scholarly journals Chemical Evolution of Heavy Elements in the Early Galaxy: Implications for Stellar Sources

2008 ◽  
Vol 25 (1) ◽  
pp. 36-43 ◽  
Author(s):  
Yong-Zhong Qian
Keyword(s):  
Chemical Evolution ◽  
The Other ◽  
Component Model ◽  
Heavy Elements ◽  
Core Collapse ◽  
Two Component ◽  
Basic Understanding ◽  
Stellar Models ◽  
Stellar Sources ◽  
Early Galaxy

AbstractAn overview of the sources for heavy elements in the early Galaxy is given. It is shown that observations of abundances in metal-poor stars can be used along with a basic understanding of stellar models to guide the search for the source of the heavy r-process nuclei (r-nuclei). Observations show that this source produces very little of the elements from C through Zn, including Fe. This strongly suggests that O–Ne–Mg core-collapse supernovae (SNe) from progenitors of ∼8–11 M⊙ are the source for the heavy r-nuclei. It is shown that a two-component model based on the abundances of Fe (from Fe core-collapse SNe) and Eu (from O–Ne–Mg core-collapse SNe) gives very good quantitative predictions for the abundances of all the other elements in metal-poor stars.

scholarly journals The Influence of Binary Stars on Post-Collapse Evolution

2007 ◽  
Vol 3 (S246) ◽  
pp. 261-262
Author(s):  
Rosemary Apple
Keyword(s):  
Binary Stars ◽  
Component Model ◽  
Core Collapse ◽  
Mass Model ◽  
The Core ◽  
Binary Formation ◽  
Two Component ◽  
Self Similar ◽  
Mass Segregation ◽  
The Masses

AbstractThe results in the N-body simulations in Giersz & Heggie (1996) show that although the masses segregate as expected during core collapse, after core collapse there is self-similar evolution with very little further evidence of mass segregation even though the system has not reached equipartition. Binary stars halt core collapse and it is possible that they also halt the tendency toward equipartition. To investigate this problem, we construct two models. One model is a two-component model which assumes that binary stars form in the region dominated by heavy stars. The other model is a single mass model which assumes that binary stars form only in the region of the core. In both models, when the binary heating term is included, we find the post-collapse evolution to be self-similar. The aim of our work is to combine these two models to form a two-component model which assumes that binary formation only occurs in the core.

scholarly journals The Early History of Our Galaxy: Chemical Evolution

1974 ◽  
Vol 58 ◽  
pp. 141-156
Author(s):  
Manuel Peimbert
Keyword(s):  
Chemical Evolution ◽  
Stellar Evolution ◽  
Local Group ◽  
Early History ◽  
The Other ◽  
Heavy Elements ◽  
Galactic Chemical Evolution ◽  
Chemical Abundance ◽  
Iron Abundance ◽  
History Of

A general review is given of chemical abundance determinations; particular emphasis is given to abundances of galactic and extragalactic metal-poor objects since presumably they represent the abundances of the primeval material from which our Galaxy was formed. The following results are stressed: (a) most of the helium present in the galaxies of the local group as well as in other galaxies was produced before these objects were formed, (b) the heavy elements were produced mainly as the result of stellar evolution, (c) there is a chemical abundance gradient in our Galaxy and, by analogy with other galaxies, it is expected to be steeper near the nucleus, (d) the carbon and oxygen content of our Galaxy increased at a rate different from the metals, reaching their present abundance earlier than the other heavy elements, and (e) the increase of the iron abundance in the disk of our Galaxy with time has been small while that of carbon is negligible; furthermore, as a group the super-metal-rich stars correspond to the old disk population. Several models of galactic chemical evolution are reviewed.

scholarly journals Experimental Approach to Explosive Hydrogen Burning in X-Ray Bursts and Core-Collapse Supernovae

2018 ◽  
Vol 184 ◽  
pp. 01010 ◽  
Author(s):  
Shigeru Kubono
Keyword(s):  
Light Curve ◽  
Experimental Approach ◽  
Mass Region ◽  
The Other ◽  
Heavy Elements ◽  
Core Collapse ◽  
Mass Measurements ◽  
Hydrogen Burning ◽  
X Ray ◽  
Medium Mass

Recent experimental challenges to study the explosive hydrogen burning at extremely high temperatures are discussed. Along the nucleosynthetic pathway, discussions were made especially for the medium mass region, where we have possible waiting points and bottle necks which influence not only the light curve but also the production of heavy elements including the anomalously abundant p-nuclei at A = 80-100. Two approaches were discussed for the problem; one is the precision mass measurements and the other one is the half-live measurement of very short lived isotopes. A scope of the field is also discussed.

