF) deficient in the highest mass stars. The critical evidence is the 0.4 dex deficiency of [O/Fe], [Mg/Fe], and other hydrostatic elements, contrasting with the normal trend of r-process [Eu/Fe] {sub r} with [Fe/H]. Supporting evidence comes from the hydrostatic element (O, Mg, Na, Al, Cu) [X/Fe] ratios, which are inconsistent with iron added to the Milky Way (MW) disk trends. Also, the ratio of hydrostatic to explosive (Si, Ca, Ti) element abundances suggests a relatively top-light IMF. Abundance similarities with the LMC, Fornax, and IC 1613 suggest that their α-element deficiencies also resulted from IMFs lacking the most massive SNe II. The top-light IMF, as well as the normal trend of r-process [Eu/Fe] {sub r} with [Fe/H] in Sgr, indicates that massive SNe II (≳30 M {sub ☉}) are not major sources of r-process elements. High [La/Y] ratios, consistent with leaky-box chemical evolution, are confirmed but ∼0.3 dex larger than theoretical asymptotic giant branch (AGB) predictions. This suggests that a substantial increase in the theoretical {sup 13}C pocket in low-mass AGB stars is required. Sgr has the lowest [Rb/Zr] ratios known, consistent with pollution by low-mass (≲2 M {sub ☉}) AGB stars near [Fe/H] = –0.6, likely resulting from leaky-box chemical evolution. The [Cu/O] trends in Sgr and the MW suggest that Cu yields increase with both metallicity and stellar mass, as expected from Cu production by the weak s-process in massive stars. Finally, we present an updated hyperfine splitting line list, an abundance analysis of Arcturus, and further develop our error analysis formalism.

  7. Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097

    CERN Document Server

    Yang, Guochao; Liu, Nian; Cui, Wenyuan; Liang, Yanchun; Zhang, Bo

    2016-01-01

    Historically, the weak s-process contribution to metal-poor stars is thought to be extremely small, due to the effect of the secondary-like nature of the neutron source 22Ne(a;n)25Mg in massive stars, which means that metal-poor weak s-process stars could not be found. ET0097 is the first observed carbon-enhanced metal-poor (CEMP) star in the Sculptor dwarf spheroidal galaxy. Because C is enriched and the elements heavier than Ba are not overabundant, ET0097 can be classified as a CEMP-no star. However, this star shows overabundances of lighter n-capture elements (i.e., Sr, Y and Zr). In this work, having adopted the abundance decomposition approach, we investigate the astrophysical origins of the elements in ET0097. We find that the light elements and iron-peak elements (from O to Zn) of the star mainly originate from the primary process of massive stars and the heavier n-capture elements (heavier than Ba) mainly come from the main r-process. However, the lighter n-capture elements such as Sr, Y and Zr shoul...

  8. Chemistry of the Sagittarius Dwarf Galaxy: a Top-Light IMF, Outflows and the R-Process

    CERN Document Server

    McWilliam, Andrew; Mottini, Marta

    2013-01-01

    From chemical abundance analysis of stars in the Sagittarius dwarf spheroidal galaxy (Sgr), we conclude that the alpha-element deficiencies cannot be due to the Type Ia supernova (SNIa) time-delay scenario of Tinsley (1979). Instead, the evidence points to low [alpha/Fe] ratios resulting from an initial mass function (IMF) deficient in the highest mass stars. The critical evidence is the 0.4 dex deficiency of [O/Fe], [Mg/Fe] and other hydrostatic elements, contrasting with the normal trend of r-process [Eu/Fe]r with [Fe/H]. Supporting evidence comes from the hydrostatic element (O, Mg, Na, Al, Cu) [X/Fe] ratios, which are inconsistent with iron added to the Milky Way (MW) disk trends. Also, the ratio of hydrostatic to explosive (Si, Ca, Ti) element abundances suggests a relatively top-light IMF. Abundance similarities with the LMC, Fornax and IC 1613, suggest that their alpha-element deficiencies also resulted from IMFs lacking the most massive SNII. For such a top-light IMF, the normal trend of r-process [Eu...

  9. Interpretation of CEMP(s) and CEMP(s + r) Stars with AGB Models

    CERN Document Server

    Bisterzo, S; Straniero, O; Aoki, W; 10.1071/AS08055

    2009-01-01

    Asymptotic Giant Branch (AGB) stars play a fundamental role in the s-process nucleosynthesis during their thermal pulsing phase. The theoretical predictions obtained by AGB models at different masses, s-process efficiencies, dilution factors and initial r-enrichment, are compared with spectroscopic observations of Carbon-Enhanced Metal-Poor stars enriched in s-process elements, CEMP(s), collected from the literature. We discuss here five stars as example, CS 22880-074, CS 22942-019, CS 29526-110, HE 0202-2204, and LP 625-44. All these objects lie on the main-sequence or on the giant phase, clearly before the TP-AGB stage: the hypothesis of mass transfer from an AGB companion, would explain the observed s-process enhancement. CS 29526-110 and LP 625-44 are CEMP(s+r) objects, and are interpreted assuming that the molecular cloud, from which the binary system formed, was already enriched in r-process elements by SNII pollution. In several cases, the observed s-process distribution may be accounted for AGB models...

  10. Metal-Poor Stars Observed with the Magellan Telescope I. Constraints on Progenitor Mass and Metallicity of AGB Stars Undergoing s-Process Nucleosynthesis

    CERN Document Server

    Placco, Vinicius M; Beers, Timothy C; Karakas, Amanda I; Kennedy, Catherine R; Rossi, Silvia; Christlieb, Norbert; Stancliffe, Richard J

    2013-01-01

    We present a comprehensive abundance analysis of two newly-discovered carbon-enhanced metal-poor (CEMP) stars. HE2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if NLTE corrections are included ([Pb/Fe] = +3.84). HE2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R ~ 2,000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R ~ 30,000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical AGB nucleosynthesis models of 1.3 Mo with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 Mo at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture materia...

  11. Study of Neutron-Capture Element Abundances in Metal-Poor Stars

    CERN Document Server

    Li, Hongjie; Liang, Shuai; Cui, Wenyuan; Zhang, Bo

    2013-01-01

    This work describes a study of elemental abundances for 30 metal-poor stars whose chemical abundances provide excellent information for setting constraints on models of neutron-capture processes. Based on the abundances of main r- and weak r-process stars, the abundance patterns of main r-process and weak r-process are obtained. The two r-process component coefficients are defined to determine the relative contributions from individual neutron-capture process to abundances of metal-poor stars. Based on the component coefficients, we find that metal-poor stars BD+4 2621 and HD 4306 are also weak r-process stars, which means that the abundance pattern produced by weak r-process is stable. All metal-poor star abundances contain the contributions of both main r-process and weak r-process. The elements produced by weak r-process have increased along with Fe over the polluted history. Most of the metal-poor star abundances do not follow the pattern observed in solar system, but there is a small fraction that do. Fo...

  12. Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097

    Science.gov (United States)

    Yang, Guochao; Li, Hongjie; Liu, Nian; Cui, Wenyuan; Liang, Yanchun; Zhang, Bo

    2016-09-01

    Historically, the weak s-process contribution to metal-poor stars is thought to be extremely small, due to the effect of the secondary-like nature of the neutron source 22Ne(α , n)25Mg in massive stars, which means that metal-poor "weak s-process stars" could not be found. ET0097 is the first observed carbon-enhanced metal-poor (CEMP) star in the Sculptor dwarf spheroidal galaxy. Because C is enriched and the elements heavier than Ba are not overabundant, ET0097 can be classified as a CEMP-no star. However, this star shows overabundances of lighter n-capture elements (i.e., Sr, Y and Zr). In this work, having adopted the abundance decomposition approach, we investigate the astrophysical origins of the elements in ET0097. We find that the light elements and iron-peak elements (from O to Zn) of the star mainly originate from the primary process of massive stars and the heavier n-capture elements (heavier than Ba) mainly come from the main r-process. However, the lighter n-capture elements such as Sr, Y and Zr should mainly come from the primary weak s-process. The contributed fractions of the primary weak s-process to the Sr, Y and Zr abundances of ET0097 are about 82 %, 84 % and 58 % respectively, suggesting that the CEMP star ET0097 should have the footprints of the weak s-process. The derived result should be a significant evidence that the weak s-process elements can be produced in metal-poor massive stars.

  13. Beta-decay properties of exotic nuclei and the astrophysical r-process

    Energy Technology Data Exchange (ETDEWEB)

    Tachibana, T. [Waseda Univ., Tokyo (Japan). Adv. Res. Center for Sci. and Eng.; Arnould, M. [Institut d`Astronomie et d`Astrophysique, Universite Libre de Bruxelles (Belgium)

    1995-05-29

    The r-process abundances are evaluated with the use of three different, {beta} decay models, i.e., the second version of the Gross Theory, the semi-Gross Theory and a QRPA approach. The necessary Q{sub {beta}}-values, as well as the neutron separation energies, are obtained from the TUYY, ETFSI and FRDM mass predictions. A comparison is made among the {beta}-decay half-lives predicted by these {beta}-decay models for the nuclei on a typical r-process path, as well as among the resulting r-process abundances. ((orig.)).

  14. s-Process in Low Metallicity Stars. III. Individual analysis of CEMP-s and CEMP-s/r with AGB models

    CERN Document Server

    Bisterzo, S; Straniero, O; Cristallo, S; Kaeppeler, F

    2012-01-01

    We provide an individual analysis of 94 carbon enhanced metal-poor stars showing an s-process enrichment (CEMP-s) collected from the literature. The s-process enhancement observed in these stars is ascribed to mass transfer by stellar winds in a binary system from a more massive companion evolving faster toward the asymptotic giant branch (AGB) phase. The theoretical AGB nucleosynthesis models have been presented in Paper I. Several CEMP-s stars show an enhancement in both s and r-process elements (CEMP-s/r). In order to explain the peculiar abundances observed in CEMP-s/r stars, we assume that the molecular cloud from which CEMP-s formed was previously enriched in r-elements by Supernovae pollution. A general discussion and the method adopted in order to interpret the observations have been provided in Paper II. We present in this paper a detailed study of spectroscopic observations of individual stars. We consider all elements from carbon to bismuth, with particular attention to the three s-process peaks, l...

  15. A holistic abundance analysis of r-rich stars

    CERN Document Server

    Zhang, Jiang; Zhang, Bo; 10.1111/j.1365-2966.2010.17374.x

    2010-01-01

    The chemical abundances of metal-poor stars are an excellent test bed by which to set new constraints on models of neutron-capture processes at low metallicity. Some r-process-rich (hereafter r-rich) metal-poor stars, such as HD221170, show an overabundance of the heavier neutron-capture elements and excesses of lighter neutron-capture elements. The study of these r-rich stars could give us a better understanding of weak and main r-process nucleosynthesis at low metallicity. Based on conclusions from the observation of metal-poor stars and neutron-capture element nucleosynthesis theory, we set up a model to determine the relative contributions from weak and main r-processes to the heavy-element abundances in metal-poor stars. Using this model, we find that the abundance patterns of light elements for most sample stars are close to the pattern of weak r-process stars, and those of heavier neutron-capture elements very similar to the pattern of main r-process stars, while the lighter neutron-capture elements ca...

  16. Beta decay rates for nuclei with 115 < < 140 for r-process nucleosynthesis

    Indian Academy of Sciences (India)

    Kamales Kar; Soumya Chakravarti; V R Manfredi

    2006-08-01

    For r-process nucleosynthesis the -decay rates for a number of neutron-rich intermediate heavy nuclei are calculated. The model for the -strength function is able to reproduce the observed half-lives quite well.

  17. Local and global effects of beta decays on r-process

    CERN Document Server

    Caballero, O L; Borzov, I N; Langanke, K; Martinez-Pinedo, G

    2014-01-01

    Nuclear beta decay rates are an essential ingredient in simulations of the astrophysical r-process. Most of these rates still rely on theoretical modeling. However, modern radioactive ion-beam facilities have allowed to measure beta half lives of some nuclei on or close to the r-process path. These data indicate that r-process half lives are in general shorter than anticipated in the standard theoretical predictions based on the Finite Range Droplet Model (FRDM). The data have also served as important constraints for improved predictions of half lives based on continuum QRPA calculations on top of the energy-density functional theory. Although these calculations are yet limited to spherical nuclei, they include the important r-process waiting point nuclei close to and at the neutron magic numbers $N=50, 82$ and 126. We have studied the impact of these new experimental and theoretical half lives on r-process nucleosynthesis within the two astrophysical sites currently favored for the r process: the neutrino-dr...

  18. Inhomogeneous chemical enrichment in the Galactic Halo

    Science.gov (United States)

    Kobayashi, Chiaki

    2016-08-01

    In a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M ⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.

  19. Subaru/HDS study of CH stars: elemental abundances for stellar neutron-capture process studies

    Science.gov (United States)

    Goswami, Aruna; Aoki, Wako; Karinkuzhi, Drisya

    2016-01-01

    A comprehensive abundance analysis providing rare insight into the chemical history of lead stars is still lacking. We present results from high-resolution (R ˜ 50 000) spectral analyses of three CH stars, HD 26, HD 198269 and HD 224959, and, a carbon star with a dusty envelope, HD 100764. Previous studies on these objects are limited by both resolution and wavelength regions and the results differ significantly from each other. We have undertaken to reanalyse the chemical composition of these objects based on high-resolution Subaru spectra covering the wavelength regions 4020-6775 Å. Considering local thermodynamic equilibrium and using model atmospheres, we have derived the stellar parameters, the effective temperatures Teff, surface gravities log g, and metallicities [Fe/H] for these objects. The derived parameters for HD 26, HD 100764, HD 198269 and HD 224959 are (5000, 1.6, -1.13), (4750, 2.0 -0.86), (4500, 1.5, -2.06) and (5050, 2.1, -2.44), respectively. The stars are found to exhibit large enhancements of heavy elements relative to iron in conformity to previous studies. Large enhancement of Pb with respect to iron is also confirmed. Updates on the elemental abundances for several s-process elements (Y, Zr, La, Ce, Nd, Sm and Pb) along with the first-time estimates of abundances for a number of other heavy elements (Sr, Ba, Pr, Eu, Er and W) are reported. Our analysis suggests that neutron-capture elements in HD 26 primarily originate in the s-process while the major contributions to the abundances of neutron-capture elements in the more metal-poor objects HD 224959 and HD 198269 are from the r-process, possibly from materials that are pre-enriched with products of the r-process.

  20. R-process Experimental Campaign at the National Superconducting Cyclotron Laboratory

    CERN Document Server

    Pereira, J; Quinn, M; Aprahamian, A; Arndt, O; Becerril, A; Elliot, T; Estrade, A; Galaviz, D; Kern, L; Kessler, R; Kratz, K L; Lorusso, G; Mantica, P; Matos, M; Montes, F; Pfeiffer, B; Schatz, H; Schertz, F; Smith, E; Walters, W B; Wöhr, A

    2006-01-01

    A JINA/VISTARS r-process campaign was completed at the A1900 Fragment Separator of the National Superconducting Cyclotron Laboratory in the fall of 2005. The purpose of the campaign was the measurement of the beta-decay half-lives and beta-delayed neutron-emission probabilities of different unknown neutron-rich nuclei participating in the r-process. From these observables it will be possible to extract information about the region between the N=56 sub-shell closure at the sudden onset of deformation at N=60 in the A=100 region, and the potential new shell structures around the possible local, spherical double sub-shell closure at Z=40, N=70, which may help clarify the origin of the calculated r-process abundance deficiencies around A=110. Moreover, the region of the chart of nuclides investigated in the campaign included some important r-process waiting-point nuclei, whose beta-decay properties are crucial for understanding the r-process abundance pattern. Details of this campaign will be presented, emphasizi...

  1. Reverse engineering nuclear properties from rare earth abundances in the r process

    Science.gov (United States)

    Mumpower, M. R.; McLaughlin, G. C.; Surman, R.; Steiner, A. W.

    2017-03-01

    The bulk of the rare earth elements are believed to be synthesized in the rapid neutron capture process or r process of nucleosynthesis. The solar r-process residuals show a small peak in the rare earths around A∼ 160, which is proposed to be formed dynamically during the end phase of the r process by a pileup of material. This abundance feature is of particular importance as it is sensitive to both the nuclear physics inputs and the astrophysical conditions of the main r process. We explore the formation of the rare earth peak from the perspective of an inverse problem, using Monte Carlo studies of nuclear masses to investigate the unknown nuclear properties required to best match rare earth abundance sector of the solar isotopic residuals. When nuclear masses are changed, we recalculate the relevant β-decay properties and neutron capture rates in the rare earth region. The feedback provided by this observational constraint allows for the reverse engineering of nuclear properties far from stability where no experimental information exists. We investigate a range of astrophysical conditions with this method and show how these lead to different predictions in the nuclear properties influential to the formation of the rare earth peak. We conclude that targeted experimental campaigns in this region will help to resolve the type of conditions responsible for the production of the rare earth nuclei, and will provide new insights into the longstanding problem of the astrophysical site(s) of the r process.

  2. First results from the CARIBU facility: mass measurements on the r-process path.

    Science.gov (United States)

    Van Schelt, J; Lascar, D; Savard, G; Clark, J A; Bertone, P F; Caldwell, S; Chaudhuri, A; Levand, A F; Li, G; Morgan, G E; Orford, R; Segel, R E; Sharma, K S; Sternberg, M G

    2013-08-09

    The Canadian Penning Trap mass spectrometer has made mass measurements of 33 neutron-rich nuclides provided by the new Californium Rare Isotope Breeder Upgrade facility at Argonne National Laboratory. The studied region includes the 132Sn double shell closure and ranges in Z from In to Cs, with Sn isotopes measured out to A=135, and the typical measurement precision is at the 100 ppb level or better. The region encompasses a possible major waiting point of the astrophysical r process, and the impact of the masses on the r process is shown through a series of simulations. These first-ever simulations with direct mass information on this waiting point show significant increases in waiting time at Sn and Sb in comparison with commonly used mass models, demonstrating the inadequacy of existing models for accurate r-process calculations.

  3. The impact of individual nuclear properties on $r$-process nucleosynthesis

    CERN Document Server

    Mumpower, M R; McLaughlin, G C; Aprahamian, A

    2015-01-01

    The astrophysical rapid neutron capture process or `$r$ process' of nucleosynthesis is believed to be responsible for the production of approximately half the heavy element abundances found in nature. This multifaceted problem remains one of the greatest open challenges in all of physics. Knowledge of nuclear physics properties such as masses, $\\beta$-decay and neutron capture rates, as well as $\\beta$-delayed neutron emission probabilities are critical inputs that go into calculations of $r$-process nucleosynthesis. While properties of nuclei near stability have been established, much still remains unknown regarding neutron-rich nuclei far from stability that may participate in the $r$ process. Sensitivity studies gauge the astrophysical response of a change in nuclear physics input(s) which allows for the isolation of the most important nuclear properties that shape the final abundances observed in nature. This review summarizes the extent of recent sensitivity studies and highlights how these studies play ...

  4. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    Energy Technology Data Exchange (ETDEWEB)

    Placco, Vinicius M.; Rossi, Silvia [Departamento de Astronomia-Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Sao Paulo, SP 05508-900 (Brazil); Frebel, Anna [Massachusetts Institute of Technology and Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Beers, Timothy C. [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States); Karakas, Amanda I.; Kennedy, Catherine R. [Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611 (Australia); Christlieb, Norbert [Zentrum fuer Astronomie der Universitaet Heidelberg, Landessternwarte, Koenigstuhl 12, D-69117 Heidelberg (Germany); Stancliffe, Richard J. [Argelander-Institut fuer Astronomie der Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2013-06-20

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R {approx} 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R {approx} 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M{sub Sun} with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 M{sub Sun} at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138-3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258-6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 {<=} M(M{sub Sun }) {<=} 1.3) and metallicities (-2.8 {<=} [Fe/H] {<=}-2.5) yield the best agreement with our observed elemental abundance patterns.

  5. Beta Decays of Isotones with Neutron Magic Number of N=126 and R-process Nucleosynthesis

    CERN Document Server

    Suzuki, Toshio; Kajino, Toshitaka; Otsuka, Takaharu

    2011-01-01

    Beta decays of the isotones with N=126 are studied by shell model calculations taking into account both the Gamow-Teller (GT) and first-forbidden (FF) transitions. The FF transitions are found to be important to reduce the half-lives, by nearly twice to several times, from those by the GT contributions only. Possible implications of the short half-lives of the waiting point nuclei on the r-process nucleosynthesis during the supernova explosions are discussed. A slight shift of the third peak of the element abundances in the r-process toward higher mass region is found.

  6. Beta decay studies of r-process nuclei at the National Superconducting Cyclotron Laboratory

    CERN Document Server

    Pereira, J; Arndt, O; Becerril, A; Elliot, T; Estrade, A; Galaviz, D; Hennrich, S; Hosmer, P; Kessler, R; Kratz, K L; Lorusso, G; Mantica, P F; Matos, M; Montes, F; Santi, P; Pfeiffer, B; Quinn, M; Schatz, H; Schertz, F; Schnorrenberger, L; Smith, E; Tomlin, B E; Walters, W; Wöhr, A

    2009-01-01

    The impact of nuclear physics on astrophysical r-process models is discussed, emphasizing the importance of beta-decay properties of neutron-rich nuclei. Several r-process motivated beta-decay experiments performed at the National Superconducting Cyclotron Laboratory are presented. The experiments include the measurement of beta-decay half-lives and neutron emission probabilities of nuclei in regions around Ni-78; Se-90; Zr-106 and Rh-120, as well as spectroscopic studies of Pd-120. A summary on the different experimental techniques employed, data analysis, results and impact on model calculations is presented.

  7. First stars evolution and nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Bahena, D. [Institute of Astronomy of the Academy of Sciences, Bocni II 1401, 14131 Praha 4, (Czech Republic); Klapp, J. [ININ, 52750 La Marquesa, Estado de Mexico (Mexico); Dehnen, H. [Fachbereich Physik, Universitat Konstanz, 78457 Konstanz (Germany)]. e-mail: bahen@hotmail.com

    2007-12-15

    The first stars in the universe were massive and luminous with typical masses M {>=} 100M. Metal-free stars have unique physical characteristics and exhibit high effective temperatures and small radii. These so called Population III stars were responsible for the initial enrichment of the intergalactic medium with heavy elements. In this work, we study the structure, evolution and nucleosynthesis of 100, 200, 250 and 300M galactic and pregalactic Population III mass losing stars with metallicities Z 10{sup -6} and Z = 10{sup -9}, during the hydrogen and helium burning phases. Using a stellar evolution code, a system of 10 structure and evolution equations together with boundary conditions, and a set of 30 nuclear reactions, are solved simultaneously, obtaining the star's structure, evolution, isotopic abundances and their ratios. Motivated by recent stability analysis, almost all very massive star (VMS) calculations during the past few years have been performed with no mass loss. However, it has recently been claimed that VMS should have strong mass loss. We present in this work new VMS calculations that includes mass loss. The main difference between zero-metal and metal-enriched stars lies in the nuclear energy generation mechanism. For the first stars, nuclear burning proceeds in a non-standard way. Since Population III stars can reach high central temperatures, this leads to the first synthesis of primary carbon through the 3 {alpha} reaction activating the CNO-cycles. Zero-metal stars produce light elements, such as He, C, N and O. Thus, very massive pregalactic Population III stars experienced self-production of C, either at the zero-age main sequence or in later phases of central hydrogen burning. In advanced evolutionary phases, these stars contribute to the chemical enrichment of the intergalactic medium through supernova explosions. (Author)

  8. r-process Production Sites as inferred from Eu Abundances in Dwarf Galaxies

    CERN Document Server

    Beniamini, Paz; Piran, Tsvi

    2016-01-01

    Recent observations of $r$-process material in ultra-faint dwarf galaxies (UFDs) shed light on the sources of these elements. Strong upper limits on the Eu mass in some UFDs combined with detections of much larger masses in a UFD, Reticulum II, and other dwarf galaxies imply that Eu production is dominated by rare events, and that the minimal Eu mass observed in any UFD is approximately the amount of Eu mass produced per event. This is consistent with other independent observations in the Galaxy. We estimate, using a model independent likelihood analysis, the rate and Eu (Fe) mass produced per $r$-process (Fe production) event in dwarf galaxies including classical dwarfs and UFDs. The mass and rate of the Fe production events are consistent with the normal core-collapse supernova~(ccSN) scenario. The Eu mass per event is $3\\times 10^{-5}M_{\\odot}<\\tilde{m}_{\\rm Eu}<2\\times 10^{-4}M_{\\odot}$, corresponding to a total $r$-process mass per event of $6\\times 10^{-3}M_{\\odot}<\\tilde{m}_{r-process}<4\\ti...

  9. Reverse engineering nuclear properties from rare earth abundances in the $r$ process

    CERN Document Server

    Mumpower, M R; Surman, R; Steiner, A W

    2016-01-01

    The bulk of the rare earth elements are believed to be synthesized in the rapid neutron capture process or $r$ process of nucleosynthesis. The solar $r$-process residuals show a small peak in the rare earths around $A\\sim 160$, which is proposed to be formed dynamically during the end phase of the $r$ process by a pileup of material. This abundance feature is of particular importance as it is sensitive to both the nuclear physics inputs and the astrophysical conditions of the main $r$ process. We explore the formation of the rare earth peak from the perspective of an inverse problem, using Monte Carlo studies of nuclear masses to investigate the unknown nuclear properties required to best match rare earth abundance sector of the solar isotopic residuals. When nuclear masses are changed, we recalculate the relevant $\\beta$-decay properties and neutron capture rates in the rare earth region. The feedback provided by this observational constraint allows for the reverse engineering of nuclear properties far from ...

  10. The impact of nuclear mass models on r-process nucleosynthesis network calculations

    Science.gov (United States)

    Vaughan, Kelly

    2002-10-01

    An insight into understanding various nucleosynthesis processes is via modelling of the process with network calculations. My project focus is r-process network calculations where the r-process is nucleosynthesis via rapid neutron capture thought to take place in high entropy supernova bubbles. One of the main uncertainties of the simulations is the Nuclear Physics input. My project investigates the role that nuclear masses play in the resulting abundances. The code tecode, involves rapid (n,γ) capture reactions in competition with photodisintegration and β decay onto seed nuclei. In order to fully analyze the effects of nuclear mass models on the relative isotopic abundances, calculations were done from the network code, keeping the initial environmental parameters constant throughout. The supernova model investigated by Qian et al (1996) in which two r-processes, of high and low frequency with seed nucleus ^90Se and of fixed luminosity (fracL_ν_e(0)r_7(0)^2 ˜= 8.77), contribute to the nucleosynthesis of the heavier elements. These two r-processes, however, do not contribute equally to the total abundance observed. The total isotopic abundance produced from both events was therefore calculated using equation refabund. Y(H+L) = fracY(H)+fY(L)f+1 applicability of the P-Scheme in relation to the other mass models to the r-process network calculations. 02 Pscheme Aprahamian,A., Gadala-Maria,A. & Cuka,N. 1996, Revista Mexicana de Fisica,42,1 code Surman,R. & Engel,J. 1998, Phys.Rev. C,54,4 thebibliography

  11. The intermediate r-process in core-collapse supernovae driven by the magneto-rotational instability

    CERN Document Server

    Nishimura, Nobuya; Takiwaki, Tomoya; Yamada, Shoichi; Thielemann, Friedrich-Karl

    2016-01-01

    Magneto-rotational supernovae are a possible astrophysical site of r-process nucleosynthesis, however, we have insufficient understanding of the explosion mechanism, especially the enhancement process of magnetic fields. We investigated the nucleosynthetic properties of magneto-rotational supernovae, based on a new explosion mechanism induced by the magneto-rotational instability (MRI). We performed a series of axisymmetric hydrodynamical simulations, numerically resolving the MRI, with detailed microphysics including neutrino heating. Explosion models driven by neutrino heating enhanced by the MRI showed mildly neutron-rich ejecta producing weak r-process nuclei $A \\sim 130$, while an explosion model with a significant effect of magnetic fields reproduces a solar-like r-process pattern. More commonly seen abundance patterns in our models are in between the weak and regular r-process, producing lighter and intermediate mass nuclei. This intermediate r-process exhibits a variety of r-process abundance distribu...

  12. Collective Flavor Oscillations Of Supernova Neutrinos and r-Process Nucleosynthesis

    CERN Document Server

    Chakraborty, Sovan; Goswami, Srubabati; Kar, Kamales

    2009-01-01

    Neutrino-neutrino interactions inside core-collapse supernovae may give rise to flavor oscillations resulting into collective swap of flavors. These oscillations depend on the initial energy spectra and initial relative fluxes or initial luminosities of the neutrinos. It has been observed that departure from energy equipartition among different flavors can give rise to one or more sharp spectral swap over energy termed as splits. We study the occurrence of splits in the neutrino and antineutrino spectra varying the initial relative fluxes for different models of initial energy spectrum in both normal and inverted hierarchy. These initial relative flux variations give rise to several possible split patterns where as variation over different models of energy spectra give similar results. We explore the effect of these spectral splits on the electron fraction, $Y_e$, that governs r-process nucleosynthesis inside supernovae. Assuming the condition $Y_e < 0.5$, needed for successful r-process nucleosynthesis we...

  13. {beta}-delayed neutron emission measurements around the third r-process abundance peak

    Energy Technology Data Exchange (ETDEWEB)

    Caballero-Folch, R.; Cortes, G.; Calvino, F.; Gomez-Hornillos, M. B.; Riego, A. [INTE-DFEN, Universitat Politecnica de Catalunya, Barcelona (Spain); Domingo-Pardo, C.; Tain, J. L.; Agramunt, J.; Rubio, B. [IFIC, CSIC-University of Valencia, Valencia (Spain); Algora, A. [IFIC, CSIC-University of Valencia, Valencia (Spain) and Inst. Nucl. Research, Debrecen (Hungary); Ameil, F.; Farinon, F.; Heil, M.; Knoebel, R.; Kojouharov, I.; Kurcewicz, J.; Kurz, N.; Litvinov, Y.; Mukha, I.; Nociforo, C. [GSI, Darmstadt (Germany); and others

    2013-06-10

    This contribution summarizes an experiment performed at GSI (Germany) in the neutron-rich region beyond N=126. The aim of this measurement is to provide the nuclear physics input of relevance for r-process model calculations, aiming at a better understanding of the third r-process abundance peak. Many exotic nuclei were measured around {sup 211}Hg and {sup 215}Tl. Final ion identification diagrams are given in this contribution. For most of them, we expect to derive halflives and and {beta}-delayed neutron emission probabilities. The detectors used in this experiment were the Silicon IMplantation and Beta Absorber (SIMBA) detector, based on an array of highly segmented silicon detectors, and the BEta deLayEd Neutron (BELEN) detector, which consisted of 30 3He counters embedded in a polyethylene matrix.

  14. Large-scale calculations of the beta-decay rates and r-process nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Borzov, I.N.; Goriely, S. [Inst. d`Astronomie et d`Astrophysique, Univ. Libre de Bruxelles, Campus Plaine, Bruxelles (Belgium); Pearson, J.M. [Inst. d`Astronomie et d`Astrophysique, Univ. Libre de Bruxelles, Campus Plaine, Bruxelles (Belgium)]|[Lab. de Physique Nucleaire, Univ. de Montreal, Montreal (Canada)

    1998-06-01

    An approximation to a self-consistent model of the ground state and {beta}-decay properties of neutron-rich nuclei is outlined. The structure of the {beta}-strength functions in stable and short-lived nuclei is discussed. The results of large-scale calculations of the {beta}-decay rates for spherical and slightly deformed nuclides of relevance to the r-process are analysed and compared with the results of existing global calculations and recent experimental data. (orig.)

  15. r-Process Nucleosynthesis in Jet-driven Core-Collapse Supernovae

    Science.gov (United States)

    Halevi, Goni; Moesta, Philipp

    2017-01-01

    We investigate rapidly rotating, strongly magnetized core-collapse supernova (CCSN) explosions as a site for the production of heavy elements through r-process nucleosynthesis. While CCSNe have long been considered a potential astrophysical site of this process explaining the origin of observed abundances for stable nuclei heavier than iron, the neutron-rich conditions necessary have not been robustly produced in simulations. There remain large uncertainties in quantifying the fraction of all core-collapse events that produce r-process material and the quantity of ejected material in a typical explosion.We perform three-dimensional (3D) dynamical-spacetime general-relativistic magnetohydrodynamic (GRMHD) simulations of jet-driven CCSNe. These simulations are run using the Einstein toolkit, an open-source community-driven numerical relativity and computational relativistic astrophysics code. They include microphysical finite-temperature equation of state effects and employ a leakage scheme that captures the overall energetics and lepton number exchange due to postbounce neutrino emission. The nuclear products of the simulated explosions are then calculated using SkyNet, a self-heating nuclear reaction network. We explore the robustness of r-process production in magnetorotational core-collapse and the properties of the ejected material.

  16. Collective flavor oscillations of supernova neutrinos and r-process nucleosynthesis

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Sovan; Kar, Kamales [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Choubey, Sandhya [Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019 (India); Goswami, Srubabati, E-mail: sovan.chakraborty@saha.ac.in, E-mail: sandhya@hri.res.in, E-mail: sruba@prl.res.in, E-mail: kamales.kar@saha.ac.in [Physical Research Laboratory, Navrangpura, Ahmedabad 380009 (India)

    2010-06-01

    Neutrino-neutrino interactions inside core-collapse supernovae may give rise to collective flavor oscillations resulting in swap between flavors. These oscillations depend on the initial energy spectra, and relative fluxes or relative luminosities of the neutrinos. It has been observed that departure from energy equipartition among different flavors can give rise to one or more sharp spectral swap over energy, termed as splits. We study the occurrence of splits in the neutrino and antineutrino spectra, varying the initial relative fluxes for different models of initial energy spectrum, in both normal and inverted hierarchy. These initial relative flux variations give rise to several possible split patterns whereas variation over different models of energy spectra give similar results. We explore the effect of these spectral splits on the electron fraction, Y{sub e}, that governs r-process nucleosynthesis inside supernovae. Since spectral splits modify the electron neutrino and antineutrino spectra in the region where r-process is postulated to happen, and since the pattern of spectral splits depends on the initial conditions of the spectra and the neutrino mass hierarchy, we show that the condition Y{sub e} < 0.5 required for successful r-process nucleosynthesis will lead to constraints on the initial spectral conditions, for a given neutrino mass hierarchy.

