Laboratory transition probabilities for studies of nucleosynthesis of Fe-group elements1

The synthesis of iron (Fe-) group elements was different in the early Galaxy than it is today. Measurements of the relative Fe-group elemental abundances in old metal-poor stars yield information on the Galactic chemical evolution and some information on early supernovae (SNe). Improved laboratory data on transition probabilities is essential to this effort. It is also essential to understand and map the limits of standard photospheric models based on one-dimensional and local thermodynamic equilibrium approximations.

Download Full-text

Carbon and oxygen in metal-poor halo stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834480 ◽

2019 ◽

Vol 622 ◽

pp. L4 ◽

Cited By ~ 14

Author(s):

A. M. Amarsi ◽

P. E. Nissen ◽

M. Asplund ◽

K. Lind ◽

P. S. Barklem

Keyword(s):

Chemical Evolution ◽

Thermodynamic Equilibrium ◽

Local Thermodynamic Equilibrium ◽

Galactic Chemical Evolution ◽

Elemental Abundances ◽

Halo Stars ◽

Effective Temperatures ◽

Population Iii Stars ◽

Hydrodynamic Effects ◽

First Time

Carbon and oxygen are key tracers of the Galactic chemical evolution; in particular, a reported upturn in [C/O] towards decreasing [O/H] in metal-poor halo stars could be a signature of nucleosynthesis by massive Population III stars. We reanalyse carbon, oxygen, and iron abundances in 39 metal-poor turn-off stars. For the first time, we take into account 3D hydrodynamic effects together with departures from local thermodynamic equilibrium (LTE) when determining both the stellar parameters and the elemental abundances, by deriving effective temperatures from 3D non-LTE Hβ profiles, surface gravities from Gaia parallaxes, iron abundances from 3D LTE Fe II equivalent widths, and carbon and oxygen abundances from 3D non-LTE C I and O I equivalent widths. We find that [C/Fe] stays flat with [Fe/H], whereas [O/Fe] increases linearly up to 0.75 dex with decreasing [Fe/H] down to −3.0 dex. Therefore [C/O] monotonically decreases towards decreasing [C/H], in contrast to previous findings, mainly because the non-LTE effects for O I at low [Fe/H] are weaker with our improved calculations.

Download Full-text

Observations of Molecules in Stellar Atmospheres - Chemistry Near Thermal Equilibrium

Symposium - International Astronomical Union ◽

10.1017/s0074180900154658 ◽

1987 ◽

Vol 120 ◽

pp. 583-598

Author(s):

David L. Lambert

Keyword(s):

Thermodynamic Equilibrium ◽

Thermal Equilibrium ◽

Local Thermodynamic Equilibrium ◽

Stellar Atmospheres ◽

Red Giants ◽

The Sun ◽

Carbon Stars ◽

General Review ◽

Elemental Abundances

A general review is given of the astrophysical information obtainable from observations of molecules in stellar photospheres. Through selected examples, the use of molecules as thermometers (e.g., the OH 3 μm V-R lines in the Sun and α Ori) and as probes of the isotopic (e.g., iMg in metal-poor dwarfs, 12C/13C in cool carbon stars) and elemental abundances (e.g., CNO in red giants) is sketched. All of the (carefully) selected analyses assume that local thermodynamic equilibrium (LTE) prevails.

Download Full-text

TOPoS

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834375 ◽

2018 ◽

Vol 620 ◽

pp. A187 ◽

Cited By ~ 3

Author(s):

P. François ◽

E. Caffau ◽

P. Bonifacio ◽

M. Spite ◽

F. Spite ◽

...

Keyword(s):

Thermodynamic Equilibrium ◽

Neutron Capture ◽

Local Thermodynamic Equilibrium ◽

Early Evolution ◽

One Dimensional ◽

Giant Stars ◽

Medium Resolution ◽

Calcium Iron ◽

Significant Spread ◽

Very High

Context. Extremely metal-poor stars are keys to understand the early evolution of our Galaxy. The ESO large programme TOPoS has been tailored to analyse a new set of metal-poor turn-off stars, whereas most of the previously known extremely metal-poor stars are giant stars. Aims. Sixty five turn-off stars (preselected from SDSS spectra) have been observed with the X-shooter spectrograph at the ESO VLT Unit Telescope 2, to derive accurate and detailed abundances of magnesium, silicon, calcium, iron, strontium and barium. Methods. We analysed medium-resolution spectra (R ≃ 10 000) obtained with the ESO X-shooter spectrograph and computed the abundances of several α and neutron-capture elements using standard one-dimensional local thermodynamic equilibrium (1D LTE) model atmospheres. Results. Our results confirms the super-solar [Mg/Fe] and [Ca/Fe] ratios in metal-poor turn-off stars as observed in metal-poor giant stars. We found a significant spread of the [α/Fe] ratios with several stars showing subsolar [Ca/Fe] ratios. We could measure the abundance of strontium in 12 stars of the sample, leading to abundance ratios [Sr/Fe] around the Solar value. We detected barium in two stars of the sample. One of the stars (SDSS J114424−004658) shows both very high [Ba/Fe] and [Sr/Fe] abundance ratios (>1 dex).

