scholarly journals Neutron stars mergers in a stochastic chemical evolution model: impact of time delay distributions

2021 ◽  
Author(s):  
L Cavallo ◽  
G Cescutti ◽  
F Matteucci
Keyword(s):  
Time Delay ◽  
Neutron Star ◽  
Neutron Stars ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Massive Stars ◽  
Initial Mass Function ◽  
Evolution Model ◽  
Chemical Evolution Model ◽  
The Eu

Abstract We study the evolution of the [Eu/Fe] ratio in the Galactic halo by means of a stochastic chemical evolution model considering merging neutron stars as polluters of europium. We improved our previous stochastic chemical evolution model by adding a time delay distribution for the coalescence of the neutron stars, instead of constant delays. The stochastic chemical evolution model can reproduce the trend and the observed spread in the [Eu/Fe] data with neutron star mergers as unique producers if we assume: i) a delay time distribution ∝t−1.5, ii) a MEu = 3e − 6M⊙ per event, iii) progenitors of neutron stars in the range 9 − 50M⊙ and iv) a constant fraction of massive stars in the initial mass function (0.02) that produce neutron star mergers. Our best model is obtained by relaxing point iv) and assuming a fraction that varies with metallicity. We confirm that the mixed scenario with both merging neutron stars and supernovae as europium producers can provide a good agreement with the data relaxing the constraints on the distribution time delays for the coalescence of neutron stars. Adopting our best model, we also reproduce the dispersion of [Eu/Fe] at a given metallicity, which depends on the fraction of massive stars that produce neutron star mergers. Future high-resolution spectroscopic surveys, such as 4MOST and WEAVE, will produce the necessary statistics to constrain at best this parameter.

scholarly journals The earliest phases of galaxy evolution: massive stars

1999 ◽  
Vol 193 ◽  
pp. 734-735
Author(s):  
Cristina Chiappini ◽  
Francesca Matteucci ◽  
Timothy C. Beers ◽  
Ken'Ichi Nomoto
Keyword(s):  
Galaxy Evolution ◽  
Chemical Evolution ◽  
Massive Stars ◽  
Solar Neighborhood ◽  
Evolution Model ◽  
Elemental Abundances ◽  
Extended Range ◽  
Solar Abundances ◽  
Early Phases ◽  
Chemical Evolution Model

In this work we study the very early phases of the evolution of our Galaxy by means of a chemical evolution model which reproduces most of the observational constraints in the solar vicinity and in the disk. We have restricted our analysis to the solar neighborhood and present the predicted abundances of several elements (C, N, 0, Mg, Si, S, Ca, Fe) over an extended range of metallicities [Fe/H] = −4.0 to 0.0 compared to previous models. We adopted the most recent yield calculations for massive stars taken from different authors (Woosley & Weaver 1995; Thielemann et al. 1996) and compared the results with a very large sample of data, one of the largest ever used to this purpose. We have obtained this by selecting the most rec.ent and higher quality abundance data from a number of sources and renormalizing them to the same solar abundances. These data have been analysed with a new and powerful statistical method which allows us to quantify the observational spread in measured elemental abundances and obtain a more meaningful comparison with the predictions from our chemical evolution model.

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.

scholarly journals The effects of different Type Ia SN yields on Milky Way chemical evolution

2021 ◽  
Vol 503 (3) ◽  
pp. 3216-3231
Author(s):  
Marco Palla
Keyword(s):  
Chemical Evolution ◽  
White Dwarf ◽  
Time Distribution ◽  
Milky Way ◽  
Massive Stars ◽  
Abundance Patterns ◽  
Type Ia ◽  
Low Metallicity ◽  
Explosion Mechanism ◽  
Chemical Evolution Model

ABSTRACT We study the effect of different Type Ia SN nucleosynthesis prescriptions on the Milky Way chemical evolution. To this aim, we run detailed one-infall and two-infall chemical evolution models, adopting a large compilation of yield sets corresponding to different white dwarf progenitors (near-Chandrasekar and sub-Chandrasekar) taken from the literature. We adopt a fixed delay time distribution function for Type Ia SNe, in order to avoid degeneracies in the analysis of the different nucleosynthesis channels. We also combine yields for different Type Ia SN progenitors in order to test the contribution to chemical evolution of different Type Ia SN channels. The results of the models are compared with recent LTE and NLTE observational data. We find that ‘classical’ W7 and WDD2 models produce Fe masses and [α/Fe] abundance patterns similar to more recent and physical near-Chandrasekar and sub-Chandrasekar models. For Fe-peak elements, we find that the results strongly depend either on the white dwarf explosion mechanism (deflagration-to-detonation, pure deflagration, double detonation) or on the initial white dwarf conditions (central density, explosion pattern). The comparison of chemical evolution model results with observations suggests that a combination of near-Chandrasekar and sub-Chandrasekar yields is necessary to reproduce the data of V, Cr, Mn and Ni, with different fractions depending on the adopted massive stars stellar yields. This comparison also suggests that NLTE and singly ionized abundances should be definitely preferred when dealing with most of Fe-peak elements at low metallicity.

scholarly journals A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

2016 ◽  
Vol 109 ◽  
pp. 02002 ◽  
Author(s):  
Zhen Yuan ◽  
Yong-Zhong Qian ◽  
Yi Peng Jing
Keyword(s):  
Chemical Evolution ◽  
Evolution Model ◽  
Chemical Evolution Model

scholarly journals Chempy: A flexible chemical evolution model for abundance fitting

2017 ◽  
Vol 605 ◽  
pp. A59 ◽  
Author(s):  
Jan Rybizki ◽  
Andreas Just ◽  
Hans-Walter Rix
Keyword(s):  
Chemical Evolution ◽  
Evolution Model ◽  
Chemical Evolution Model

scholarly journals Light Element Evolution at the Solar Neighborhood

2000 ◽  
Vol 198 ◽  
pp. 563-564
Author(s):  
Andreu Alibés ◽  
Javier Labay ◽  
Ramon Canal
Keyword(s):  
Chemical Evolution ◽  
Light Element ◽  
Cosmic Ray ◽  
Big Bang ◽  
Solar Neighborhood ◽  
Evolution Model ◽  
Element Evolution ◽  
Galactic Cosmic Ray ◽  
Chemical Evolution Model

We present the Light Element Evolution resulting from our new Chemical Evolution model. The LiBeB evolution is correctly fitted by taking into account several sources: Big Bang, Galactic Cosmic Ray Nucleosynthesis, the ν-process, novae and AGB and C-stars.

scholarly journals Abundance ratios in stars vs. hot gas in elliptical galaxies

2009 ◽  
Vol 5 (H15) ◽  
pp. 281-281
Author(s):  
Antonio Pipino
Keyword(s):  
Interstellar Medium ◽  
Chemical Evolution ◽  
Elliptical Galaxies ◽  
Evolution Model ◽  
X Ray ◽  
Galactic Wind ◽  
Hot Gas ◽  
Self Consistent ◽  
Chemical Evolution Model ◽  
Gas Properties

AbstractI present predictions from a chemical evolution model for a self-consistent study of optical (i.e., stellar) and X-ray (i.e., gas) properties of present-day elliptical galaxies. Detailed cooling and heating processes in the interstellar medium are taken into account and allow a reliable modelling of the SN-driven galactic wind. The model simultaneously reproduces the mass-metallicity, colour-magnitude, LX - LB and LX - T relations, and the observed trend of [Mg/Fe] with σ. The "iron discrepancy" can be solved by taking into account the dust presence.

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