Low‐Temperature Opacities

Ferguson, Jason W.; Alexander, D. R.; Barman, Travis; Bodnarik, J.; Hauschildt, P. H.; Heffner-Wong, Amanda; Tamanai, Akemi

doi:10.1086/428642

Cited by 1,219 publications

(1,222 citation statements)

References 64 publications

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“…Finally, updated low-temperature molecular opacities with varying C/O ratios are used. To this end, we adopted the low-temperature opacities computed at Wichita State University (Ferguson et al 2005) and presented by Weiss & Ferguson (2009). In LPCODE, molecular opacities are computed by adopting the opacity tables with the correct abundances of the unenhanced metals (e.g., Fe) and C/O ratio.…”

Section: Numerical Toolsmentioning

confidence: 99%

New evolutionary sequences for extremely low-mass white dwarfs

Althaus

Bertolami

Córsico

2013

A&A

249

475

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Context. The number of detected extremely low-mass (ELM) white dwarf stars has increased drastically in recent years, thanks to the results of many surveys. In addition, some of these stars have been found to exhibit pulsations, making them potential targets for asteroseismology. Aims. We provide a fine and homogeneous grid of evolutionary sequences for helium (He) core white dwarfs for the whole range of their expected masses (0.15 M * /M 0.45), including the mass range for ELM white dwarfs (M * /M 0.20). The grid is appropriate for mass and age determination of these stars, as well as for studying their adiatabic pulsational properties. Methods. White dwarf sequences have been computed by performing full evolutionary calculations that consider the main energy sources and processes of chemical abundance changes during white dwarf evolution. Realistic initial models for the evolving white dwarfs have been obtained by computing the nonconservative evolution of a binary system consisting of an initially 1 M ZAMS star and a 1.4 M neutron star for various initial orbital periods. To derive cooling ages and masses for He-core white dwarfs, we perform a least square fitting of the M(T eff , g) and Age(T eff , g) relations provided by our sequences by using a scheme that takes into account the time spent by models in different regions of the T eff − g plane. This is particularly useful when multiple solutions for cooling age and mass determinations are possible in the case of CNO-flashing sequences. We also explore in a preliminary way the adiabatic pulsational properties of models near the critical mass for the development of CNO flashes (∼0.2 M ). This is motivated by the discovery of pulsating white dwarfs with stellar masses near this threshold value. Results. We obtain reliable and homogeneous mass and cooling age determinations for 58 very low-mass white dwarfs, including three pulsating stars. Also, we find substantial differences in the period spacing distributions of g-modes for models with stellar masses near ∼0.2 M , which could be used as a seismic tool to distinguish stars that have undergone CNO flashes in their early cooling phase from those that have not. Finally, for an easy application of our results, we provide a reduced grid of values useful to obtain the masses and ages of He-core white dwarfs.

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Section: Numerical Toolsmentioning

confidence: 99%

New evolutionary sequences for extremely low-mass white dwarfs

Althaus

Bertolami

Córsico

2013

A&A

249

475

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“…• The OPAL equation of state (Rogers & Nayfonov 2002) and OPAL opacities (Iglesias & Rogers 1996) were used, augmented by low-temperature opacities from Ferguson et al (2005). C-O enhanced opacity tables were considered during the helium-core burning (HeCB) phase.…”

Section: Physical Inputsmentioning

confidence: 99%

Determining stellar parameters of asteroseismic targets: going beyond the use of scaling relations

Rodrigues

Bossini

Miglio

et al. 2017

Mon. Not. R. Astron. Soc.

103

119

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Asteroseismic parameters allow us to measure the basic stellar properties of field giants observed far across the Galaxy. Most of such determinations are, up to now, based on simple scaling relations involving the large frequency separation, ∆ν, and the frequency of maximum power, ν max . In this work, we implement ∆ν and the period spacing, ∆P , computed along detailed grids of stellar evolutionary tracks, into stellar isochrones and hence in a Bayesian method of parameter estimation. Tests with synthetic data reveal that masses and ages can be determined with typical precision of 5 and 19 per cent, respectively, provided precise seismic parameters are available. Adding independent information on the stellar luminosity, these values can decrease down to 3 and 10 per cent respectively. The application of these methods to NGC 6819 giants produces a mean age in agreement with those derived from isochrone fitting, and no evidence of systematic differences between RGB and RC stars. The age dispersion of NGC 6819 stars, however, is larger than expected, with at least part of the spread ascribable to stars that underwent mass-transfer events.

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“…Convection has been treated according to the Full Spectrum of Turbulence model (Canuto & Mazzitelli 1991). We used the opacity tables from the OPAL website , and for the low temperature opacities we followed Ferguson et al (2005). The conductive opacities by Potekhin et al (1999) For each chemical composition we computed evolutionary tracks with mass in the range 0.35 M < M < 1.10 M , spaced with a step of 0.05 M ; the evolution was followed from the pre-MS up to the tip of the RGB.…”

Section: Evolutionary Modelsmentioning

confidence: 99%

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

Tailo

Criscienzo

D’Antona

et al. 2016

Mon. Not. R. Astron. Soc.

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We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch data. The reproduction of the observed color magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: 1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ∼ 0.5 Gyr time interval; in particular the most metal rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y∼0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = + 0.7); 2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub giant data. 3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

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Low‐Temperature Opacities

Cited by 1,219 publications

References 64 publications

New evolutionary sequences for extremely low-mass white dwarfs

New evolutionary sequences for extremely low-mass white dwarfs

Determining stellar parameters of asteroseismic targets: going beyond the use of scaling relations

The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

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