Download Full-text

Observational constraints on the origin of the elements

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936603 ◽

2020 ◽

Vol 635 ◽

pp. A38 ◽

Cited By ~ 6

Author(s):

P. Eitner ◽

M. Bergemann ◽

C. J. Hansen ◽

G. Cescutti ◽

I. R. Seitenzahl ◽

...

Keyword(s):

Chemical Evolution ◽

Globular Clusters ◽

Local Thermodynamic Equilibrium ◽

Galactic Chemical Evolution ◽

Galactic Disc ◽

Milky Way Galaxy ◽

Halo Stars ◽

Type Ia ◽

Low Metallicity ◽

Different Sources

The abundance ratios of manganese to iron in late-type stars across a wide metallicity range place tight constraints on the astrophysical production sites of Fe-group elements. In this work, we investigate the chemical evolution of Mn in the Milky Way galaxy using high-resolution spectroscopic observations of stars in the Galactic disc and halo stars, as well as a sample of globular clusters. Our analysis shows that local thermodynamic equilibrium (LTE) leads to a strong imbalance in the ionisation equilibrium of Mn I and Mn II lines. Mn I produces systematically (up to 0.6 dex) lower abundances compared to the Mn II lines. Non-LTE (NLTE) radiative transfer satisfies the ionisation equilibrium across the entire metallicity range, of −3 ≲ [Fe/H] ≲ −1, leading to consistent abundances from both ionisation stages of the element. We compare the NLTE abundances with Galactic Chemical Evolution models computed using different sources of type Ia and type II supernova (SN Ia and SN II) yields. We find that a good fit to our observations can be obtained by assuming that a significant (∼75%) fraction of SNe Ia stem from a sub-Chandrasekhar (sub-Mch) channel. While this fraction is larger than that found in earlier studies (∼50%), we note that we still require ∼25% near-Mch SNe Ia to obtain solar [Mn/Fe] at [Fe/H] = 0. Our new data also suggest higher SN II Mn yields at low metallicity than typically assumed in the literature.

Download Full-text

Impact of Hypernova νp-process Nucleosynthesis on the Galactic Chemical Evolution of Mo and Ru

The Astrophysical Journal ◽

10.3847/1538-4357/ac34f8 ◽

2022 ◽

Vol 924 (1) ◽

pp. 29

Author(s):

Hirokazu Sasaki ◽

Yuta Yamazaki ◽

Toshitaka Kajino ◽

Motohiko Kusakabe ◽

Takehito Hayakawa ◽

...

Keyword(s):

Theoretical Prediction ◽

Observational Data ◽

Chemical Evolution ◽

Elemental Abundance ◽

Core Collapse ◽

Galactic Chemical Evolution ◽

Main Contributor ◽

Elemental Abundances ◽

The Galaxy ◽

Low Metallicity

Abstract We calculate the Galactic Chemical Evolution of Mo and Ru by taking into account the contribution from ν p-process nucleosynthesis. We estimate yields of p-nuclei such as 92,94Mo and 96,98Ru through the ν p-process in various supernova progenitors based upon recent models. In particular, the ν p-process in energetic hypernovae produces a large amount of p-nuclei compared to the yield in ordinary core-collapse SNe. Because of this, the abundances of 92,94Mo and 96,98Ru in the Galaxy are significantly enhanced at [Fe/H] = 0 by the ν p-process. We find that the ν p-process in hypernovae is the main contributor to the elemental abundance of 92Mo at low metallicity [Fe/H] < −2. Our theoretical prediction of the elemental abundances in metal-poor stars becomes more consistent with observational data when the ν p-process in hypernovae is taken into account.

