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.

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 Chemical Evolution of Galaxies: Abundance Trends and Implications

1991 ◽  
Vol 145 ◽  
pp. 13-19
Author(s):  
James W. Truran
Keyword(s):  
Massive Stars ◽  
Current Knowledge ◽  
Spectroscopic Studies ◽  
Early History ◽  
Elemental Abundance ◽  
Type Ii ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Abundance Trends ◽  
History Of

Recent spectroscopic studies of the elemental abundance patterns associated with extremely metal deficient field halo stars and globular cluster stars are briefly reviewed. These metal deficient stellar populations have been found to be characterized by abundance patterns which differ quite distinctly from those of solar system abundances, but are consistent with the view that they reflect primarily the nucleosynthesis products of the evolution of massive stars and associated Type II supernovae. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints upon theories of the formation and early history of our Galaxy.

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 The Oldest Stars as Tracers of Heavy Element Formation at Early Epochs

2001 ◽  
Vol 204 ◽  
pp. 333-334 ◽  
Author(s):  
James W. Truran
Keyword(s):  
Star Formation ◽  
Theoretical Models ◽  
Elemental Abundance ◽  
Agb Stars ◽  
Lower Mass ◽  
Set Constraints ◽  
Abundance Patterns ◽  
History Of ◽  
R Process ◽  
Process Elements

Elemental abundance patterns in very metal-poor halo field stars and globular cluster stars play a crucial role both in guiding theoretical models of nucleosynthesis and in providing constraints upon the early star formation and concomitant nucleosynthesis history of our Galaxy. The abundance patterns characterizing the oldest and most metal deficient stars ([Fe/H] ≤ −3) are entirely consistent with their being products of metal-poor massive stars of lifetimes τ ≤ 108years. This includes both the elevated abundances of thealpha-elements (O, Mg, Si, S, Ca, and Ti) relative to iron-peak elements and the dominance of r-process elements over s-process elements. The nucleosynthetic contributions of lower mass AGB stars of longer lifetimes (τ ≈ 109years) begin to appear at metallicities [Fe/H] ≈ −2.5, while clear evidence for iron-peak nuclei produced in supernovae Ia (τ ≥ 1-2x109years?) does not appear until metallicities approaching [Fe/H] ~ −1. Similar trends are also suggested by abundances determined for gas clouds at high redshifts. We review the manner in which a knowledge of the abundances of the stellar and gas components of early populations, as a function of [Fe/H], time, and/or redshift, can be used to set constraints on their star formation and nucleosynthesis histories.

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 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 Globular Clusters and Field Halo Stars

1988 ◽  
Vol 126 ◽  
pp. 133-148
Author(s):  
Bruce W. Carney
Keyword(s):  
Distribution Function ◽  
Globular Clusters ◽  
Chemical Properties ◽  
Elemental Abundance ◽  
Stellar Kinematics ◽  
Halo Stars ◽  
Abundance Patterns ◽  
Halo Population ◽  
Metallicity Distribution ◽  
And Chemical Properties

Recent work on the chemistry and kinematics of the field halo population stars is reviewed, including the metallicity distribution function, elemental abundance patterns, primordial abundances, and their relations with stellar kinematics. The important role played by these stars in determining the ages of the globular clusters is discussed. A comparison is made between the kinematic and chemical properties of the field and cluster stars to ascertain if they share a common history.

scholarly journals Using failed supernovae to constrain the Galactic r-process element production

2019 ◽  
Vol 487 (2) ◽  
pp. 1745-1753 ◽  
Author(s):  
B Wehmeyer ◽  
C Fröhlich ◽  
B Côté ◽  
M Pignatari ◽  
F-K Thielemann
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Large Fraction ◽  
Capture Process ◽  
Compact Binary ◽  
Halo Stars ◽  
The Galaxy ◽  
Binary Mergers ◽  
R Process ◽  
Process Elements