  17. Star Clusters

    OpenAIRE

    Gieles, M.

    1993-01-01

    Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which they are formed. Many (70%) of the young clusters will not survive the fist 10 Myr, due to t...

  18. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  19. Stars and Star Myths.

    Science.gov (United States)

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  20. The astrophysical r-process and its dependence on properties of nuclei far from stability beta strength functions and neutron capture rates

    CERN Document Server

    Klapdor-Kleingrothaus, H V; Metzinger, J; Oda, T; Thielemann, F K

    1981-01-01

    It is shown that the astrophysical r-process and the question of its site are very sensitive to 'standard' nuclear physics parameters like the beta decay properties and neutron capture rates. Since for these quantities in almost all r-process calculations up to now, and also in all estimates of the production rates of chronometric pairs, only very rough assumptions have been made, it is attempted to present procedures which put the calculation of these quantities for nuclei far from stability on a reliable physical basis. This is done by a microscopic description of the beta strength function and by using a statistical model based on a 'next to first principles' optical potential including effects of deformation for the neutron capture rates. The beta -decay rates for approximately 6000 nuclei between the beta -stability line and the neutron drip line are calculated. The heavy element synthesis by explosive He burning then is calculated using these beta -rates and using realistic star models treating the supe...

  1. The odd-isotope fractions of Barium in CEMP-r/s star HE 0338-3945 and r-II star CS 31082-001

    CERN Document Server

    Meng, Xiaoying; Shi, Jianrong; Jiang, Xiaohua; Zhao, Gang; Zhang, Bo; Li, Ji

    2016-01-01

    We report the first measurement of the odd-isotope fractions for barium, \\fodd\\, in two extremely metal-poor stars: a CEMP-r/s star \\he\\ (\\feh\\,$=-2.42\\pm0.11$) and an r-II star \\cs\\ (\\feh\\,$=-2.90\\pm0.13$). The measured \\fodd\\ values are $0.23\\pm0.12$ corresponding to $34.3\\pm34.3$\\% of the r-process contributions for \\he\\ and $0.43\\pm0.09$ corresponding to $91.4\\pm25.7$\\% of the r-process contribution to Ba production for \\cs. The high r-process signature of barium in \\cs\\ ($91.4\\pm25.7\\%$) suggests that the majority of the heavy elements in this star were synthesised via an r-process path, while the lower r-process value ($34.3\\pm34.3\\%$) found in \\he\\ indicates that the heavy elements in this star formed through a mix of s-process and r-process synthesis. These conclusions are consistent with studies based on AGB model calculations to fit their abundance distributions.

  2. Looking for imprints of the first stellar generations in metal-poor bulge field stars

    Science.gov (United States)

    Siqueira-Mello, C.; Chiappini, C.; Barbuy, B.; Freeman, K.; Ness, M.; Depagne, E.; Cantelli, E.; Pignatari, M.; Hirschi, R.; Frischknecht, U.; Meynet, G.; Maeder, A.

    2016-09-01

    detected in our sample. The heavy elements Y, Zr, Ba, La, and Eu also exhibit oversolar abundances. Three out of the five stars analysed here show slightly enhanced [Y/Ba] ratios similar to those found in other metal-poor bulge globular clusters (NGC 6522 and M 62). Conclusions: This sample shows enhancement in the first-to-second peak abundance ratios of heavy elements, as well as dominantly s-process element excesses. This can be explained by different nucleosynthesis scenarios: (a) the main r-process plus extra mechanisms, such as the weak r-process; (b) mass transfer from asymptotic giant branch stars in binary systems; (c) an early generation of fast-rotating massive stars. Larger samples of moderately metal-poor bulge stars, with detailed chemical abundances, are needed to better constrain the source of dominantly s-process elements in the early Universe. Observations collected at the European Southern Observatory, Paranal, Chile (ESO), under programmes 089.B-0208(A).

  3. Nuclear structure theory for the astrophysical rp-process and r-process

    Energy Technology Data Exchange (ETDEWEB)

    Brown, B.A.; Clement, R.; Schatz, H.; Giansiracusa, J.; Richter, W.A.; Hjorth-Jensen, M.; Kratz, K.-L.; Pfeiffer, B.; Walters, W.B

    2003-05-19

    The astrophysical processes of rapid-proton capture and rapid-neutron capture require the knowledge of many nuclear properties which are not known from experiment. I will describe two examples of how theoretical models are used to provide this input. The first of these uses the Hartree-Fock method for displacement energies to obtain the masses of proton-rich nuclei needed for the rp-process. The second uses a model for configuration mixing near {sup 132}Sn to provide Q values and beta-decay lifetimes for the r-process.

  4. Single Neutron Transfer Experiments Close to the r-Process Path

    Energy Technology Data Exchange (ETDEWEB)

    Grzywacz-Jones, Kate L [ORNL; Adekola, Aderemi S [ORNL; Bardayan, Daniel W [ORNL; Blackmon, Jeff C [ORNL; Chae, Kyung Yuk [ORNL; Chipps, K. [Colorado School of Mines, Golden; Cizewski, Jolie [ORNL; Dean, David Jarvis [ORNL; Erikson, Luke [Colorado School of Mines, Golden; Fitzgerald, R. P. [University of North Carolina, Chapel Hill; Gaddis, A. L. [Furman University; Greife, U. [Colorado School of Mines, Golden; Harlin, Christopher W [ORNL; Hatarik, Robert [Rutgers University; Howard, Joshua A [ORNL; Johnson, Micah [ORNL; Kozub, R. L. [Tennessee Technological University; Liang, J Felix [ORNL; Livesay, Jake [ORNL; Ma, Zhanwen [ORNL; Moazen, Brian [University of Tennessee, Knoxville (UTK); O' Malley, Patrick [Rutgers University; Nesaraja, Caroline D [ORNL; Pain, S. D. [Rutgers University; Patterson, N. P. [University of Surrey, UK; Paulauskas, Stanley V [ORNL; Shapira, Dan [ORNL; ShrinerJr., J. F. [Tennessee Technological University; Sissom, D. J. [Tennessee Technological University; Smith, Michael Scott [ORNL; Swan, T. P. [University of Surrey, UK; Thomas, J. S. [Rutgers University

    2007-01-01

    The first measurements using the (d, p) transfer reaction to study single- particle states in nuclei on the expected r-process path have been made at the Holifield Radioactive Ion Beam Facility. The shell closure at N = 50 has been crossed using the 82Ge(d, p) and 84Se(d, p) reactions. The prop- erties of the lowest-lying states have been determined. Furthermore, the 132Sn(d, p) reaction has been used for the first time to populate single- particle states in 133Sn.

  5. Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances

    Science.gov (United States)

    Hansen, C. J.; Jofré, P.; Koch, A.; McWilliam, A.; Sneden, C. S.

    2017-01-01

    Blue metal-poor (BMP) stars are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B-V and U-B colour cuts.Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator of their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2 dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity and lithium. Using a sample of 80 BMP stars (T > 6300 K), we find that 97% of the BMP binaries have V-Ks0 < 1.08 ± 0.03, while BMP stars that are not binaries lie above this cut in two thirds of the cases. This cut can help classify stars that lack radial velocities from follow-up observations. We then trace the origin of two BMP stars from the photometric sample by conducting a full chemical analysis using new high-resolution and high signal-to-noise spectra. Based on their radial velocities, Li, α and s- and r-process abundances we show that BPS CS22874-042 is a single star (A(Li) = 2.38 ± 0.10 dex) while with A(Li)= 2.23 ± 0.07 dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using (V-Ks) colours with a fraction of single stars polluting the binary sample, but not vice versa. These two groups can only be properly separated by using information from

  6. Hot Subluminous Stars

    Science.gov (United States)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  7. Approaching the precursor nuclei of the third r-process peak with RIBs

    CERN Document Server

    Domingo-Pardo, C; Agramunt, J.; Algora, A.; Arcones, A.; Ameil, F.; Ayyad, Y.; Benlliure, J.; Bowry, M.; Calvino, F.; Cano-Ott, D.; Cortes, G.; Davinson, T.; Dillmann, I.; Estrade, A.; Evdokimov, A.; Faestermann, T.; Farinon, F.; Galaviz, D.; Garcia-Rios, A.; Geissel, H.; Gelletly, W.; Gernhauser, R.; Gomez-Hornillos, M.B.; Guerrero, C.; Heil, M.; Hinke, C.; Knobel, R.; Kojouharov, I.; Kurcewicz, J.; Kurz, N.; Litvinov, Y.; Maier, L.; Marganiec, J.; Marta, M.; Martinez, T.; Martinez-Pinedo, G.; Meyer, B.S.; Montes, F.; Mukha, I.; Napoli, D.R.; Nociforo, Ch.; Paradela, C.; Pietri, S.; Podolyak, Z.; Prochazka, A.; Rice, S.; Riego, A.; Rubio, B.; Schaffner, H.; Scheidenberger, Ch.; Smith, K.; Sokol, E.; Steiger, K.; Sun, B.; Tain, J.L.; Takechi, M.; Testov, D.; Weick, H.; Wilson, E.; Winfield, J.S.; Wood, R.; Woods, P.; Yeremin, A.

    2013-01-01

    The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary $^{238}$U beam at GSI we were able to measure such properties for several neutron-rich nuclei from $^{208}$Hg to $^{218}$Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the beta-decay rates and with beta-delayed neutron emission is illustrated on the basis of $r$-process network calculations. In order to obtain a reasonable reproduction of the third $r$-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based ...

  8. Beta-delayed fission probabilities of transfermium nuclei, involved in the r-process

    Science.gov (United States)

    Panov, I.; Lutostansky, Yu; Thielemann, F.-K.

    2016-01-01

    For the nucleosynthesis of heavy and superheavy nuclei fission becomes very important when the r-process runs in a very high neutron density environment. In part, fission is responsible for the formation of heavy nuclei due to the inclusion of fission products as new seed nuclei (fission cycling). More than that, beta-delayed fission, along with spontaneous fission, is responsible in the late stages of the r-process for the suppression of superheavy element yields. For beta-delayed fission probability calculations a model description of the beta-strength- functions is required. Extended theoretical predictions for astro-physical applications were provided long ago, and new predictions also for superheavy nuclei with uptodate nuclear input are needed. For the further extension of data to heavier transactinides the models of strength- functions should be modified, taking into account more complicated level schemes. In our present calculations the strength-function model is based on the quasi-particle approximation of Finite Fermi Systems Theory. The probabilities of beta-delayed fission and beta-delayed neutron emission are calculated for some transfermium neutron-rich nuclei, and the influence of beta-delayed fission upon superheavy element formation is discussed.

  9. Theoretical neutron-capture cross sections for r-process nucleosynthesis in the $^{48}$Ca region

    CERN Document Server

    Rauscher, T; Kratz, K -L; Balogh, W; Oberhummer, H

    2015-01-01

    We calculate neutron capture cross sections for r-process nucleosynthesis in the $^{48}$Ca region, namely for the isotopes $^{40-44}$S, $^{46-50}$Ar, $^{56-66}$Ti, $^{62-68}$Cr, and $^{72-76}$Fe. While previously only cross sections resulting from the compound nucleus reaction mechanism (Hauser-Feshbach) have been considered, we recalculate not only that contribution to the cross section but also include direct capture on even-even nuclei. The level schemes, which are of utmost importance in the direct capture calculations, are taken from quasi-particle states obtained with a folded-Yukawa potential and Lipkin-Nogami pairing. Most recent deformation values derived from experimental data on $\\beta$-decay half lives are used where available. Due to the consideration of direct capture, the capture rates are enhanced and the "turning points" in the r-process path are shifted to slightly higher mass numbers. We also discuss the sensitivity of the direct capture cross sections on the assumed deformation.

  10. Approximating the r-Process on Earth with Thermonuclear Explosions. Lessons Learned and Unanswered Questions

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Stephen Allan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-01-28

    During the astrophysical r-process, multiple neutron captures occur so rapidly on target nuclei that their daughter nuclei generally do not have time to undergo radioactive decay before another neutron is captured. The r-process can be approximately simulated on Earth in certain types of thermonuclear explosions through an analogous process of rapid neutron captures known as the "prompt capture" process. Between 1952 and 1969, 23 nuclear tests were fielded by the US which were involved (at least partially) with the "prompt capture" process. Of these tests, 15 were at least partially successful. Some of these tests were conducted under the Plowshare Peaceful Nuclear Explosion Program as scientific research experiments. It is now known that the USSR conducted similar nuclear tests during 1966 to 1979. The elements einsteinium and fermium were first discovered by this process. The most successful tests achieved 19 successive neutron captures on the initial target nuclei. A review of the US program, target nuclei used, heavy element yields, scientific achievements of the program, and how some of the results have been used by the astrophysical community is given. Finally, some unanswered questions concerning very neutron-rich nuclei that could potentially have been answered with additional nuclear experiments is presented.

  11. Origins of carbon enhanced metal poor stars

    CERN Document Server

    Sharma, Mahavir; Frenk, Carlos; Cooke, Ryan

    2016-01-01

    We investigate the nature of carbon-enhanced metal poor (CEMP) stars in Milky Way (MW) analogues selected from the EAGLE cosmological hydrodynamical simulation. The stellar evolution model in EAGLE includes the physics of enrichment by asymptotic giant branch (AGB) stars, winds from massive stars, and type I and type II supernovae (SNe). In the simulation, star formation in young MW progenitors is bursty due to efficient stellar feedback, which causes poor metal mixing leading to the formation of CEMP stars with extreme abundance patterns. In this scenario, two classes of CEMP stars emerge: those mostly enriched by low-metallicity type II SNe with low Fe yields that drive galactic outflows, and those mostly enriched by AGB stars when a gas-poor progenitor accretes pristine gas. The first class resembles CEMP-no stars with high [C/Fe] and low [C/O], the second class resembles CEMP-s stars overabundant in s-process elements and high values of [C/O]. This scenario explains several trends seen in data: (i) the in...

  12. Diversity of abundance patterns of neutron-capture elements in very metal-poor stars

    Science.gov (United States)

    Aoki, Misa; Aoki, Wako; Ishimaru, Yuhri; Wanajo, Shinya

    2014-05-01

    Observations of Very Metal-Poor stars indicate that there are at least two sites to r-process; "weak r-process" and "main r-process". A question is whether these two are well separated or there exists a variation in the r-process. We present the results of abundance analysis of neutron-capture elements in the two Very Metal-Poor stars HD107752 and HD110184 in the Milky Way halo observed with the Subaru Telescope HDS. The abundance patterns show overabundace at light n-capture elements (e.g. Sr, Y), inferring the element yielding of weak r-process, while heavy neutron-capture elements (e.g. Ba, Eu) are deficient; however, the overabundance of light ones is not as significant as that previously found in stars representing the weak r-process (e.g. HD122563; Honda et al. 2006). Our study show diversity in the abundance patterns from light to heavy neutron-capture elements in VMP stars, suggesting a variation in r-process, which may depend on electron fraction of environment.

  13. Hot subluminous stars

    CERN Document Server

    Heber, Ulrich

    2016-01-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich vs. He-poor hot subdwarf stars of the globular clusters omega Cen and NGC~2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope phase of evolution.They provide a clean-cut laboratory to study this important but yet purely understood phase of stellar evolution. Substellar companions to sdB stars have also been found. For HW~Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the pulsator V391 ...

  14. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star.......Denne rapport beskriver numeriske beregninger af forskellige flydergeometrier for bølgeenergianlæget Wave Star....

  15. β-decay measurements of A simeq 70 - 110 r-process nuclei at the National Superconducting Cyclotron Laboratory

    Science.gov (United States)

    Pereira, J.; Aprahamian, A.; Arndt, O.; Becerril, A.; Elliot, T.; Estrade, A.; Galaviz, D.; Hennrich, S.; Hosmer, P.; Kessler, R.; Kratz, K.-L.; Lorusso, G.; Mantica, P. F.; Matos, M.; Montes, F.; Pfeiffer, B.; Quinn, M.; Santi, P.; Schatz, H.; Schertz, F.; Schnorrenberger, L.; Smith, E.; Stolz, A.; Walters, W. B.; Wöhr, A.

    2011-09-01

    The present paper reports on several r-process motivated β-decay experiments undertaken at the National Superconducting Cyclotron Laboratory. β-decay half-lives and β-delayed neutron-emission probabilities were measured for nuclei around the r-process A = 70-80 and A = 90 - 110 mass regions. The data are discussed on the basis of quasi-random phase approximation calculations. The emphasis is made on the impact of these data upon calculations of r-process abundances.

  16. Massive Stars

    Science.gov (United States)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  17. Merger of binary neutron stars: Gravitational waves and electromagnetic counterparts

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Masaru

    2016-12-15

    Late inspiral and merger phases of binary neutron stars are the valuable new experimental fields for exploring nuclear physics because (i) gravitational waves from them will bring information for the neutron-star equation of state and (ii) the matter ejected after the onset of the merger could be the main site for the r-process nucleosynthesis. We will summarize these aspects of the binary neutron stars, describing the current understanding for the merger process of binary neutron stars that has been revealed by numerical-relativity simulations.

  18. Life Cycle of Stars

    Science.gov (United States)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  19. Mass measurements beyond the major r-process waiting point $^{80}$Zn

    CERN Document Server

    Baruah, S; Blaum, K; Dworschak, M; George, S; Guenaut, C; Hager, U; Herfurth, F; Herlert, A; Kellerbauer, A G; Kluge, H J; Lunney, D; Schatz, H; Schweikhard, L; Yazidjian, C

    2008-01-01

    High-precision mass measurements on neutron-rich zinc isotopes $^{71m,72-81}$Zn have been performed with the Penning trap mass spectrometer ISOLTRAP. For the first time the mass of $^{81}$Zn has been experimentally determined. This makes $^{80}$Zn the first of the few major waiting points along the path of the astrophysical rapid neutron capture process where neutron separation energy and neutron capture $Q$-value are determined experimentally. As a consequence, the astrophysical conditions required for this waiting point and its associated abundance signatures to occur in $r$-process models can now be mapped precisely. The measurements also confirm the robustness of the $N = 50$ shell closure for $Z = 30$ farther from stability.

  20. An extremely primitive halo star

    CERN Document Server

    Caffau, E; François, P; Sbordone, L; Monaco, L; Spite, M; Spite, F; Ludwig, H -G; Cayrel, R; Zaggia, S; Hammer, F; Randich, S; Molaro, P; Hill, V; 10.1038/nature10377

    2012-01-01

    The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium1, almost all other elements were created in stars and supernovae. The mass fraction, Z, of elements more massive than helium, is called "metallicity". A number of very metal poor stars have been found some of which, while having a low iron abundance, are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with metallicities lower than Z=1.5E-5, it has been suggested that low mass stars (M<0.8M\\odot, the ones that survive to the present day) cannot form until the interstellar medium has been enriched above a critical value, estimated to lie in the range 1.5E-8\\leqZ\\leq1.5E-6, although competing theories claiming the contrary do exist. Here we report the chemical composition of a star with a very low Z\\leq6.9E-7 (4.5E-5 of that of the Sun) and a chemical pattern typical of classical extremely metal poor stars, meaning without the enrichment of carbon, nitroge...

  1. Hadron star models. [neutron stars

    Science.gov (United States)

    Cohen, J. M.; Boerner, G.

    1974-01-01

    The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

  2. The host galaxy and environment of a neutron star merger

    CERN Document Server

    Postigo, A de Ugarte; Rowlinson, A; Garcia-Benito, R; Levan, A J; Gorosabel, J; Goldoni, P; Schulze, S; Zafar, T; Wiersema, K; Sanchez-Ramirez, R; Melandri, A; D'Avanzo, P; Oates, S; D'Elia, V; De Pasquale, M; Kruehler, T; van der Horst, A J; Xu, D; Watson, D; Piranomonte, S; Vergani, S; Milvang-Jensen, B; Kaper, L; Malesani, D; Fynbo, J P U; Cano, Z; Covino, S; Flores, H; Greiss, S; Hammer, F; Hartoog, O E; Hellmich, S; Heuser, C; Hjorth, J; Jakobsson, P; Mottola, S; Sparre, M; Sollerman, J; Tagliaferri, G; Tanvir, N R; Vestergaard, M; Wijers, R A M J

    2013-01-01

    The mergers of neutron stars have been predicted to cause an r-process supernova - a luminous near-infrared transient powered by the radioactive decay of freshly formed heavy metals. An r-process supernova, or kilonova, has recently been discovered coincident with the short-duration gamma-ray burst GRB 130603B, simultaneously confirming the widely-held theory of the origin of most short-durations GRBs in neutron star mergers. We report here the absorption spectrum of the afterglow of this GRB. From it we determine the redshift of the burst and the properties of the host galaxy and the environment in which the merger occurred. The merger is not associated with the most star-forming region of the galaxy; however, it did occur in a dense region, implying a rapid merger or a low natal kick velocity for the neutron star binary.

  3. CNO production in first generation stars

    CERN Document Server

    Ekström, S; Maeder, A; Ekstr\\"om, Sylvia; Meynet, Georges; Maeder, Andr\\'e

    2006-01-01

    Big Bang nucleosynthesis produces only light elements and the very first generation stars are thus formed from metal-free clouds. They start the production of heavy elements during their life, and enrich the interstellar medium through their explosive death. Stellar evolution models show that the treatment of rotation has important effects on the evolution of those metal-free stars: for example, rotating models produce up to five orders of magnitude more primary nitrogen than non rotating models, due to internal mixing. This will have an impact in the composition of the second generation stars, some of which may now be observed in the Galactic halo. In the case Population III stars were very massive and would end up as direct black holes, rotation again have an interesting effect of enhancing mass loss through centrifugal force and surface enrichment. CNO composition patterns observed in ultra metal-poor halo stars may be explained by a 'wind only' contribution.

  4. Nucleosynthesis in decompressing neutron star matter

    CERN Document Server

    Jaikumar, P; Otsuki, K; Ouyed, R; Jaikumar, Prashanth; Meyer, Bradley S.; Otsuki, Kaori; Ouyed, Rachid

    2006-01-01

    We explore heavy-element nucleosynthesis by rapid neutron capture (r-process) in the decompressing ejecta from the surface of a neutron star. The decompression is triggered by a violent phase transition to strange quark matter (quark-nova scenario). The presence of neutron-rich large Z nuclei (40,95)<(Z,A)<(70,177), the large neutron-to-seed ratio, and the low electron fraction Ye ~ 0.03 in the decompressing ejecta present favorable conditions for the r-process. We perform network calculations that are adapted to the quark-nova conditions, and which mimic usual (n-\\gamma) equilibrium r-process calculations during the initially cold decompression phase. They match to dynamical r-process calculations at densities below neutron drip (4x10^11 g/cc). We present results for the final element abundance distribution with and without heating from nuclear reactions, and compare to the solar abundance pattern of r-process elements. We highlight the distinguishing features of quark-novae by contrasting it with conv...

  5. Star Surface Polluted by Planetary Debris

    Science.gov (United States)

    2007-07-01

    Looking at the chemical composition of stars that host planets, astronomers have found that while dwarf stars often show iron enrichment on their surface, giant stars do not. The astronomers think that the planetary debris falling onto the outer layer of the star produces a detectable effect in a dwarf star, but this pollution is diluted by the giant star and mixed into its interior. "It is a little bit like a Tiramisu or a Capuccino," says Luca Pasquini from ESO, lead-author of the paper reporting the results. "There is cocoa powder only on the top!' ESO PR Photo 29/07 ESO PR Photo 29/07 The Structure of Stars Just a few years after the discovery of the first exoplanet it became evident that planets are preferentially found around stars that are enriched in iron. Planet-hosting stars are on average almost twice as rich in metals than their counterparts with no planetary system. The immediate question is whether this richness in metals enhances planet formation, or whether it is caused by the presence of planets. The classic chicken and egg problem. In the first case, the stars would be metal-rich down to their centre. In the second case, debris from the planetary system would have polluted the star and only the external layers would be affected by this pollution. When observing stars and taking spectra, astronomers indeed only see the outer layers and can't make sure the whole star has the same composition. When planetary debris fall onto a star, the material will stay in the outer parts, polluting it and leaving traces in the spectra taken. A team of astronomers has decided to tackle this question by looking at a different kind of stars: red giants. These are stars that, as will the Sun in several billion years, have exhausted the hydrogen in their core. As a result, they have puffed up, becoming much larger and cooler. Looking at the distribution of metals in fourteen planet-hosting giants, the astronomers found that their distribution was rather different from

  6. The first stars: a classification of CEMP-no stars

    CERN Document Server

    Maeder, Andre

    2015-01-01

    We propose and apply a new classification for the CEMP-no stars, which are "carbon-enhanced metal-poor" stars with no overabundance of s-elements and with [Fe/H] generally inferior or equal to -2.5. This classification is based on the changes in abundances for the elements and isotopes involved in the CNO, Ne-Na, and Mg-Al nuclear cycles. These abundances change very much owing to successive back and forth mixing motions between the He- and H-burning regions in massive stars (the "source stars" responsible for the chemical enrichment of the CEMP-no stars). The wide variety of the ratios [C/Fe], 12C/13C, [N/Fe], [O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe], [Sr/Fe], and [Ba/Fe], which are the main characteristics making the CEMP-no and low s stars so peculiar, is described well in terms of the proposed nucleosynthetic classification. We note that the [(C+N+O)/Fe] ratios significantly increase for lower values of [Fe/H]. The classification of CEMP-no stars and the behavior of [(C+N+O)/Fe] support the presence, in the firs...

  7. Star Wreck

    OpenAIRE

    Kusenko, Alexander; Shaposhnikov, Mikhail E.; Tinyakov, P. G.; Tkachev, Igor I.

    1998-01-01

    Electroweak models with low-energy supersymmetry breaking predict the existence of stable non-topological solitons, Q-balls, that can be produced in the early universe. The relic Q-balls can accumulate inside a neutron star and gradually absorb the baryons into the scalar condensate. This causes a slow reduction in the mass of the star. When the mass reaches a critical value, the neutron star becomes unstable and explodes. The cataclysmic destruction of the distant neutron stars may be the or...

  8. Star polygons

    OpenAIRE

    Riosa, Blažka

    2014-01-01

    In mathematics we often encounter polygons, such us triangle, square, hexagon, etc., but we hardly encounter star polygons. Despite the fact that we do not meet them so often in mathematics, in nature they can be traced almost on every step. In this paper the emphasis is on the geometric meaning of regular star polygons. Star polygon is a generalization of the concept of regular polygons. In star polygons also non-adjacent sides intersect. Up to similarity they are determined by Schläfli symb...

  9. Three carbon-enhanced metal-poor dwarf stars from the SDSS. Chemical abundances from CO5BOLD 3D hydrodynamical model atmospheres

    Science.gov (United States)

    Behara, N. T.; Bonifacio, P.; Ludwig, H.-G.; Sbordone, L.; González Hernández, J. I.; Caffau, E.

    2010-04-01

    Context. The origin of carbon-enhanced metal-poor stars enriched with both s and r elements is highly debated. Detailed abundances of these types of stars are crucial to understand the nature of their progenitors. Aims: The aim of this investigation is to study in detail the abundances of SDSS J1349-0229, SDSS J0912+0216 and SDSS J1036+1212, three dwarf CEMP stars, selected from the Sloan Digital Sky Survey. Methods: Using high resolution VLT/UVES spectra (R ~ 30 000) we determine abundances for Li, C, N, O, Na, Mg, Al, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni and 21 neutron-capture elements. We made use of CO5BOLD 3D hydrodynamical model atmospheres in the analysis of the carbon, nitrogen and oxygen abundances. NLTE corrections for Ci and Oi lines were computed using the Kiel code. Results: We classify SDSS J1349-0229 and SDSS J0912+0216 as CEMP-r+s stars. SDSS J1036+1212 belongs to the class CEMP-no/s, with enhanced Ba, but deficient Sr, of which it is the third member discovered to date. Radial-velocity variations have been observed in SDSS J1349-0229, providing evidence that it is a member of a binary system. Conclusions: The chemical composition of the three stars is generally compatible with mass transfer from an AGB companion. However, many details remain difficult to explain. Most notably of those are the abundance of Li at the level of the Spite plateau in SDSS J1036+1212 and the large over-abundance of the pure r-process element Eu in all three stars. Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (programmes 078.D-0217 and 383.D-0927).

  10. Approaching the r-process "waiting point" nuclei below $^{132}$Sn: quadrupole collectivity in $^{128}$Cd

    CERN Multimedia

    Reiter, P; Blazhev, A A; Nardelli, S; Voulot, D; Habs, D; Schwerdtfeger, W; Iwanicki, J S

    We propose to investigate the nucleus $^{128}$Cd neighbouring the r-process "waiting point" $^{130}$Cd. A possible explanation for the peak in the solar r-abundances at A $\\approx$ 130 is a quenching of the N = 82 shell closure for spherical nuclei below $^{132}$Sn. This explanation seems to be in agreement with recent $\\beta$-decay measurements performed at ISOLDE. In contrast to this picture, a beyond-mean-field approach would explain the anomaly in the excitation energy observed for $^{128}$Cd rather with a quite large quadrupole collectivity. Therefore, we propose to measure the reduced transition strengths B(E2) between ground state and first excited 2$^{+}$-state in $^{128}$Cd applying $\\gamma$-spectroscopy with MINIBALL after "safe" Coulomb excitation of a post-accelerated beam obtained from REX-ISOLDE. Such a measurement came into reach only because of the source developments made in 2006 for experiment IS411, in particular the use of a heated quartz transfer line. The result from the proposed measure...

  11. Nucleosynthesis of Binary low mass zero-metallicity stars

    Science.gov (United States)

    Lau, Ho Bun Herbert; Stancliffe, R. J.; Tout, C. A.

    The Cambridge STARS code is used to model the evolution and nucleosynthesis of binary zero- metallicity low to intermediate mass stars. The surfaces of these stars are enriched in CNO ele- ments after second dredge up. During binary interaction metals can be released from these stars and the secondary enriched in CNO. The observed abundances of HE 0107-5240 can be repro- duced from enhanced wind accretion from a 7 M after second dredge up. HE 1327-2326, richer in nitrogen and Sr, can similarly be formed by wind accretion in a later AGB phase after third dredge up.

  12. STAR Calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Jacobs, W W, E-mail: jacobsw@indiana.ed [Indiana University Cyclotron Facility and Department of Physics, 2401 Milo B. Sampson Lane, Bloomington IN 47408 (United States)

    2009-04-01

    The main STAR calorimeters comprise a full Barrel EMC and single Endcap EMC plus a Forward Meson Spectrometer. Together they give a nearly complete coverage over the range -1 < pseudorapidity < 4 and provide EM readout and triggering that help drive STAR physics capabilities. Their description, status, performance and operations (and a few physics anecdotes) are briefly presented and discussed.

  13. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Brorsen, Michael; Frigaard, Peter

    Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star.......Nærværende rapport beskriver numeriske beregninger af den hydrodynamiske interaktion mellem 5 flydere i bølgeenergianlægget Wave Star....

  14. Star Imager

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Jørgensen, John Leif; Thuesen, Gøsta;

    1997-01-01

    The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol.......The version of the star imager developed for Astrid II is described. All functions and features are described as well as the operations and the software protocol....

  15. La and Eu Abundances in Metal-poor Halo Stars

    Science.gov (United States)

    Cardillo, Harrison; Burris, Debra L.

    2016-01-01

    Elements with atomic number greater than Z=26 (the Iron Peak) cannot be formed through fusion in a star's core; the majority of these elements are produced through one of two neutron-capture processes. Early in the history of the Galaxy, the rapid neutron-capture process (r-process) is believed to be responsible for the production of elements Z=56 and beyond. These elements require at least one generation of stars to have completed their life cycle in order to be synthesized. Therefore, if we observe the heavy metal abundances in what are called Population II stars (metal-poor stars), then we can begin to make inferences about the chemistry of the earliest stars in the Galaxy. To contribute to this picture of the early universe, the Lanthanum and Europium abundances of low-metallicity stars will be measured and trends in these abundances based on comparisons to existing related literature will be sought.

  16. First Stars. I. Evolution without mass loss

    CERN Document Server

    Bahena, D

    2010-01-01

    The first generation of stars was formed from primordial gas. Numerical simulations suggest that the first stars were predominantly very massive, with typical masses M > 100 Mo. These stars were responsible for the reionization of the universe, the initial enrichment of the intergalactic medium with heavy elements, and other cosmological consequences. In this work, we study the structure of Zero Age Main Sequence stars for a wide mass and metallicity range and the evolution of 100, 150, 200, 250 and 300 Mo galactic and pregalactic Pop III very massive stars without mass loss, with metallicity Z=10E-6 and 10E-9, respectively. Using a stellar evolution code, a system of 10 equations together with boundary conditions are solved simultaneously. For the change of chemical composition, which determines the evolution of a star, a diffusion treatment for convection and semiconvection is used. A set of 30 nuclear reactions are solved simultaneously with the stellar structure and evolution equations. Several results on...

  17. Rising Star

    OpenAIRE

    Worley, Christiana

    2012-01-01

    Rising Star is a novel about appearances. Thailand Allen is a girl who thinks she understands what she sees. But when what she sees are cracks in her perfect world, maturation and new sight are not far off. Before growth can occur, Thailand must undergo a painful process of learning that carries with it embarrassment, sorrow, anger and confusion. Thailand lives with her mother in a small Texas town called Rising Star. Rising Star is like every other small town with its community gather...

  18. Observational Effects of Magnetism in O Stars: Surface Nitrogen Abundances

    Science.gov (United States)

    Martins, F.; Escolano, C.; Wade, G. A.; Donati, J. F.; Bouret, J. C.

    2011-01-01

    Aims. We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star Tau Sco.. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. Methods. We conduct a quantitative spectroscopic analysis of the ample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. Results. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results shOuld be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.

  19. Rock Stars

    Institute of Scientific and Technical Information of China (English)

    张国平

    2000-01-01

    Around the world young people are spending unbelievable sums of money to listen to rock music. Forbes Magazine reports that at least fifty rock stars have incomes between two million and six million dollars per year.

  20. Carbon Stars

    Indian Academy of Sciences (India)

    T. Lloyd Evans

    2010-12-01

    In this paper, the present state of knowledge of the carbon stars is discussed. Particular attention is given to issues of classification, evolution, variability, populations in our own and other galaxies, and circumstellar material.