scholarly journals TWO-COMPONENT MODEL FOR CHEMICAL EVOLUTION OF THE GALACTIC DISK

2001 ◽  
pp. 237-239
Author(s):  
R.X. CHANG ◽  
J. L. HOU ◽  
C.G. SHU ◽  
C.Q. FU
Keyword(s):  
Chemical Evolution ◽  
Galactic Disk ◽  
Component Model ◽  
Two Component

The Effect of H2 Dilution on the Stability of a-Si:H based Solar Cells

1994 ◽  
Vol 336 ◽  
Author(s):  
Liyou Yang ◽  
Liang-Fan Chen
Keyword(s):  
Solar Cells ◽  
Substrate Temperature ◽  
Structural Properties ◽  
Recovery Process ◽  
The Other ◽  
Component Model ◽  
Device Stability ◽  
Two Component ◽  
The Stability ◽  
Kinetics Of

ABSTRACTWe have systematically investigated the effect of H2 dilution on the stability of a-Si:H based solar cells. The results clearly show that the device stability against light soaking improves substantially with increasing H2 dilution until a threshold is reached. Beyond this threshold which depends on the substrate temperature, the stability no longer changes with further increase in H2 dilution. On the other hand, at a given ratio of H2 to the reactant gases, the device stability generally improves with increasing substrate temperature. Multi-step light soaking experiments have shown that devices made with H2 dilution saturate much faster (∼100 hours) under one-sun illumination and exhibit little overshoot effect in the recovery process, in sharp contrast to devices made without H2 dilution. Based on the simple two-component model for defect kinetics, these observations and the fact that the apparent saturation time coincides with the time constant of the “fast” defects strongly suggest that negligible amount of “slow” defects exist in materials made with H2 dilution. While H2 dilution generally suppresses the formation of microstructure giving rise to dihydride bonding and microvoids, the differences in the kinetics of light induced degradation cannot always be traced to obvious differences in these structural properties.

scholarly journals Evolution of Globular Clusters by Tidally-Captured Binaries through Core Collapse

1988 ◽  
Vol 126 ◽  
pp. 667-668
Author(s):  
Thomas S. Statler ◽  
Jeremiah P. Ostriker ◽  
Haldan N. Cohn
Keyword(s):  
Cross Sections ◽  
Stellar Evolution ◽  
Globular Clusters ◽  
Component Model ◽  
Core Collapse ◽  
Initial State ◽  
One Dimensional ◽  
Cluster Evolution ◽  
Two Component ◽  
Stellar Mergers

We present calculations of globular cluster evolution performed by a modified Fokker-Planck approach, in which binaries formed by tidal capture are followed explicitly, along with subsequent heating mechanisms. The cluster is simulated by a two component model, using the cross sections of Press and Teukolsky (1977) for tidal capture, those of Hut (1984) for the single-binary encounters and for distant binary-binary encounters, and those of Mikkola (1983) for the strong binary-binary encounters. The initial state of the cluster is a Plummer model with N = 3 × 105 and scale radius ro = 1.13 pc. All stars are identical, with mass M∗ = 0.7M⊙ and R∗ = 0.57R⊙. This gives an initial core radius rc = 0.8 pc, and one-dimensional dispersion σ = 11.6 km s-1. All binaries are assumed to be identical, with separation a = 2.5R∗. There are no binaries in the cluster initially. Additional important effects, such as tidal truncation, tidal shocks, stellar evolution and mass loss, and stellar mergers, are not included.

scholarly journals Chemical Evolution of the Juvenile Universe

2009 ◽  
Vol 26 (3) ◽  
pp. 184-193 ◽  
Author(s):  
G. J. Wasserburg ◽  
Y.-Z. Qian
Keyword(s):  
Neutron Stars ◽  
Chemical Evolution ◽  
Massive Stars ◽  
Good Description ◽  
Initial Mass Function ◽  
Component Model ◽  
Abundance Pattern ◽  
Two Component ◽  
Low Mass ◽  
Process Elements

