TOPoS

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

Abundance analyses: methods, results and implications

Symposium - International Astronomical Union ◽

10.1017/s0074180900151794 ◽

1986 ◽

Vol 118 ◽

pp. 413-424

Author(s):

P. L. Cottrell

Keyword(s):

Quantum Efficiency ◽

Thermodynamic Equilibrium ◽

Local Thermodynamic Equilibrium ◽

Galactic Evolution ◽

Late Type ◽

High Quantum Efficiency ◽

Growth Technique ◽

Giant Stars ◽

High Quantum

The methods by which abundance analyses can be undertaken, especially with the growing use of high quantum efficiency digital detectors, are reviewed. The importance of the differential curve of growth technique is discussed, followed by a review of some recent results involving both late-type dwarf and giant stars. These include (1) the F and G dwarf abundance analyses of the elements sodium through nickel, which show an important differentiation between stars belonging to the young and old disk populations, (2) the possibility that departures from local thermodynamic equilibrium can effect sodium and aluminium abundances in late-type giants and supergiants and (3) that significant differences exist between the abundances of carbon, nitrogen and oxygen in old disk and young disk giant stars. Finally, the implications of these abundances in terms of stellar and galactic evolution are briefly addressed.

Download Full-text

Abundance patterns of the light neutron-capture elements in very and extremely metal-poor stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732096 ◽

2018 ◽

Vol 611 ◽

pp. A30 ◽

Cited By ~ 13

Author(s):

F. Spite ◽

M. Spite ◽

B. Barbuy ◽

P. Bonifacio ◽

E. Caffau ◽

...

Keyword(s):

Thermodynamic Equilibrium ◽

Neutron Capture ◽

Local Thermodynamic Equilibrium ◽

Abundance Patterns ◽

Element Pattern ◽

The Mean ◽

R Process ◽

Peak Abundance ◽

Second Peak

Aims. The abundance patterns of the neutron-capture elements in metal-poor stars provide a unique record of the nucleosynthesis products of the earlier massive primitive objects. Methods. We measured new abundances of so-called light neutron-capture of first peak elements using local thermodynamic equilibrium (LTE) 1D analysis; this analysis resulted in a sample of 11 very metal-poor stars, from [Fe/H] = –2.5 to [Fe/H] = –3.4, and one carbon-rich star, CS 22949-037 with [Fe/H] = –4.0. The abundances were compared to those observed in two classical metal-poor stars: the typical r-rich star CS 31082-001 ([Eu/Fe] > +1.0) and the r-poor star HD 122563 ([Eu/Fe] < 0.0), which are known to present a strong enrichment of the first peak neutron-capture elements relative to the second peak. Results. Within the first peak, the abundances are well correlated in analogy to the well-known correlation inside the abundances of the second-peak elements. In contrast, there is no correlation between any first peak element with any second peak element. We show that the scatter of the ratio of the first peak abundance over second peak abundance increases when the mean abundance of the second peak elements decreases from r-rich to r-poor stars. We found two new r-poor stars that are very similar to HD 122563. A third r-poor star, CS 22897-008, is even more extreme; this star shows the most extreme example of first peak elements enrichment to date. On the contrary, another r-poor star (BD–18 5550) has a pattern of first peak elements that is similar to the typical r-rich stars CS 31082-001, however this star has some Mo enrichment. Conclusions. The distribution of the neutron-capture elements in our very metal-poor stars can be understood as the combination of at least two mechanisms: one that enriches the forming stars cloud homogeneously through the main r-process and leads to an element pattern similar to the r-rich stars, such as CS 31082-001; and another that forms mainly lighter, first peak elements.

Download Full-text

NON-LOCAL THERMODYNAMIC EQUILIBRIUM 1.5D MODELING OF RED GIANT STARS

The Astrophysical Journal ◽

10.1088/0004-637x/787/1/43 ◽

2014 ◽

Vol 787 (1) ◽

pp. 43 ◽

Cited By ~ 2

Author(s):

Mitchell. E. Young ◽

C. Ian Short

Keyword(s):

Thermodynamic Equilibrium ◽

Local Thermodynamic Equilibrium ◽

Giant Stars ◽

Non Local ◽

Red Giant Stars ◽

Red Giant

Download Full-text

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

Canadian Journal of Physics ◽

10.1139/cjp-2016-0689 ◽

2017 ◽

Vol 95 (9) ◽

pp. 783-789 ◽

Cited By ~ 4

Author(s):

J.E. Lawler ◽

C. Sneden ◽

J.J. Cowan ◽

E.A. Den Hartog ◽

M.P. Wood

Keyword(s):

Chemical Evolution ◽

Thermodynamic Equilibrium ◽

Local Thermodynamic Equilibrium ◽

Transition Probabilities ◽

Laboratory Data ◽

Galactic Chemical Evolution ◽

One Dimensional ◽

Elemental Abundances ◽

Yield Information ◽

Early Galaxy

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

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