  1. Radioactive Ages of Metal-Poor Halo Stars

    Institute of Scientific and Technical Information of China (English)

    Ji Li; Gang Zhao

    2004-01-01

    The abundances of long-lived radioactive elements Th and U observed in metal-poor halo stars can be used as chronometers to determine the age of individual stars, and hence set a lower limit on the age of the Galaxy and hence of the universe.This radioactive dating requires the zero-decay productions of Th and U, which involves complicated r-process nucleosynthesis calculations. Several parametric rprocess models have been used to calculate the initial abundance ratios of Th/Eu and U/Th, but, due to the sharp sensitivity of these models to nuclear physics inputs, the calculations have relatively large uncertainties which lead to large uncertainties in the age determinations. In order to reduce these uncertainties, we present a simple method to estimate the initial productions of Th and U, which only depends on the solar system abundances and the stellar abundances of stable r-process elements.From our calculations of the initial abundance ratios of Th/Eu and U/Th, we reestimate the ages of those very metal-poor halo stars with published abundances of Th and U. Our age estimates are consistent, within the errors, with the other age determinations derived from r-process models, and offer useful constrains for r-process theoretical calculations. The advantages and limitations of our simple method of radioactive dating are discussed.

  2. Simulating cosmic metal enrichment by the first galaxies

    CERN Document Server

    Pallottini, A; Gallerani, S; Salvadori, S; D'Odorico, V

    2014-01-01

    We study cosmic metal enrichment via AMR hydrodynamical simulations in a (10 Mpc/h)$^3$ volume following the Pop III-Pop II transition and for different Pop III IMFs. We have analyzed the joint evolution of metal enrichment on galactic and intergalactic scales at z=6 and z=4. Galaxies account for $10^{4.5}$K) state. Due to these physical conditions, CIV absorption line experiments can probe only ~2% of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the Pop III star formation history is almost insensitive to the chosen Pop III IMF. Pop III stars are preferentially formed in truly pristine (Z=0) gas pockets, well outside polluted regions created by previous star formation episodes.

  3. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Byggeri og Anlæg med bølgeenergianlæget Wave Star....

  4. STAR POLYMERS

    OpenAIRE

    Ch. von Ferber; Yu.Holovatch

    2002-01-01

    It is our great pleasure to present a collection of papers devoted to theoretical, numerical, and experimental studies in the field of star polymers. Since its introduction in the early 80-ies, this field has attracted increasing interest and has become an important part of contemporary polymer physics. While research papers in this field appear regularly in different physical and chemical journals, the present collection is an attempt to join together the studies of star polymers showing the...

  5. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Andersen, Thomas Lykke

    Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star.......Nærværende rapport beskriver modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star....

  6. Beryllium in Disk and Halo Stars -- Evidence for a Beryllium Dispersion in Old Stars

    CERN Document Server

    Boesgaard, A M; Boesgaard, Ann Merchant; Novicki, Megan C.

    2006-01-01

    The study of Be in stars of differing metal content can elucidate the formation mechanisms and the Galactic chemical evolution of Be. We have obtained high-resolution, high signal-to-noise spectra of the resonance lines of Be II in eight stars with the high-dispersion spectrograph (HDS) on the Subaru 8.2 m telescope on Mauna Kea. Abundances of Be have been determined through spectrum synthesis. The stars with [Fe/H] values > -1.1 conform to the published general trend of Be vs Fe. We have confirmed the high Be abundance in HD 94028 and have found a similarly high Be abundance in another star, HD 132475, at the same metallicity: [Fe/H] = -1.5. These two stars are 0.5 - 0.6 dex higher in Be than the Be-Fe trend. While that general trend contains the evidence for a Galaxy-wide enrichment in Be and Fe, the higher Be abundances in those two stars indicates local Be enrichments. Possible enrichment mechanisms include hypernovae and multiple supernova explosions contained in a superbubble. The star G 64-37 has [Fe/]...

  7. Determination of the Neutron-Capture Rate of 17C for the R-process Nucleosynthesis

    CERN Document Server

    Heine, M; Wu, M -R; Adachi, T; Aksyutina, Y; Alcantara, J; Altstadt, S; Alvarez-Pol, H; Ashwood, N; Aumann, T; Avdeichikov, V; Barr, M; Beceiro-Novo, S; Bemmerer, D; Benlliure, J; Bertulani, C A; Boretzky, K; Borge, M J G; Burgunder, G; Caamano, M; Caesar, C; Casarejos, E; Catford, W; Cederkäll, J; Chakraborty, S; Chartier, M; Chulkov, L V; Cortina-Gil, D; Crespo, R; Pramanik, U Datta; Fernandez, P Diaz; Dillmann, I; Elekes, Z; Enders, J; Ershova, O; Estrade, A; Farinon, F; Fraile, L M; Freer, M; Freudenberger, M; Fynbo, H O U; Galaviz, D; Geissel, H; Gernhäuser, R; Göbel, K; Golubev, P; Diaz, D Gonzalez; Hagdahl, J; Heftrich, T; Heil, M; Heinz, A; Henriques, A; Holl, M; Ickert, G; Ignatov, A; Jakobsson, B; Johansson, H T; Jonson, B; Kalantar-Nayestanaki, N; Kanungo, R; Kelic-Heil, A; Knöbel, R; Kröll, T; Krücken, R; Kurcewicz, J; Kurz, N; Labiche, M; Langer, C; Bleis, T Le; Lemmon, R; Lepyoshkina, O; Lindberg, S; Machado, J; Marganiec, J; Martínez-Pinedo, G; Maroussov, V; Mostazo, M; Movsesyan, A; Najafi, A; Neff, T; Nilsson, T; Nociforo, C; Panin, V; Paschalis, S; Perea, A; Petri, M; Pietri, S; Plag, R; Prochazka, A; Rahaman, A; Rastrepina, G; Reifarth, R; Ribeiro, G; Ricciardi, M V; Rigollet, C; Riisager, K; Röder, M; Rossi, D; del Rio, J Sanchez; Savran, D; Scheit, H; Simon, H; Sorlin, O; Stoica, V; Streicher, B; Taylor, J T; Tengblad, O; Terashima, S; Thies, R; Togano, Y; Uberseder, E; Van de Walle, J; Velho, P; Volkov, V; Wagner, A; Wamers, F; Weick, H; Weigand, M; Wheldon, C; Wilson, G; Wimmer, C; Winfield, J S; Woods, P; Yakorev, D; Zhukov, M V; Zilges, A; Zuber, K

    2016-01-01

    With the R$^{3}$B-LAND setup at GSI we have measured exclusive relative-energy spectra of the Coulomb dissociation of $^{18}$C at a projectile energy around 425~AMeV on a lead target, which are needed to determine the radiative neutron-capture cross sections of $^{17}$C into the ground state of $^{18}$C. Those data have been used to constrain theoretical calculations for transitions populating excited states in $^{18}$C. This allowed to derive the astrophysical cross section $\\sigma^{*}_{\\mathrm{n}\\gamma}$ accounting for the thermal population of $^{17}$C target states in astrophysical scenarios. The experimentally verified capture rate is significantly lower than those of previously obtained Hauser-Feshbach estimations at temperatures $T_{9}\\leq{}1$~GK. Network simulations with updated neutron-capture rates and hydrodynamics according to the neutrino-driven wind model as well as the neutron-star merger scenario reveal no pronounced influence of neutron capture of $^{17}$C on the production of second- and thi...

  8. Star clusters as laboratories for stellar and dynamical evolution

    CERN Document Server

    Kalirai, Jason S

    2009-01-01

    Open and globular star clusters have served as benchmarks for the study of stellar evolution due to their supposed nature as simple stellar populations of the same age and metallicity. After a brief review of some of the pioneering work that established the importance of imaging stars in these systems, we focus on several recent studies that have challenged our fundamental picture of star clusters. These new studies indicate that star clusters can very well harbour multiple stellar populations, possibly formed through self-enrichment processes from the first-generation stars that evolved through post-main-sequence evolutionary phases. Correctly interpreting stellar evolution in such systems is tied to our understanding of both chemical-enrichment mechanisms, including stellar mass loss along the giant branches, and the dynamical state of the cluster. We illustrate recent imaging, spectroscopic and theoretical studies that have begun to shed new light on the evolutionary processes that occur within star cluste...

  9. Diversity of abundance patterns of neutron-capture elements in very metal-poor stars

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Misa; Ishimaru, Yuhri [International Christian University 10-2, Osawa, Mitaka, Tokyo 181-0015 (Japan); Aoki, Wako; Wanajo, Shinya [National Astronomical Observatory of Japan (NAOJ) 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)

    2014-05-02

    Observations of Very Metal-Poor stars indicate that there are at least two sites to r-process; “weak r-process” and “main r-process”. A question is whether these two are well separated or there exists a variation in the r-process. We present the results of abundance analysis of neutron-capture elements in the two Very Metal-Poor stars HD107752 and HD110184 in the Milky Way halo observed with the Subaru Telescope HDS. The abundance patterns show overabundace at light n-capture elements (e.g. Sr, Y), inferring the element yielding of weak r-process, while heavy neutron-capture elements (e.g. Ba, Eu) are deficient; however, the overabundance of light ones is not as significant as that previously found in stars representing the weak r-process (e.g. HD122563; Honda et al. 2006). Our study show diversity in the abundance patterns from light to heavy neutron-capture elements in VMP stars, suggesting a variation in r-process, which may depend on electron fraction of environment.

  10. Near-Field Cosmology with Metal-Poor Stars

    CERN Document Server

    Frebel, Anna

    2015-01-01

    The oldest, most metal-poor stars in the Galactic halo and satellite dwarf galaxies present an opportunity to explore the chemical and physical conditions of the earliest star forming environments in the Universe. We review the fields of stellar archaeology and dwarf galaxy archaeology by examining the chemical abundance measurements of various elements in extremely metal-poor stars. Focus on the carbon-rich and carbon-normal halo star populations illustrates how these provide insight into the Population III star progenitors responsible for the first metal enrichment events. We extend the discussion to near-field cosmology, which is concerned with the formation of the first stars and galaxies and how metal-poor stars can be used to constrain these processes. Complementary abundance measurements in high-redshift gas clouds further help to establish the early chemical evolution of the Universe. The data appear consistent with the existence of two distinct channels of star formation at the earliest times.

  11. Star Formation for Predictive Primordial Galaxy Formation

    Science.gov (United States)

    Milosavljević, Miloš; Safranek-Shrader, Chalence

    The elegance of inflationary cosmology and cosmological perturbation theory ends with the formation of the first stars and galaxies, the initial sources of light that launched the phenomenologically rich process of cosmic reionization. Here we review the current understanding of early star formation, emphasizing unsolved problems and technical challenges. We begin with the first generation of stars to form after the Big Bang and trace how they influenced subsequent star formation. The onset of chemical enrichment coincided with a sharp increase in the overall physical complexity of star forming systems. Ab-initio computational treatments are just now entering the domain of the predictive and are establishing contact with local observations of the relics of this ancient epoch.

  12. Uranium Conversion & Enrichment

    Energy Technology Data Exchange (ETDEWEB)

    Karpius, Peter Joseph [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-02-06

    The isotopes of uranium that are found in nature, and hence in ‘fresh’ Yellowcake’, are not in relative proportions that are suitable for power or weapons applications. The goal of conversion then is to transform the U3O8 yellowcake into UF6. Conversion and enrichment of uranium is usually required to obtain material with enough 235U to be usable as fuel in a reactor or weapon. The cost, size, and complexity of practical conversion and enrichment facilities aid in nonproliferation by design.

  13. Search for spin-orbit-force reduction at {sup 106,108}Zr around r-process path

    Energy Technology Data Exchange (ETDEWEB)

    Sumikama, T.; Yoshinaga, K. [Department of Physics, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510 (Japan); Watanabe, H. [RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); and others

    2012-11-12

    Shell gap at the magic number N= 82 is important to reproduce the 2nd peak of r-process abundance. If a spin-orbit force is reduced in a very neutron-rich region, a shell quenching at N= 82 and a new shell closure at N70 are predicted. A shell evolution by the spin-orbit-force reduction can be searched for through the shape evolution of Zr isotopes around an expected double magic nuclei, {sup 110}Zr(Z = 40,N = 70). We performed {beta}-{gamma} and isomer spectroscopy at RIBF to observe low-lying states in {sup 106,108}Zr. The present results indicate a well deformed shape for {sup 106,108}Zr. The drastic reduction of the spin-orbit force most likely does not occur around {sup 110}Zr on an r-process path.

  14. Shell-model half-lives for r-process waiting point nuclei including first-forbidden contributions

    CERN Document Server

    Zhi, Q; Cuenca-García, J J; Langanke, K; Martínez-Pinedo, G; Sieja, K

    2013-01-01

    We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilities of the r-process waiting point nuclei at the magic neutron numbers N=50, 82, and 126. The calculations include contributions from allowed Gamow-Teller and first-forbidden transitions. We find good agreement with the measured half-lives for the N=50 nuclei with charge numbers Z=28-32 and for the N=82 nuclei 129Ag and 130Cd. The contribution of forbidden transitions reduce the half-lives of the N=126 waiting point nuclei significantly, while they have only a small effect on the half-lives of the N=50 and 82 r-process nuclei.

  15. Precision mass measurements on neutron-rich Zn isotopes and their consequences on the astrophysical r-process

    Energy Technology Data Exchange (ETDEWEB)

    Baruah, Sudarshan

    2008-07-15

    The rapid neutron-capture or the r-process is responsible for the origin of about half of the neutron-rich atomic nuclei in the universe heavier than iron. For the calculation of the abundances of those nuclei, atomic masses are required as one of the input parameters with very high precision. In the present work, the masses of the neutron rich Zn isotopes (A=71 to 81) lying in the r-process path have been measured in the ISOLTRAP experiment at ISOLDE/CERN. The mass of {sup 81}Zn has been measured directly for the rst time. The half-lives of the nuclides ranged from 46.5 h ({sup 72}Zn) down to 290 ms ({sup 81}Zn). In case of all the nuclides, the relative mass uncertainty ({delta}m=m) achieved was in the order of 10{sup -8} corresponding to a 100-fold improvement in precision over previous measurements. (orig.)

  16. Impact of the first-forbidden β decay on the production of A ∼ 195 r-process peak

    Science.gov (United States)

    Nishimura, Nobuya; Podolyák, Zsolt; Fang, Dong-Liang; Suzuki, Toshio

    2016-05-01

    We investigated the effects of first-forbidden transitions in β decays on the production of the r-process A ∼ 195 peak. The theoretical calculated β-decay rates with β-delayed neutron emission were examined using several astrophysical conditions. As the FF decay is dominant in N ∼ 126 neutron-rich nuclei, their inclusion shortens β-decay lifetimes and shifts the abundance peak towards higher masses. Additionally, the inclusion of the β-delayed neutron emission results in a wider abundance peak, and smoothens the mass distribution by removing the odd-even mass staggering. The effects are commonly seen in the results of all adopted astrophysical models. Nevertheless there are quantitative differences, indicating that remaining uncertainty in the determination of half-lives for N = 126 nuclei is still significant in order to determine the production of the r-process peak.

  17. Impact of the first-forbidden $\\beta$ decay on the production of $A \\sim 195$ r-process peak

    CERN Document Server

    Nishimura, Nobuya; Fang, Dong-Liang; Suzuki, Toshio

    2016-01-01

    We investigated the effects of first-forbidden transitions in $\\beta$ decays on the production of the r-process $A \\sim 195$ peak. The theoretical calculated $\\beta$-decay rates with $\\beta$-delayed neutron emission were examined using several astrophysical conditions. As the first-borbidden decay is dominant in $N \\sim 126$ neutron-rich nuclei, their inclusion shortens $\\beta$-decay lifetimes and shifts the abundance peak towards higher masses. Additionally, the inclusion of the $\\beta$-delayed neutron emission results in a wider abundance peak, and smoothens the mass distribution by removing the odd-even mass staggering. The effects are commonly seen in the results of all adopted astrophysical models. Nevertheless there are quantitative differences, indicating that remaining uncertainty in the determination of half-lives for $N=126$ nuclei is still significant in order to determine the production of the r-process peak.

  18. Impact of the first-forbidden β decay on the production of A∼195 r-process peak

    Directory of Open Access Journals (Sweden)

    Nobuya Nishimura

    2016-05-01

    Full Text Available We investigated the effects of first-forbidden transitions in β decays on the production of the r-process A∼195 peak. The theoretical calculated β-decay rates with β-delayed neutron emission were examined using several astrophysical conditions. As the FF decay is dominant in N∼126 neutron-rich nuclei, their inclusion shortens β-decay lifetimes and shifts the abundance peak towards higher masses. Additionally, the inclusion of the β-delayed neutron emission results in a wider abundance peak, and smoothens the mass distribution by removing the odd–even mass staggering. The effects are commonly seen in the results of all adopted astrophysical models. Nevertheless there are quantitative differences, indicating that remaining uncertainty in the determination of half-lives for N=126 nuclei is still significant in order to determine the production of the r-process peak.

  19. Discovery of the magnetic field in the pulsating B star β Cephei

    NARCIS (Netherlands)

    Henrichs, H.F.; de Jong, J.A.; Verdugo, E.; Schnerr, R.S.; Neiner, C.; Donati, J.-F.; Catala, C.; Shorlin, S.L.S.; Wade, G.A.; Veen, P.M.; Nichols, J.S.; Damen, E.M.F.; Talavera, A.; Hill, G.M.; Kaper, L.; Tijani, A.M.; Geers, V.C.; Wiersema, K.; Plaggenborg, B.; Rygl, K.L.J.

    2013-01-01

    Context. Although the star itself is not helium enriched, the periodicity and the variability in the UV wind lines of the pulsating B1 IV star β Cephei are similar to what is observed in magnetic helium-peculiar B stars, suggesting that β Cep is magnetic. Aims. We searched for a magnetic field using

  20. Enriching the Catalog

    Science.gov (United States)

    Tennant, Roy

    2004-01-01

    After decades of costly and time-consuming effort, nearly all libraries have completed the retrospective conversion of their card catalogs to electronic form. However, bibliographic systems still are really not much more than card catalogs on wheels. Enriched content that Amazon.com takes for granted--such as digitized tables of contents, cover…

  1. Morning Star

    OpenAIRE

    Harris, Mark

    2010-01-01

    Morning Star comprises a group of paintings and drawings whose imagery derives from photographs of 1960s American hippie communes. The paintings are made using oil paint on linen. Their dimensions vary between 180 x 120, and 228 x 217 centimetres. The drawings are in pencil on watercolour paper and are all 56 x 76 centimetres. The work has been exhibited in conventional form, hanging on gallery walls. For Morning Star I made pencil drawings and oil paintings derived from images in Dick Fa...

  2. Evolution of long-lived globular cluster stars III. Effect of the initial helium spread on the position of stars in a synthetic Hertzsprung-Russell diagram

    OpenAIRE

    Chantereau, William; Charbonnel, Corinne; Meynet, Georges

    2016-01-01

    Context. Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. Aims. We pre...

  3. Toward ab initio extremely metal poor stars

    CERN Document Server

    Ritter, Jeremy S; Milosavljevic, Milos; Bromm, Volker

    2016-01-01

    Extremely metal poor stars have been the focus of much recent attention owing to the expectation that their chemical abundances can shed light on the metal and dust yields of the earliest supernovae. We present our most realistic simulation to date of the astrophysical pathway to the first metal enriched stars. We simulate the radiative and supernova hydrodynamic feedback of a 60 Msun Population III star starting from cosmological initial conditions realizing Gaussian density fluctuations. We follow the gravitational hydrodynamics of the supernova remnant at high spatial resolution through its freely-expanding, adiabatic, and radiative phases, until gas, now metal-enriched, has resumed runaway gravitational collapse. Our findings are surprising: while the Population III progenitor exploded with a low energy of 10^51 erg and injected an ample metal mass of 6 Msun, the first cloud to collapse after the supernova explosion is a dense surviving primordial cloud on which the supernova blastwave deposited metals on...

  4. Pulsating stars

    CERN Document Server

    Catelan, M?rcio

    2014-01-01

    The most recent and comprehensive book on pulsating stars which ties the observations to our present understanding of stellar pulsation and evolution theory.  Written by experienced researchers and authors in the field, this book includes the latest observational results and is valuable reading for astronomers, graduate students, nuclear physicists and high energy physicists.

  5. Stars Underground

    CERN Multimedia

    Jean Leyder

    1996-01-01

    An imaginary voyage in time where we were witness of the birth of the universe itself, the time of the Big-Bang 15 billion years ago. Particules from the very first moments of time : protons, neutrons and electrons, and also much more energetic one. These particules are preparing to interact collider and generating others which will be the birth to the stars ........

  6. STAR Highlights

    OpenAIRE

    Masui, Hiroshi; collaboration, for the STAR

    2011-01-01

    We report selected results from STAR collaboration at RHIC, focusing on jet-hadron and jet-like correlations, quarkonium suppression and collectivity, di-electron spectrum in both p+p and Au+Au, and higher moments of net-protons as well as azimuthal anisotropy from RHIC Beam Energy Scan program.

  7. Young α-enriched giant stars in the solar neighbourhood

    DEFF Research Database (Denmark)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva

    2015-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investig......We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We...

  8. Young α-enriched giant stars in the solar neighbourhood

    DEFF Research Database (Denmark)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva

    2015-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investig...

  9. Young α-enriched giant stars in the solar neighbourhood

    DEFF Research Database (Denmark)

    Martig, Marie; Rix, Hans-Walter; Aguirre, Victor Silva;

    2015-01-01

    We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investig......We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and [alpha/Fe] values from APOGEE DR12 (Apache Point Observatory Galactic Evolution Experiment Data Release 12) are available. We...

  10. Chemical enrichment in Ultra-Faint Dwarf galaxies

    Science.gov (United States)

    Romano, Donatella

    2016-08-01

    Our view of the Milky Way's satellite population has radically changed after the discovery, ten years ago, of the first Ultra-Faint Dwarf galaxies (UFDs). These extremely faint, dark-matter dominated, scarcely evolved stellar systems are found in ever-increasing number in our cosmic neighbourhood and constitute a gold-mine for studies of early star formation conditions and early chemical enrichment pathways. Here we show what can be learned from the measurements of chemical abundances in UFD stars read through the lens of chemical evolution studies, point out the limitations of the classic approach, and discuss the way to go to improve the models.

  11. The CH fraction of Carbon stars at high Galactic latitudes

    CERN Document Server

    Goswami, Aruna; Shantikumar, N S

    2009-01-01

    CH stars form a distinct class of objects with characteristic properties like iron deficiency, enrichment of carbon and overabundance in heavy elements. These properties can provide strong observational constraints for theoretical computation of nucleosynthesis at low-metallicity. An important question is the relative surface density of CH stars which can provide valuable inputs to our understanding on the role of low to intermediate-mass stars in the early Galactic chemical evolution. Spectroscopic characterization provides an effective way of identifying CH stars. The present analysis is aimed at a quantitative assessment of the fraction of CH stars in a sample of stars using a set of spectral classification criteria. The sample consists of 92 objects selected from a collection of candidate Faint High Latitude Carbon stars from the Hamburg/ESO survey. Medium resolution (R ~ 1300) spectra for these objects were obtained using OMR at VBO, Kavalur and HFOSC at HCT, IAO, Hanle, during 2007 - 2009 spanning a wav...

  12. The neutron long counter NERO for studies of beta-delayed neutron emission in the r-process

    CERN Document Server

    Pereira, J; Lorusso, G; Santi, P; Couture, A; Daly, J; Del Santo, M; Elliot, T; Goerres, J; Herlitzius, C; Kratz, K -L; Lamm, L O; Lee, H Y; Montes, F; Ouellette, M; Pellegrini, E; Reeder, P; Schatz, H; Schertz, F; Schnorrenberger, L; Smith, K; Stech, E; Strandberg, E; Ugalde, C; Wiescher, M; Woehr, A; 10.1016/j.nima.2010.02.262

    2010-01-01

    The neutron long counter NERO was built at the National Superconducting Cyclotron Laboratory (NSCL), Michigan State University, for measuring beta-delayed neutron-emission probabilities. The detector was designed to work in conjunction with a beta-decay implantation station, so that beta decays and beta-delayed neutrons emitted from implanted nuclei can be measured simultaneously. The high efficiency of about 40%, for the range of energies of interest, along with the small background, are crucial for measuring beta-delayed neutron emission branchings for neutron-rich r-process nuclei produced as low intensity fragmentation beams in in-flight separator facilities.

  13. The neutron long counter NERO for studies of β-delayed neutron emission in the r-process

    Science.gov (United States)

    Pereira, J.; Hosmer, P.; Lorusso, G.; Santi, P.; Couture, A.; Daly, J.; Del Santo, M.; Elliot, T.; Görres, J.; Herlitzius, C.; Kratz, K.-L.; Lamm, L. O.; Lee, H. Y.; Montes, F.; Ouellette, M.; Pellegrini, E.; Reeder, P.; Schatz, H.; Schertz, F.; Schnorrenberger, L.; Smith, K.; Stech, E.; Strandberg, E.; Ugalde, C.; Wiescher, M.; Wöhr, A.

    2010-06-01

    The neutron long counter NERO was built at the National Superconducting Cyclotron Laboratory (NSCL), Michigan State University, for measuring β-delayed neutron-emission probabilities. The detector was designed to work in conjunction with a β-delay implantation station, so that β decays and β-delayed neutrons emitted from implanted nuclei can be measured simultaneously. The high efficiency of about 40%, for the range of energies of interest, along with the small background, are crucial for measuring β-delayed neutron emission branchings for neutron-rich r-process nuclei produced as low intensity fragmentation beams in in-flight separator facilities.

  14. Production cross sections of heavy neutron-rich nuclei approaching the nucleosynthesis r-process path around A =195

    Science.gov (United States)

    Kurtukian-Nieto, T.; Benlliure, J.; Schmidt, K.-H.; Audouin, L.; Becker, F.; Blank, B.; Casarejos, E.; Farget, F.; Fernández-Ordóñez, M.; Giovinazzo, J.; Henzlova, D.; Jurado, B.; Pereira, J.; Yordanov, O.

    2014-02-01

    In the present work we were able to synthesize and measure with high accuracy the production cross sections of more than 190 heavy neutron-rich nuclei by the in-flight fragmentation of relativistic 208Pb projectiles, 26 of which were produced for the first time. This work has shown that the N =126 region far below the doubly magic 208Pb has become accessible experimentally and represents a step further towards the study of heavy neutron-rich nuclei approaching the r-process waiting point at A =195.

  15. Wave Star

    DEFF Research Database (Denmark)

    Kramer, Morten; Frigaard, Peter; Brorsen, Michael

    Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004.......Nærværende rapport beskriver foreløbige hovedkonklusioner på modelforsøg udført på Aalborg Universitet, Institut for Vand, Jord og Miljøteknik med bølgeenergianlægget Wave Star i perioden 13/9 2004 til 12/11 2004....

  16. Planck stars

    CERN Document Server

    Rovelli, Carlo

    2014-01-01

    A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density --not by size-- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

  17. The delayed time distribution of massive double compact star mergers

    CERN Document Server

    Mennekens, N

    2016-01-01

    In order to investigate the temporal evolution of binary populations in general, double compact star binaries and mergers in particular within a galactic evolution context, a most straightforward method is obviously the implementation of a detailed binary evolutionary model in a galactic chemical evolution code. To our knowledge, only the Brussels galactic code explicitly accounts for binaries. With a galactic code that does not explicitly include binaries, the temporal evolution of the population of double compact star binaries and mergers can be estimated with reasonable accuracy if the delayed time distribution (DTD) for these mergers is available. The DTD for supernovae type Ia has been studied extensively the last decade. In the present paper we present the DTD for merging double neutron star binaries and mixed systems consisting of a neutron star and a black hole. The latter mergers are very promising sites for the production of r-process elements and the DTDs can be used to study the galactic evolution...

  18. Zero-Metallicity Stars and the Effects of the First Stars on Reionization.

    Science.gov (United States)

    Tumlinson; Shull

    2000-01-10

    We present stellar structure and atmosphere models of metal-free stars and examine them from a cosmological point of view. Metal-free stars exhibit high effective temperatures and small sizes relative to metal-enriched stars of equal mass. These unique physical characteristics enhance the ionizing photon production by metal-free stars, particularly in the He ii (hnu>/=4 ryd) continuum. The star formation rate of metal-free stars necessary to reionize the hydrogen in the universe by z=5 is consistent with the inferred star formation rate at that epoch. However, the hard stellar spectra are inconsistent with the observations of He ii opacity in the intergalactic medium (IGM) at z approximately 3, indicating that the period of metal-free star formation ended before that epoch. We examine the effects of these stars on the ionization balance of the IGM, the radiative feedback of the first luminous objects, and the extragalactic radiation field. We comment on the prospects for detecting metal-free stellar populations with the lambda1640 and lambda4686 recombination lines of He ii.

  19. Star Maps History, Artistry, and Cartography

    CERN Document Server

    Kanas, Nick

    2012-01-01

    Star Maps captures the beauty and awe of the heavens through celestial prints and star atlases. It traces the history of celestial cartography and relates this history to the changing ideas of humanity's place in the universe. The text of this Second Edition is enriched with 263 photographs, 91 in color, showing images from actual antiquarian celestial books and atlases, each one with an explanation of its astronomical and cartographic features. This new edition of Star Maps: History, Artistry, and Cartography includes: - over 50 new pages of text and 44 new images (16 in color) - completely new sections on celestial frontispieces, deep-sky objects, playing card maps, additional cartographers, and modern computerized star maps - updated figures and text about celestial globes, volvelles, telescopes, and planets and asteroids - revised and updated text and illustrations throughout. The book focuses on the development of celestial cartography from ancient to modern times and describes the relationships between ...

  20. The Nature and Nurture of Star Clusters

    CERN Document Server

    Elmegreen, Bruce G

    2009-01-01

    Star clusters have hierarchical patterns in space and time, suggesting formation processes in the densest regions of a turbulent interstellar medium. Clusters also have hierarchical substructure when they are young, which makes them all look like the inner mixed parts of a pervasive stellar hierarchy. Young field stars share this distribution, presumably because some of them came from dissolved clusters and others formed in a dispersed fashion in the same gas. The fraction of star formation that ends up in clusters is apparently not constant, but may increase with interstellar pressure. Hierarchical structure explains why stars form in clusters and why many of these clusters are self-bound. It also explains the cluster mass function. Halo globular clusters share many properties of disk clusters, including what appears to be an upper cluster cutoff mass. However, halo globulars are self-enriched and often connected with dwarf galaxy streams. The mass function of halo globulars could have initially been like th...

  1. Nucleosynthesis in the Ejecta of Neutron Star Mergers

    CERN Document Server

    Martin, Dirk; Arcones, Almudena; Korobkin, Oleg; Thielemann, Friedrich-Karl

    2015-01-01

    Heavy elements like gold, platinum or uranium are produced in the r-process, which needs neutron-rich and explosive environments. Neutron star mergers are a promising candidate for an r-process site. They exhibit three different channels for matter ejection fulfilling these conditions: dynamic ejecta due to tidal torques, neutrino-driven winds and evaporating matter from the accretion disk. We present a first study of the integrated nucleosynthesis for a neutrino-driven wind from a neutron star merger with a hyper-massive neutron star. Trajectories from a recent hydrodynamical simulation are divided into four different angle regions and post-processed with a reaction network. We find that the electron fraction varies around $Y_e \\approx 0.1 - 0.4$, but its distribution differs for every angle of ejection. Hence, the wind ejecta do not undergo a robust r-process, but rather possess distinct nucleosynthesis yields depending on the angle range. Compared to the dynamic ejecta, a smaller amount of neutron-rich mat...

  2. Diversity of Abundance Patterns of Light Neutron-capture Elements in Very-metal-poor Stars

    Science.gov (United States)

    Aoki, Misa; Ishimaru, Yuhri; Aoki, Wako; Wanajo, Shinya

    2017-03-01

    We determine the abundances of neutron-capture elements from Sr to Eu for five very-metal-poor stars (-3 universal pattern in the main r-process, similar to the abundance pattern of the r-process component of solar-system material. Still, it is uncertain whether the abundance pattern of the weak r-process shows universality or diversity, due to the sparseness of measured light neutron-capture elements. We have detected the key elements, Mo, Ru, and Pd, in five target stars to give an answer to this question. The abundance patterns of light neutron-capture elements from Sr to Pd suggest a diversity in the weak r-process. In particular, scatter in the abundance ratio between Ru and Pd is significant when the abundance patterns are normalized at Zr. Our results are compared with the elemental abundances predicted by nucleosynthesis models of supernovae with parameters such as electron fraction or proto-neutron-star mass, to investigate sources of such diversity in the abundance patterns of light neutron-capture elements. This paper presents that the variation in the abundances of observed stars can be explained with a small range of parameters, which can serve as constraints on future modeling of supernova models. Study based on data collected with the Subaru Telescope, operated by the National Astronomical Observatory of Japan.

  3. Globular cluster formation with multiple stellar populations: self-enrichment in fractal massive molecular clouds

    Science.gov (United States)

    Bekki, Kenji

    2017-08-01

    Internal chemical abundance spreads are one of fundamental properties of globular clusters (GCs) in the Galaxy. In order to understand the origin of such abundance spreads, we numerically investigate GC formation from massive molecular clouds (MCs) with fractal structures using our new hydrodynamical simulations with star formation and feedback effects of core-collapse supernovae (SNe) and asymptotic giant branch (AGB) stars. We particularly investigate star formation from gas chemically contaminated by SNe and AGB stars ('self-enrichment') in forming GCs within MCs with different initial conditions and environments. The principal results are as follows. GCs with multiple generations of stars can be formed from merging of hierarchical star cluster complexes that are developed from high-density regions of fractal MCs. Feedback effects of SNe and AGB stars can control the formation efficiencies of stars formed from original gas of MCs and from gas ejected from AGB stars. The simulated GCs have strong radial gradients of helium abundances within the central 3 pc. The original MC masses need to be as large as 107 M⊙ for a canonical initial stellar mass function (IMF) so that the final masses of stars formed from AGB ejecta can be ∼105 M⊙. Since star formation from AGB ejecta is rather prolonged (∼108 yr), their formation can be strongly suppressed by SNe of the stars themselves. This result implies that the so-called mass budget problem is much more severe than ever thought in the self-enrichment scenario of GC formation and thus that IMF for the second generation of stars should be 'top-light'.

