scholarly journals r-Process Elements as Tracers of Enrichment Processes in the Early Halo

2015 ◽  
Vol 11 (S317) ◽  
pp. 272-273
Author(s):  
Johannes Andersen ◽  
Birgitta Nordström ◽  
Terese T. Hansen
Keyword(s):  
Mass Transfer ◽  
Neutron Capture ◽  
Binary Systems ◽  
Chemical Enrichment ◽  
Halo Stars ◽  
Standard Scenario ◽  
R Process ◽  
Process Elements

AbstractSignificant 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.

scholarly journals Production and Recycling of Carbon in the Early Galactic Halo

2015 ◽  
Vol 11 (A29B) ◽  
pp. 158-159
Author(s):  
Johannes Andersen ◽  
Birgitta Nordström ◽  
Terese T. Hansen
Keyword(s):  
Mass Transfer ◽  
Binary Systems ◽  
First Generation ◽  
Galactic Halo ◽  
Large Fraction ◽  
Halo Stars ◽  
Production Site ◽  
Standard Scenario ◽  
Shed Light

AbstractA large fraction of extremely metal-poor halo stars are strongly enriched in carbon (CEMP stars). The standard scenario for their origin is mass transfer in binary systems, but this assumes that they are binaries. If not, the C must have been implanted in their natal clouds from a distant production site(s) in the preceding - possibly first - generation of stars. The binary population of CEMP subgroups can shed light on these processes.

Distribution of R- and S-Process Elements in the Galactic Halo

1988 ◽  
Vol 132 ◽  
pp. 501-506
Author(s):  
C. Sneden ◽  
C. A. Pilachowski ◽  
K. K. Gilroy ◽  
J. J. Cowan
Keyword(s):  
Heavy Element ◽  
Galactic Halo ◽  
Low Noise ◽  
Heavy Elements ◽  
Process Synthesis ◽  
Element Abundances ◽  
Halo Stars ◽  
Abundance Patterns ◽  
R Process ◽  
Process Elements

Current observational results for the abundances of the very heavy elements (Z>30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

scholarly journals Constraining nucleosynthesis in two CEMP progenitors using fluorine

2020 ◽  
Vol 498 (3) ◽  
pp. 3549-3559
Author(s):  
Aldo Mura-Guzmán ◽  
D Yong ◽  
C Abate ◽  
A Karakas ◽  
C Kobayashi ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Slow Neutron ◽  
Asymptotic Giant Branch ◽  
Capture Process ◽  
Upper Limit ◽  
Infrared Spectrometer ◽  
Binary Evolution ◽  
Vibration Rotation ◽  
R Process ◽  
Process Elements

ABSTRACT We present new fluorine abundance estimations in two carbon enhanced metal-poor (CEMP) stars, HE 1429−0551 and HE 1305+0007. HE 1429−0551 is also enriched in slow neutron-capture process (s-process) elements, a CEMP-s, and HE 1305+0007 is enhanced in both, slow and rapid neutron-capture process elements, a CEMP-s/r. The F abundances estimates are derived from the vibration–rotation transition of the HF molecule at 23358.6 Å  using high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrometer (IGRINS) at the 4-m class Lowell Discovery Telescope. Our results include an F abundance measurement in HE 1429−0551 of A(F) = +3.93 ([F/Fe] = +1.90) at [Fe/H] = −2.53, and an F upper limit in HE 1305+0007 of A(F) < +3.28 ([F/Fe] < +1.00) at [Fe/H] = −2.28. Our new derived F abundance in HE 1429−0551 makes this object the most metal-poor star where F has been detected. We carefully compare these results with literature values and state-of-the-art CEMP-s model predictions including detailed asymptotic giant branch (AGB) nucleosynthesis and binary evolution. The modelled fluorine abundance for HE 1429−0551 is within reasonable agreement with our observed abundance, although is slightly higher than our observed value. For HE 1429−0551, our findings support the scenario via mass transfer by a primary companion during its thermally pulsing phase. Our estimated upper limit in HE 1305+0007, along with data from the literature, shows large discrepancies compared with AGB models. The discrepancy is principally due to the simultaneous s- and r-process element enhancements which the model struggles to reproduce.

scholarly journals Interpretation of CEMP(s) and CEMP(s + r) Stars with AGB Models

2009 ◽  
Vol 26 (3) ◽  
pp. 314-321 ◽  
Author(s):  
Sara Bisterzo ◽  
Roberto Gallino ◽  
Oscar Straniero ◽  
Wako Aoki
Keyword(s):  
Mass Transfer ◽  
Binary System ◽  
Neutron Capture ◽  
Molecular Cloud ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Spectroscopic Observations ◽  
Theoretical Predictions ◽  
Process Elements

AbstractAsymptotic Giant Branch (AGB) stars play a fundamental role in 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 thermally pulsing 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 by AGB models of different initial masses with proper 13C-pocket efficiencies and dilution factors. Na (and Mg), produced via the neutron capture chain starting from 22Ne, may provide an indicator of the initial AGB mass.