ABSTRACT Rapid neutron capture process (r-process) elements have been detected in a large fraction of metal-poor halo stars, with abundances relative to iron (Fe) that vary by over two orders of magnitude. This scatter is reduced to less than a factor of 3 in younger Galactic disc stars. The large scatter of r-process elements in the early Galaxy suggests that the r-process is made by rare events, like compact binary mergers and rare sub-classes of supernovae. Although being rare, neutron star mergers alone have difficulties to explain the observed enhancement of r-process elements in the lowest metallicity stars compared to Fe. The supernovae producing the two neutron stars already provide a substantial Fe abundance where the r-process ejecta from the merger would be injected. In this work we investigate another complementary scenario, where the r-process occurs in neutron star-black hole mergers in addition to neutron star mergers. Neutron star-black hole mergers would eject similar amounts of r-process matter as neutron star mergers, but only the neutron star progenitor would have produced Fe. Furthermore, a reduced efficiency of Fe production from single stars significantly alters the age–metallicity relation, which shifts the onset of r-process production to lower metallicities. We use the high-resolution [(20 pc)3/cell] inhomogeneous chemical evolution tool ‘ICE’ to study the outcomes of these effects. In our simulations, an adequate combination of neutron star mergers and neutron star-black hole mergers qualitatively reproduces the observed r-process abundances in the Galaxy.

The origin of r-process elements

Science ◽  
2021 ◽  
Vol 371 (6532) ◽  
pp. 901.18-903
Author(s):  
Keith T. Smith
Keyword(s):  
R Process ◽  
Process Elements

scholarly journals The AMBRE Project: r-process elements in the Milky Way thin and thick discs

2018 ◽  
Vol 619 ◽  
pp. A143 ◽  
Author(s):  
G. Guiglion ◽  
P. de Laverny ◽  
A. Recio-Blanco ◽  
N. Prantzos
Keyword(s):  
Chemical Evolution ◽  
Milky Way ◽  
Element Abundances ◽  
Thick Disc ◽  
Thin Disc ◽  
Solar Metallicity ◽  
R Process ◽  
Process Elements ◽  
Process Element ◽  
The Eu

Context. The chemical evolution of neutron capture elements in the Milky Way disc is still a matter of debate. There is a lack of statistically significant catalogues of such element abundances, especially those of the r-process. Aims. We aim to understand the chemical evolution of r-process elements in Milky Way disc. We focus on three pure r-process elements Eu, Gd, and Dy. We also consider a pure s-process element, Ba, in order to disentangle the different nucleosynthesis processes. Methods. We take advantage of high-resolution FEROS, HARPS, and UVES spectra from the ESO archive in order to perform a homogeneous analysis on 6500 FGK Milky Way stars. The chemical analysis is performed thanks to the automatic optimization pipeline GAUGUIN. We present abundances of Ba (5057 stars), Eu (6268 stars), Gd (5431 stars), and Dy (5479 stars). Based on the [α/Fe] ratio determined previously by the AMBRE Project, we chemically characterize the thin and the thick discs, and a metal-rich α-rich population. Results. First, we find that the [Eu/Fe] ratio follows a continuous sequence from the thin disc to the thick disc as a function of the metallicity. Second, in thick disc stars, the [Eu/Ba] ratio is found to be constant, while the [Gd/Ba] and [Dy/Ba] ratios decrease as a function of the metallicity. These observations clearly indicate a different nucleosynthesis history in the thick disc between Eu and Gd–Dy. The [r/Fe] ratio in the thin disc is roughly around +0.1 dex at solar metallicity, which is not the case for Ba. We also find that the α-rich metal-rich stars are also enriched in r-process elements (like thick disc stars), but their [Ba/Fe] is very different from thick disc stars. Finally, we find that the [r/α] ratio tends to decrease with metallicity, indicating that supernovae of different properties probably contribute differently to the synthesis of r-process elements and α-elements. Conclusions. We provide average abundance trends for [Ba/Fe] and [Eu/Fe] with rather small dispersions, and for the first time for [Gd/Fe] and [Dy/Fe]. This data may help to constrain chemical evolution models of Milky Way r- and s-process elements and the yields of massive stars. We emphasize that including yields of neutron-star or black hole mergers is now crucial if we want to quantitatively compare observations to Galactic chemical evolution models.

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