  4. Measure of the stars

    Energy Technology Data Exchange (ETDEWEB)

    Henbest, N.

    1984-12-13

    The paper concerns the Hertzsprung-Russel (H-R) diagram, which is graph relating the brightness to the surface temperature of the stars. The diagram provides a deep insight into the fundamental properties of the stars. Evolution of the stars; the death of a star; distances; and dating star clusters, are all briefly discussed with reference to the H-R diagram.

  5. When stars collide

    NARCIS (Netherlands)

    Glebbeek, E.; Pols, O.R.

    2007-01-01

    When two stars collide and merge they form a new star that can stand out against the background population in a star cluster as a blue straggler. In so called collision runaways many stars can merge and may form a very massive star that eventually forms an intermediate mass blackhole. We have perfor

  6. The Rb problem in massive AGB stars.

    Science.gov (United States)

    Pérez-Mesa, V.; García-Hernández, D. A.; Zamora, O.; Plez, B.; Manchado, A.; Karakas, A. I.; Lugaro, M.

    2017-03-01

    The asymptotic giant branch (AGB) is formed by low- and intermediate-mass stars (0.8 M_{⊙} develop thermal pulses (TP) and suffer extreme mass loss. AGB stars are the main contributor to the enrichment of the interstellar medium (ISM) and thus to the chemical evolution of galaxies. In particular, the more massive AGB stars (M > 4 M_{⊙}) are expected to produce light (e.g., Li, N) and heavy neutron-rich s-process elements (such as Rb, Zr, Ba, Y, etc.), which are not formed in lower mass AGB stars and Supernova explosions. Classical chemical analyses using hydrostatic atmospheres revealed strong Rb overabundances and high [Rb/Zr] ratios in massive AGB stars of our Galaxy and the Magellanic Clouds (MC), confirming for the first time that the ^{22}Ne neutron source dominates the production of s-process elements in these stars. The extremely high Rb abundances and [Rb/Zr] ratios observed in the most massive stars (specially in the low-metallicity MC stars) uncovered a Rb problem; such extreme Rb and [Rb/Zr] values are not predicted by the s-process AGB models, suggesting fundamental problems in our present understanding of their atmospheres. We present more realistic dynamical model atmospheres that consider a gaseous circumstellar envelope with a radial wind and we re-derive the Rb (and Zr) abundances in massive Galactic AGB stars. The new Rb abundances and [Rb/Zr] ratios derived with these dynamical models significantly resolve the problem of the mismatch between the observations and the theoretical predictions of the more massive AGB stars.

  7. Chemical enrichment and physical conditions in I Zw 18

    CERN Document Server

    Lebouteiller, Vianney; Hubeny, Ivan; Kunth, Daniel

    2013-01-01

    Abridged. Low-metallicity star-forming dwarf galaxies are prime targets to understand the chemical enrichment of the interstellar medium. The HI region provides important constraints on the dispersal and mixing of heavy elements released by successive star-formation episodes. Our primary objective is to study the enrichment of the HI region and the interplay between star-formation history and metallicity evolution. We observed the most metal-poor star-forming galaxy in the Local Universe, I Zw 18, with Hubble/COS. The abundances in the neutral gas are derived from far-UV absorption-lines (HI, CII, CII*, NI, OI, ...) and are compared to the abundances in the HII region. Models are constructed to calculate the ionization structure and the thermal processes. We investigate the gas cooling in the HI region through physical diagnostics drawn from the fine-structure level of C+. We find that HI region abundances are lower by a factor of ~2 as compared to the HII region. There is no differential depletion on dust be...

  8. External Photoevaporation of the Solar Nebula: Jupiter's Noble Gas Enrichments

    CERN Document Server

    Monga, Nikhil

    2014-01-01

    We present a model explaining elemental enrichments in Jupiter's atmosphere, particularly the noble gases Ar, Kr, and Xe. While He, Ne and O are depleted, seven other elements show similar enrichments ($\\sim$3 times solar, relative to H). Being volatile, Ar is difficult to fractionate from ${\\rm H}_{2}$. We argue that external photoevaporation by far ultraviolet (FUV) radiation from nearby massive stars removed ${\\rm H}_{2}$, He, and Ne from the solar nebula, but Ar and other species were retained because photoevaporation occurred at large heliocentric distances where temperatures were cold enough ($\\lt 30$ K) to trap them in amorphous water ice. As the solar nebula lost H it became relatively and uniformly enriched in other species. Our model improves on the similar model of Guillot \\& Hueso (2006). We recognize that cold temperatures alone do not trap volatiles; continuous water vapor production also is necessary. We demonstrate that FUV fluxes that photoevaporated the disk generated sufficient water va...

  9. Fluorine in R Coronae Borealis Stars

    CERN Document Server

    Pandey, Gajendra; Rao, N Kameswara

    2007-01-01

    Neutral fluorine (F I) lines are identified in the optical spectra of several R Coronae Borealis stars (RCBs) at maximum light. These lines provide the first measurement of the fluorine abundance in these stars. Fluorine is enriched in some RCBs by factors of 800 to 8000 relative to its likely initial abundance. The overabundances of fluorine are evidence for the synthesis of fluorine. These results are discussed in the light of the scenario that RCBs are formed by accretion of an He white dwarf by a C-O white dwarf. Sakurai's object (V4334 Sgr), a final He-shell flash product, shows no detectable F I lines.

  10. Thermal breeder fuel enrichment zoning

    Science.gov (United States)

    Capossela, Harry J.; Dwyer, Joseph R.; Luce, Robert G.; McCoy, Daniel F.; Merriman, Floyd C.

    1992-01-01

    A method and apparatus for improving the performance of a thermal breeder reactor having regions of higher than average moderator concentration are disclosed. The fuel modules of the reactor core contain at least two different types of fuel elements, a high enrichment fuel element and a low enrichment fuel element. The two types of fuel elements are arranged in the fuel module with the low enrichment fuel elements located between the high moderator regions and the high enrichment fuel elements. Preferably, shim rods made of a fertile material are provided in selective regions for controlling the reactivity of the reactor by movement of the shim rods into and out of the reactor core. The moderation of neutrons adjacent the high enrichment fuel elements is preferably minimized as by reducing the spacing of the high enrichment fuel elements and/or using a moderator having a reduced moderating effect.

  11. Preserving chemical signatures of primordial star formation in the first low-mass stars

    CERN Document Server

    Ji, Alexander P; Bromm, Volker

    2015-01-01

    We model early star forming regions and their chemical enrichment by Population III (Pop III) supernovae with nucleosynthetic yields featuring high [C/Fe] ratios and pair-instability supernova (PISN) signatures. We aim to test how well these chemical abundance signatures are preserved in the gas prior to forming the first long-lived low-mass stars (or second-generation stars). Our results show that second-generation stars can retain the nucleosynthetic signature of their Pop III progenitors, even in the presence of nucleosynthetically normal Pop III core-collapse supernovae. We find that carbon-enhanced metal-poor stars are likely second-generation stars that form in minihaloes. Furthermore, it is likely that the majority of Pop III supernovae produce high [C/Fe] yields. In contrast, metals ejected by a PISN are not concentrated in the first star forming haloes, which may explain the absence of observed PISN signatures in metal-poor stars. We also find that unique Pop III abundance signatures in the gas are q...

  12. Production of Star-Grazing and Star-Impacting Planetestimals via Orbital Migration of Extrasolar Planets

    Science.gov (United States)

    Quillen, A. C.; Holman, M.

    2000-01-01

    During the orbital migration of a giant extrasolar planet via ejection of planetesimals (as studied by Murray et al. in 1998), inner mean-motion resonances can be strong enough to cause planetesimals to graze or impact the star. We integrate numerically the motions of particles which pass through the 3:1 or 4:1 mean-motion resonances of a migrating Jupiter-mass planet. We find that many particles can be trapped in the 3:1 or 4:1 resonances and pumped to high enough eccentricities that they impact the star. This implies that for a planet migrating a substantial fraction of its semimajor axis, a fraction of its mass in planetesimals could impact the star. This process may be capable of enriching the metallicity of the star at a time when the star is no longer fully convective. Upon close approaches to the star, the surfaces of these planetesimals will be sublimated. Orbital migration should cause continuing production of evaporating bodies, suggesting that this process should be detectable with searches for transient absorption lines in young stars. The remainder of the particles will not impact the star but can be ejected subsequently by the planet as it migrates further inward. This allows the planet to migrate a substantial fraction of its initial semimajor axis by ejecting planetesimals.

  13. DISTRIBUTIONS OF LONG-LIVED RADIOACTIVE NUCLEI PROVIDED BY STAR-FORMING ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Fatuzzo, Marco [Department of Physics, Xavier University, Cincinnati, OH 45207 (United States); Adams, Fred C. [Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States)

    2015-11-01

    Radioactive nuclei play an important role in planetary evolution by providing an internal heat source, which affects planetary structure and helps facilitate plate tectonics. A minimum level of nuclear activity is thought to be necessary—but not sufficient—for planets to be habitable. Extending previous work that focused on short-lived nuclei, this paper considers the delivery of long-lived radioactive nuclei to circumstellar disks in star forming regions. Although the long-lived nuclear species are always present, their abundances can be enhanced through multiple mechanisms. Most stars form in embedded cluster environments, so that disks can be enriched directly by intercepting ejecta from supernovae within the birth clusters. In addition, molecular clouds often provide multiple episodes of star formation, so that nuclear abundances can accumulate within the cloud; subsequent generations of stars can thus receive elevated levels of radioactive nuclei through this distributed enrichment scenario. This paper calculates the distribution of additional enrichment for {sup 40}K, the most abundant of the long-lived radioactive nuclei. We find that distributed enrichment is more effective than direct enrichment. For the latter mechanism, ideal conditions lead to about 1 in 200 solar systems being directly enriched in {sup 40}K at the level inferred for the early solar nebula (thereby doubling the abundance). For distributed enrichment from adjacent clusters, about 1 in 80 solar systems are enriched at the same level. Distributed enrichment over the entire molecular cloud is more uncertain, but can be even more effective.

  14. Asymmetric core-collapse of rapidly-rotating massive star

    CERN Document Server

    Gilkis, Avishai

    2016-01-01

    Non-axisymmetric features are found in the core-collapse of a rapidly-rotating massive star, which may have important implications for magnetic field amplification and production of a bipolar outflow that can explode the star, as well as for r-process nucleosynthesis and natal kicks. The collapse of an evolved rapidly-rotating massive star is followed in three-dimensional hydrodynamic simulations using the FLASH code with neutrino leakage. A rotating proto-neutron star (PNS) forms with a non-zero linear velocity. This process might contribute to the natal kick of the remnant compact object. The PNS is surrounded by a turbulent medium, where high shearing is likely to amplify magnetic fields, which in turn can drive a bipolar outflow. Neutron-rich material in the PNS vicinity may induce strong r-process nucleosynthesis. The rapidly-rotating PNS possesses a rotational energy of E>10foe, some of which may possibly be deposited later on in the SN ejecta through a magnetar spin down process. These processes may be...

  15. Neutron-Capture Nucleosynthesis in the First Stars

    CERN Document Server

    Roederer, Ian U; Thompson, Ian B; Shectman, Stephen A; Sneden, Chris

    2014-01-01

    Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly-rotating massive stars a...

  16. Cerium the lithium substitute in post-AGB stars

    CERN Document Server

    Reyniers, M; Biemont, E; Quinet, P; Reyniers, Maarten; Winckel, Hans Van; Biemont, Emile; Quinet, Pascal

    2002-01-01

    In this letter we present an alternative identification for the line detected in the spectra of s-process enriched low-mass post-AGB stars around 6708A and which was interpreted in the literature as due to Li. Newly released line lists of lanthanide species reveal, however, the likely identification of the line to be due to a CeII transition. We argue that this identification is consistent with the Ce abundance of all the objects discussed in the literature and conclude that in none of the low-mass s-process enriched post-AGB stars there is indication for Li-production.

  17. Can strange stars mimic dark energy stars?

    CERN Document Server

    Deb, Debabrata; Guha, B K; Ray, Saibal

    2016-01-01

    The possibility of strange stars mixed with dark energy to be one of candidates for dark energy stars is the main issue of the present study. Our investigation shows that quark matter is acting as dark energy after certain yet unknown critical condition inside the quark stars. Our proposed model reveals that strange stars mixed with dark energy feature not only a physically acceptable stable model but also mimic characteristics of dark energy stars. The plausible connections are shown through the mass-radius relation as well as the entropy and temperature. We particulary note that two-fluid distribution is the major reason for anisotropic nature of the spherical stellar system.

  18. ENRICHMENT OF OBO ONTOLOGIES

    Science.gov (United States)

    Bada, Michael; Hunter, Lawrence

    2006-01-01

    This paper describes a frame-based integration of the three GO subontologies, the Chemicals of Biological Interest ontology (ChEBI), and the Cell Type Ontology (CTO) in which relationships between elements of the ontologies are modeled in a way that better captures the relational semantics between biological concepts represented by the terms, rather than between the terms themselves, than previous frame-based efforts. We also describe a methodology for creating suggested enriching assertions of the form (subject, relationship, object) by identifying patterns in GO terms, mapping these patterns and subpatterns to relationships, matching concepts to these patterns and subpatterns, and integrating these assertions into the ontologies. Using this methodology, a large number of reliable assertions linking previously unlinked OBO terms using a wide variety of specific, hierarchically arranged relationships were created: A predicted assertion was made for 62% of GO terms that matched one of 31 patterns, and 97% of these predicted assertions were assessed to be valid; a further 429 assertions (corresponding to 6% of the matching terms) were manually created, resulting in an initial set of 4,497 assertions. Furthermore, this methodology programmatically integrates assertions into a base ontology such that each assertion is fully consistent with respect to higher (i.e., more general) relevant class and slot levels. Such an integration is absent from previous compositional efforts, and we argue its necessity for the creation of coherent biological ontologies when linking previously unlinked terms. PMID:17011833

  19. Earthquake forecast enrichment scores

    Directory of Open Access Journals (Sweden)

    Christine Smyth

    2012-03-01

    Full Text Available The Collaboratory for the Study of Earthquake Predictability (CSEP is a global project aimed at testing earthquake forecast models in a fair environment. Various metrics are currently used to evaluate the submitted forecasts. However, the CSEP still lacks easily understandable metrics with which to rank the universal performance of the forecast models. In this research, we modify a well-known and respected metric from another statistical field, bioinformatics, to make it suitable for evaluating earthquake forecasts, such as those submitted to the CSEP initiative. The metric, originally called a gene-set enrichment score, is based on a Kolmogorov-Smirnov statistic. Our modified metric assesses if, over a certain time period, the forecast values at locations where earthquakes have occurred are significantly increased compared to the values for all locations where earthquakes did not occur. Permutation testing allows for a significance value to be placed upon the score. Unlike the metrics currently employed by the CSEP, the score places no assumption on the distribution of earthquake occurrence nor requires an arbitrary reference forecast. In this research, we apply the modified metric to simulated data and real forecast data to show it is a powerful and robust technique, capable of ranking competing earthquake forecasts.

  20. City model enrichment

    Science.gov (United States)

    Smart, Philip D.; Quinn, Jonathan A.; Jones, Christopher B.

    The combination of mobile communication technology with location and orientation aware digital cameras has introduced increasing interest in the exploitation of 3D city models for applications such as augmented reality and automated image captioning. The effectiveness of such applications is, at present, severely limited by the often poor quality of semantic annotation of the 3D models. In this paper, we show how freely available sources of georeferenced Web 2.0 information can be used for automated enrichment of 3D city models. Point referenced names of prominent buildings and landmarks mined from Wikipedia articles and from the OpenStreetMaps digital map and Geonames gazetteer have been matched to the 2D ground plan geometry of a 3D city model. In order to address the ambiguities that arise in the associations between these sources and the city model, we present procedures to merge potentially related buildings and implement fuzzy matching between reference points and building polygons. An experimental evaluation demonstrates the effectiveness of the presented methods.

  1. Mass ejection in neutron star mergers

    Science.gov (United States)

    Rosswog, S.; Liebendörfer, M.; Thielemann, F.-K.; Davies, M. B.; Benz, W.; Piran, T.

    1999-01-01

    We present the results of 3D Newtonian SPH simulations of the merger of a neutron star binary. The microscopic properties of matter are described by the physical equation of state of Lattimer and Swesty (LS-EOS). To check the model dependence of the results we vary the resolution ( ~ 21000 and ~ 50000 particles), the equation of state (stiff and soft polytropes), the artificial viscosity scheme, the stellar masses, we include neutrinos (free-streaming limit), switch off the gravitational backreaction force, and vary the initial stellar spins. In addition we test the influence of the initial configuration, i.e. spherical stars versus corotating equilibrium configurations. The final matter distribution consists of a rapidly spinning central object with 2.5 to 3.1 Msun of baryonic mass that probably collapses to a black hole, a thick disk of 0.1 to 0.3 Msun and an extended low density region. In the case of corotation this low density material forms spiral arms that expand explosively due to an increase of the adiabatic exponent and the release of nuclear binding energy in the case of the LS-EOS, but remain narrow and well defined for the stiff polytropic equation of state. The main and new result is that for the realistic LS-EOS, depending on the initial spin, between 4*10(-3) and 4*10(-2) Msun of material become unbound. If, as suggested, large parts of this matter consist of r-process nuclei, neutron star mergers could account for the whole observed r-process material in the Galaxy.

  2. Lifestyles of the Stars.

    Science.gov (United States)

    National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

    Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)

  3. Detailed Abundances of Two Very Metal-Poor Stars in Dwarf Galaxies

    CERN Document Server

    Kirby, Evan N

    2012-01-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae. These supernovae could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two Milky Way dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[alpha/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of supernova yields is the cause. The earlies...

  4. Hydrogen-enriched fuels

    Energy Technology Data Exchange (ETDEWEB)

    Roser, R. [NRG Technologies, Inc., Reno, NV (United States)

    1998-08-01

    NRG Technologies, Inc. is attempting to develop hardware and infrastructure that will allow mixtures of hydrogen and conventional fuels to become viable alternatives to conventional fuels alone. This commercialization can be successful if the authors are able to achieve exhaust emission levels of less than 0.03 g/kw-hr NOx and CO; and 0.15 g/kw-hr NMHC at full engine power without the use of exhaust catalysts. The major barriers to achieving these goals are that the lean burn regimes required to meet exhaust emissions goals reduce engine output substantially and tend to exhibit higher-than-normal total hydrocarbon emissions. Also, hydrogen addition to conventional fuels increases fuel cost, and reduces both vehicle range and engine output power. Maintaining low emissions during transient driving cycles has not been demonstrated. A three year test plan has been developed to perform the investigations into the issues described above. During this initial year of funding research has progressed in the following areas: (a) a cost effective single-cylinder research platform was constructed; (b) exhaust gas speciation was performed to characterize the nature of hydrocarbon emissions from hydrogen-enriched natural gas fuels; (c) three H{sub 2}/CH{sub 4} fuel compositions were analyzed using spark timing and equivalence ratio sweeping procedures and finally; (d) a full size pick-up truck platform was converted to run on HCNG fuels. The testing performed in year one of the three year plan represents a baseline from which to assess options for overcoming the stated barriers to success.

  5. CLEAN: CLustering Enrichment ANalysis

    Directory of Open Access Journals (Sweden)

    Medvedovic Mario

    2009-07-01

    Full Text Available Abstract Background Integration of biological knowledge encoded in various lists of functionally related genes has become one of the most important aspects of analyzing genome-wide functional genomics data. In the context of cluster analysis, functional coherence of clusters established through such analyses have been used to identify biologically meaningful clusters, compare clustering algorithms and identify biological pathways associated with the biological process under investigation. Results We developed a computational framework for analytically and visually integrating knowledge-based functional categories with the cluster analysis of genomics data. The framework is based on the simple, conceptually appealing, and biologically interpretable gene-specific functional coherence score (CLEAN score. The score is derived by correlating the clustering structure as a whole with functional categories of interest. We directly demonstrate that integrating biological knowledge in this way improves the reproducibility of conclusions derived from cluster analysis. The CLEAN score differentiates between the levels of functional coherence for genes within the same cluster based on their membership in enriched functional categories. We show that this aspect results in higher reproducibility across independent datasets and produces more informative genes for distinguishing different sample types than the scores based on the traditional cluster-wide analysis. We also demonstrate the utility of the CLEAN framework in comparing clusterings produced by different algorithms. CLEAN was implemented as an add-on R package and can be downloaded at http://Clusteranalysis.org. The package integrates routines for calculating gene specific functional coherence scores and the open source interactive Java-based viewer Functional TreeView (FTreeView. Conclusion Our results indicate that using the gene-specific functional coherence score improves the reproducibility of the

  6. Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies

    Science.gov (United States)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2008-12-01

    Preface; SOC and LOC; Participants; Life at the conference; Conference photo; Session I. Population III and Metal-Free Star Formation: 1. Open questions in the study of population III star formation S. C. O. Glover, P. C. Clark, T. H. Greif, J. L. Johnson, V. Bromm, R. S. Klessen and A. Stacy; 2. Protostar formation in the early universe Naoki Yoshida; 3. Population III.1 stars: formation, feedback and evolution of the IMF Jonathan C. Tan; 4. The formation of the first galaxies and the transition to low-mass star formation T. H. Greif, D. R. G. Schleicher, J. L. Johnson, A.-K. Jappsen, R. S. Klessen, P. C. Clark, S. C. O. Glover, A. Stacy and V. Bromm; 5. Low-metallicity star formation: the characteristic mass and upper mass limit Kazuyuki Omukai; 6. Dark stars: dark matter in the first stars leads to a new phase of stellar evolution Katherine Freese, Douglas Spolyar, Anthony Aguirre, Peter Bodenheimer, Paolo Gondolo, J. A. Sellwood and Naoki Yoshida; 7. Effects of dark matter annihilation on the first stars F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara and P. Marigo; 8. Searching for Pop III stars and galaxies at high redshift Daniel Schaerer; 9. The search for population III stars Sperello di Serego Alighieri, Jaron Kurk, Benedetta Ciardi, Andrea Cimatti, Emanuele Daddi and Andrea Ferrara; 10. Observational search for population III stars in high-redshift galaxies Tohru Nagao; Session II. Metal Enrichment, Chemical Evolution, and Feedback: 11. Cosmic metal enrichment Andrea Ferrara; 12. Insights into the origin of the galaxy mass-metallicity relation Henry Lee, Eric F. Bell and Rachel S. Somerville; 13. LSD and AMAZE: the mass-metallicity relation at z > 3 F. Mannucci and R. Maiolino; 14. Three modes of metal-enriched star formation at high redshift Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea and Michael L. Norman; 15. Primordial supernovae and the assembly of the first galaxies Daniel Whalen, Bob Van Veelen, Brian W. O

  7. Neutrino Flavor Evolution in Binary Neutron Star Merger Remnants

    CERN Document Server

    Frensel, Maik; Volpe, Cristina; Perego, Albino

    2016-01-01

    We study the neutrino flavor evolution in the neutrino-driven wind from a binary neutron star merger remnant consisting of a massive neutron star surrounded by an accretion disk. With the neutrino emission characteristics and the hydrodynamical profile of the remnant consistently extracted from a three-dimensional simulation, we compute the flavor evolution by taking into account neutrino coherent forward scattering off ordinary matter and neutrinos themselves. We employ a "single-trajectory" approach to investigate the dependence of the flavor evolution on the neutrino emission location and angle. We also show that the flavor conversion in the merger remnant can affect the (anti-)neutrino absorption rates on free nucleons and may thus impact the $r$-process nucleosynthesis in the wind. We discuss the sensitivity of such results on the change of neutrino emission characteristics, also from different neutron star merger simulations.

  8. Role of ($\\alpha$,n) reactions under $r$-process conditions in neutrino-driven winds revisited

    CERN Document Server

    Mohr, Peter

    2016-01-01

    Background: The astrophysical $r$-process occurs in an explosive astrophysical event under extremely neutron-rich conditions, leading to (n,$\\gamma$)-($\\gamma$,n) equilibrium along isotopic chains which peaks around neutron separation energies of a few MeV. Nuclei with larger $Z$ are usually produced by $\\beta^-$-decay, but under certain conditions also $\\alpha$-induced reactions may become relevant for the production of nuclei with $Z+2$. Purpose: The uncertainties of the reaction rates of these $\\alpha$-induced reactions are discussed within the statistical model. As an example, $\\alpha$-induced ($\\alpha$,n) and $(\\alpha$,$x$n) reaction cross sections for the neutron-rich $^{86}$Se nucleus are studied in detail. Method: In a first step, the relevance of ($\\alpha$,n) and $(\\alpha$,$x$n) reactions is analyzed. Next the uncertainties are determined from a variation of the $\\alpha$-nucleus potential which is the all-dominant parameter for the astrophysical $Z \\rightarrow Z+2$ reaction rate. Results: It is found...

  9. Stability beyond the neutron drip-line near the third peak of the r-process nucleosynthesis

    CERN Document Server

    Sharma, M M

    2011-01-01

    We have investigated the nuclear shell effects at N=126 in the region of the third peak of the r-process nucleosynthesis within the framework of the relativistic mean-field theory using the Lagrangian model NL-SV1 with the vector self-coupling of omega-meson. Our study encompasses even-even nuclei with N=110-140 in the isotopic chains of Hf (Z=72) down to Ba (Z=56). It is shown that the nuclear shell effects at N=126 remain strong even as one moves far away from the line of the beta-stability. As the neutron drip line approaches N=126, nuclei exhibit vanishingly small neutron separation energy. However, going beyond the neutron drip line, we observe an interesting feature in that some nuclei near N ~ 132-134 for the isotopic chains of Z=62-68 show enhanced neutron separation energy. This is especially pronounced for the isotopes of Gd (Z=64) and Dy (Z=66). These nuclei exhibit the phenomenon of stability beyond the neutron drip line. Our analysis of the single-particle spectrum shows that this is engendered b...

  10. A Study of the r-Process Path Nuclides,$^{137,138,139}$Sb using the Enhanced Selectivity of Resonance Ionization Laser Ionization

    CERN Multimedia

    Walters, W

    2002-01-01

    The particular features of the r-process abundances with 100 < A < 150 have demonstrated the close connection between knowledge of nuclear structure and decay along the r-process path and the astrophysical environement in which these elements are produced. Key to this connection has been the measurement of data for nuclides (mostly even-N nuclides) that lie in the actual r-process path. Such data are of direct use in r-process calculations and they also serve to refine and test the predictive power of nuclear models where little or no data now exist. In this experiment we seek to use the newly developed ionization scheme for the Resonance Ionization Laser Ion Source (RILIS) to achieve selective ionization of neutron-rich antimony isotopes in order to measure the decay properties of r-process path nuclides $^{137,138,139}$Sb. These properties include the half-lives, delayed neutron branches, and daughter $\\gamma$-rays. The new nuclear structure data for the daughter Te nuclides is also of considerable in...

  11. The Cambridge Double Star Atlas

    Science.gov (United States)

    MacEvoy, Bruce; Tirion, Wil

    2015-12-01

    Preface; What are double stars?; The binary orbit; Double star dynamics; Stellar mass and the binary life cycle; The double star population; Detecting double stars; Double star catalogs; Telescope optics; Preparing to observe; Helpful accessories; Viewing challenges; Next steps; Appendices: target list; Useful formulas; Double star orbits; Double star catalogs; The Greek alphabet.

  12. Isotopic enrichment of forming planetary systems from supernova pollution

    Science.gov (United States)

    Lichtenberg, Tim; Parker, Richard J.; Meyer, Michael R.

    2016-11-01

    Heating by short-lived radioisotopes (SLRs) such as 26Al and 60Fe fundamentally shaped the thermal history and interior structure of Solar system planetesimals during the early stages of planetary formation. The subsequent thermo-mechanical evolution, such as internal differentiation or rapid volatile degassing, yields important implications for the final structure, composition and evolution of terrestrial planets. SLR-driven heating in the Solar system is sensitive to the absolute abundance and homogeneity of SLRs within the protoplanetary disc present during the condensation of the first solids. In order to explain the diverse compositions found for extrasolar planets, it is important to understand the distribution of SLRs in active planet formation regions (star clusters) during their first few Myr of evolution. By constraining the range of possible effects, we show how the imprint of SLRs can be extrapolated to exoplanetary systems and derive statistical predictions for the distribution of 26Al and 60Fe based on N-body simulations of typical to large clusters (103-104 stars) with a range of initial conditions. We quantify the pollution of protoplanetary discs by supernova ejecta and show that the likelihood of enrichment levels similar to or higher than the Solar system can vary considerably, depending on the cluster morphology. Furthermore, many enriched systems show an excess in radiogenic heating compared to Solar system levels, which implies that the formation and evolution of planetesimals could vary significantly depending on the birth environment of their host stars.

  13. A barium-rich binary central star in Abell 70

    CERN Document Server

    Boffin, Henri M J; Frew, D J; Acker, A; Köppen, J; Moffat, A F J; Parker, Q A

    2011-01-01

    We have found the central star of Abell 70 (PN G038.1-25.4, hereafter A 70) to be a binary consisting of a G8 IV-V secondary and a hot white dwarf. The secondary shows enhanced Ba II and Sr II features, firmly classifying it as a barium star. The nebula is found to have Type-I chemical abundances with helium and nitrogen enrichment, which combined with future abundance studies of the central star, will establish A 70 as a unique laboratory for studying s-process AGB nucleosynthesis.

  14. Deep Hubble Space Telescope imaging of Sextans A. III. The star formation history

    NARCIS (Netherlands)

    Dolphin, AE; Saha, A; Skillman, ED; Dohm-Palmer, RC; Tolstoy, E; Cole, AA; Gallagher, JS; Hoessel, JG; Mateo, M

    2003-01-01

    We present a measurement of the star formation history of Sextans A, based on WFPC2 photometry that is 50% complete to V = 27.5 (M-V similar to +1.9) and I = 27.0. The star formation history and chemical enrichment history have been measured through modeling of the color-magnitude diagram (CMD). We

  15. Quantifying the Drivers of Star Formation on Galactic Scales. I. The Small Magellanic Cloud

    CERN Document Server

    Zaritsky, D; Zaritsky, Dennis; Harris, Jason

    2004-01-01

    We use the star formation history of the Small Magellanic Cloud (SMC) to place quantitative limits on the effect of tidal interactions and gas infall on the star formation and chemical enrichment history of the SMC. The coincident timing of two recent ( 10% and could be as large as 70%.

  16. An investigation of the RCB star candidate GDS J0702414-023501

    CERN Document Server

    Huemmerich, Stefan

    2016-01-01

    2MASS J07024146-0235017 = GDS J0702414-023501 was included in the "Catalogue enriched with R CrB stars" on grounds of its near- and mid-infrared colours. The object, which corresponds to the carbon star IRAS 07001-0230 = CGCS 6197, has been found to exhibit large amplitude variability in its Bochum Galactic Disk Survey light curve. Taking into account all available data, GDS J0702414-023501 is here proposed as a new candidate Mira star.

  17. Theoretical uncertainty of (α ,n ) reactions relevant for the nucleosynthesis of light r -process nuclei in neutrino-driven winds

    Science.gov (United States)

    Pereira, J.; Montes, F.

    2016-03-01

    Background: Neutrino-driven winds following core-collapse supernova explosions have been proposed as a possible site where light r -process nuclei (between Fe and Ag) might be synthesized. In these events, (α ,n ) reactions are key to moving matter towards the region of higher proton number. Abundance network calculations are very sensitive to the rates for this type of reactions. Purpose: The present work aims at evaluating the theoretical uncertainty of these (α ,n ) reactions calculated with reaction codes based on the Hauser-Feshbach model. Method: We compared several (α ,n ) rates taken from talys and the non-smoker database to determine the uncertainties owing to the existing technical differences between both codes. In addition, we evaluated the sensitivity of talys rates to variations in the α optical potentials, masses, level densities, optical potentials, preequilibrium intranuclear transition rates, level structure, radiative transmission coefficients, and width-fluctuation correction factors. Results: The main source of uncertainty at low temperature is mostly attributable to the use of different α optical potentials. Differences between talys and non-smoker at high temperatures arise from the energy-binning algorithm used by each code. We have also noticed that the (α ,n ) rates from the non-smoker database correspond to the inclusive reaction, instead of the exclusive (α ,1 n ) channel calculated in the present work and used in network calculations. Conclusions: Theoretical uncertainties in calculated reaction rates can be as high as one to two orders of magnitude and strongly dependent on the temperature of the environment. Besides direct measurements of the inclusive and exclusive (α ,1 n ) reaction rates, experimental studies of α optical potentials are crucial to improve the performance of reaction codes.

  18. How plausible are the proposed formation scenarios of CEMP-r/s stars?

    CERN Document Server

    Abate, Carlo; Liu, Zheng-Wei

    2016-01-01

    CEMP-$r/s$ stars are metal-poor stars with enhanced abundances of carbon and heavy elements associated with the slow ($s$-) and rapid ($r$-) neutron-capture process. It is believed that carbon and $s$-elements were accreted from the wind of an AGB primary star, a scenario that is generally accepted to explain the formation of CEMP stars that are only enhanced in $s$-elements (CEMP-$s$ stars). The origin of $r$-element-enrichment in CEMP-$r/s$ stars is debated and many formation scenarios have been put forward. We aim to determine the likelihood of the scenarios proposed to explain the formation of CEMP-$r/s$ stars. We calculate the frequency of CEMP-$r/s$ stars among CEMP-$s$ stars for a variety of scenarios, and we compare it with that determined from an observed sample of CEMP-$r/s$ stars collected from the literature. The theoretical frequency of CEMP-$r/s$ stars predicted in most scenarios underestimates the observed ratio by at least a factor of 5. If the enrichments in $s$- and $r$-elements are independ...