scholarly journals Chemical Evolution of R-process Elements in the Hierarchical Galaxy Formation

2015 ◽  
Vol 11 (S317) ◽  
pp. 318-319
Author(s):  
Yutaka Komiya ◽  
Toshikazu Shigeyama
Keyword(s):  
Neutron Star ◽  
Chemical Evolution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Chemical Evolution ◽  
Halo Stars ◽  
R Process ◽  
Process Elements ◽  
Milky Way Halo

AbstractThe main astronomical source of r-process elements has not yet been identified. One plausible site is neutron star mergers (NSMs). From the perspective of Galactic chemical evolution, however, it has been pointed out that the NSM scenario is incompatible with observations. Recently, Tsujimoto & Shigeyama (2014) pointed out that NSM ejecta can spread into much larger volume than ejecta from a supernova. We re-examine the chemical evolution of r-process elements under the NSM scenario considering this difference in propagation of the ejecta. We find that the NSM scenario can be compatible with the observed abundances of the Milky Way halo stars.

scholarly journals Carbon-Enhanced Metal-Poor (CEMP) stars

2009 ◽  
Vol 5 (S265) ◽  
pp. 111-116 ◽  
Author(s):  
Wako Aoki
Keyword(s):  
Neutron Capture ◽  
Significant Fraction ◽  
Agb Stars ◽  
Iron Deficient ◽  
R Process ◽  
Process Elements

AbstractA significant fraction of metal-poor stars have large over-abundances of carbon, and are called Carbon-Enhanced Metal-Poor (CEMP) stars. Most of CEMP stars also show excesses of heavy neutron-capture elements like Ba, indicating that their origin is the nucleosynthesis in AGB stars. Remaining CEMP stars that have Ba abundances as low as non-carbon-rich stars appear in the lowest metallicity range ([Fe/H]≲−2.5), and connections with the two most iron-deficient stars (so-called Hyper Metal-Poor stars) are suggested. Although the origins of the carbon-excesses in these objects have not been well identified, some objects suggest contributions of faint supernovae. Remaining problems on CEMP stars, such as the binary fraction, excess of r-process elements, are discussed.

scholarly journals The GALAH survey: temporal chemical enrichment of the galactic disc

2019 ◽  
Vol 491 (2) ◽  
pp. 2043-2056 ◽  
Author(s):  
Jane Lin ◽  
Martin Asplund ◽  
Yuan-Sen Ting ◽  
Luca Casagrande ◽  
Sven Buder ◽  
...  
Keyword(s):  
Main Sequence ◽  
Abundance Ratio ◽  
Core Collapse ◽  
Chemical Enrichment ◽  
R Process ◽  
Short Time ◽  
Process Elements ◽  
Process Element ◽  
Larger Sample ◽  
Short Time Delay

ABSTRACT We present isochrone ages and initial bulk metallicities ($\rm [Fe/H]_{bulk}$, by accounting for diffusion) of 163 722 stars from the GALAH Data Release 2, mainly composed of main-sequence turn-off stars and subgiants ($7000\, \mathrm{ K}> T_{\mathrm{ eff}}> 4000\, \mathrm{ K}$ and $\log g>3$ dex). The local age–metallicity relationship (AMR) is nearly flat but with significant scatter at all ages; the scatter is even higher when considering the observed surface abundances. After correcting for selection effects, the AMR appears to have intrinsic structures indicative of two star formation events, which we speculate are connected to the thin and thick discs in the solar neighbourhood. We also present abundance ratio trends for 16 elements as a function of age, across different $\rm [Fe/H]_{bulk}$ bins. In general, we find the trends in terms of [X/Fe] versus age from our far larger sample to be compatible with studies based on small (∼100 stars) samples of solar twins, but we now extend them to both sub- and supersolar metallicities. The α-elements show differing behaviour: the hydrostatic α-elements O and Mg show a steady decline with time for all metallicities, while the explosive α-elements Si, Ca, and Ti are nearly constant during the thin-disc epoch (ages $\lesssim \! 12$ Gyr). The s-process elements Y and Ba show increasing [X/Fe] with time while the r-process element Eu has the opposite trend, thus favouring a primary production from sources with a short time delay such as core-collapse supernovae over long-delay events such as neutron star mergers.

scholarly journals A Spectroscopic Study of Barium Stars

2008 ◽  
Vol 4 (S252) ◽  
pp. 425-426
Author(s):  
G. Q. Liu ◽  
Y. C. Liang ◽  
L. Deng
Keyword(s):  
Neutron Capture ◽  
Binary Systems ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Agb Stars ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
Capture Process ◽  
Abundance Patterns ◽  
Process Elements