AbstractModels of average Galactic chemical abundances are in good general agreement with observations for [Fe/H] > –1.5, but there are gross discrepancies at lower metallicities. Only massive stars contribute to the chemical evolution of the ‘juvenile universe’ corresponding to [Fe/H] ≲ –1.5. If Type II supernovae (SNe II) are the only relevant sources, then the abundances in the interstellar medium of the juvenile epoch are simply the sum of different SN II contributions. Both low-mass (∼8–11 M⊙) and normal (∼12–25 M⊙) SNe II produce neutron stars, which have intense neutrino-driven winds in their nascent stages. These winds produce elements such as Sr, Y and Zr through charged-particle reactions (CPR). Such elements are often called the ‘light r-process elements’, but are considered here as products of CPR and not the r process. The observed absence of production of the low-A elements (Na through Zn including Fe) when the true r-process elements (Ba and above) are produced requires that only low-mass SNe II be the site if the r process occurs in SNe II. Normal SNe II produce the CPR elements in addition to the low-A elements. This results in a two-component model that is quantitatively successful in explaining the abundances of all elements relative to hydrogen for –3 ≲ [Fe/H] ≲ –1.5. This model explicitly predicts that [Sr/Fe] ≥ –0.32. Recent observations show that there are stars with [Sr/Fe] ≲ –2 and [Fe/H] < –3. This proves that the two-component model is not correct and that a third component is necessary to explain the observations. The production of CPR elements associated with the formation of neutron stars requires that the third component must be massive stars ending as black holes. It is concluded that stars of ∼25–50 M⊙ (possibly up to ∼100 M⊙) are the appropriate candidates. These produce hypernovae (HNe) that have very high Fe yields and are observed today. Stars of ∼140–260 M⊙ are completely disrupted upon explosion. However, they produce an abundance pattern greatly deficient in elements of odd atomic numbers, which is not observed, and therefore they are not considered as a source here. Using a Salpeter initial mass function, it is shown that HNe are a source of Fe that far outweighs normal SNe II, with the former and the latter contributing ∼24% and ∼9% of the solar Fe abundance, respectively. It follows that the usual assignment of ∼⅓ of the solar Fe abundance to normal SNe II is not correct. This leads to a simple three-component model including low-mass and normal SNe II and HNe, which gives a good description of essentially all the data for stars with [Fe/H] ≲ –1.5. We conclude that HNe are more important than normal SNe II in the chemical evolution of the low-A elements from Na through Zn (including Fe), in sharp distinction to earlier models.

Radiometric Chronology of Neh–nar Glacier, Kashmir

1982 ◽  
Vol 28 (98) ◽  
pp. 91-105 ◽  
Author(s):  
V. N. Nijampurkar ◽  
N. Bhandari ◽  
C. P. Vohra ◽  
V. Krishnan
Keyword(s):  
Average Rate ◽  
Component Model ◽  
Vertical Profiles ◽  
Kashmir Valley ◽  
Movement Rate ◽  
Accumulation Zone ◽  
Core Samples ◽  
Surface Samples ◽  
Two Component

AbstractSurface and core samples of Neh–nar Glacier in the Kashmir Valley have been analysed for the radionuclides 32Si. 210Pb, 40K, and 137Cs. The lateral and vertical profiles (at an altitude of about 4 140 m) reveal:(1)32Si activity decreasing slowly from the accumulation zone to 4 050 m altitude and then abruptly towards the snout.(2)Five zones of alternating high and low 210Pb activity in the surface samples.(3)An horizon at between 2 and 3 m depth containing 210Pb activity above natural levels. This horizon is also associated with 137Cs and a maximum in total ß activity.The ice samples have been dated on the basis of a simplified two–component model, the “fresh“contribution determined by 2l0Pb and the old component by 32Si. The following conclusions can be drawn from these observations:(1)The model age of the snout ice is c. 850 years.(2)The average rate of ice movement in the lower glacier is about 2 m/year, which compares well with the annual movement rate of 2.65 m/year observed since 1974.

scholarly journals Estimation of Galactic Model Parameters by Interval Method

1996 ◽  
Vol 169 ◽  
pp. 713-714
Author(s):  
S. A. Kutuzov
Keyword(s):  
Mutual Interaction ◽  
Component Model ◽  
Model Parameters ◽  
Interval Method ◽  
Two Component ◽  
The Galaxy ◽  
Galactic Model

The interval method of estimating model parameters (MPs) for the Galaxy was suggested earlier (Kutuzov 1988). Intervals are proposed to be used both for observational estimates of galactic parameters (GPs) and for the values of MPs. In this work we consider a model as a tool for studying mutual interaction of GPs. Two-component model is considered (Kutuzov, Ossipkov 1989). We have to estimate the array P of eight MPs.

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