  19. Blocking Metal Accretion onto Population III Stars by Stellar Wind

    Science.gov (United States)

    Tanaka, Shuta J.; Chiaki, Gen; Tominaga, Nozomu; Susa, Hajime

    2017-08-01

    Low-mass population III (PopIII) stars of ≲ 0.8 {M}⊙ could survive up until the present. The nondetection of low-mass PopIII stars in our Galaxy has already put a stringent constraint on the initial mass function (IMF) of PopIII stars, suggesting that PopIII stars have a top-heavy IMF. On the other hand, some claim that the lack of such stars stems from metal enrichment of their surfaces by the accretion of heavy elements from the interstellar medium (ISM). We investigate the effects of the stellar wind on metal accretion onto low-mass PopIII stars because accretion of the local ISM onto the Sun is prevented by the solar wind, even for neutrals. The stellar wind and radiation of low-mass PopIII stars are modeled based on knowledge of nearby low-mass stellar systems, including our Sun. We find that low-mass PopIII stars traveling across the Galaxy form a stellar magnetosphere in most of their life. Once the magnetosphere is formed, most of the neutral interstellar particles are photoionized before reaching the stellar surface and are blown away by the wind. Especially, the accretion abundance of iron will be reduced by a factor of constraining the IMF of PopIII stars.

  20. Revisiting The First Galaxies: The Epoch of Population III Stars

    Science.gov (United States)

    Muratov, Alexander; Gnedin, O. Y.; Gnedin, N. Y.; Zemp, M. K.

    2013-01-01

    We study the formation of the first galaxies using new hydrodynamic cosmological simulations with the ART code. Our simulations feature a recently developed model for dust-based formation of molecular gas. Here, we develop and implement a new recipe for the formation of metal-free Pop III stars. We reach a spatial resolution of 2 pc at z=10 and resolve star-forming galaxies with the masses above 10^6 solar masses. We find the epoch during which Pop III stars dominate the energy and metal budget of the universe to be short-lived. While these stars seed their host galaxies with metals, they cannot drive significant outflows to enrich the IGM in our simulations. Feedback from pair instability supernovae causes Pop III star formation to self-terminate within their host galaxies, but is not strong enough to suppress star formation in external galaxies. Within any individual galaxy, Pop II stars overtake Pop III stars within ~50-150 Myr. A threshold of M = 3 * 10^6 solar masses separates galaxies that lose a significant fraction of their baryons due to Pop III feedback from those that do not. Understanding the nature of the transition between Pop III and Pop II star formation is of key importance for studying the dawn of galaxy formation.

  1. Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies

    Science.gov (United States)

    Lowenstein, Michael

    2013-01-01

    The amount of metals in the Intracluster Medium (ICM) in rich galaxy clusters exceeds that expected based on the observed stellar population by a large factor. We quantify this discrepancy--which we term the "cluster elemental abundance paradox"--and investigate the required properties of the ICM-enriching population. The necessary enhancement in metal enrichment may, in principle, originate in the observed stellar population if a larger fraction of stars in the supernova-progenitor mass range form from an initial mass function (IMF) that is either bottom-light or top-heavy, with the latter in some conflict with observed ICM abundance ratios. Other alternatives that imply more modest revisions to the IMF, mass return and remnant fractions, and primordial fraction, posit an increase in the fraction of 3-8 solar mass stars that explode as SNIa or assume that there are more stars than conventionally thought--although the latter implies a high star formation efficiency. We discuss the feasibility of these various solutions and the implications for the diversity of star formation, the process of elliptical galaxy formation, and the nature of this hidden source of ICM metal enrichment in light of recent evidence of an elliptical galaxy IMF that, because it is skewed to low masses, deepens the paradox.

  2. Development of Solvent Extraction Approach to Recycle Enriched Molybdenum Material

    Energy Technology Data Exchange (ETDEWEB)

    Tkac, Peter [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Brown, M. Alex [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Sen, Sujat [Argonne National Lab. (ANL), Argonne, IL (United States). Energy Systems Division; Bowers, Delbert L. [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Wardle, Kent [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Copple, Jacqueline M. [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Pupek, Krzysztof Z. [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Dzwiniel, Trevor L. [Argonne National Lab. (ANL), Argonne, IL (United States). Energy Systems Division; Pereira, Candido [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division; Krumdick, Gregory K. [Argonne National Lab. (ANL), Argonne, IL (United States). Energy Systems Division; Vandegrift, George F. [Argonne National Lab. (ANL), Argonne, IL (United States). Nuclear Engineering Division

    2016-06-01

    Argonne National Laboratory, in cooperation with Oak Ridge National Laboratory and NorthStar Medical Technologies, LLC, is developing a recycling process for a solution containing valuable Mo-100 or Mo-98 enriched material. Previously, Argonne had developed a recycle process using a precipitation technique. However, this process is labor intensive and can lead to production of large volumes of highly corrosive waste. This report discusses an alternative process to recover enriched Mo in the form of ammonium heptamolybdate by using solvent extraction. Small-scale experiments determined the optimal conditions for effective extraction of high Mo concentrations. Methods were developed for removal of ammonium chloride from the molybdenum product of the solvent extraction process. In large-scale experiments, very good purification from potassium and other elements was observed with very high recovery yields (~98%).

  3. Fluorine variations in the globular cluster NGC 6656 (M22): implications for internal enrichment timescales

    CERN Document Server

    D'Orazi, Valentina; Lugaro, Maria; Gratton, Raffaele G; Angelou, George; Bragaglia, Angela; Carretta, Eugenio; Alves-Brito, Alan; Ivans, Inese I; Masseron, Thomas; Mucciarelli, Alessio

    2012-01-01

    Observed chemical (anti)correlations in proton-capture elements among globular cluster stars are presently recognised as the signature of self-enrichment from now extinct, previous generations of stars. This defines the multiple population scenario. Since fluorine is also affected by proton captures, determining its abundance in globular clusters provides new and complementary clues regarding the nature of these previous generations, and supplies strong observational constraints to the chemical enrichment timescales. In this paper we present our results on near-infrared CRIRES spectroscopic observations of six cool giant stars in NGC 6656 (M22): the main objective is to derive the F content and its internal variation in this peculiar cluster, which exhibits significant changes in both light and heavy element abundances. We detected F variations across our sample beyond the measurement uncertainties and found that the F abundances are positively correlated with O and anticorrelated with Na, as expected accordi...

  4. Top Stars: An Opportunity for Educators

    Science.gov (United States)

    Kinnison, S. M. P.

    2010-08-01

    Think you're a Top Star? Want to find out what it takes? Learn about NASA's Top Stars contest and how you can participate. Throughout its lifetime, the Hubble Space Telescope has inspired and promoted education. The final Hubble servicing mission in May of this year and the celebration of Hubble's 20th anniversary in 2010 are key mission milestones, and both enrich activities for the 2009 International Year of Astronomy. U.S. formal (K-12 and college) and informal educators are invited to submit their best examples of using NASA's Hubble Space Telescope for science, technology, engineering or mathematics education. Those selected as Top Stars will receive national recognition and awards. Participants will learn about the contest, the recognition and awards, and how to register and save their entries on the Top Stars Web site. Educators are allowed and encouraged to revise, improve and re-submit their entries up to the final deadline of January 2, 2010. The contest is open to individuals and teams of up to four people who are U.S. citizens and are at least 21 years old. NASA and Institute for Global Environmental Strategies (IGES) employees or their contractors are not eligible. IGES is conducting Top Stars with NASA funding and in cooperation with the Space Telescope Science Institute.

  5. ENERGY STAR Certified Boilers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Boilers that are effective as of October 1,...

  6. ENERGY STAR Certified Furnaces

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 4.0 ENERGY STAR Program Requirements for Furnaces that are effective as of February 1,...

  7. ENERGY STAR Certified Computers

    Data.gov (United States)

    U.S. Environmental Protection Agency — Certified models meet all ENERGY STAR requirements as listed in the Version 6.1 ENERGY STAR Program Requirements for Computers that are effective as of June 2, 2014....

  8. Metal Enrichment of $Ly-\\alpha$ Clouds and Intergalactic Medium

    CERN Document Server

    Murakami, I; Murakami, Izumi; Yamashita, Kazuyuki

    1997-01-01

    We have examined the metal enrichment of the intergalactic medium (IGM) based on a galactic wind model. A galactic wind driven by supernovae brings metallic gas to the IGM but not so far beyond the gravitational potential. The expanding velocity of the outflow depends on the star formation timescale. Examining 3D calculation for the IGM in CDM model, we find that only 10 % region has metallicity larger than $10^{-2}Z_{\\odot}$ at $z=3$. Wide range of the IGM metallicity produces variety of CIV column densities for a fixed HI column density.

  9. Autonomous Star Tracker Algorithms

    DEFF Research Database (Denmark)

    Betto, Maurizio; Jørgensen, John Leif; Kilsgaard, Søren

    1998-01-01

    Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances.......Proposal, in response to an ESA R.f.P., to design algorithms for autonomous star tracker operations.The proposal also included the development of a star tracker breadboard to test the algorithms performances....

  10. Star operations and Pullbacks

    OpenAIRE

    Fontana, Marco; Park, Mi Hee

    2003-01-01

    In this paper we study the star operations on a pullback of integral domains. In particular, we characterize the star operations of a domain arising from a pullback of ``a general type'' by introducing new techniques for ``projecting'' and ``lifting'' star operations under surjective homomorphisms of integral domains. We study the transfer in a pullback (or with respect to a surjective homomorphism) of some relevant classes or distinguished properties of star operations such as $v-, t-, w-, b...

  11. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jian-Ying; Ibragimov, Rashid

    2013-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting ...

  12. Covering tree with stars

    DEFF Research Database (Denmark)

    Baumbach, Jan; Guo, Jiong; Ibragimov, Rashid

    2015-01-01

    We study the tree edit distance problem with edge deletions and edge insertions as edit operations. We reformulate a special case of this problem as Covering Tree with Stars (CTS): given a tree T and a set of stars, can we connect the stars in by adding edges between them such that the resulting ...

  13. Magnetism in massive stars

    NARCIS (Netherlands)

    Henrichs, H.F.

    2012-01-01

    Stars with mass more than 8 solar masses end their lives as neutron stars, which we mostly observe as highly magnetized objects. Where does this magnetic field come from? Such a field could be formed during the collapse, or is a (modified) remnant of a fossil field since the birth of the star, or ot

  14. Managing the star performer.

    Science.gov (United States)

    Hills, Laura

    2013-01-01

    Our culture seems to be endlessly fascinated with its stars in entertainment, athletics, politics, and business, and holds fast to the idea that extraordinary talent accounts for an individual's extraordinary performance. At first glance, managing a star performer in your medical practice may seem like it would be an easy task. However, there's much more to managing a star performer than many practice managers realize. The concern is how to keep the star performer happy and functioning at a high level without detriment to the rest of the medical practice team. This article offers tips for practice managers who manage star performers. It explores ways to keep the star performer motivated, while at the same time helping the star performer to meld into the existing medical practice team. This article suggests strategies for redefining the star performer's role, for holding the star performer accountable for his or her behavior, and for coaching the star performer. Finally, this article offers practical tips for keeping the star performer during trying times, for identifying and cultivating new star performers, and for managing medical practice prima donnas.

  15. America's Star Libraries

    Science.gov (United States)

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  16. America's Star Libraries

    Science.gov (United States)

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  17. To rescue a star

    OpenAIRE

    1996-01-01

    Massless neutrinos are exchanged in a neutron star, leading to long range interactions. Many body forces of this type follow and we resum them. Their net contribution to the total energy is negligible as compared to the star mass. The stability of the star is not in danger, contrary to recent assertions.

  18. Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. II. Statistical analysis of a sample of 67 CEMP-$s$ stars

    CERN Document Server

    Abate, C; Izzard, R G; Karakas, A I

    2015-01-01

    Many observed CEMP stars are found in binary systems and show enhanced abundances of $s$-elements. The origin of the chemical abundances of these CEMP-$s$ stars is believed to be accretion in the past of enriched material from a primary star in the AGB phase. We investigate the mechanism of mass transfer and the process of nucleosynthesis in low-metallicity AGB stars by modelling the binary systems in which the observed CEMP-$s$ stars were formed. For this purpose we compare a sample of $67$ CEMP-$s$ stars with a grid of binary stars generated by our binary evolution and nucleosynthesis model. We classify our sample CEMP-$s$ stars in three groups based on the observed abundance of europium. In CEMP$-s/r$ stars the europium-to-iron ratio is more than ten times higher than in the Sun, whereas it is lower than this threshold in CEMP$-s/nr$ stars. No measurement of europium is currently available for CEMP-$s/ur$ stars. On average our models reproduce well the abundances observed in CEMP-$s/nr$ stars, whereas in C...

  19. Chemical Enrichment and Physical Conditions in IZw18*

    Science.gov (United States)

    Lebouteiller, V.; Heap, S.; Hubeny, I.; Kunth, D.

    2013-01-01

    Low-metallicity star-forming dwarf galaxies are prime targets to understand the chemical enrichment of the interstellar medium. The H I region contains the bulk of the mass in blue compact dwarfs, and it provides important constraints on the dispersal and mixing of heavy elements released by successive star-formation episodes. The metallicity of the H I region is also a critical parameter to investigate the future star-formation history, as metals provide most of the gas cooling that will facilitate and sustain star formation. Aims. Our primary objective is to study the enrichment of the H I region and the interplay between star-formation history and metallicity evolution. Our secondary obje ctive is to constrain the spatial- and time-scales over which the HI and H II regions are enriched, and the mass range of stars responsible for the heavy element production. Finally, we aim to examine the gas heating and cooling mechanisms in the H I region. Methods. We observed the most metal-poor star-forming galaxy in the Local Universe, I Zw 18, with the Cosmic Origin Spectrograph onboard Hubble. The abundances in the neutral gas are derived from far-ultraviolet absorption-lines (H I, CIII, CIIi*, N I, OI,...) and are compared to the abundances in the H II region. Models are constructed to calculate the ionization structure and the thermal processes. We investigate the gas cooling in the HIi region through physical diagnostics drawn from the fine-structure level of C+. Results. We find that H I region abundances are lower by a factor of approx 2 as compared to the H II region. There is no differential depletion on dust between the H I and H II region. Using sulfur as a metallicity tracer, we calculate a metallicity of 1/46 Z(solar) (vs. 1/31 Z(solar) in the H II region). From the study of the C/O, [O/Fe], and N/O abundance ratios, we propose that C, N, O, and Fe are mainly produced in massive stars. We argue that the H I envelope may contain pockets of pristine gas with a

  20. The MaGICC Baryon Cycle: The Enrichment History of Simulated Disc Galaxies

    CERN Document Server

    Brook, C B; Gibson, B K; Shen, S; Macciò, A V; Wadsley, J; Quinn, T

    2013-01-01

    Using cosmological galaxy formation simulations from the MaGICC project, spanning more than three magnitudes in stellar mass (~10^7-3x10^{10} Msun), we trace the baryonic cycle of infalling gas from the virial radius through to its participation in the star formation process. An emphasis is placed upon the temporal history of chemical enrichment during its passage through the corona and CGM. We derive the distributions of time between gas crossing the virial radius and being accreted to the star forming region (which allows mixing within the corona), as well as the time between gas being accreted to the star forming region and then forming stars (which allows mixing within the disc). Significant numbers of stars are formed from gas that cycles back through the hot halo after first accreting to the star forming region. Gas entering high mass galaxies is pre-enriched in low mass proto-galaxies prior to entering the virial radius of the central progenitor, with only small amounts of primordial gas accreted, even...

  1. β decay of nuclei around 90Se: Search for signatures of a N=56 subshell closure relevant to the r process

    Science.gov (United States)

    Quinn, M.; Aprahamian, A.; Pereira, J.; Surman, R.; Arndt, O.; Baumann, T.; Becerril, A.; Elliot, T.; Estrade, A.; Galaviz, D.; Ginter, T.; Hausmann, M.; Hennrich, S.; Kessler, R.; Kratz, K.-L.; Lorusso, G.; Mantica, P. F.; Matos, M.; Montes, F.; Pfeiffer, B.; Portillo, M.; Schatz, H.; Schertz, F.; Schnorrenberger, L.; Smith, E.; Stolz, A.; Walters, W. B.; Wöhr, A.

    2012-03-01

    Background: Nuclear structure plays a significant role on the rapid neutron capture process (r process) since shapes evolve with the emergence of shells and subshells. There was some indication in neighboring nuclei that we might find examples of a new N=56 subshell, which may give rise to a doubly magic 3490Se56 nucleus.Purpose: β-decay half-lives of nuclei around 90Se have been measured to determine if this nucleus has in fact a doubly magic character.Method: The fragmentation of a 136Xe beam at the National Superconducting Cyclotron Laboratory at Michigan State University was used to create a cocktail of nuclei in the A=90 region.Results: We have measured the half-lives of 22 nuclei near the r-process path in the A=90 region. The half-lives of 88As and 90Se have been measured for the first time. The values were compared with theoretical predictions in the search for nuclear-deformation signatures of a N=56 subshell, and its possible role in the emergence of a potential doubly magic 90Se. The impact of such hypothesis on the synthesis of heavy nuclei, particularly in the production of Sr, Y, and Zr elements was investigated with a weak r-process network.Conclusions: The new half-lives agree with results obtained from a standard global QRPA model used in r-process calculations, indicating that 90Se has a quadrupole shape incompatible with a closed N=56 subshell in this region. The impact of the measured 90Se half-life in comparison with a former theoretical predication associated with a spherical half-life on the weak r process is shown to be strong.

  2. The Star Formation Histories of Disk and E/S0 Galaxies from Resolved Stars

    CERN Document Server

    Olsen, Knut A G; Saha, Abhijit; Skillman, Evan; Williams, Benjamin F; Wyse, Rosemary F G

    2009-01-01

    The resolved stellar populations of local galaxies, from which it is possible to derive complete star formation and chemical enrichment histories, provide an important way to study galaxy formation and evolution that is complementary to lookback time studies. We propose to use photometry of resolved stars to measure the star formation histories in a statistical sample of galaxy disks and E/S0 galaxies near their effective radii. These measurements would yield strong evidence to support critical questions regarding the formation of galactic disks and spheroids. The main technological limitation is spatial resolution for photometry in heavily crowded fields, for which we need improvement by a factor of ~10 over what is possible today with filled aperture telescopes.

  3. Enrichment of light hydrocarbon mixture

    Science.gov (United States)

    Yang; Dali; Devlin, David; Barbero, Robert S.; Carrera, Martin E.; Colling, Craig W.

    2010-08-10

    Light hydrocarbon enrichment is accomplished using a vertically oriented distillation column having a plurality of vertically oriented, nonselective micro/mesoporous hollow fibers. Vapor having, for example, both propylene and propane is sent upward through the distillation column in between the hollow fibers. Vapor exits neat the top of the column and is condensed to form a liquid phase that is directed back downward through the lumen of the hollow fibers. As vapor continues to ascend and liquid continues to countercurrently descend, the liquid at the bottom of the column becomes enriched in a higher boiling point, light hydrocarbon (propane, for example) and the vapor at the top becomes enriched in a lower boiling point light hydrocarbon (propylene, for example). The hollow fiber becomes wetted with liquid during the process.

  4. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2015-01-01

    Most elements are synthesized, or ""cooked"", by thermonuclear reactions in stars. The newly formed elements are released into the interstellar medium during a star's lifetime, and are subsequently incorporated into a new generation of stars, into the planets that form around the stars, and into the life forms that originate on the planets. Moreover, the energy we depend on for life originates from nuclear reactions that occur at the center of the Sun. Synthesis of the elements and nuclear energy production in stars are the topics of nuclear astrophysics, which is the subject of this book

  5. Magnetic chemically peculiar stars

    CERN Document Server

    Schöller, Markus

    2015-01-01

    Chemically peculiar (CP) stars are main-sequence A and B stars with abnormally strong or weak lines for certain elements. They generally have magnetic fields and all observables tend to vary with the same period. Chemically peculiar stars provide a wealth of information; they are natural atomic and magnetic laboratories. After a brief historical overview, we discuss the general properties of the magnetic fields in CP stars, describe the oblique rotator model, explain the dependence of the magnetic field strength on the rotation, and concentrate at the end on HgMn stars.

  6. 31 CFR 540.316 - Uranium enrichment.

    Science.gov (United States)

    2010-07-01

    ... 31 Money and Finance: Treasury 3 2010-07-01 2010-07-01 false Uranium enrichment. 540.316 Section... FOREIGN ASSETS CONTROL, DEPARTMENT OF THE TREASURY HIGHLY ENRICHED URANIUM (HEU) AGREEMENT ASSETS CONTROL REGULATIONS General Definitions § 540.316 Uranium enrichment. The term uranium enrichment means the process...

  7. Galactic chemical evolution: The role of the first stars

    CERN Document Server

    Cescutti, Gabriele

    2013-01-01

    The massive First Stars (the first ones to contribute to the chemical enrichment of the Universe due to their short lifetimes) are long dead, and even though efforts to directly observe them in high redshift galaxies are underway, a step forward in this field will have to wait for JWST and ELT. The only way to currently validate the picture arising from the most modern hydro-dynamical simulations of the formation of First Stars is to search for their imprints left on the oldest stars in our Galaxy. Which imprints are we looking for? In the last years our group has found that many chemical anomalies observed in very metal-poor halo stars, as well in the oldest bulge globular cluster, suggest the first stellar generations to have been fast rotators. After giving a brief overview of the aforementioned results, we highlight the impact of fast rotating metal-poor massive stars on the chemical enrichment of heavy-elements such as Sr and Ba. Indeed, in fast rotating massive stars the s-process production is boosted....

  8. ELEMENTAL ABUNDANCES AND THEIR IMPLICATIONS FOR THE CHEMICAL ENRICHMENT OF THE BOOeTES I ULTRAFAINT GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Gilmore, Gerard [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Norris, John E.; Yong, David [Research School of Astronomy and Astrophysics, The Australian National University, Weston, ACT 2611 (Australia); Monaco, Lorenzo [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19 (Chile); Wyse, Rosemary F. G. [Department of Physics and Astronomy, The Johns Hopkins University, 3900 North Charles Street, Baltimore, MD 21218 (United States); Geisler, D., E-mail: gil@ast.cam.ac.uk, E-mail: jen@mso.anu.edu.au, E-mail: yong@mso.anu.edu.au, E-mail: lmonaco@eso.org, E-mail: wyse@pha.jhu.edu, E-mail: dgeisler@astro-udec.cl [Departamento de Astronomia, Universidad de Concepcion (Chile)

    2013-01-20

    We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Booetes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from -3.7 to -1.9 and include a CEMP-no star with [Fe/H] = -3.33. We conclude from our chemical abundance data that Booetes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [{alpha}/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [{alpha}/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and 'carbon-normal'.

  9. THE FIRST STARS

    Directory of Open Access Journals (Sweden)

    Daniel J. Whalen

    2013-12-01

    Full Text Available Pop III stars are the key to the character of primeval galaxies, the first heavy elements, the onset of cosmological reionization, and the seeds of supermassive black holes. Unfortunately, in spite of their increasing sophistication, numerical models of Pop III star formation cannot yet predict the masses of the first stars. Because they also lie at the edge of the observable universe, individual Pop III stars will remain beyond the reach of observatories for decades to come, and so their properties are unknown. However, it will soon be possible to constrain their masses by direct detection of their supernovae, and by reconciling their nucleosynthetic yields to the chemical abundances measured in ancient metal-poor stars in the Galactic halo, some of which may bear the ashes of the first stars. Here, I review the state of the art in numerical simulations of primordial stars and attempts to directly and indirectly constrain their properties.

  10. Highly efficient star formation in NGC 5253 possibly from stream-fed accretion

    CERN Document Server

    Turner, J L; Benford, D J; Consiglio, S M; Ho, P T P; Kovács, A; Meier, D S; Zhao, J -H

    2015-01-01

    A local dwarf galaxy, NGC 5253, has a young super star cluster that may provide an example of highly efficient star formation. Here we report the detection and imaging, with the Submillimeter Array, of the J= 3-2 rotational transition of CO at the location of the massive cluster associated with the supernebula. The gas cloud is hot, dense, quiescent, and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by Wolf-Rayet stars within the embedded star cluster. Its star formation efficiency exceeds 50%, ten times higher than clouds in the Milky Way: this cloud is a factory of stars and soot. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.

  11. The elusive origin of Carbon-Enhanced Metal-Poor stars

    CERN Document Server

    Abate, C; Izzard, R G; Mohamed, S S; de Mink, S E

    2013-01-01

    Carbon-enhanced metal-poor (CEMP) stars count for 9-25% of all the very metal-poor stars of the halo. In at least some CEMP stars the chemical enrichment is believed to be due to wind mass transfer in the past from an AGB donor star on to a low-mass companion. However, binary population synthesis models predict much lower CEMP fractions. As an alternative to the canonical Bondi-Hoyle-Lyttleton (BHL) wind accretion model, recent hydrodynamical simulations suggest an efficient mode of wind mass transfer, called wind Roche-lobe overflow (WRLOF), can reproduce observations of AGB winds in binary systems. We use our population synthesis model to test the consequences of WRLOF on a population of CEMP stars. Compared to previous predictions based on the BHL model we find a modest increase of the fraction of CEMP stars and substantial differences in the distributions of carbon and periods in the population of CEMP stars.

  12. The interplay between chemical and mechanical feedback from the first generation of stars

    CERN Document Server

    Maio, Umberto; Johnson, Jarrett L; Ciardi, Benedetta

    2010-01-01

    We study cosmological simulations of early structure formation, including non-equilibrium molecular chemistry, metal pollution from stellar evolution, transition from population III (popIII) to population II (popII) star formation, regulated by a given critical metallicity, and feedback effects. We investigate the properties of early metal spreading from the different stellar populations and its interplay with primordial molecular gas. We find that, independently of the details about popIII modeling, after the onset of star formation, regions enriched below the critical level are mostly found in isolated environments, while popII star formation regions are much more clumped. Typical star forming haloes show average SN driven outflow rates of up to 10^{-4} Msun/yr in enriched gas, initially leaving the original star formation regions almost devoid of metals. The polluted material, which is gravitationally incorporated in over-dense environments on timescales of 10^7 yr, is mostly coming from external, nearby s...

  13. Late Pop III Star Formation During the Epoch of Reionization: Results from the Renaissance Simulations

    Science.gov (United States)

    Xu, Hao; Norman, Michael L.; O'Shea, Brian W.; Wise, John H.

    2016-06-01

    We present results on the formation of Population III (Pop III) stars at redshift 7.6 from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich radiation transport hydrodynamics cosmological adaptive-mesh refinement simulations of high-redshift galaxy formation performed on the Blue Waters supercomputer. In a survey volume of about 220 comoving Mpc3, we found 14 Pop III galaxies with recent star formation. The surprisingly late formation of Pop III stars is possible due to two factors: (i) the metal enrichment process is local and slow, leaving plenty of pristine gas to exist in the vast volume; and (ii) strong Lyman-Werner radiation from vigorous metal-enriched star formation in early galaxies suppresses Pop III formation in (“not so”) small primordial halos with mass less than ˜3 × 107 M ⊙. We quantify the properties of these Pop III galaxies and their Pop III star formation environments. We look for analogs to the recently discovered luminous Ly α emitter CR7, which has been interpreted as a Pop III star cluster within or near a metal-enriched star-forming galaxy. We find and discuss a system similar to this in some respects, however, the Pop III star cluster is far less massive and luminous than CR7 is inferred to be.

  14. Early type stars at high galactic latitudes II. Four evolved B-type stars of unusual chemical composition

    CERN Document Server

    Ramspeck, M; Edelmann, H

    2001-01-01

    We present the result of differential spectral analyses of a further four apparently normal B-type stars. Abundance anomalies (e.g. He, C, N enrichment), slow rotation and/or high gravities suggest that the programme stars are evolved low-mass B-type stars. In order to trace their evolutionary status several scenarios are discussed. Post-AGB evolution can be ruled out. PG 0229+064 and PG 1400+389 could be horizontal branch (HB) stars, while HD 76431 and SB 939 have already evolved away from the extreme HB (EHB). The low helium abundance of HD 76431 is consistent with post-EHB evolution. The enrichment in helium, carbon and nitrogen of the remaining stars can be explained either by deep mixing of nuclearly processed material to the surface or by diffusion processes modified by magnetic fields and/or stellar winds. A kinematic study of their galactic orbits indicates that the stars belong to an old disk population.

  15. The Fate of the Compact Remnant in Neutron Star Mergers

    CERN Document Server

    Fryer, Chris L; Ramirez-Ruiz, Enrico; Rosswog, Stephan; Shen, Gang; Steiner, Andrew W

    2015-01-01

    Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of merger calculations and equation of state studies to determine the fate of the cores of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3-2.4 solar masses. If quick black hole formation is essential in producing gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constr...

  16. DETAILED ABUNDANCES OF TWO VERY METAL-POOR STARS IN DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Kirby, Evan N.; Cohen, Judith G. [Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125 (United States)

    2012-12-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[{alpha}/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at -3 < [Fe/H] < -2 sample SNe with [Fe/H] << -3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] {approx} -3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo.

  17. Detailed Abundances of Two Very Metal-poor Stars in Dwarf Galaxies

    Science.gov (United States)

    Kirby, Evan N.; Cohen, Judith G.

    2012-12-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[α/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at -3 < [Fe/H] < -2 sample SNe with [Fe/H] Lt -3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] ~ -3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo. Data herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  18. Nematode Indicators of Organic Enrichment

    NARCIS (Netherlands)

    Ferris, H.; Bongers, A.M.T.

    2006-01-01

    The organisms of the soil food web, dependent on resources from plants or on amendment from other sources, respond characteristically to enrichment of their environment by organic matter. Primary consumers of the incoming substrate, including bacteria, fungi, plant-feeding nematodes, annelids, and

  19. Nematode Indicators of Organic Enrichment

    NARCIS (Netherlands)

    Ferris, H.; Bongers, A.M.T.

    2006-01-01

    The organisms of the soil food web, dependent on resources from plants or on amendment from other sources, respond characteristically to enrichment of their environment by organic matter. Primary consumers of the incoming substrate, including bacteria, fungi, plant-feeding nematodes, annelids, and s

  20. On the Likelihood of Supernova Enrichment of Protoplanetary Disks

    Science.gov (United States)

    Williams, Jonathan P.; Gaidos, Eric

    2007-07-01

    We estimate the likelihood of direct injection of supernova ejecta into protoplanetary disks using a model in which the number of stars with disks decreases linearly with time, and clusters expand linearly with time such that their surface density is independent of stellar number. The similarity of disk dissipation and main-sequence lifetimes implies that the typical supernova progenitor is very massive, ~75-100 Msolar. Such massive stars are found only in clusters with >~104 members. Moreover, there is only a small region around a supernova within which disks can survive the blast yet be enriched to the level observed in the solar system. These two factors limit the overall likelihood of supernova enrichment of a protoplanetary disk to radionucleides in meteorites is to be explained in this way, however, the solar system most likely formed in one of the largest clusters in the Galaxy, more than 2 orders of magnitude greater than Orion, where multiple supernovae impacted many disks in a short period of time.

  1. On the likelihood of supernova enrichment of protoplanetary disks

    CERN Document Server

    Williams, Jonathan P

    2007-01-01

    We estimate the likelihood of direct injection of supernova ejecta into protoplanetary disks using a model in which the number of stars with disks decreases linearly with time, and clusters expand linearly with time such that their surface density is independent of stellar number. The similarity of disk dissipation and main sequence lifetimes implies that the typical supernova progenitor is very massive, ~ 75-100 Msun. Such massive stars are found only in clusters with > 10^4 members. Moreover, there is only a small region around a supernova within which disks can survive the blast yet be enriched to the level observed in the Solar System. These two factors limit the overall likelihood of supernova enrichment of a protoplanetary disk to < 1%. If the presence of short lived radionucleides in meteorites is to be explained in this way, however, the Solar System most likely formed in one of the largest clusters in the Galaxy, more than two orders of magnitude greater than Orion, where multiple supernovae impac...

  2. Multiplicity of massive stars

    CERN Document Server

    Preibisch, T; Zinnecker, H; Preibisch, Thomas; Weigelt, Gerd; Zinnecker, Hans

    2000-01-01

    We discuss the observed multiplicity of massive stars and implications on theories of massive star formation. After a short summary of the literature on massive star multiplicity, we focus on the O- and B-type stars in the Orion Nebula Cluster, which constitute a homogenous sample of very young massive stars. 13 of these stars have recently been the targets of a bispectrum speckle interferometry survey for companions. Considering the visual and also the known spectroscopic companions of these stars, the total number of companions is at least 14. Extrapolation with correction for the unresolved systems suggests that there are at least 1.5 and perhaps as much as 4 companions per primary star on average. This number is clearly higher than the mean number of about 0.5 companions per primary star found for the low-mass stars in the general field population and also in the Orion Nebula cluster. This suggests that a different mechanism is at work in the formation of high-mass multiple systems in the dense Orion Nebu...

  3. Star Clusters within FIRE

    Science.gov (United States)

    Perez, Adrianna; Moreno, Jorge; Naiman, Jill; Ramirez-Ruiz, Enrico; Hopkins, Philip F.

    2017-01-01

    In this work, we analyze the environments surrounding star clusters of simulated merging galaxies. Our framework employs Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high resolution cosmological simulation that resolves star forming regions and incorporates stellar feedback in a physically realistic way. The project focuses on analyzing the properties of the star clusters formed in merging galaxies. The locations of these star clusters are identified with astrodendro.py, a publicly available dendrogram algorithm. Once star cluster properties are extracted, they will be used to create a sub-grid (smaller than the resolution scale of FIRE) of gas confinement in these clusters. Then, we can examine how the star clusters interact with these available gas reservoirs (either by accreting this mass or blowing it out via feedback), which will determine many properties of the cluster (star formation history, compact object accretion, etc). These simulations will further our understanding of star formation within stellar clusters during galaxy evolution. In the future, we aim to enhance sub-grid prescriptions for feedback specific to processes within star clusters; such as, interaction with stellar winds and gas accretion onto black holes and neutron stars.

  4. Dark stars: a review.

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  5. Dark stars: a review

    Science.gov (United States)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  6. Star-Branched Polymers (Star Polymers)

    KAUST Repository

    Hirao, Akira

    2015-09-01

    The synthesis of well-defined regular and asymmetric mixed arm (hereinafter miktoarm) star-branched polymers by the living anionic polymerization is reviewed in this chapter. In particular, much attention is being devoted to the synthetic development of miktoarm star polymers since 2000. At the present time, the almost all types of multiarmed and multicomponent miktoarm star polymers have become feasible by using recently developed iterative strategy. For example, the following well-defined stars have been successfully synthesized: 3-arm ABC, 4-arm ABCD, 5-arm ABCDE, 6-arm ABCDEF, 7-arm ABCDEFG, 6-arm ABC, 9-arm ABC, 12-arm ABC, 13-arm ABCD, 9-arm AB, 17-arm AB, 33-arm AB, 7-arm ABC, 15-arm ABCD, and 31-arm ABCDE miktoarm star polymers, most of which are quite new and difficult to synthesize by the end of the 1990s. Several new specialty functional star polymers composed of vinyl polymer segments and rigid rodlike poly(acetylene) arms, helical polypeptide, or helical poly(hexyl isocyanate) arms are introduced.

