New asymptotic giant branch models for a range of metallicities

Weiß, Achim; Ferguson, Jason W.

doi:10.1051/0004-6361/200912043

Cited by 160 publications

(376 citation statements)

References 76 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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“…In fact, trying to fit all available observational constraints by means of a simple overshooting prescription might not be even possible [see Weiss & Ferguson (2009); Karakas & Lattanzio (2014);Miller Bertolami (2016)]. This fact, together with the lack of compelling theoretical arguments and the lack of a common observational benchmark for AGB theoretical evolution models has led authors to the adoption of very different approaches.…”

Section: And Hot Bottom Burning (Hbb) To Develop At Lower Initial Masmentioning

confidence: 99%

On the production of He, C, and N by low- and intermediate-mass stars: a comparison of observed and model-predicted planetary nebula abundances

Henry

Stephenson

Bertolami

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The primary goal of this paper is to make a direct comparison between the measured and modelpredicted abundances of He, C and N in a sample of 35 well-observed Galactic planetary nebulae (PN). All observations, data reductions, and abundance determinations were performed in house to ensure maximum homogeneity. Progenitor star masses (M ≤ 4 M ⊙ ) were inferred using two published sets of post-AGB model tracks and L and T ef f values. We conclude the following: 1) the mean values of N/O across the progenitor mass range exceeds the solar value, indicating significant N enrichment in the majority of our objects; 2) the onset of hot bottom burning appears to begin around 2 M ⊙ , i.e., lower than ∼ 5 M ⊙ implied by theory; 3) most of our objects show a clear He enrichment, as expected from dredge-up episodes; 4) the average sample C/O value is 1.23, consistent with the effects of third dredge-up; and 5) model grids used to compare to observations successfully span the distribution over metallicity space of all C/O and many He/H data points but mostly fail to do so in the case of N/O. The evident enrichment of N in PN and the general discrepancy between the observed and model-predicted N/O abundance ratios signal the need for extra-mixing as an effect of rotation and/or thermohaline mixing in the models. The unexpectedly high N enrichment that is implied here for low mass stars, if confirmed, will likely impact our conclusions about the source of N in the Universe.

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“…We use the standard set of evolutionary tracks for post-AGB stars obtained by Blöcker (1995), which are supplemented with lower-mass models from Schönberner (1983). Alternative post-AGB model tracks are presented by Vassiliadis & Wood (1994) and Weiss & Ferguson (2009). We assume that the post-AGB stars evolve as hydrogen burners.…”

Section: Post-agb Model Tracksmentioning

confidence: 99%

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

Gęsicki

Zijlstra

Hajduk

et al. 2014

A&A

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Aims. We study the star-formation history of the Galactic bulge, as derived from the age distribution of the central stars of planetary nebulae that belong to this stellar population. Methods. The high resolution imaging and spectroscopic observations of 31 compact planetary nebulae are used to derive their central star masses. We use the Blöcker post asymptotic giant branch (post-AGB) evolutionary models, which are accelerated by a factor of three in this case to better fit the white dwarf mass distribution and asteroseismological masses. Initial-final mass relations (IFMR) are derived using white dwarfs in clusters. These are applied to determine original stellar masses and ages. The age distribution is corrected for observational bias as a function of stellar mass. We predict that there are about 2000 planetary nebulae in the bulge. Results. The planetary nebula population points at a young bulge population with an extended star-formation history. The Blöcker tracks with the cluster IFMR result in ages, which are unexpectedly young. We find that the Blöcker post-AGB tracks need to be accelerated by a factor of three to fit the local white dwarf masses. This acceleration extends the age distribution. We adjust the IFMR as a free parameter to map the central star ages on the full age range of bulge stellar populations. This fit requires a steeper IFMR than the cluster relation. We find a star-formation rate in the Galactic bulge, which is approximately constant between 3 and 10 Gyr ago. The result indicates that planetary nebulae are mainly associated with the younger and more metal-rich bulge populations. Conclusions. The constant rate of star-formation between 3 and 10 Gyr agrees with suggestions that the metal-rich component of the bulge is formed during an extended process, such as a bar interaction.

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New asymptotic giant branch models for a range of metallicities

Cited by 160 publications

References 76 publications

New evolutionary sequences for extremely low-mass white dwarfs

New evolutionary sequences for extremely low-mass white dwarfs

On the production of He, C, and N by low- and intermediate-mass stars: a comparison of observed and model-predicted planetary nebula abundances

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

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