Download Full-text

Strontium in the era of Gaia and LAMOST

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313006765 ◽

2013 ◽

Vol 9 (S298) ◽

pp. 409-409

Author(s):

Camilla J. Hansen ◽

Elisabetta Caffau ◽

Maria Bergemann

Keyword(s):

Chemical Evolution ◽

Spectral Resolution ◽

Neutron Capture ◽

Local Thermodynamic Equilibrium ◽

Heavy Elements ◽

Galactic Chemical Evolution ◽

Non Local ◽

Formation And Evolution ◽

Open Question ◽

Insight Into

AbstractThe formation and evolution of the heavy neutron-capture elements (Z > 37) are to date not well understood. Therefore, abundance and galactic chemical evolution (GCE) studies of these heavy elements may carry key information to this open question. Strontium (Sr) is one of the two heavy elements (Sr and Ba) that show intrinsically very strong absorption lines even in extremely metal-poor stars (and remains detectable at low spectral resolution). Hence, the 4077 Å Sr II line provides a unique insight into the behaviour of heavy neutron-capture elements at all metallicities and resolutions. Here the focus is on strontium, its 3D and NLTE (non-local thermodynamic equilibrium) corrections, as well as chemical evolution.

Download Full-text

Solar Elemental Abundances

Oxford Research Encyclopedia of Planetary Science ◽

10.1093/acrefore/9780190647926.013.145 ◽

2020 ◽

Author(s):

Katharina Lodders

Keyword(s):

Solar System ◽

Chemical Evolution ◽

Molecular Cloud ◽

The Sun ◽

Galactic Chemical Evolution ◽

Dwarf Star ◽

Dwarf Stars ◽

Elemental Abundances ◽

System Composition ◽

Solar Composition

Solar elemental abundances, or solar system elemental abundances, refer to the complement of chemical elements in the entire Solar System. The Sun contains more than 99% of the mass in the solar system and therefore the composition of the Sun is a good proxy for the composition of the overall solar system. The solar system composition can be taken as the overall composition of the molecular cloud within the interstellar medium from which the solar system formed 4.567 billion years ago. Active research areas in astronomy and cosmochemistry model collapse of a molecular cloud of solar composition into a star with a planetary system and the physical and chemical fractionation of the elements during planetary formation and differentiation. The solar system composition is the initial composition from which all solar system objects (the Sun, terrestrial planets, gas giant planets, planetary satellites and moons, asteroids, Kuiper-belt objects, and comets) were derived. Other dwarf stars (with hydrostatic hydrogen-burning in their cores) like the Sun (type G2V dwarf star) within the solar neighborhood have compositions similar to the Sun and the solar system composition. In general, differential comparisons of stellar compositions provide insights about stellar evolution as functions of stellar mass and age and ongoing nucleosynthesis but also about galactic chemical evolution when elemental compositions of stellar populations across the Milky Way Galaxy is considered. Comparisons to solar composition can reveal element destruction (e.g., Li) in the Sun and in other dwarf stars. The comparisons also show element production of, for example, C, N, O, and the heavy elements made by the s-process in low to intermediate mass stars (3–7 solar masses) after these evolved from their dwarf-star stage into red giant stars (where hydrogen and helium burning can occur in shells around their cores). The solar system abundances are and have been a critical test composition for nucleosynthesis models and models of galactic chemical evolution, which aim ultimately to track the production of the elements heavier than hydrogen and helium in the generation of stars that came forth after the Big Bang 13.4 billion years ago.

Download Full-text

Blackbody Radiation, Boltzmann Statistics, Temperature, and Thermodynamic Equilibrium

10.1093/oso/9780199662104.003.0003 ◽

2017 ◽

Author(s):

Kelly Chance ◽

Randall V. Martin

Keyword(s):

Thermodynamic Equilibrium ◽

Local Thermodynamic Equilibrium ◽

Photophysical Properties ◽

Blackbody Radiation ◽

Boltzmann Constant ◽

Noise Sources ◽

Atmospheric Molecules ◽

Tightly Coupled ◽

Boltzmann Statistics ◽

Planck’S Law

Blackbody radiation, temperature, and thermodynamic equilibrium give a tightly coupled description of systems (atmospheres, volumes, surfaces) that obey Boltzmann statistics. They provide descriptions of systems when Boltzmann statistics apply, either approximately or nearly exactly. These apply most of the time in the Earth’s stratosphere and troposphere, and in other planetary atmospheres as long as the density is sufficient that collisions among atmospheric molecules, rather than photochemical and photophysical properties, determine the energy populations of the ensemble of molecules. Thermodynamic equilibrium and the approximation of local thermodynamic equilibrium are introduced. Boltzmann statistics, blackbody radiation, and Planck’s law are described. The chapter introduces the Rayleigh-Jeans limit, description of noise sources as temperatures, Kirchoff’s law, the Stefan-Boltzmann constant, and Wien’s law.

Download Full-text