  7. Touchstone Stars: Highlights from the Cool Stars 18 Splinter Session

    CERN Document Server

    Mann, Andrew W; Boyajian, Tabetha; Gaidos, Eric; von Braun, Kaspar; Feiden, Gregory A; Metcalfe, Travis; Swift, Jonathan J; Curtis, Jason L; Deacon, Niall R; Filippazzo, Joseph C; Gillen, Ed; Hejazi, Neda; Newton, Elisabeth R

    2014-01-01

    We present a summary of the splinter session on "touchstone stars" -- stars with directly measured parameters -- that was organized as part of the Cool Stars 18 conference. We discuss several methods to precisely determine cool star properties such as masses and radii from eclipsing binaries, and radii and effective temperatures from interferometry. We highlight recent results in identifying and measuring parameters for touchstone stars, and ongoing efforts to use touchstone stars to determine parameters for other stars. We conclude by comparing the results of touchstone stars with cool star models, noting some unusual patterns in the differences.

  8. SPECTROSCOPIC ANALYSIS OF METAL-POOR STARS FROM LAMOST: EARLY RESULTS

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hai-Ning; Zhao, Gang; Wang, Liang; Wang, Wei; Yuan, Hailong [Key Lab of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang, Beijing 100012 (China); Christlieb, Norbert [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Zhang, Yong; Hou, Yonghui, E-mail: lhn@nao.cas.cn, E-mail: gzhao@nao.cas.cn [Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042 (China)

    2015-01-10

    We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.

  9. Evolution of long-lived globular cluster stars III. Effect of the initial helium spread on the position of stars in a synthetic Hertzsprung-Russel diagram

    CERN Document Server

    Chantereau, William; Meynet, Georges

    2016-01-01

    Context. Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. Aims. We present the distribution of helium-rich stars in present-day globular clusters as it is expected in the original framework of the fast-rotating massive stars scenario (FRMS) as first-population polluters. We focus on NGC 6752. (to be continued)

  10. External Shaping of Circumstellar Envelopes of Evolved Stars

    Science.gov (United States)

    Cox, N. L. J.

    2015-08-01

    The circumstellar envelopes of asymptotic giant branch (AGB) stars and red supergiants (RSGs) are complex chemical and physical environments, and the specifics of their mass-loss history are important for both stellar and galactic evolution. One key aspect in this is to understand how the circumstellar medium of these stars can be shaped and affected by both internal and external mechanisms. These influences can skew our view on the (dust) chemistry and mass-loss history of these stars, and hence their role in the chemical enrichment of galaxies. This contribution focuses on the external mechanism related to the interaction between the slow dusty stellar wind and the local ambient medium. I will discuss what recent observations and hydrodynamical simulations have revealed and how these can help us learn more about AGB stars and RSGs, as well as the interstellar medium (ISM).

  11. Gravity Assist and Scattering off AGB Stars off Molecular Clouds

    Directory of Open Access Journals (Sweden)

    Ahmad H. Abdelhadi

    2009-01-01

    Full Text Available The scattering of stellar orbits by galactic molecular clouds is studied in hope of explaining isotopic peculiarities of presolar grains from Asymptotic Giant Branch (AGB stars. Silicon isotopic anomalies found in the mainstream Silicon Carbide (SiC grains are observed to have heavy isotopes enriched. To explain the isotopic heaviness I propose that AGB stars that formed in the interior region of the galaxy, with metallicity higher than solar, change their orbits during close encounters with molecular clouds. The AGB stars give up their SiC grains in winds deposited in the solar neighborhood prior to the birth of the Sun. I model the dynamics by superposing on a standard axisymmetric galactic potential the discrete potentials of thousands of molecular clouds moving in constant circular orbits. Gravity assist occurs when a star scattered into a crossing orbit by one cloud experiences forward scattering from a second cloud.

  12. LANL/Green Star spectrometer tests

    Energy Technology Data Exchange (ETDEWEB)

    Sampson, T.E.; Cremers, T.L.; Vo, D.T. [Los Alamos National Lab., NM (United States); Seldiakov, Y.P.; Dorin, A.B.; Kondrashov, M.V. [Green Star, Moscow (Russian Federation); Timoshin, V.I. [VNIINM, Moscow (Russian Federation)

    1997-12-01

    The US and Russia have agreed to the joint development of a nondestructive assay system for use to support the dismantlement of nuclear weapons in Russia. This nondestructive assay system will be used to measure plutonium produced by the conversion of Russian nuclear weapons. The NDA system for Russia will be patterned after the ARIES NDA system being constructed at Los Alamos. One goal of the program is to produce an NDA system for use in Russia that maximizes the use of Russian resources to facilitate maintenance and future upgrades. The Green Star SBS50 Single Board Spectrometer system (Green Star Ltd., Moscow, Russia) has been suggested for use as the data acquisition component for gamma ray instruments in the system. Possible uses are for plutonium isotopic analysis and also segmented gamma scanning. Green Star has also developed analysis software for the SBS50. This software, both plutonium isotopic analysis and uranium enrichment analysis, was developed specifically for customs/border inspection applications (low counting rate applications and identification as opposed to quantification) and was not intended for MC and A applications. Because of the relative immaturity of the Green Star plutonium isotopic analysis software (it has been under development for only one year and is patterned after US development circa 1980), it was tentatively agreed, before the tests, that the Russian NDA system would use the Los Alamos PC/FRAM software for plutonium isotopic analysis. However, it was also decided to include the Green Star plutonium isotopic software in the testing, both to quantify its performance for MC and A applications and also to provide additional data to Green Star for further development of their software. The main purpose of the testing was to evaluate the SBS-50 spectrometer as a data acquisition device for use with LANL software.

  13. Outflows from neutron star merger remnant disks: nucleosynthesis and kilonovae

    Science.gov (United States)

    Fernandez, Rodrigo; Lippuner, Jonas; Roberts, Luke; Tchekhovskoy, Alexander; Foucart, Francois; Metzger, Brian; Kasen, Daniel; Quataert, Eliot

    2016-03-01

    The accretion disk formed in a neutron star merger can drive powerful winds on timescales of 100ms to seconds after coalescence. The wind material is more strongly irradiated by neutrinos than the dynamical ejecta, and hence has a less neutron-rich composition, with implications for r-process element synthesis and the radioactively-powered kilonova transient. This talk will present preliminary results from projects aimed at quantifying (1) the nucleosynthesis yield from disks around hypermassive neutron stars, (2) the effect of MHD turbulence on mass ejection when a black hole sits at the center, and (3) the interaction between disk wind and dynamical ejecta when the relative masses of these components vary.

  14. Interaction of massive stars with their surroundings

    CERN Document Server

    Hensler, Gerhard

    2008-01-01

    Due to their short lifetimes but their enormous energy release in all stages of their lives massive stars are the major engines for the comic matter circuit. They affect not only their close environment but are also responsible to drive mass flows on galactic scales. Recent 2D models of radiation-driven and wind-blown HII regions are summarized which explore the impact of massive stars to the interstellar medium but find surprisingly small energy transfer efficiencies while an observable Carbon self-enrichment in the Wolf-Rayet phase is detected in the warm ionized gas. Finally, the focus is set on state-of-the-art modelling of HII regions and its present weaknesses with respect to uncertainties and simplifications but on a perspective of the requested art of their modelling in the 21st century.

  15. STAR in CTO PCI: When is STAR not a star?

    Science.gov (United States)

    Hira, Ravi S; Dean, Larry S

    2016-04-01

    Subintimal tracking and reentry (STAR) has been used as a bailout strategy and involves an uncontrolled dissection and recanalization into the distal lumen to reestablish vessel patency. In the current study, thrombolysis in myocardial infarction (TIMI) flow < 3 was the only variable which they found to be significantly associated with restenosis and reocclusion after stent placement. It may be reasonable to consider second generation drug eluting stent placement in patients receiving STAR that have TIMI 3 flow, however, this should only be done if there is no compromise of major side branches. If unsure, we recommend to perform balloon angioplasty without stenting. © 2016 Wiley Periodicals, Inc.

  16. Chemical abundances and kinematics of barium stars

    CERN Document Server

    de Castro, D B; Roig, F; Jilinski, E; Drake, N A; Chavero, C; Silva, J V Sales

    2016-01-01

    In this paper we present an homogeneous analysis of photospheric abundances based on high-resolution spectroscopy of a sample of 182 barium stars and candidates. We determined atmospheric parameters, spectroscopic distances, stellar masses, ages, luminosities and scale height, radial velocities, abundances of the Na, Al, $alpha$-elements, iron-peak elements, and s-process elements Y, Zr, La, Ce, and Nd. We employed the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code {\\sc moog}. We found that the metallicities, the temperatures and the surface gravities for barium stars can not be represented by a single gaussian distribution. The abundances of $alpha$-elements and iron peak elements are similar to those of field giants with the same metallicity. Sodium presents some degree of enrichment in more evolved stars that could be attributed to the NeNa cycle. As expected, the barium stars show overabundance of the elements created by the s-process. By measuring the mean heav...

  17. Massive Star Clusters in Dwarf Galaxies

    CERN Document Server

    Larsen, Soeren S

    2015-01-01

    Dwarf galaxies can have very high globular cluster specific frequencies, and the GCs are in general significantly more metal-poor than the bulk of the field stars. In some dwarfs, such as Fornax, WLM, and IKN, the fraction of metal-poor stars that belong to GCs can be as high as 20%-25%, an order of magnitude higher than the 1%-2% typical of GCs in halos of larger galaxies. Given that chemical abundance anomalies appear to be present also in GCs in dwarf galaxies, this implies severe difficulties for self-enrichment scenarios that require GCs to have lost a large fraction of their initial masses. More generally, the number of metal-poor field stars in these galaxies is today less than what would originally have been present in the form of low-mass clusters if the initial cluster mass function was a power-law extending down to low masses. This may imply that the initial GC mass function in these dwarf galaxies was significantly more top-heavy than typically observed in present-day star forming environments.

  18. The First Stars

    Science.gov (United States)

    Yoshida, Naoki

    2010-10-01

    The standard cosmological model predicts that the first cosmological objects are formed when the age of the universe is a few hundred million years. Recent theoretical studies and numerical simulations consistently suggest that the first objects are very massive primordial stars. We introduce the key physics and explain why the first stars are thought to be massive, rather than to be low-mass stars. The state-of-the-art simulations include all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to very high ``stellar'' densities. Evolutionary calculations of the primordial stars suggest the formation of massive blackholes in the early universe. Finally, we show the results from high-resolution simulations of star formation in a low-metallicity gas. Vigorous fragmentation is triggered in a star-forming gas cloud at a metallicity of as low as Z = 10-5Zsolar.

  19. Implication of the Steady State Equilibrium Condition for Electron-Positron Gas in the Neutrino-driven Wind from Proto-Neutron Star

    CERN Document Server

    Liu, Men-Quan

    2010-01-01

    Based on the steady state equilibrium condition for neutron-proton-electron-positron gas in the neutrino-driven wind from protoneutron star, we estimate the initial electron fraction in the wind in a simple and effective way. We find that the condition in the wind might be propriate for the r-process nucleosynthesis.

  20. Strange nonchaotic stars

    CERN Document Server

    Lindner, John F; Kia, Behnam; Hippke, Michael; Learned, John G; Ditto, William L

    2015-01-01

    The unprecedented light curves of the Kepler space telescope document how the brightness of some stars pulsates at primary and secondary frequencies whose ratios are near the golden mean, the most irrational number. A nonlinear dynamical system driven by an irrational ratio of frequencies generically exhibits a strange but nonchaotic attractor. For Kepler's "golden" stars, we present evidence of the first observation of strange nonchaotic dynamics in nature outside the laboratory. This discovery could aid the classification and detailed modeling of variable stars.

  1. Interacting binary stars

    CERN Document Server

    Sahade, Jorge; Ter Haar, D

    1978-01-01

    Interacting Binary Stars deals with the development, ideas, and problems in the study of interacting binary stars. The book consolidates the information that is scattered over many publications and papers and gives an account of important discoveries with relevant historical background. Chapters are devoted to the presentation and discussion of the different facets of the field, such as historical account of the development in the field of study of binary stars; the Roche equipotential surfaces; methods and techniques in space astronomy; and enumeration of binary star systems that are studied

  2. ENERGY STAR Unit Reports

    Data.gov (United States)

    Department of Housing and Urban Development — These quarterly Federal Fiscal Year performance reports track the ENERGY STAR qualified HOME units that Participating Jurisdictions record in HUD's Integrated...

  3. Strange Nonchaotic Stars

    Science.gov (United States)

    Lindner, John F.; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G.; Ditto, William L.

    2015-08-01

    Exploiting the unprecedented capabilities of the planet-hunting Kepler space telescope, which stared at 150 000 stars for four years, we discuss recent evidence that certain stars dim and brighten in complex patterns with fractal features. Such stars pulsate at primary and secondary frequencies whose ratios are near the famous golden mean, the most irrational number. A nonlinear system driven by an irrational ratio of frequencies is generically attracted toward a “strange” behavior that is geometrically fractal without displaying the “butterfly effect” of chaos. Strange nonchaotic attractors have been observed in laboratory experiments and have been hypothesized to describe the electrochemical activity of the brain, but a bluish white star 16 000 light years from Earth in the constellation Lyra may manifest, in the scale-free distribution of its minor frequency components, the first strange nonchaotic attractor observed in the wild. The recognition of stellar strange nonchaotic dynamics may improve the classification of these stars and refine the physical modeling of their interiors. We also discuss nonlinear analysis of other RR Lyrae stars in Kepler field of view and discuss some toy models for modeling these stars.References: 1) Hippke, Michael, et al. "Pulsation period variations in the RRc Lyrae star KIC 5520878." The Astrophysical Journal 798.1 (2015): 42.2) Lindner, John F., et al. "Strange nonchaotic stars." Phys. Rev. Lett. 114, 054101 (2015)

  4. Heavy elements and chemical enrichment in globular clusters

    CERN Document Server

    James, G; Bonifacio, P; Carretta, E; Gratton, R G; Spite, F

    2004-01-01

    High resolution (R > 40 000) and high S/N spectra have been acquired with UVES on the VLT-Kueyen (Paranal Observatory, ESO Chile) for several main sequence turnoff stars (V ~ 17 mag) and subgiants at the base of the Red Giant Branch (V ~ 16 mag) in three globular clusters (NGC 6397, NGC 6752 and 47 Tuc/NGC 104) at different metallicities (respectively [Fe/H] = -2.0; -1.5; -0.7$). Spectra for a sample of 25 field halo subdwarves have also been taken with equal resolution, but higher S/N. These data have been used to determine the abundances of several neutron-capture elements in these three clusters: strontium, yttrium, barium and europium. This is the first abundance determination of these heavy elements for such unevolved stars in these three globular clusters. These values, together with the [Ba/Eu] and [Sr/Ba] abundance ratios, have been used to test the self-enrichment scenario. A comparison is done with field halo stars and other well known Galactic globular clusters in which heavy elements have already ...

  5. Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

    CERN Document Server

    Abate, C; Stancliffe, R J; Izzard, R G; Karakas, A I; Beers, T C; Lee, Y S

    2015-01-01

    The stellar population in the Galactic halo is characterised by a large fraction of CEMP stars. Most CEMP stars are enriched in $s$-elements (CEMP-$s$ stars), and some of these are also enriched in $r$-elements (CEMP-$s/r$ stars). One formation scenario proposed for CEMP stars invokes wind mass transfer in the past from a TP-AGB primary star to a less massive companion star which is presently observed. We generate low-metallicity populations of binary stars to reproduce the observed CEMP-star fraction. In addition, we aim to constrain our wind mass-transfer model and investigate under which conditions our synthetic populations reproduce observed abundance distributions. We compare the CEMP fractions and the abundance distributions determined from our synthetic populations with observations. Several physical parameters of the binary stellar population of the halo are uncertain, e.g. the initial mass function, the mass-ratio and orbital-period distributions, and the binary fraction. We vary the assumptions in o...

  6. Horizontal Branch stars as AmFm/HgMn stars

    CERN Document Server

    Michaud, G

    2008-01-01

    Recent observations and models for horizontal branch stars are briefly described and compared to models for AmFm stars. The limitations of those models are emphasized by a comparison to observations and models for HgMn stars.

  7. Low-metallicity Star Formation (IAU S255)

    Science.gov (United States)

    Hunt, Leslie K.; Madden, Suzanne C.; Schneider, Raffaella

    2009-01-01

    Preface; SOC and LOC; Participants; Life at the conference; Conference photo; Session I. Population III and Metal-Free Star Formation: 1. Open questions in the study of population III star formation S. C. O. Glover, P. C. Clark, T. H. Greif, J. L. Johnson, V. Bromm, R. S. Klessen and A. Stacy; 2. Protostar formation in the early universe Naoki Yoshida; 3. Population III.1 stars: formation, feedback and evolution of the IMF Jonathan C. Tan; 4. The formation of the first galaxies and the transition to low-mass star formation T. H. Greif, D. R. G. Schleicher, J. L. Johnson, A.-K. Jappsen, R. S. Klessen, P. C. Clark, S. C. O. Glover, A. Stacy and V. Bromm; 5. Low-metallicity star formation: the characteristic mass and upper mass limit Kazuyuki Omukai; 6. Dark stars: dark matter in the first stars leads to a new phase of stellar evolution Katherine Freese, Douglas Spolyar, Anthony Aguirre, Peter Bodenheimer, Paolo Gondolo, J. A. Sellwood and Naoki Yoshida; 7. Effects of dark matter annihilation on the first stars F. Iocco, A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara and P. Marigo; 8. Searching for Pop III stars and galaxies at high redshift Daniel Schaerer; 9. The search for population III stars Sperello di Serego Alighieri, Jaron Kurk, Benedetta Ciardi, Andrea Cimatti, Emanuele Daddi and Andrea Ferrara; 10. Observational search for population III stars in high-redshift galaxies Tohru Nagao; Session II. Metal Enrichment, Chemical Evolution, and Feedback: 11. Cosmic metal enrichment Andrea Ferrara; 12. Insights into the origin of the galaxy mass-metallicity relation Henry Lee, Eric F. Bell and Rachel S. Somerville; 13. LSD and AMAZE: the mass-metallicity relation at z > 3 F. Mannucci and R. Maiolino; 14. Three modes of metal-enriched star formation at high redshift Britton D. Smith, Matthew J. Turk, Steinn Sigurdsson, Brian W. O'Shea and Michael L. Norman; 15. Primordial supernovae and the assembly of the first galaxies Daniel Whalen, Bob Van Veelen, Brian W. O

  8. Enrichment of lanthanides in aragonite

    Institute of Scientific and Technical Information of China (English)

    瞿成利; 路波; 刘刚

    2009-01-01

    Using the constant addition technique,the coprecipitation of lanthanum,gadolinium,and lutetium with aragonite in seawater was experimentally investigated at 25 ℃.Their concentrations in aragonite overgrowths were determined by inductive coupled plasma mass spectrometer.All these lanthanides were strongly enriched in aragonite overgrowths.The amount of lanthanum,gadolinium,and lutetium incorporated into aragonite accounted for 57%-99%,50%-89%,and 40%-91% of their initial total amount,respectively.With the in...

  9. Enrichment and aggression in primates.

    Science.gov (United States)

    Honess, P E; Marin, C M

    2006-01-01

    There is considerable evidence that primates housed under impoverished conditions develop behavioural abnormalities, including, in the most extreme example, self-harming behaviour. This has implications for all contexts in which primates are maintained in captivity from laboratories to zoos since by compromising the animals' psychological well-being and allowing them to develop behavioural abnormalities their value as appropriate educational and research models is diminished. This review examines the extensive body of literature documenting attempts to improve living conditions with a view to correcting behavioural abnormalities and housing primates in such a way that they are encouraged to exhibit a more natural range and proportion of behaviours, including less self-directed and social aggression. The results of housing, feeding, physical, sensory and social enrichment efforts are examined with specific focus on their effect on aggressive behaviour and variation in their use and efficacy. It is concluded that while inappropriate or poorly distributed enrichment may encourage aggressive competition, enrichment that is species, sex, age and background appropriate can dramatically reduce aggression, can eliminate abnormal behaviour and substantially improve the welfare of primates maintained in captivity.

  10. Segue 1 - A Compressed Star Formation History Before Reionization

    CERN Document Server

    Webster, David; Bland-Hawthorn, Joss

    2015-01-01

    Segue 1 is the current best candidate for a "first galaxy", a system which experienced only a single short burst of star formation and has since remained unchanged. Here we present possible star formation scenarios which can explain its unique metallicity distribution. While the majority of stars in all other ultra-faint dwarfs (UFDs) are within 0.5 dex of the mean [Fe/H] for the galaxy, 5 of the 7 stars in Segue 1 have a spread of $\\Delta$[Fe/H] $>0.8$ dex. We show that this distribution of metallicities canot be explained by a gradual build-up of stars, but instead requires clustered star formation. Chemical tagging allows the separate unresolved delta functions in abundance space to be associated with discrete events in space and time. This provides an opportunity to put the enrichment events into a time sequence and unravel the history of the system. We investigate two possible scenarios for the star formation history of Segue 1 using Fyris Alpha simulations of gas in a $10^7$ M$_\\odot$ dark matter halo. ...

  11. Extent of pollution in planet-bearing stars

    CERN Document Server

    Li, S -L; Liu, X -W

    2008-01-01

    (abridged) Search for planets around main-sequence (MS) stars more massive than the Sun is hindered by their hot and rapidly spinning atmospheres. This obstacle has been sidestepped by radial-velocity surveys of those stars on their post-MS evolutionary track (G sub-giant and giant stars). Preliminary observational findings suggest a deficiency of short-period hot Jupiters around the observed post MS stars, although the total fraction of them with known planets appears to increase with their mass. Here we consider the possibility that some very close- in gas giants or a population of rocky planets may have either undergone orbital decay or been engulfed by the expanding envelope of their intermediate-mass host stars. If such events occur during or shortly after those stars' main sequence evolution when their convection zone remains relatively shallow, their surface metallicity can be significantly enhanced by the consumption of one or more gas giants. We show that stars with enriched veneer and lower-metallic...

  12. Population III Stars and Remnants in High Redshift Galaxies

    CERN Document Server

    Xu, Hao; Norman, Michael L

    2013-01-01

    Recent simulations of Population III star formation have suggested that some fraction form in binary systems, in addition to having a characteristic mass of tens of solar masses. The deaths of metal-free stars result in the initial chemical enrichment of the universe and the production of the first stellar-mass black holes. Here we present a cosmological adaptive mesh refinement simulation of an overdense region that forms a few 10^9 Msun dark matter halos and over 13,000 Population III stars by redshift 15. We find that most halos do not form Population III stars until they reach Mvir ~ 10^7 Msun because this biased region is quickly enriched from both Population III and galaxies, which also produce high levels of ultraviolet radiation that suppress H2 formation. Nevertheless, Population III stars continue to form, albeit in more massive halos, at a rate of ~ 10^{-4} Msun yr^{-1} Mpc^{-3} at redshift 15. The most massive starless halo has a mass of 7 x 10^7 Msun, which could host massive black hole formation...

  13. A super lithium-rich red-clump star in the open cluster Trumpler 5

    Science.gov (United States)

    Monaco, L.; Boffin, H. M. J.; Bonifacio, P.; Villanova, S.; Carraro, G.; Caffau, E.; Steffen, M.; Ahumada, J. A.; Beletsky, Y.; Beccari, G.

    2014-04-01

    Context. The existence of lithium-rich low-mass red giant stars still represents a challenge for stellar evolution models. Stellar clusters are privileged environments for this kind of investigation. Aims: To investigate the chemical abundance pattern of the old open cluster Trumpler 5, we observed a sample of four red-clump stars with high-resolution optical spectrographs. One of them (#3416) reveals extremely strong lithium lines in its spectrum. Methods: One-dimensional, local thermodynamic equilibrium analysis was performed on the spectra of the observed stars. A 3D-NLTE analysis was performed to derive the lithium abundance of star #3416. Results: Star #3416 is super Li-rich with A(Li) = 3.75 dex. The lack of 6Li enrichment (6Li/7Li Cameron & Fowler mechanism. Conclusions: We identified a super Li-rich core helium-burning, red-clump star in an open cluster. Internal production is the most likely cause of the observed enrichment. Given the expected short duration of a star's Li-rich phase, enrichment is likely to have occurred at the red clump or in the immediately preceding phases, namely during the He-flash at the tip of the red giant branch (RGB) or while ascending the brightest portion of the RGB. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 088.D-0045(A).Appendix A is available in electronic form at http://www.aanda.org

  14. Lithium Inventory of 2 $M_\\odot$ Red Clump Stars in Open Clusters: A Test of the Helium Flash Mechanism

    CERN Document Server

    Carlberg, Joleen K; Smith, Verne V

    2016-01-01

    The temperature distribution of field Li-rich red giants suggests the presence of a population of Li-rich red clump (RC) stars. One proposed explanation for this population is that all stars with masses near 2 $M_\\odot$ experience a short-lived phase of Li-richness at the onset of core He-burning. Many of these stars have low 12C/13C, a signature of deep mixing that is presumably associated with the Li regeneration. To test this purported mechanism of Li enrichment, we measured abundances in 38 RC stars and 6 red giant branch (RGB) stars in four open clusters selected to have RC masses near 2 $M_\\odot$. We find six Li-rich stars (A(Li) > 1.50 dex) of which only two may be RC stars. None of the RC stars have Li exceeding the levels observed in the RGB stars, but given the brevity of the suggested Li-rich phase and the modest sample size, it is probable that stars with larger Li-enrichments were missed simply by chance. However, we find very few stars in our sample with low 12C/13C. Such low 12C/13C, seen in ma...

  15. Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in Omega Centauri

    CERN Document Server

    Karakas, Amanda I; Nataf, David M

    2014-01-01

    We investigate the effect of helium enrichment on the evolution and nucleosynthesis of low-mass asymptotic giant branch (AGB) stars of 1.7Msun and 2.36Msun with a metallicity of Z=0.0006 ([Fe/H] = -1.4). We calculate evolutionary sequences with the primordial helium abundance (Y = 0.24) and with helium-enriched compositions (Y = 0.30, 0.35, 0.40). For comparison we calculate models of the same mass but at a lower metallicity Z=0.0003 ([Fe/H] = -1.8) with Y=0.24. Post-processing nucleosynthesis calculations are performed on each of the evolutionary sequences to determine the production of elements from hydrogen through to bismuth. Elemental surface abundance predictions and stellar yields are presented for each model. The models with enriched helium have shorter main sequence and AGB lifetimes, and enter the AGB with a more massive hydrogen exhausted core than the primordial helium model. The main consequences are 1) low-mass AGB models with enhanced helium will evolve more than twice as fast, giving them the ...

  16. Star Trek in the Schools

    Science.gov (United States)

    Journal of Aerospace Education, 1977

    1977-01-01

    Describes specific educational programs for using the Star Trek TV program from kindergarten through college. For each grade level lesson plans, ideas for incorporating Star Trek into future classes, and reports of specific programs utilizing Star Trek are provided. (SL)

  17. Network-based functional enrichment

    Directory of Open Access Journals (Sweden)

    Poirel Christopher L

    2011-11-01

    Full Text Available Abstract Background Many methods have been developed to infer and reason about molecular interaction networks. These approaches often yield networks with hundreds or thousands of nodes and up to an order of magnitude more edges. It is often desirable to summarize the biological information in such networks. A very common approach is to use gene function enrichment analysis for this task. A major drawback of this method is that it ignores information about the edges in the network being analyzed, i.e., it treats the network simply as a set of genes. In this paper, we introduce a novel method for functional enrichment that explicitly takes network interactions into account. Results Our approach naturally generalizes Fisher’s exact test, a gene set-based technique. Given a function of interest, we compute the subgraph of the network induced by genes annotated to this function. We use the sequence of sizes of the connected components of this sub-network to estimate its connectivity. We estimate the statistical significance of the connectivity empirically by a permutation test. We present three applications of our method: i determine which functions are enriched in a given network, ii given a network and an interesting sub-network of genes within that network, determine which functions are enriched in the sub-network, and iii given two networks, determine the functions for which the connectivity improves when we merge the second network into the first. Through these applications, we show that our approach is a natural alternative to network clustering algorithms. Conclusions We presented a novel approach to functional enrichment that takes into account the pairwise relationships among genes annotated by a particular function. Each of the three applications discovers highly relevant functions. We used our methods to study biological data from three different organisms. Our results demonstrate the wide applicability of our methods. Our algorithms are

  18. Stars and Flowers, Flowers and Stars

    Science.gov (United States)

    Minti, Hari

    2012-12-01

    The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

  19. Hybrid stars that masquerade as neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Mark Paris; Mark Alford; Matt Braby; Sanjay Reddy

    2004-11-01

    We show that a hybrid (nuclear + quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state, and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M{sub solar} for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.

  20. Hot subdwarf stars in close-up view - III. Metal abundances of subdwarf B stars

    CERN Document Server

    Geier, S

    2012-01-01

    Context: Hot subdwarf B stars (sdBs) are considered to be core helium-burning stars with very thin hydrogen envelopes situated on or near the extreme horizontal branch (EHB). The formation of sdBs is still unclear as well as the chemical composition of their atmospheres. The observed helium depletion is attributed to atmospheric diffusion. Metal abundances have been determined for about a dozen sdBs only resulting in puzzling patterns with enrichment of heavy metals and depletion of lighter ones. Aims: In this paper we present a detailed metal abundance analysis of 106 sdBs. Methods: From high resolution spectra we measured elemental abundances of up to 24 different ions per star. A semi-automatic analysis pipeline was developed to calculate and fit LTE models to a standard set of spectral lines. Results: A general trend of enrichment was found with increasing temperature for most of the heavier elements. The lighter elements like carbon, oxygen and nitrogen are depleted and less affected by temperature. Alth...

  1. Second-generation stars in globular clusters from rapid radiative cooling of pre-supernova massive star winds

    Science.gov (United States)

    Lochhaas, Cassandra; Thompson, Todd A.

    2017-09-01

    Following work by Wünsch and collaborators, we investigate a self-enrichment scenario for second-generation star formation in globular clusters wherein wind material from the first-generation massive stars rapidly radiatively cools. Radiative energy loss allows retention of fast winds within the central regions of clusters, where it fuels star formation. Secondary star formation occurs in ∼3-5 Myr, before supernovae, producing uniform iron abundances in both populations. We derive the critical criteria for radiative cooling of massive star winds and the second-generation mass as a function of cluster mass, radius and metallicity. We derive a critical condition on M/R, above which second-generation star formation can occur. We speculate that above this threshold the strong decrease in the cluster wind energy and momentum allows ambient gas to remain from the cluster formation process. We reproduce large observed second-generation fractions of ∼30-80 per cent if wind material mixes with ambient gas. Importantly, the mass of ambient gas required is only of order the first generation's stellar mass. Second-generation helium enrichment ΔY is inversely proportional to mass fraction in the second generation; a large second generation can form with ΔY ∼ 0.001-0.02, while a small second generation can reach ΔY ∼ 0.16. Like other self-enrichment models for the second generation, we are not able to simultaneously account for both the full range of the Na-O anticorrelation and the second-generation fraction.

  2. Fluorine in R Coronae Borealis and Extreme Helium Stars

    CERN Document Server

    Pandey, Gajendra; Rao, N Kameswara

    2007-01-01

    Neutral fluorine lines are identified in the optical spectra of several R Coronae Borealis stars (RCBs) at maximum light. These lines provide the first measurement of the fluorine abundance in these stars. Fluorine is enriched in some RCBs by factors of 800 to 8000 relative to its likely initial abundance. The overabundances of fluorine are evidence for the synthesis of fluorine. These results are discussed in the light of the scenario that RCBs are formed by accretion of an He white dwarf by a C-O white dwarf. Sakurai's object (V4334 Sgr), a final He-shell flash product, shows no detectable neutral fluorine lines.

  3. NEAT: an efficient network enrichment analysis test

    OpenAIRE

    Signorelli, Mirko; Vinciotti, Veronica; Wit, Ernst C

    2016-01-01

    Background Network enrichment analysis is a powerful method, which allows to integrate gene enrichment analysis with the information on relationships between genes that is provided by gene networks. Existing tests for network enrichment analysis deal only with undirected networks, they can be computationally slow and are based on normality assumptions. Results We propose NEAT, a test for network enrichment analysis. The test is based on the hypergeometric distribution, which naturally arises ...

  4. PAHs and star formation

    NARCIS (Netherlands)

    Tielens, AGGM; Peeters, E; Bakes, ELO; Spoon, HWW; Hony, S; Johnstone, D; Adams, FC; Lin, DNC; Neufeld, DA; Ostriker, EC

    2004-01-01

    Strong IR emission features at 3.3, 6.2, 7.7, 8.6, and 11.2 mum are a common characteristic of regions of massive star formation. These features are carried by large (similar to 50 C-atom) Polycyclic Aromatic Hydrocarbon molecules which are pumped by the strong FUV photon flux from these stars. Thes

  5. Observing Double Stars

    Science.gov (United States)

    Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

    2012-05-01

    Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

  6. How do stars form

    Science.gov (United States)

    Tscharnuter, W. M.

    1980-02-01

    Modes and model concept of star formation are reviewed, beginning with the theory of Kant (1755), via Newton's exact mathematical formulation of the laws of motion, his recognition of the universal validity of general gravitation, to modern concepts and hypotheses. Axisymmetric and spherically symmetric collapse models are discussed, and the origin of double and multiple star systems is examined.