AbstractWe present an analysis of eight barium stars, providing their atmospheric parameters (Teff, log g, [Fe/H], ξt) and chemical abundances, based on the high signal-to-noise ratio and high resolution Echelle spectra. The s-process elements Y, Zr, Ba, La, Eu show obvious overabundance relative to the Sun. And Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Ni show comparable abundances to the Solar ones. The results of theoretical model of wind accretion for binary systems can explain the observed abundance patterns of the neutron capture process elements in these Ba stars, which means that their overabundant heavy-elements could be caused by accreting the ejecta of AGB stars, the progenitors of the present white dwarf companions in the binary systems.

scholarly journals Chemical Evolution and Extremely Metal-Poor Stars

1998 ◽  
Vol 11 (1) ◽  
pp. 49-52
Author(s):  
Andrew McWilliam
Keyword(s):  
Neutron Capture ◽  
Heavy Element ◽  
Massive Stars ◽  
Small Sample ◽  
Heavy Elements ◽  
High Mass ◽  
Type Ii ◽  
Element Abundances ◽  
Halo Stars ◽  
R Process

Early abundance studies (e.g. Pagel 1968) showed that neutron-capture heavy elements (Z > 30) are present in halo stars, but deficient relative iron. Truran (1981) argued that at low [Fe/H] the chemical enrichment time scale was shorter than the lifetime of low-mass AGB progenitors, which are the main source of solar system heavy elements. He proposed that in the halo the heavy elements were produced by high mass stars, in type II supernova events (SNII), by rapid neutron capture nucleosynthesis (the r-process). Spite & Spite (1978) investigated the trend of heavy element abundances with metallicity, from a small sample of halo stars. They found that at [Fe/H]~ -1.5 the halo [heavy element/Fe] ratio is approximately solar; but at lower [Fe/H] there is a roughly linear decrease of [heavy element/Fe] with declining [Fe/H]. Subsequent observations confirmed the general trend of heavy elements in the halo: [M/Fe]~0 down to [Fe/H]~ -2, followed by a linear decline in [M/Fe] to lower [Fe/H] (e.g. Gilroy et al 1988, Lambert 1987). Additional evidence for the role of SNII in halo heavy element synthesis comes from the trend of [Eu/Fe] with [Fe/H]. Europium is an almost pure r-process element (Käppeler et al. 1989) and its abundance trend with metallicity is similar to the α element trend (e.g. O and Mg made in massive stars). The element ratios show an increase in [M/Fe] as [Fe/H] decreases from 0 to —1; below this point [Eu/Fe] and [α/Fe] remain constant at ~+0.3 dex. For α elements this behavior is thought to be due to the change in the relative contributions from type II SN and type la SN in the disk and halo (Tinsley 1979). The trend for Eu also indicates production by massive stars (e.g. SNII). Near [Fe/H]~ -2.5 Eu appears to decline relative to [Fe/H] (like other heavy elements, but unlike the α elements). This abundance trend has been used to constrain the numerous proposed astrophysical sites of the r-process (e.g. Mathews & Cowan 1990).

scholarly journals S-Process Deficiencies in Low-Mass Supergiant Variables

1989 ◽  
Vol 106 ◽  
pp. 154-154
Author(s):  
Howard E. Bond ◽  
R. Earle Luck
Keyword(s):  
Variable Stars ◽  
Elemental Abundance ◽  
Type Ii ◽  
Hydrogen Burning ◽  
Halo Stars ◽  
Low Mass ◽  
R Process ◽  
Nuclear Processing ◽  
Halo Population ◽  
Process Elements

We have carried out abundance analyses of four low-mass supergiant variable stars (the RV Tauri or RV Tau-like variables AI Cmi, RU Cen, and U Mon, and the Type II Cepheid Kappa Pav) and two Population I Cepheids (CO Aur and V378 Cen). We used model atmospheres in which hydrostatic equilibrium, plane-parallel geometry, and local thermodynamic equilibrium (LTE) were assumed. Discussion of the results, and of published analyses of additional low-mass variables, leads to the following conclusions. (1) The Population I Cepheids show normal, solar elemental abundance ratios (except for the CNO elements, which have been altered by hydrogen burning), lending some support to the validity of the above assumptions for analyses of luminous variable stars. (2) The low-mass variables show metallicities ranging from solar down to [Fe/H] values typical of thick-disk and, in a few cases, of halo stars. (3) Most low-mass variables show a systematic underabundance of the heavy s- and r-process elements. In a few cases this may indicate that the stars were initially of extremely low metal content, and are now hydrogen deficient. However, most of the variables do not appear to belong to the halo population, nor do they show other abundance patterns seen in halo stars. The origin of these underabundances, and their apparent confinement to luminous variables, are difficult to understand in the context of nuclear processing. (4) The heavy-element underabundances correlate with second ionization potential in a manner suggesting that they are non-LTE phenomenan arising from overionization by Lyman-continuum photons. Why a similar effect is not seen in Population I Cepheids is unclear, but may be related to their generally weaker hydrogen emission. (5) Several low-mass variables, including RU Cen and V553 Cen, show carbon enhancements and solar s-process abundances. Relative to the majority of the Type II variables, these stars are s-process enhanced, and we argue that they are related to the Ba II and CH stars.

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