Low-temperature gas opacity

Marigo, Paola; Aringer, B.

doi:10.1051/0004-6361/200912598

Cited by 206 publications

(220 citation statements)

References 74 publications

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“…Opacities in the high-temperature regime, 4.2 ≤ log(T /K) ≤ 8.7, are obtained from the Opacity Project At Livermore (OPAL) team [2] while, in the low-temperature regime, 3.2 ≤ log(T /K) ≤ 4.1, we use opacities generated with our AESOPUS 2 code [3]. Conductive opacities are included following [4].…”

Section: Equation Of State Nuclear Reaction Rates Opacities and Neumentioning

confidence: 99%

Red Giant evolution and specific problems

Bressan

Marigo

Girardi

et al. 2013

EPJ Web of Conferences

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Abstract. In spite of the great effort made in the last decades to improve our understanding of stellar evolution, significant uncertainties still remain due to our poor knowledge of some complex physical processes that still require an empirical calibration, such as the efficiency of convective heat transport and interior mixing. Here we will review the impact of these uncertainties on the evolution of red giant stars.

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Section: Equation Of State Nuclear Reaction Rates Opacities and Neumentioning

confidence: 99%

Red Giant evolution and specific problems

Bressan

Marigo

Girardi

et al. 2013

EPJ Web of Conferences

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“…The LPCODE employs the EOS of Segretain et al (1994) for the high-density regime (above a density of 8 × 10 2 g/cm 3 ) complemented with an updated version of the EOS of Magni & Mazzitelli (1979) for the low-density regime. Radiative opacities above 11 000 K and neutrino energy losses are as in the BaSTI code, while for temperatures below 8000 K radiative opacities from the AESOPUS database (Marigo & Aringer 2009) are employed, and in the intermediate regime an interpolation between OPAL and AESOPUS opacities is performed; OPAL radiative opacities are calculated directly from the interpolation routine provided by OPAL (version: Arnold Boothroyd, April 27, 2001). Arbitrary hydrogen abundances and arbitrary amounts of excess carbon and oxygen are always allowed.…”

Section: Appendix A: Codes and Input Physicsmentioning

confidence: 99%

Comparison of theoretical white dwarf cooling timescales

Salaris

Althaus

Garcı́a–Berro

2013

A&A

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Context. An accurate assessment of white dwarf cooling times is paramount so that white dwarf cosmochronology of Galactic populations can be put on more solid grounds. This issue is particularly relevant in view of the enhanced observational capabilities provided by the next generation of extremely large telescopes, that will offer more avenues to use white dwarfs as probes of Galactic evolution and test-beds of fundamental physics. Aims. We estimate for the first time the consistency of results obtained from independent evolutionary codes for white dwarf models with fixed mass and chemical stratification, when the same input physics is employed in the calculations. Methods. We compute and compare cooling times obtained from two independent and widely used stellar evolution codes, BaSTI and LPCODE evolutionary codes, using exactly the same input physics for 0.55 M white dwarf models with both pure carbon and uniform carbon-oxygen (50/50 mass fractions) cores, and pure hydrogen layers with mass fraction q H = 10 −4 M WD on top of pure helium buffers of mass q He = 10 −2 M WD . Results. Using the same radiative and conductive opacities, photospheric boundary conditions, neutrino energy loss rates, and equation of state, cooling times from the two codes agree within ∼2% at all luminosities, except when log(L/L ) > −1.5 where differences up to ∼8% do appear, because of the different thermal structures of the first white dwarf converged models at the beginning of the cooling sequence. This agreement is true for both pure carbon and uniform carbon-oxygen stratification core models, and also when the release of latent heat and carbon-oxygen phase separation are considered. We have also determined quantitatively and explained the effect of varying equation of state, low-temperature radiative opacities, and electron conduction opacities in our calculations, Conclusions. We have assessed for the first time the maximum possible accuracy in the current estimates of white dwarf cooling times, resulting only from the different implementations of the stellar evolution equations and homogeneous input physics in two independent stellar evolution codes. This accuracy amounts to ∼2% at luminosities lower than log (L/L ) ∼ −1.5. This difference is smaller than the uncertainties in cooling times attributable to the present uncertainties in the white dwarf chemical stratification. Finally, we extend the scope of our work by providing tabulations of our cooling sequences and the required input physics that can be used as a comparison test of cooling times obtained from other white dwarf evolutionary codes.

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“…These opacities are supplemented at low temperatures with the molecular opacities for pure hydrogen composition of Marigo & Aringer (2009). The conductive opacities of Cassisi et al (2007) were used as well.…”

Section: Input Physicsmentioning

confidence: 99%

The evolution of white dwarfs with a varying gravitational constant

Althaus

Córsico

Torres

et al. 2011

A&A

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Context. Within the theoretical framework of some modern unification theories the constants of nature are functions of cosmological time. White dwarfs offer the possibility of testing a possible variation of G and, thus, to place constraints on these theories. Aims. We present full white dwarf evolutionary calculations for a scenario where G decreases with time. Methods. White dwarf evolution is computed in a self-consistent way, including the most up-to-date physical inputs, non-gray model atmospheres and a detailed core chemical composition that results from the calculation of the full evolution of progenitor stars. Results. We find that the mechanical structure and the energy balance of white dwarfs are strongly modified by a varying G. In particular, for a rate of change of G higher thanĠ/G = −1 × 10 −12 yr −1 , the evolution of cool white dwarfs is markedly affected. The impact of a varying G is more pronounced for more massive white dwarfs. Conclusions. In view of the recent results reporting that a very accurate white dwarf cooling age can be derived for the old and metal-rich open cluster NGC 6791, our study suggests that this cluster could be a potential target to constrain or detect a hypothetical secular variation of G.

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Low-temperature gas opacity

Cited by 206 publications

References 74 publications

Red Giant evolution and specific problems

Red Giant evolution and specific problems

Comparison of theoretical white dwarf cooling timescales

The evolution of white dwarfs with a varying gravitational constant

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