  7. First stars XVI. STIS/HST abundances of heavy-elements in the uranium-rich star CS 31082-001

    CERN Document Server

    Mello, C Siqueira; Barbuy, B; Spite, F; Caffau, E; Hill, V; Wanajo, S; Primas, F; Plez, B; Cayrel, R; Andersen, J; Nordström, B; Sneden, C; Beers, T C; Bonifacio, P; François, P; Molaro, P

    2012-01-01

    Detailed abundances of the elements produced by r-process nucleosynthesis in various circumstances are our best observational clues to their origin, since the site(s) of r-element production is(are) still not known with certainty. A small fraction of extremely metal-poor (EMP) stars exhibit excesses of heavy neutron-capture elements produced in the r-process, and CS 31082-001 is among the 4 well-known r-process-enhanced EMP stars. Observations with HST/STIS provide abundances for elements observable only from the UV region. Here we aim to supplement the optical data with abundances from near-UV spectroscopy of the first and second peak of the r-elements, which are crucial to giving insight into the nucleosynthesis of the elements beyond iron. The UVES spectrum provided additional measurements, thereby improving the previous results. The spectra were analyzed with the OSMARCS LTE model atmosphere and with a consistent approach based on the spectrum synthesis code Turbospectrum to derive abundances of heavy ele...

  8. Enriching Music and Language Arts Experiences

    Science.gov (United States)

    Flohr, John W.

    2006-01-01

    The article focuses on enriching music and language arts experiences of students. Music can enrich literature and language arts, poetry, theater arts, transitions, science, and math, as well as help meet special learner needs. A well-understood example of enrichment is the alphabet song. A music or classroom teacher using the alphabet song helps…

  9. How Did the IGM Become Enriched?

    CERN Document Server

    Aguirre, A; Aguirre, Anthony; Schaye, Joop

    2006-01-01

    The enrichment of the intergalactic medium with heavy elements is a process that lies at the nexus of poorly-understood aspects of physical cosmology. We review current understanding of the processes that may remove metals from galaxies, the basic predictions of these models, the key observational constraints on enrichment, and how intergalactic enrichment may be used to test cosmological simulations.

  10. Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way.

    Science.gov (United States)

    Howes, L M; Casey, A R; Asplund, M; Keller, S C; Yong, D; Nataf, D M; Poleski, R; Lind, K; Kobayashi, C; Owen, C I; Ness, M; Bessell, M S; Da Costa, G S; Schmidt, B P; Tisserand, P; Udalski, A; Szymański, M K; Soszyński, I; Pietrzyński, G; Ulaczyk, K; Wyrzykowski, Ł; Pietrukowicz, P; Skowron, J; Kozłowski, S; Mróz, P

    2015-11-26

    The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon.

  11. NLTE strontium abundance in a sample of extremely metal poor stars and the Sr/Ba ratio in the early Galaxy

    CERN Document Server

    Andrievsky, S M; Korotin, S A; Francois, P; Spite, M; Bonifacio, P; Cayrel, R; Hill, V

    2011-01-01

    Heavy element abundances in extremely metal-poor stars provide strong constraints on the processes of forming these elements in the first stars. We attempt to determine precise abundances of strontium in a homogeneous sample of extremely metal-poor stars. The abundances of strontium in 54 very or extremely metal-poor stars, was redetermined by abandoning the local thermodynamic equilibrium (LTE) hypothesis, and fitting non-LTE (NLTE) profiles to the observed spectral lines. The corrected Sr abundances and previously obtained NLTE Ba abundances are compared to the predictions of several hypothetical formation processes for the lighter neutron-capture elements. Our NLTE abundances confirm the previously determined huge scatter of the strontium abundance in low metallicity stars. This scatter is also found (and is even larger) at very low metallicities (i. e. early in the chemical evolution). The Sr abundance in the extremely metal-poor (EMP) stars is compatible with the main r-process involved in other processe...

  12. A study of the effect of rotational mixing on massive stars evolution: surface abundances of Galactic O7-8 giant stars

    Science.gov (United States)

    Martins, F.; Simón-Díaz, S.; Barbá, R. H.; Gamen, R. C.; Ekström, S.

    2017-02-01

    Context. Massive star evolution remains only partly constrained. In particular, the exact role of rotation has been questioned by puzzling properties of OB stars in the Magellanic Clouds. Aims: Our goal is to study the relation between surface chemical composition and rotational velocity, and to test predictions of evolutionary models including rotation. Methods: We have performed a spectroscopic analysis of a sample of fifteen Galactic O7-8 giant stars. This sample is homogeneous in terms of mass, metallicity and evolutionary state. It is made of stars with a wide range of projected rotational velocities. Results: We show that the sample stars are located on the second half of the main sequence, in a relatively narrow mass range (25-40 M⊙). Almost all stars with projected rotational velocities above 100 km s-1 have N/C ratios about ten times the initial value. Below 100 km s-1 a wide range of N/C values is observed. The relation between N/C and surface gravity is well reproduced by various sets of models. Some evolutionary models including rotation are also able to consistently explain slowly rotating, highly enriched stars. This is due to differential rotation which efficiently transports nucleosynthesis products and allows the surface to rotate slower than the core. In addition, angular momentum removal by winds amplifies surface braking on the main sequence. Comparison of the surface composition of O7-8 giant stars with a sample of B stars with initial masses about four times smaller reveal that chemical enrichment scales with initial mass, as expected from theory. Conclusions: Although evolutionary models that include rotation face difficulties in explaining the chemical properties of O- and B-type stars at low metallicity, some of them can consistently account for the properties of main-sequence Galactic O stars in the mass range 25-40 M⊙.

  13. Neutron Stars and Pulsars

    CERN Document Server

    Becker, Werner

    2009-01-01

    Neutron stars are the most compact astronomical objects in the universe which are accessible by direct observation. Studying neutron stars means studying physics in regimes unattainable in any terrestrial laboratory. Understanding their observed complex phenomena requires a wide range of scientific disciplines, including the nuclear and condensed matter physics of very dense matter in neutron star interiors, plasma physics and quantum electrodynamics of magnetospheres, and the relativistic magneto-hydrodynamics of electron-positron pulsar winds interacting with some ambient medium. Not to mention the test bed neutron stars provide for general relativity theories, and their importance as potential sources of gravitational waves. It is this variety of disciplines which, among others, makes neutron star research so fascinating, not only for those who have been working in the field for many years but also for students and young scientists. The aim of this book is to serve as a reference work which not only review...

  14. Mira Symbiotic Stars

    Institute of Scientific and Technical Information of China (English)

    Guo-Liang Lü; Chun-Hua Zhu; Zhan-Wen Han

    2007-01-01

    We have carried out a detailed study of Mira symbiotic stars by means of a population synthesis code. We estimate the number of Mira symbiotic stars in the Galaxy as 1700 - 3100 and the Galactic occurrence rate of Mira symbiotic novae as from ~ 0.9 to 6.0 yr-1,depending on the model assumptions. The distributions of the orbital periods, the masses of the components, mass-loss rates of cool components, mass-accretion rates of hot components and Mira pulsation periods in Mira symbiotic stars are simulated. By a comparison of the number ratio of Mira symbiotic stars to all symbiotic stars, we find the model with the stellar wind model of Winters et al. to be reasonable.

  15. Revised Anatomy of Stars

    CERN Document Server

    Dubin, M; Dubin, Maurice; Soberman, Robert K.

    1997-01-01

    Stars accrete near invisible hydrogen dominated agglomerates. This population, the `dark matter,' effects the nature of stars. Measurements show plasma streams impacting Earth, planets, Sun and stars. This mass-energy source contradicts nebula collapse model for stars. The visual derived model, to which later discoveries (e.g., fusion) were appended, is confounded and contradicted by new observations. Discovery of a quantity of beryllium 7 (53 day half-life) in the Earth's upper atmosphere, fusion produced, hence from the solar outer zone, proves core fusion wrong. Magnetically pinched plasmas from aggregates impact stars at hundreds of km/s, create impulsive conditions for nuclear explosions below the surface. Disks with planets aid cluster capture. Planets modulate the influx varying fusion, hence luminosity (e.g., solar cycle). This population, with no assumptions or ad hoc physics, explains mysterious phenomena, e.g., luminosity/wind variation, sunspots, high temperature corona, CMEs, etc. Standard explan...

  16. The Carbon Star Phenomenon

    Science.gov (United States)

    Wing, Robert F.

    2000-06-01

    The atmospheres of many stars have chemical compositions that are significantly different from that of the interstellar medium from which they are formed. This symposium considered all kinds of late-type stars showing altered compositions, the carbon stars being simply the best-known of these. All stages of stellar evolution from the main sequence to the ejection of a planetary nebula were considered, with emphasis on the changes that occur on the asymptotic giant branch. The spectroscopic properties of the photospheres and circumstellar envelopes of chemically-peculiar red giant stars, their origins via single-star evolution or mass transfer in binary systems, and the methods currently used to study them were all discussed in detail. This volume includes the full texts of papers given orally at the symposium and abstracts of the posters. Link: http://www.wkap.nl/book.htm/0-7923-6347-7

  17. Gaia and Variable Stars

    CERN Document Server

    Udalski, A; Skowron, D M; Skowron, J; Pietrukowicz, P; Mróz, P; Poleski, R; Szymański, M K; Kozłowski, S; Wyrzykowski, Ł; Ulaczyk, K; Pawlak, M

    2016-01-01

    We present a comparison of the Gaia DR1 samples of pulsating variable stars - Cepheids and RR Lyrae type - with the OGLE Collection of Variable Stars aiming at the characterization of the Gaia mission performance in the stellar variability domain. Out of 575 Cepheids and 2322 RR Lyrae candidates from the Gaia DR1 samples located in the OGLE footprint in the sky, 559 Cepheids and 2302 RR Lyrae stars are genuine pulsators of these types. The number of misclassified stars is low indicating reliable performance of the Gaia data pipeline. The completeness of the Gaia DR1 samples of Cepheids and RR Lyrae stars is at the level of 60-75% as compared to the OGLE Collection dataset. This level of completeness is moderate and may limit the applicability of the Gaia data in many projects.

  18. Ages of young stars

    CERN Document Server

    Soderblom, David R; Jeffries, Rob D; Mamajek, Eric E; Naylor, Tim

    2013-01-01

    Determining the sequence of events in the formation of stars and planetary systems and their time-scales is essential for understanding those processes, yet establishing ages is fundamentally difficult because we lack direct indicators. In this review we discuss the age challenge for young stars, specifically those less than ~100 Myr old. Most age determination methods that we discuss are primarily applicable to groups of stars but can be used to estimate the age of individual objects. A reliable age scale is established above 20 Myr from measurement of the Lithium Depletion Boundary (LDB) in young clusters, and consistency is shown between these ages and those from the upper main sequence and the main sequence turn-off -- if modest core convection and rotation is included in the models of higher-mass stars. Other available methods for age estimation include the kinematics of young groups, placing stars in Hertzsprung-Russell diagrams, pulsations and seismology, surface gravity measurement, rotation and activ...

  19. Producing Runaway Stars

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    How are the hypervelocity stars weve observed in our galaxy produced? A recent study suggests that these escapees could be accelerated by a massive black hole in the center of the Large Magellanic Cloud.A Black Hole SlingshotSince their discovery in 2005, weve observed dozens of candidate hypervelocity stars stars whose velocity in the rest frame of our galaxy exceeds the local escape velocity of the Milky Way. These stars present a huge puzzle: how did they attain these enormous velocities?One potential explanation is known as the Hills mechanism. In this process, a stellar binary is disrupted by a close encounter with a massive black hole (like those thought to reside at the center of every galaxy). One member of the binary is flung out of the system as a result of the close encounter, potentially reaching very large velocities.A star-forming region known as LHA 120-N 11, located within the LMC. Some binary star systems within the LMC might experience close encounters with a possible massive black hole at the LMCs center. [ESA/NASA/Hubble]Blame the LMC?Usually, discussions of the Hills mechanism assume that Sagittarius A*, the supermassive black hole at the center of the Milky Way, is the object guilty of accelerating the hypervelocity stars weve observed. But what if the culprit isnt Sgr A*, but a massive black hole at the center of the Large Magellanic Cloud (LMC), one of the Milky Ways satellite galaxies?Though we dont yet have evidence of a massive black hole at the center of the LMC, the dwarf galaxy is large enough to potentially host one as large as 100,000 solar masses. Assuming that it does, two scientists at the University of Cambridge, Douglas Boubert and Wyn Evans, have now modeled how this black hole might tear apart binary star systems and fling hypervelocity stars around the Milky Way.Models for AccelerationBoubert and Evans determined that the LMCs hypothetical black hole could easily eject stars at ~100 km/s, which is the escape velocity of the

  20. Neutron stars - General review

    Science.gov (United States)

    Cameron, A. G. W.; Canuto, V.

    1974-01-01

    A review is presented of those properties of neutron stars upon which there is general agreement and of those areas which currently remain in doubt. Developments in theoretical physics of neutron star interiors are summarized with particular attention devoted to hyperon interactions and the structure of interior layers. Determination of energy states and the composition of matter is described for successive layers, beginning with the surface and proceeding through the central region into the core. Problems encountered in determining the behavior of matter in the ultra-high density regime are discussed, and the effects of the magnetic field of a neutron star are evaluated along with the behavior of atomic structures in the field. The evolution of a neutron star is outlined with discussion centering on carbon detonation, cooling, vibrational damping, rotation, and pulsar glitches. The role of neutron stars in cosmic-ray propagation is considered.

  1. Heavy elements in Globular Clusters: the role of AGB stars

    CERN Document Server

    Straniero, Oscar; Piersanti, Luciano

    2014-01-01

    Recent observations of heavy elements in Globular Clusters reveal intriguing deviations from the standard paradigm of the early galactic nucleosynthesis. If the r-process contamination is a common feature of halo stars, s-process enhancements are found in a few Globular Clusters only. We show that the combined pollution of AGB stars with mass ranging between 3 to 6 M$_\\odot$ may account for most of the features of the s-process overabundance in M4 and M22. In these stars, the s process is a mixture of two different neutron-capture nucleosynthesis episodes. The first is due to the 13C(a,n)16O reaction and takes place during the interpulse periods. The second is due to the 22Ne(a,n)25Mg reaction and takes place in the convective zones generated by thermal pulses. The production of the heaviest s elements (from Ba to Pb) requires the first neutron burst, while the second produces large overabundances of light s (Sr, Y, Zr). The first mainly operates in the less-massive AGB stars, while the second dominates in th...

  2. Lead abundance in the uranium star CS 31082-001

    CERN Document Server

    Plez, B; Cayrel, R; Spite, M; Barbuy, B; Beers, T C; Bonifacio, P; Primas, F; Nordström, B

    2004-01-01

    In a previous paper we were able to measure the abundance of uranium and thorium in the very-metal poor halo giant BPS CS 31082-001, but only obtained an upper limit for the abundance of lead (Pb). We have got from ESO 17 hours of additional exposure on this star in order to secure a detection of the minimum amount of lead expected to be present in CS 31082-001, the amount arising from the decay of the original content of Th and U in the star. We report here this successful detection. We find an LTE abundance log(Pb/H)+12=-0.55 \\pm 0.15 dex, one dex below the upper limits given by other authors for the similar stars CS 22892-052 and BD +17d3248, also enhanced in r-process elements. From the observed present abundances of Th and U in the star, the expected amount of Pb produced by the decay of 232Th, and 238U alone, over 12-15 Gyr is -0.73\\pm 0.17 dex. The decay of 235U is more difficult to estimate, but is probably slightly below the contribution of 238U, making the contribution of the 3 actinides only slight...

  3. THE FATE OF THE COMPACT REMNANT IN NEUTRON STAR MERGERS

    Energy Technology Data Exchange (ETDEWEB)

    Fryer, Chris L. [Department of Physics, The University of Arizona, Tucson, AZ 85721 (United States); Belczynski, Krzysztoff [Astronomical Observatory, University of Warsaw, Al Ujazdowskie 4, 00-478 Warsaw (Poland); Ramirez-Ruiz, Enrico [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Rosswog, Stephan [The Oskar klein Center, Department of Astronomy, AlbaNova, Stockholm University, SE-106 91 Stockholm (Sweden); Shen, Gang [Institute for Nuclear Theory, University of Washington, Seattle, WA 98195 (United States); Steiner, Andrew W. [Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States)

    2015-10-10

    Neutron star (binary neutron star and neutron star–black hole) mergers are believed to produce short-duration gamma-ray bursts (GRBs). They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and advanced VIRGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of Newtonian merger calculations and equation of state studies to determine the fate of the cores of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3–2.4 solar masses. If quick black hole formation is essential in producing GRBs, LIGO/Virgo observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.

  4. [$\\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars

    CERN Document Server

    Vargas, Luis C; Geha, Marla C; Tollerud, Erik J; Kirby, Evan N; Guhathakurta, Puragra

    2014-01-01

    We present alpha element to iron abundance ratios, [$\\alpha$/Fe], for four stars in the outer stellar halo of the Andromeda Galaxy (M 31). The stars were identified as high-likelihood field halo stars by Gilbert et al. (2012) and lie at projected distances between 70 and 140 kpc from M 31's center. These are the first alpha abundances measured for a halo star in a galaxy beyond the Milky Way. The stars range in metallicity between [Fe/H]= -2.2 and [Fe/H]= -1.4. The sample's average [$\\alpha$/Fe] ratio is +0.20+/-0.20. The best-fit average value is elevated above solar which is consistent with rapid chemical enrichment from Type II supernovae. The mean [$\\alpha$/Fe] ratio of our M31 outer halo sample agrees (within the uncertainties) with that of Milky Way inner/outer halo stars that have a comparable range of [Fe/H].

  5. The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars

    CERN Document Server

    Karakas, Amanda I

    2014-01-01

    The chemical evolution of the Universe is governed by the chemical yields from stars, which in turn is determined primarily by the initial stellar mass. Even stars as low as 0.9Msun can, at low metallicity, contribute to the chemical evolution of elements. Stars less massive than about 10Msun experience recurrent mixing events that can significantly change the surface composition of the envelope, with observed enrichments in carbon, nitrogen, fluorine, and heavy elements synthesized by the slow neutron capture process (the s-process). Low and intermediate mass stars release their nucleosynthesis products through stellar outflows or winds, in contrast to massive stars that explode as core-collapse supernovae. Here we review the stellar evolution and nucleosynthesis for single stars up to ~10Msun from the main sequence through to the tip of the asymptotic giant branch (AGB). We include a discussion of the main uncertainties that affect theoretical calculations and review the latest observational data, which are...

  6. Monte Carlo simulation of star/linear and star/star blends with chemically identical monomers

    Energy Technology Data Exchange (ETDEWEB)

    Theodorakis, P E [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Avgeropoulos, A [Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina (Greece); Freire, J J [Departamento de Ciencias y Tecnicas FisicoquImicas, Universidad Nacional de Educacion a Distancia, Facultad de Ciencias, Senda del Rey 9, 28040 Madrid (Spain); Kosmas, M [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece); Vlahos, C [Department of Chemistry, University of Ioannina, 45110 Ioannina (Greece)

    2007-11-21

    The effects of chain size and architectural asymmetry on the miscibility of blends with chemically identical monomers, differing only in their molecular weight and architecture, are studied via Monte Carlo simulation by using the bond fluctuation model. Namely, we consider blends composed of linear/linear, star/linear and star/star chains. We found that linear/linear blends are more miscible than the corresponding star/star mixtures. In star/linear blends, the increase in the volume fraction of the star chains increases the miscibility. For both star/linear and star/star blends, the miscibility decreases with the increase in star functionality. When we increase the molecular weight of linear chains of star/linear mixtures the miscibility decreases. Our findings are compared with recent analytical and experimental results.

  7. Ejection of Supernova-Enriched Gas From Dwarf Disk Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Fragile, P C; Murray, S D; Lin, D C

    2004-06-15

    We examine the efficiency with which supernova-enriched gas may be ejected from dwarf disk galaxies, using a methodology previously employed to study the self-enrichment efficiency of dwarf spheroidal systems. Unlike previous studies that focused on highly concentrated starbursts, in the current work we consider discrete supernova events spread throughout various fractions of the disk. We model disk systems having gas masses of 10{sup 8} and 10{sup 9} M{sub {circle_dot}} with supernova rates of 30, 300, and 3000 Myr{sup -1}. The supernova events are confined to the midplane of the disk, but distributed over radii of 0, 30, and 80% of the disk radius, consistent with expectations for Type II supernovae. In agreement with earlier studies, we find that the enriched material from supernovae is largely lost when the supernovae are concentrated near the nucleus, as expected for a starburst event. In contrast, we find the loss of enriched material to be much less efficient (as low as 21%) when the supernovae occur over even a relatively small fraction of the disk. The difference is due to the ability of the system to relax following supernova events that occur over more extended regions. Larger physical separations also reduce the likelihood of supernovae going off within low-density ''chimneys'' swept out by previous supernovae. We also find that, for the most distributed systems, significant metal loss is more likely to be accompanied by significant mass loss. A comparison with theoretical predications indicates that, when undergoing self-regulated star formation, galaxies in the mass range considered shall efficiently retain the products of Type II supernovae.

  8. Gas distribution, metal enrichment, and baryon fraction in Gaussian and non-Gaussian universes

    CERN Document Server

    Maio, Umberto

    2011-01-01

    We study the cosmological evolution of baryons in universes with and without primordial non-Gaussianities via (large scale) N-body/hydrodynamical simulations, including gas cooling, star formation, stellar evolution, chemical enrichment from both population III and population II regimes, and feedback effects. We find that large fnl values for non-Gaussianities can alter the gas probability distribution functions, the metal pollution history, the halo baryon, gas and stellar fractions, mostly at early times. More precisely: (i) non-Gaussianities lead to an earlier evolution of primordial gas, structures, and star formation; (ii) metal enrichment starts earlier (with respect to the Gaussian scenario) in non-Gaussian models with larger fnl; (iii) gas fractions within the haloes are not significantly affected by the different values of fnl, with deviations of ~1-10%; (iv) the stellar fraction is quite sensitive to non-Gaussianities at early times, with discrepancies reaching up to a factor of ~10 at very high z, ...

  9. Coronae of Stars with Supersolar Elemental Abundances

    Science.gov (United States)

    Peretz, Uria; Behar, Ehud; Drake, Stephen A.

    2015-01-01

    Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the first ionization potential (FIP). This study focuses on the coronal composition of stars with supersolar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, iota Hor, HR 7291, tau Boo, and alpha Cen A and B. These stars all have high-statistics X-ray spectra, three of which are presented for the first time. The abundances we measured were obtained using the line-resolved spectra of the Reflection Grating Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera spectra onboard the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components is found to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respective photospheres. For 11 LMi and tau Boo no FIP effect is present, while iota Hor, HR 7291, and alpha Cen A and B show a clear FIP trend. These conclusions hold whether the comparison is made with solar abundances or the individual stellar abundances. Unlike the solar corona, where low-FIP elements are enriched, in these stars the FIP effect is consistently due to a depletion of high-FIP elements with respect to actual photospheric abundances. A comparison with solar (instead of stellar) abundances yields the same fractionation trend as on the Sun. In both cases, a similar FIP bias is inferred, but different fractionation mechanisms need to be invoked.

  10. Enrichment planting without soil treatment

    Energy Technology Data Exchange (ETDEWEB)

    Hagner, Mats

    1998-12-31

    Where enrichment planting had been carried out with either of the two species Picea abies and Pinus contorta, the survival of the planted seedlings was at least as good as after planting in a normal clear cut area treated with soil scarification. This was in spite of the fact that the seedlings were placed shallow in the humus layer without any soil treatment. However, they were sheltered from insects by treatment before planting. Where enrichment planting was carried out with Pinus sylvestris the survival in dense forest was poor, but in open forest the survival was good. The growth of planted seedlings was enhanced by traditional clearing and soil treatment. However, this was for Pinus sylvestris not enough to compensate for the loss of time, 1-2 years, caused by arrangement of soil scarification. The growth of seedlings planted under crown cover was directly related to basal area of retained trees. However, the variation in height growth among individual seedlings was very big, which meant that some seedlings grow well also under a fairly dense forest cover. The pioneer species Pinus sylvestris reacted more strongly to basal area of retained trees than did the shade tolerant species Picea abies. Enrichment planting seems to be a necessary tool for preserving volume productivity, at places where fairly intensive harvest of mature trees has been carried out in stands of ordinary forest type in central Sweden. If double seedlings, with one Picea abies and one Pinus sylvestris, are used, the probability for long term establishment is enhanced 13 refs, 20 figs, 4 tabs

  11. Catch a Star!

    Science.gov (United States)

    2006-11-01

    ESO and the European Association for Astronomy Education are launching today the 2007 edition of 'Catch a Star!', their international astronomy competition for school students. Now in its fifth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. Students are invited to 'become astronomers' and embark on a journey to explore the Universe. ESO PR Photo 42/06 The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. For the artistically minded, 'Catch a Star!' also includes an artwork competition, 'Catch a Star Artists'. "'Catch a Star!' offers a unique opportunity for students to learn more about astronomy and about the methods scientists use to discover new things about the Universe", said Douglas Pierce-Price, Education Officer at ESO. In teams, students choose an astronomical topic to study and produce an in-depth report. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes or a telescope of the future can contribute to their investigations of the subject. As well as the top prize - a trip to one of ESO's observatory sites in Chile - visits to observatories in Germany, Austria and Spain, and many other prizes are also available to be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners chosen with the help of a public online vote. The first editions of 'Catch a Star!' have attracted several hundred entries from more than 25 countries worldwide. Previous winning entries have included "Star clusters and the structure of the Milky Way" (Budapest, Hungary), "Vega" (Acqui Terme, Italy) and "Venus

  12. Boron enrichment in martian clay.

    Directory of Open Access Journals (Sweden)

    James D Stephenson

    Full Text Available We have detected a concentration of boron in martian clay far in excess of that in any previously reported extra-terrestrial object. This enrichment indicates that the chemistry necessary for the formation of ribose, a key component of RNA, could have existed on Mars since the formation of early clay deposits, contemporary to the emergence of life on Earth. Given the greater similarity of Earth and Mars early in their geological history, and the extensive disruption of Earth's earliest mineralogy by plate tectonics, we suggest that the conditions for prebiotic ribose synthesis may be better understood by further Mars exploration.

  13. Boron Enrichment in Martian Clay

    Science.gov (United States)

    Nagashima, Kazuhide; Freeland, Stephen J.

    2013-01-01

    We have detected a concentration of boron in martian clay far in excess of that in any previously reported extra-terrestrial object. This enrichment indicates that the chemistry necessary for the formation of ribose, a key component of RNA, could have existed on Mars since the formation of early clay deposits, contemporary to the emergence of life on Earth. Given the greater similarity of Earth and Mars early in their geological history, and the extensive disruption of Earth's earliest mineralogy by plate tectonics, we suggest that the conditions for prebiotic ribose synthesis may be better understood by further Mars exploration. PMID:23762242

  14. Digital doorway: enriching your mind

    CSIR Research Space (South Africa)

    Cambridge

    2008-11-01

    Full Text Available stream_source_info Cambridge_P_2008.pdf.txt stream_content_type text/plain stream_size 4576 Content-Encoding UTF-8 stream_name Cambridge_P_2008.pdf.txt Content-Type text/plain; charset=UTF-8 Digital Doorway: Enriching... your mind G CAMBRIDGE Meraka Institute, CSIR, PO Box 395, Pretoria, 0001 gcambrid@csir.co.za The Digital Doorway is a joint project between the South African Department of Science and Technology (DST) and the Meraka Institute of the CSIR...

  15. Identifying CEMP-s and CEMP-no Stars within Milky Way Halo Structures

    Science.gov (United States)

    Dietz, Sarah Eliana; Beers, Timothy C.; Carollo, Daniela; Yoon, Jinmi; Placco, Vinicius M.

    2017-01-01

    Carbon-enhanced metal-poor (CEMP) stars are ancient objects used to probe the star-formation history of the first generations of stars in the Galactic halo. CEMP stars may be further separated into sub-classes based on the presence or absence of heavy elements associated with different neutron-capture processes. Here we examine CEMP stars enriched with the nucleosynthesis products of the slow neutron-capture process (CEMP-s stars) and those that exhibit no strong neutron-capture element enrichments (CEMP-no stars), which are preferentially found in the Galaxy’s inner and outer halo regions, respectively [1,2].Recent structure-finding algorithms have been applied to samples of K giants from SDSS to identify groups of associated stars and classify them as members of known structures, such as the Sagittarius tidal debris stream [3]. Here we investigate whether CEMP-s and CEMP-no stars are associated in different proportion with such structures or with the diffuse halo. We distinguish CEMP-s stars from CEMP-no stars using metallicity ([Fe/H]) and carbonicity ([C/Fe]), a method that has been demonstrated to be as effective as separation based on the presence of Ba enhancements used in the past [4]. We discuss the impact of our results on our understanding of the nature of CEMP stars and their progenitor populations, as well as on the assembly history of the Milky Way.This work received partial support from PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation.References:[1] Carollo, D. et al. 2007, Nature, 450, 1020[2] Carollo, D. et al. 2010, ApJ, 712, 692[3] Janesh, W. et al. 2016, ApJ, 816, 80[4] Yoon, J. et al. 2016, ApJ, in press (arXiv:1607.06336)

  16. Lithium Inventory of 2 Solar Mass Red Clump Stars in Open Clusters: A Test of the Helium Flash Mechanism

    Science.gov (United States)

    Carlberg, Joleen K.; Cunha, Katia; Smith, Verne V.

    2016-01-01

    The temperature distribution of field Li-rich red giants suggests the presence of a population of Li-rich red clump (RC) stars. One proposed explanation for this population is that all stars with masses near 2 solar mass experience a shortlived phase of Li-richness at the onset of core He-burning. Many of these stars have low C-12/C-13, a signature of deep mixing that is presumably associated with the Li regeneration. To test this purported mechanism of Li enrichment, we measured abundances in 38 RC stars and 6 red giant branch (RGB) stars in four open clusters selected to have RC masses near 2 solar mass. We find six Li-rich stars (A(Li) greater than or equal to 1.50 dex) of which only two may be RC stars. None of the RC stars have Li exceeding the levels observed in the RGB stars, but given the brevity of the suggested Li-rich phase and the modest sample size, it is probable that stars with larger Li-enrichments were missed simply by chance. However, we find very few stars in our sample with low C-12/C-13. Such low C-12/C-13, seen in many field Li-rich stars, should persist even after lithium has returned to normal low levels. Thus, if Li synthesis during the He flash occurs, it is a rare, but potentially long-lived occurrence rather than a short-lived phase for all stars. We estimate a conservative upper limit of the fraction of stars going through a Li-rich phase to be less than 47%, based on stars that have low C-12/C-13 for their observed A(Li).

  17. Lithium Inventory of 2 M ⊙ Red Clump Stars in Open Clusters: A Test of the Helium Flash Mechanism

    Science.gov (United States)

    Carlberg, Joleen K.; Cunha, Katia; Smith, Verne V.

    2016-08-01

    The temperature distribution of field Li-rich red giants suggests the presence of a population of Li-rich red clump (RC) stars. One proposed explanation for this population is that all stars with masses near 2 M ⊙ experience a short-lived phase of Li-richness at the onset of core He-burning. Many of these stars have low 12C/13C, a signature of deep mixing that is presumably associated with the Li regeneration. To test this purported mechanism of Li enrichment, we measured abundances in 38 RC stars and 6 red giant branch (RGB) stars in four open clusters selected to have RC masses near 2 M ⊙. We find six Li-rich stars (A(Li) ≥ 1.50 dex) of which only two may be RC stars. None of the RC stars have Li exceeding the levels observed in the RGB stars, but given the brevity of the suggested Li-rich phase and the modest sample size, it is probable that stars with larger Li-enrichments were missed simply by chance. However, we find very few stars in our sample with low 12C/13C. Such low 12C/13C, seen in many field Li-rich stars, should persist even after lithium has returned to normal low levels. Thus, if Li synthesis during the He flash occurs, it is a rare, but potentially long-lived occurrence rather than a short-lived phase for all stars. We estimate a conservative upper limit of the fraction of stars going through a Li-rich phase to be \\lt 47 % , based on stars that have low 12C/13C for their observed A(Li).

  18. Beta-decay half-lives and beta-delayed neutron emisison probabilities of nuclei in the region A. 110, relevant for the r-process

    Energy Technology Data Exchange (ETDEWEB)

    Moller, Peter [Los Alamos National Laboratory; Pereira, J [MSU; Hennrich, S [MSU; Aprahamian, A [UNIV OF NOTRE DAME; Arndt, O [GERMANY; Becerril, A [MSU; Elliot, T [MSU; Estrade, A [MSU; Galaviz, D [MSU; Kessler, R [UNIV MAINZ; Kratz, K - L [GERMANY; Lorusso, G [MSU; Mantica, P F [MSU; Matos, M [MSU; Montes, F [MSU; Pfeiffer, B [UNIV MAINZ; Schatz, F [MSU; Schnorrenberger, L [GERMANY; Smith, E [MSU; Stolz, A [MSU; Quinn, M [UNIV OF NOTRE DAME; Walters, W B [UNIV OF MARYLAND; Wohr, A [UNIV OF NOTRE DAME

    2009-01-01

    Measurements of the {beta}-decay properties of A {approx}< 110 r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. {beta}-decay half-lives for {sup 105}Y, {sup 106,107}Zr and {sup 108,111}Mo, along with ,B-delayed neutron emission probabilities of 104Y, 109,11OMo and upper limits for 105Y, 103-107Zr and 108,111 Mo have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.

  19. Beta-decay half-lives and beta-delayed neutron emission probabilities of nuclei in the region below A=110, relevant for the r-process

    CERN Document Server

    Pereira, J; Aprahamian, A; Arndt, O; Becerril, A; Elliot, T; Estrade, A; Galaviz, D; Kessler, R; Kratz, K -L; Lorusso, G; Mantica, P F; Matos, M; Møller, P; Montes, F; Pfeiffer, B; Schatz, H; Schertz, F; Schnorrenberger, L; Smith, E; Stolz, A; Quinn, M; Walters, W B; Wöhr, A

    2009-01-01

    Measurements of the beta-decay properties of r-process nuclei below A=110 have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. Beta-decay half-lives for Y-105, Zr-106,107 and Mo-111, along with beta-delayed neutron emission probabilities of Y-104, Mo-109,110 and upper limits for Y-105, Zr-103,104,105,106,107 and Mo-108,111 have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.

  20. β-decay half-lives and β-delayed neutron emission probabilities of nuclei in the region A≲110, relevant for the r process

    Science.gov (United States)

    Pereira, J.; Hennrich, S.; Aprahamian, A.; Arndt, O.; Becerril, A.; Elliot, T.; Estrade, A.; Galaviz, D.; Kessler, R.; Kratz, K.-L.; Lorusso, G.; Mantica, P. F.; Matos, M.; Möller, P.; Montes, F.; Pfeiffer, B.; Schatz, H.; Schertz, F.; Schnorrenberger, L.; Smith, E.; Stolz, A.; Quinn, M.; Walters, W. B.; Wöhr, A.

    2009-03-01

    Measurements of β-decay properties of A≲110 r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory at Michigan State University. β-decay half-lives for Y105, Zr106,107, and Mo111, along with β-delayed neutron emission probabilities of Y104, Mo109,110 and upper limits for Y105, Zr103-107, and Mo108,111 have been measured for the first time. Studies on the basis of the quasi-random-phase approximation are used to analyze the ground-state deformation of these nuclei.

  1. Distributions of Long-Lived Radioactive Nuclei Provided by Star Forming Environments

    CERN Document Server

    Fatuzzo, M

    2015-01-01

    Radioactive nuclei play an important role in planetary evolution by providing an internal heat source, which affects planetary structure and helps facilitate plate tectonics. A minimum level of nuclear activity is thought to be necessary --- but not sufficient --- for planets to be habitable. Extending previous work that focused on short-lived nuclei, this paper considers the delivery of long-lived radioactive nuclei to circumstellar disks in star forming regions. Although the long-lived nuclear species are always present, their abundances can be enhanced through multiple mechanisms. Most stars form in embedded cluster environments, so that disks can be enriched directly by intercepting ejecta from supernovae within the birth clusters. In addition, molecular clouds often provide multiple episodes of star formation, so that nuclear abundances can accumulate within the cloud; subsequent generations of stars can thus receive elevated levels of radioactive nuclei through this distributed enrichment scenario. This...

  2. Heavy Stars Thrive among Heavy Elements

    Science.gov (United States)

    2002-08-01

    , with a sprinkling of the light element lithium. At our epoch, the visible ("baryonic") matter in the Universe still mostly consists of hydrogen and helium. However, progressively heavier elements have been built up via fusion processes in the interior of stars ever since the Big Bang. Some of the heaviest elements are also produced when massive stars die in gigantic stellar explosions, observed as "supernovae". This gradual process, referred to as "chemical evolution" , occurs with different speeds in different regions of the Universe, being fastest in those regions where star formation is most intense. In the relatively "quiet" region of the Milky Way galaxy where our Solar System was born some 4,600 million years ago, it took nearly 10,000 million years to produce all the heavy elements now found in our neighbourhood . Contrarily, in the innermost regions ( the "nuclei" ) of normal galaxies and especially in so-called "active galaxies", the same or even higher heavy-element "enrichment" levels were reached in much shorter time, less than about 1,000 to 2,000 million years. This is the result of observations of particularly active galaxy nuclei ("quasars") in the distant (i.e., early) Universe. Star formation in highly enriched environments Little is presently known about such highly enriched environments. Since astronomers refer to elements heavier than hydrogen and helium as "metals" , they talk about "metal-rich" regions . This is readily observable from the presence of strong lines from heavier elements in the spectra of the interstellar gas in such regions. A central, still unresolved question is whether under such special conditions, stars can still form with the same diversity of masses, as this happens in other, less extreme areas of the Universe . Indeed, some current theories of star formation and certain indirect observations appear to indicate that very heavy stars - with masses more than 20 - 30 times that of our Sun - could not possibly form in metal

  3. Environmental enrichment for primates in laboratories

    Science.gov (United States)

    Buchanan-Smith, H. M.

    2010-06-01

    Environmental enrichment is a critical component of Refinement, one of the 3Rs underlying humane experimentation on animals. In this paper I discuss why primates housed in laboratories, which often have constraints of space and study protocols, are a special case for enrichment. I outline a framework for categorising the different types of enrichment, using the marmoset as a case study, and summarise the methods used to determine what animals want/prefer. I briefly review the arguments that enrichment does not negatively affect experimental outcomes. Finally I focus on complexity and novelty, choice and control, the underlying features of enrichment that makes it successful, and how combined with a thorough understanding of natural history we can put effective enrichment into practice in laboratories. Throughout the paper I emphasise the need to evaluate enrichment to ensure it is having the desired effect.

  4. Population III Star Formation In Large Cosmological Simulations I. Halo Temporal and Physical Environment

    CERN Document Server

    Crosby, Brian D; Smith, Britton D; Turk, Matthew J; Hahn, Oliver

    2013-01-01

    We present a semi-analytic, computationally inexpensive model to identify halos capable of forming a Population III star in cosmological simulations across a wide range of times and environments. This allows for a much more complete and representative set of Population III star forming halos to be constructed, which will lead to Population III star formation simulations that more accurately reflect the diversity of Population III stars, both in time and halo mass. This model shows that Population III and chemically enriched stars coexist beyond the formation of the first generation of stars in a cosmological simulation until at least z~10, and likely beyond, though Population III stars form at rates that are 4-6 orders of magnitude lower than chemically enriched stars by z=10. A catalog of more than 40,000 candidate Population III forming halos were identified, with formation times temporally ranging from z=30 to z=10, and ranging in mass from 2.3x10^5 M_sun to 1.2x10^10 M_sun. At early times, the environment...

  5. Cooling of Neutron Stars

    Directory of Open Access Journals (Sweden)

    Grigorian H.

    2010-10-01

    Full Text Available We introduce the theoretical basis for modeling the cooling evolution of compact stars starting from Boltzmann equations in curved space-time. We open a discussion on observational verification of different neutron star models by consistent statistics. Particular interest has the question of existence of quark matter deep inside of compact object, which has to have a specific influence on the cooling history of the star. Besides of consideration of several constraints and features of cooling evolution, which are susceptible of being critical for internal structure of hot compact stars we have introduced a method of extraction of the mass distribution of the neutron stars from temperature and age data. The resulting mass distribution has been compared with the one suggested by supernove simulations. This method can be considered as an additional checking tool for the consistency of theoretical modeling of neutron stars. We conclude that the cooling data allowed existence of neutron stars with quark cores even with one-flavor quark matter.

  6. Dense Axion Stars

    CERN Document Server

    Braaten, Eric; Zhang, Hong

    2015-01-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure.If the axion mass energy is $mc^2= 10^{-4}$ eV, these dilute axion stars have a maximum mass of about $10^{-14} M_\\odot$. We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If $mc^2 = 10^{-4}$ eV, the first branch of these dense axion stars has mas...

  7. Dense Axion Stars

    Science.gov (United States)

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-01

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10-14M⊙ if the axion mass is 10-4 eV . We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10-20M⊙ to about M⊙ . If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  8. Dense Axion Stars

    Science.gov (United States)

    Mohapatra, Abhishek; Braaten, Eric; Zhang, Hong

    2016-03-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. If the axion mass energy is mc2 =10-4 eV, these dilute axion stars have a maximum mass of about 10-14M⊙ . We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If mc2 =10-4 4 eV, the first branch of these dense axion stars has mass ranging from about 10-11M⊙ toabout M⊙.

  9. Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy

    CERN Document Server

    Sadakane, K; Ikuta, C; Aoki, W; Jablonka, P; Tajitsu, A

    2004-01-01

    With the HDS (High Dispersion Spectrograph) on the Subaru telescope, we obtained high resolution optical region spectra of three red giant stars (cos 4, cos 82, and cos 347) in the Ursa Minor dwarf spheriodal galaxy. Chemical abundances in these stars have been analysed for 26 elements including alpha-, iron-peak, and neutron capture elements. All three stars show low abundances of alpha-elements (Mg, Si, and Ca) and two stars (cos 82 and cos 347) show high abundance of Mn compared to Galactic halo stars of similar metallicity. One star (cos 4) has been confirmed to be very metal deficient ([Fe/H]=-2.7) and found to show anomalously low abundances of Mn, Cu, and Ba. In another star cos 82 ([Fe/H]=-1.5), we have found large excess of heavy neutron-capture elements with the general abundance pattern similar to the scaled solar system r-process abundance curve. These observational results are rather puzzling: low abundances of alpha-elements and high abundance of Mn seem to sugggest a significant contribution of...

  10. A Novel Approach for Star Extraction from Star Image

    Institute of Scientific and Technical Information of China (English)

    ZHENGSheng; LIUJian; TIANJinwen; YANGRuijuan

    2005-01-01

    Star acquisition is one of the most timeconsuming routines in star tracker operation. One star Point spread function (PSF) forms a near Gaussian distribution in the star image, the star image can be regarded as 2-D intensity surface, and every pixel is the sampled point. The star cluster grouping is to find the highes tintensity pixel among the PSFs and collect the adjacent pixels and group them. The possible highest intensity pixels are the maximum extremum points of the 2-D intensity surface. To efficiently extract star from the star image, a novel star acquisition approach, which uses the simplified least squares support vector machines regression algorithm to find the optimal intensity surface function and predictthe maximum extremum points, is proposed. Comput erexperiments are carried out for the simulated star images.The experimental results demonstrate that the proposed method has a lot of advantages, including the high efficiency and good robustness over a wide range of sensor noise.

  11. Abundances and ADFs in PNe with WC central stars

    CERN Document Server

    García-Rojas, Jorge; Morisset, Christophe; Ruiz, Maria Teresa

    2011-01-01

    We present preliminary results obtained from the analysis of very deep echelle spectra of a dozen planetary nebulae with [WC] or weak emission lines (wels) central stars. The computed abundance discrepancy factors (ADFs) are moderate, with values lower than 4. In principle, no evidence of the H-poor metal enriched inclusions proposed by Liu et al. (2000) have been found. However, a detailed analysis of the data is in progress.

  12. Infrared spectroscopy of stars

    Science.gov (United States)

    Merrill, K. M.; Ridgway, S. T.

    1979-01-01

    This paper reviews applications of IR techniques in stellar classification, studies of stellar photospheres, elemental and isotopic abundances, and the nature of remnant and ejected matter in near-circumstellar regions. Qualitative IR spectral classification of cool and hot stars is discussed, along with IR spectra of peculiar composite star systems and of obscured stars, and IR characteristics of stellar populations. The use of IR spectroscopy in theoretical modeling of stellar atmospheres is examined, IR indicators of stellar atmospheric composition are described, and contributions of IR spectroscopy to the study of stellar recycling of interstellar matter are summarized. The future of IR astronomy is also considered.

  13. Nuclear physics of stars

    CERN Document Server

    Iliadis, Christian

    2007-01-01

    Thermonuclear reactions in stars is a major topic in the field of nuclear astrophysics, and deals with the topics of how precisely stars generate their energy through nuclear reactions, and how these nuclear reactions create the elements the stars, planets and - ultimately - we humans consist of. The present book treats these topics in detail. It also presents the nuclear reaction and structure theory, thermonuclear reaction rate formalism and stellar nucleosynthesis. The topics are discussed in a coherent way, enabling the reader to grasp their interconnections intuitively. The book serves bo

  14. Entropy Production of Stars

    Directory of Open Access Journals (Sweden)

    Leonid M. Martyushev

    2015-06-01

    Full Text Available The entropy production (inside the volume bounded by a photosphere of main-sequence stars, subgiants, giants, and supergiants is calculated based on B–V photometry data. A non-linear inverse relationship of thermodynamic fluxes and forces as well as an almost constant specific (per volume entropy production of main-sequence stars (for 95% of stars, this quantity lies within 0.5 to 2.2 of the corresponding solar magnitude is found. The obtained results are discussed from the perspective of known extreme principles related to entropy production.

  15. Constraints of the physics of low-mass AGB stars from CH and CEMP stars

    CERN Document Server

    Cristallo, S; Goswami, A; Piersanti, L; Gobrecht, D

    2016-01-01

    We analyze a set of published elemental abundances from a sample of CH stars which are based on high resolution spectral analysis of ELODIE and SUBARU/HDS spectra. All the elemental abundances were derived from local thermodynamic equilibrium analysis usingmodel atmospheres, and thus, they represent the largest homogeneous abundance data available for CH stars up to date. For this reason, we can use the set to constrain the physics and the nucleosynthesis occurring in low mass AGB stars. CH stars have been polluted in the past from an already extinct AGB companion and thus show s-process enriched surfaces. We discuss the effects induced on the surface AGB s-process distributions by different prescriptions for convection and rotation. Our reference theoretical FRUITY set fits only part of the observations. Moreover, the s-process observational spread for a fixed metallicity cannot be reproduced. At Fe/H]>-1, a good fit is found when rotation and a different treatment of the inner border of the convective envel...

  16. On the conversion of neutron stars into quark stars

    CERN Document Server

    Pagliara, Giuseppe

    2013-01-01

    The possible existence of two families of compact stars, neutron stars and quark stars, naturally leads to a scenario in which a conversion process between the two stellar objects occurs with a consequent release of energy of the order of $10^{53}$ erg. We discuss recent hydrodynamical simulations of the burning process and neutrino diffusion simulations of cooling of a newly formed strange star. We also briefly discuss this scenario in connection with recent measurements of masses and radii of compact stars.

  17. Beta-decay of nuclei around Se-90. Search for signatures of a N=56 sub-shell closure relevant the r-process

    CERN Document Server

    Quinn, M; Pereira, J; Surman, R; Arndt, O; Baumann, T; Becerril, A; Elliot, T; Estrade, A; Galaviz, D; Ginter, T; Hausmann, M; Hennrich, S; Kessler, R; Kratz, K -L; Lorusso, G; Mantica, P F; Matos, M; Moller, P; Montes, F; Pfeiffer, B; Portillo, M; Hennrich, S; Schatz, H; Schertz, F; Schnorrenberger, L; Smith, E; Stolz, A; Walters, W B; Wohr, A

    2011-01-01

    Nuclear structure plays a significant role on the rapid neutron capture process (r-process) since shapes evolve with the emergence of shells and sub-shells. There was some indication in neighboring nuclei that we might find examples of a new N=56 sub-shell, which may give rise to a doubly magic Se-90 nucleus. Beta-decay half lives of nuclei around Se-90 have been measured to determine if this nucleus has in fact a doubly-magic character. The fragmentation of Xe-136 beam at the National Superconducting Cyclotron Laboratory at Michigan State University was used to create a cocktail of nuclei in the A=90 region. We have measured the half lives of twenty-two nuclei near the r-process path in the A=90 region. The half lives of As-88 and Se-90 have been measured for the first time. The values were compared with theoretical predictions in the search for nuclear-deformation signatures of a N=56 sub-shell, and its possible role in the emergence of a potential doubly-magic Se-90. The impact of such hypothesis on the sy...

  18. Half-lives and branchings for {\\beta}-delayed neutron emission for neutron-rich Co-Cu isotopes in the r-process

    CERN Document Server

    Hosmer, P; Aprahamian, A; Arndt, O; Clement, R R C; Estrade, A; Farouqi, K; Kratz, K -L; Liddick, S N; Lisetskiy, A F; Mantica, P F; Möller, P; Mueller, W F; Montes, F; Morton, A C; Ouellette, M; Pellegrini, E; Pereira, J; Pfeiffer, B; Reeder, P; Santi, P; Steiner, M; Stolz, A; Tomlin, B E; Walters, W B; Wöhr, A; 10.1103/PhysRevC.82.025806

    2010-01-01

    The {\\beta} decays of very neutron-rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL {\\beta}-counting station in conjunction with the neutron detector NERO. We measured the branchings for {\\beta}-delayed neutron emission (Pn values) for 74Co (18 +/- 15%) and 75-77Ni (10 +/- 2.8%, 14 +/- 3.6%, and 30 +/- 24%, respectively) for the first time, and remeasured the Pn values of 77-79Cu, 79,81Zn, and 82Ga. For 77-79Cu and for 81Zn we obtain significantly larger Pn values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of 75Co (30 +/- 11 ms) and 80Cu (170+110 -50 ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron-capture process (r-process) is explored. We find that with our new data, the classical r-process model is bet...

  19. On the Radial Abundance Gradients of Europium and Oxygen of Stars Inside the Disk of a Simulated Milky Way

    Science.gov (United States)

    Ruiz-Rocha, Krystal; Montes, Gabriela; Ramirez-Ruiz, Enrico

    2017-01-01

    Studies of galaxy evolution and formation through simulations and observations have yielded valuable insight into the life of stars. Abundance gradients, in particular, provide useful information about the element assembly history in the Milky Way. To study these gradients we use data from a simulation titled Eris which has been constructed with the goal of reproducing the properties of the Milky Way, to find the gradients of stars located in the disk that have been enriched by Supernovae and Neutron Star Mergers. We compare these gradients to the observations acquired from looking at Cepheids and field stars in the disk of our Milky Way. We also aim to understand whether radial metallicity gradients can be used to differentiate between Neutron Star Merger versus Type II Supernovae enrichment.

  20. Oxygen-rich droplets and the enrichment of the ISM

    CERN Document Server

    Stasinska, G; Rodríguez, M; Henney, W J

    2007-01-01

    We argue that the discrepancies observed in HII regions between abundances derived from optical recombination lines (ORLs) and collisionally excited lines (CELs) might well be the signature of a scenario of the enrichment of the interstellar medium (ISM) proposed by Tenorio-Tagle (1996). In this scenario, the fresh oxygen released during massive supernova explosions is confined within the hot superbubbles as long as supernovae continue to explode. Only after the last massive supernova explosion, the metal-rich gas starts cooling down and falls on the galaxy within metal-rich droplets. Full mixing of these metal-rich droplets and the ISM occurs during photoionization by the next generations of massive stars. During this process, the metal-rich droplets give rise to strong recombination lines of the metals, leading to the observed ORL-CEL discrepancy. (The full version of this work is submitted to Astronomy and Astrophysics.)

  1. A grid of MARCS model atmospheres for S stars

    CERN Document Server

    Van Eck, Sophie; Plez, Bertrand; Jorissen, Alain; Edvardsson, Bengt; Eriksson, Kjell; Gustafsson, Bengt; Jorgensen, Uffe-Grae; Nordlund, Ake

    2010-01-01

    S-type stars are late-type giants whose atmosphere is enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. A large grid of S-star model atmospheres has been computed covering the range 2700 < Teff < 4000 K with 0.5 < C/O < 0.99. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle Teff, C/O and [s/Fe]. A "best-model finding tool" was developed using a set of well-chosen indices and checked against photometry as well as low- and high-resolution spectroscopy. It is found that applying M-star model atmospheres (i.e., with a solar C/O ratio) to S stars can lead to errors on Teff up to 400K. We constrain the parameter space occupied by S stars of the vast sample of Henize stars in terms of Teff, [C/O] and [s/Fe].

  2. The Number of Supernovae From Primordial Stars in the Universe

    Energy Technology Data Exchange (ETDEWEB)

    Wise, J

    2004-12-15

    Recent simulations of the formation of the first luminous objects in the universe predict isolated very massive stars to form in dark matter halos with virial temperatures large enough to allow significant amounts of molecular hydrogen to form. We construct a semi-analytic model based on the Press-Schechter formalism and calibrate the minimum halos mass that may form a primordial star with the results from extensive adaptive mesh refinement simulations. The model also includes star formation in objects with virial temperatures in excess of ten thousand Kelvin. The free parameters are tuned to match the optical depth measurements by the WMAP satellite. The models explicitly includes the negative feedback of the destruction of molecular hydrogen by a soft UV background which is computed self-consistently. We predict high redshift supernova rates as one of the most promising tools to test the current scenario of primordial star formation. The supernova rate from primordial stars peaks at redshifts {approx}20. Using an analytic model for the luminosities of pair-instability supernovae we predict observable magnitudes and discuss possible observational strategies. Such supernovae would release enough metals corresponding to a uniform enrichment to a few hundred thousands of solar metalicity. If some of these stars produce gamma ray bursts our rates will be directly applicable to understanding the anticipated results from the SWIFT satellite. This study highlights the great potential for the James Webb space telescope in probing cosmic structure at redshifts greater than 20.

  3. The True origin of Wolf-Rayet stars

    CERN Document Server

    Vink, Jorick S

    2015-01-01

    The Wolf-Rayet (WR) phenomenon is widespread in astronomy. It involves classical WRs, very massive stars (VMS), WR central stars of planetary nebula CSPN [WRs], and supernovae (SNe). But what is the root cause for a certain type of object to turn into an emission-line star? In this contribution, I discuss the basic aspects of radiation-driven winds that might reveal the ultimate difference between WR stars and canonical O-type stars. I discuss the aspects of (i) self-enrichment via CNO elements, (ii) high effective temperatures Teff, (iii) an increase in the helium abundance Y, and finally (iv) the Eddington factor Gamma. Over the last couple of years, we have made a breakthrough in our understanding of Gamma-dependent mass loss, which will have far-reaching consequences for the evolution and fate of the most massive stars in the Universe. Finally, I discuss the prospects for studies of the WR phenomenon in the highest redshift Ly-alpha and He II emitting galaxies.

  4. GRACES observations of young [alpha/Fe]-rich stars

    CERN Document Server

    Yong, David; Venn, Kim A; Chene, Andre-Nicolas; Keown, Jared; Malo, Lison; Martioli, Eder; Alves-Brito, Alan; Asplund, Martin; Dotter, Aaron; Martell, Sarah L; Melendez, Jorge; Schlesinger, Katharine J

    2016-01-01

    We measure chemical abundance ratios and radial velocities in four massive (i.e., young) [alpha/Fe]-rich red giant stars using high-resolution high-S/N spectra from ESPaDOnS fed by Gemini-GRACES. Our differential analysis ensures that our chemical abundances are on the same scale as the Alves-Brito et al. (2010) study of bulge, thin and thick disk red giants. We confirm that the program stars have enhanced [alpha/Fe] ratios and are slightly metal poor. Aside from lithium enrichment in one object, the program stars exhibit no chemical abundance anomalies when compared to giant stars of similar metallicity throughout the Galaxy. This includes the elements Li, O, Si, Ca, Ti, Cr, Ni, Cu, Ba, La, and Eu. Therefore, there are no obvious chemical signatures that can help to reveal the origin of these unusual stars. While our new observations show that only one star (not the Li-rich object) exhibits a radial velocity variation, simulations indicate that we cannot exclude the possibility that all four could be binarie...

  5. Complex Organic and Inorganic Compounds in Shells of Lithium-rich K Giant Stars

    CERN Document Server

    de la Reza, Ramiro; Oliveira, Isa; Rengaswamy, Sridharan

    2015-01-01

    Hydrocarbon organic material, as found in the interstellar medium, exists in complex mixtures of aromatic and aliphatic forms. It is considered to be originated from carbon enriched giant stars during their final stages of evolution, when very strong mass loss occurs in a few thousand years on their way to become planetary nebulae. We show here that the same organic compounds appear to be formed in previous stages of the evolution of giant stars. More specifically, during the first ascending giant branch K-type stars. According to our model this happens only when these stars are being abruptly enriched with lithium together with the formation of a circumstellar shell with a strong mass loss during just a few thousand years. This sudden mass loss is, on an average, a thousand times larger than that of normal Li-poor K giant stars. This shell would later be detached, specially when the star stops its Li enrichment and a rapid photospheric Li depletion occurs. In order to gain extra carbon-based material to form...

  6. Interferometric star tracker Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Optical Physics Company (OPC) proposes to develop a high accuracy version of its interferometric star tracker capable of meeting the milli-arcsecond-level pointing...

  7. Notes on Star Formation

    CERN Document Server

    Krumholz, Mark R

    2015-01-01

    This book provides an introduction to the field of star formation at a level suitable for graduate students or advanced undergraduates in astronomy or physics. The structure of the book is as follows. The first two chapters begin with a discussion of observational techniques, and the basic phenomenology they reveal. The goal is to familiarize students with the basic techniques that will be used throughout, and to provide a common vocabulary for the rest of the book. The next five chapters provide a similar review of the basic physical processes that are important for star formation. Again, the goal is to provide a basis for what follows. The remaining chapters discuss star formation over a variety of scales, starting with the galactic scale and working down to the scales of individual stars and their disks. The book concludes with a brief discussion of the clearing of disks and the transition to planet formation. The book includes five problem sets, complete with solutions.

  8. Spectroscopy among the stars.

    Science.gov (United States)

    Winnewisser, G

    1996-06-01

    The space between the stars is not void, but filled with interstellar matter, mainly composed of dust and gas, which gather in large interstellar clouds. In our Galaxy these interstellar clouds are distributed along a thin, but extended layer which basically traces out the spiral distribution of matter: the stars, the gas, and the dust component. Up to the present time more than 100 different molecules have been identified in interstellar molecular clouds. The majority of the interstellar molecules constitute carbon containing organic substances. During the past years, overwhelming evidence has been gathered, mainly through spectroscopic observations, that interstellar molecular clouds provide the birthplaces for stars. In fact detailed high spectral and spatial resolution spectroscopic measurements reveal physical and chemical processes of the intricate star formation process.

  9. Sports Stars Shine

    Institute of Scientific and Technical Information of China (English)

    Yu Yan

    2012-01-01

    Alive and exciting award ceremony drew the attention of numerous Chinese households on the night of January 15.The most popular Chinese sports stars attended the 2011 CCTV Sports Personality Award Ceremony at the National Indoor Stadium in Beijing.

  10. Temperature of neutron stars

    Science.gov (United States)

    Tsuruta, Sachiko

    2016-07-01

    We start with a brief introduction to the historical background in the early pioneering days when the first neutron star thermal evolution calculations predicted the presence of neutron stars hot enough to be observable. We then report on the first detection of neutron star temperatures by ROSAT X-ray satellite, which vindicated the earlier prediction of hot neutron stars. We proceed to present subsequent developments, both in theory and observation, up to today. We then discuss the current status and the future prospect, which will offer useful insight to the understanding of basic properties of ultra-high density matter beyond the nuclear density, such as the possible presence of such exotic particles as pion condensates.

  11. Magnetospheres of massive stars

    Science.gov (United States)

    Küker, M.

    We study the interaction of line-driven winds from massive stars with the magnetic field rooted in these stars by carrying out numerical simulations using the Nirvana MHD code in 2D in spherical polar coordinates. The code's adaptive mesh refinement feature allows high spatial resolution across the whole simulation box. We study both O and Wolf-Rayet stars for a range of magnetic field strengths from weak to strong as measured by the confinement parameter. For weak fields our simulations show that the initially dipolar field opens up far away from the star and a thin disk-like structure forms in the equatorial plane of the magnetic field. For stronger fields the disk is disrupted close to the stellar surface and closed field lines persist at low latitudes. For very strong fields a pronounced magnetosphere forms where the gas is forced to move along the field lines and eventually falls back to the stellar surface.

  12. Stars resembling the Sun

    Science.gov (United States)

    Cayrel de Strobel, G.

    This review is primarily directed to the question whether photometric solar analogues remain such when subjected to detailed spectroscopic analyses and interpreted with the help of internal stucture models. In other words, whether the physical parameters: mass, chemical composition, age (determining effective temperature and luminosity), chromospheric activity, equatorial rotation, lithium abundance, velocity fields etc., we derive from the spectral analysis of a photometric solar analogue, are really close to those of the Sun. We start from 109 photometric solar analogues extracted from different authors. The stars selected had to satisfy three conditions: i) their colour index (B-V) must be contained in the interval: Δ (B-V) = 0.59-0.69, ii) they must possess a trigonometric parallax, iii) they must have undergone a high resolution detailed spectroscopic analysis. First, this review presents photometric and spectrophotometric researches on solar analogues and recalls the pionneering work on these stars by the late Johannes Hardorp. After a brief discussion on low and high resolution spectroscopic researches, a comparison is made between effective temperatures as obtained, directly, from detailed spectral analyses and those obtained, indirectly, from different photometric relations. An interesting point in this review is the discussion on the tantalilizing value of the (B-V)solar of the Sun, and the presentation of a new reliable value of this index. A short restatement of the kinematic properties of the sample of solar analogues is also made. And, finally, the observational ( T eff, M bol) diagram, obtained with 99 of the initially presented 109 analogues, is compared to a theoretical ( T eff, M bol) diagram. This latter has been constructed with a grid of internal structure models for which, (very important for this investigation), the Sun was used as gauge. In analysing the position, with respect to the Sun, of each star we hoped to find a certain number of

  13. Neutron Stars Recent Developments

    CERN Document Server

    Heiselberg, H

    1999-01-01

    Recent developments in neutron star theory and observation are discussed. Based on modern nucleon-nucleon potentials more reliable equations of state for dense nuclear matter have been constructed. Furthermore, phase transitions such as pion, kaon and hyperon condensation, superfluidity and quark matter can occur in cores of neutron stars. Specifically, the nuclear to quark matter phase transition and its mixed phases with intriguing structures is treated. Rotating neutron stars with and without phase transitions are discussed and compared to observed masses, radii and glitches. The observations of possible heavy $\\sim 2M_\\odot$ neutron stars in X-ray binaries and QPO's require relatively stiff equation of states and restrict strong phase transitions to occur at very high nuclear densities only.

  14. Worlds around other stars

    Science.gov (United States)

    Black, David C.

    1991-01-01

    The possible, though tentative, detection of planetary companions to other stars which may be capable of supporting life as we know it through the use of a new generation of detectors and telescopes, combined with some innovative detection techniques, is discussed. The current view of the origin of the solar system, based on the nebular hypothesis, is discussed as it pertains to the formation of how and where planets form and, hence, how and where to search for them. Both direct methods of search for other planetary systems, which involve detecting reflected light or infrared radiation form the planets themselves, and indirect methods, which involve the scrutinization of a star for signs that it is responding to the gravitational tug of an orbiting planet, are discussed at length. In particular, various methods for detecting minute velocity perturbations of stars are discussed. It is noted that the study of brown dwarfs may also provide clues on the formation of stars and planets.

  15. A quantitative study of O stars in NGC2244 and the Mon OB2 association

    CERN Document Server

    Martins, F; Rauw, G; Hillier, D J

    2011-01-01

    Our goal is to determine the stellar and wind properties of seven O stars in the cluster NGC2244 and three O stars in the OB association MonOB2. These properties give us insight into the mass loss rates of O stars, allow us to check the validity of rotational mixing in massive stars, and to better understand the effects of the ionizing flux and wind mechanical energy release on the surrounding interstellar medium and its influence on triggered star formation. We collect optical and UV spectra of the target stars which are analyzed by means of atmosphere models computed with the code CMFGEN. The spectra of binary stars are disentangled and the components are studied separately. All stars have an evolutionary age less than 5 million years, with the most massive stars being among the youngest. Nitrogen surface abundances show no clear relation with projected rotational velocities. Binaries and single stars show the same range of enrichment. This is attributed to the youth and/or wide separation of the binary sys...

  16. Imprints of fast-rotating massive stars in the Galactic Bulge.

    Science.gov (United States)

    Chiappini, Cristina; Frischknecht, Urs; Meynet, Georges; Hirschi, Raphael; Barbuy, Beatriz; Pignatari, Marco; Decressin, Thibaut; Maeder, André

    2011-04-28

    The first stars that formed after the Big Bang were probably massive, and they provided the Universe with the first elements heavier than helium ('metals'), which were incorporated into low-mass stars that have survived to the present. Eight stars in the oldest globular cluster in the Galaxy, NGC 6522, were found to have surface abundances consistent with the gas from which they formed being enriched by massive stars (that is, with higher α-element/Fe and Eu/Fe ratios than those of the Sun). However, the same stars have anomalously high abundances of Ba and La with respect to Fe, which usually arises through nucleosynthesis in low-mass stars (via the slow-neutron-capture process, or s-process). Recent theory suggests that metal-poor fast-rotating massive stars are able to boost the s-process yields by up to four orders of magnitude, which might provide a solution to this contradiction. Here we report a reanalysis of the earlier spectra, which reveals that Y and Sr are also overabundant with respect to Fe, showing a large scatter similar to that observed in extremely metal-poor stars, whereas C abundances are not enhanced. This pattern is best explained as originating in metal-poor fast-rotating massive stars, which might point to a common property of the first stellar generations and even of the 'first stars'.

  17. Highly efficient star formation in NGC 5253 possibly from stream-fed accretion.

    Science.gov (United States)

    Turner, J L; Beck, S C; Benford, D J; Consiglio, S M; Ho, P T P; Kovács, A; Meier, D S; Zhao, J-H

    2015-03-19

    Gas clouds in present-day galaxies are inefficient at forming stars. Low star-formation efficiency is a critical parameter in galaxy evolution: it is why stars are still forming nearly 14 billion years after the Big Bang and why star clusters generally do not survive their births, instead dispersing to form galactic disks or bulges. Yet the existence of ancient massive bound star clusters (globular clusters) in the Milky Way suggests that efficiencies were higher when they formed ten billion years ago. A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. Here we report the detection of the J = 3→2 rotational transition of CO at the location of the massive cluster. The gas cloud is hot, dense, quiescent and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by the embedded star cluster. Its star-formation efficiency exceeds 50 per cent, tenfold that of clouds in the Milky Way. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.

  18. Catch a Star 2008!

    Science.gov (United States)

    2007-10-01

    ESO and the European Association for Astronomy Education have just launched the 2008 edition of 'Catch a Star', their international astronomy competition for school students. Now in its sixth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. CAS logo The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. In teams, students investigate an astronomical topic of their choice and write a report about it. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes such as the Very Large Telescope (VLT) or future telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Extremely Large Telescope (E-ELT) could contribute to investigations of the topic. Students may also include practical activities such as observations or experiments. For the artistically minded, 'Catch a Star' also offers an artwork competition, 'Catch a Star Artists'. Last year, hundreds of students from across Europe and beyond took part in 'Catch a Star', submitting astronomical projects and artwork. "'Catch a Star' gets students thinking about the wonders of the Universe and the science of astronomy, with a chance of winning great prizes. It's easy to take part, whether by writing about astronomy or creating astronomically inspired artwork," said Douglas Pierce-Price, Education Officer at ESO. As well as the top prize - a trip to ESO's Very Large Telescope in Chile - visits to observatories in Austria and Spain, and many other prizes, can also be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners

  19. Alkaline broadening in Stars

    CERN Document Server

    De Kertanguy, A

    2015-01-01

    Giving new insight for line broadening theory for atoms with more structure than hydrogen in most stars. Using symbolic software to build precise wave functions corrected for ds;dp quantum defects. The profiles obtained with that approach, have peculiar trends, narrower than hydrogen, all quantum defects used are taken from atomic database topbase. Illustration of stronger effects of ions and electrons on the alkaline profiles, than neutral-neutral collision mechanism. Keywords : Stars: fundamental parameters - Atomic processes - Line: profiles.

  20. Chaotic Star Birth

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives. The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region. The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333. In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.