The ages of stars: The horizontal branch

Catelan, M.

doi:10.1017/s174392130903186x

Cited by 5 publications

(4 citation statements)

References 47 publications

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“…Aside from metallicity as the "first parameter", age , He content, mass-loss, and cluster central density have been suggested as candidates to be the second, or even third, parameter affecting the morphology of the HB (Fusi Pecci & Bellazzini 1997;Catelan 2008;Dotter et al 2010;Gratton et al 2010;McDonald & Zijlstra 2015;D'Antona et al 2002;Caloi & D'Antona 2005, .etc.). Most of these parameters involve an effect on the mass of the stars which populate the cluster HB.…”

Section: Horizontal Branch Morphologymentioning

confidence: 99%

New parsec data base of α-enhanced stellar evolutionary tracks and isochrones – I. Calibration with 47 Tuc (NGC 104) and the improvement on RGB bump

Bressan

Marigo

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Precise studies on the Galactic bulge, globular cluster, Galactic halo and Galactic thick disk require stellar models with α enhancement and various values of helium content. These models are also important for extra-Galactic population synthesis studies. For this purpose we complement the existing PARSEC models, which are based on the solar partition of heavy elements, with α-enhanced partitions. We collect detailed measurements on the metal mixture and helium abundance for the two populations of 47 Tuc (NGC 104) from the literature, and calculate stellar tracks and isochrones with these α-enhanced compositions. By fitting the precise color-magnitude diagram with HST ACS/WFC data, from low main sequence till horizontal branch, we calibrate some free parameters that are important for the evolution of low mass stars like the mixing at the bottom of the convective envelope. This new calibration significantly improves the prediction of the RGB bump brightness. Comparison with the observed RGB and HB luminosity functions also shows that the evolutionary lifetimes are correctly predicted. As a further result of this calibration process, we derive the age, distance modulus, reddening, and the red giant branch mass loss for 47 Tuc. We apply the new calibration and α-enhanced mixtures of the two 47 Tuc populations ( [α/Fe] ∼0.4 and 0.2) to other metallicities. The new models reproduce the RGB bump observations much better than previous models. This new PARSEC database, with the newly updated α-enhanced stellar evolutionary tracks and isochrones, will also be part of the new stellar products for Gaia .

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Section: Horizontal Branch Morphologymentioning

confidence: 99%

New parsec data base of α-enhanced stellar evolutionary tracks and isochrones – I. Calibration with 47 Tuc (NGC 104) and the improvement on RGB bump

Bressan

Marigo

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…However, the exact treatment depends on the modeling of winds on the red giant branch and thermal pulses on the asymptotic giant branch (e.g., see Weidemann 2000 andHabing 1996), phases of stellar evolution that are poorly understood. As Catelan (2008) summarizes, mass loss prescriptions along the red giant branch alone show very different behaviors with metallicity. For example, over a 1 dex metallicity change from [Fe/H] = −1.0 to 0.0, the Mullan (1978) and Schröder & Cuntz (2005) laws predict that ∆M RGB should increase by 0.05 M ⊙ whereas the Goldberg (1979) and Judge & Stencel (1991) laws suggest ∆M increases by 0.15 -0.25 M ⊙ .…”

Section: The Dependence Of Mass Loss On Metallicitymentioning

confidence: 99%

The Masses of Population Ii White Dwarfs

Kalirai¹,

Davis²,

Richer³

et al. 2009

ApJ

131

160

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Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main-sequence today. Almost all of the stars born with more mass than 0.8 M ⊙ have evolved to form the white dwarf cooling sequence of these systems, and the distribution and properties of these remnants uniquely holds clues related to the nature of the now evolved progenitor stars. With ultra-deep HST imaging observations, rich white dwarf populations of four nearby Milky Way globular clusters have recently been uncovered, and are found to extend an impressive 5 -8 magnitudes in the faint-blue region of the H-R diagram. In this paper, we characterize the properties of these population II remnants by presenting the first direct mass measurements of individual white dwarfs near the tip of the cooling sequence in the nearest of the Milky Way globulars, M4. Based on Gemini/GMOS and Keck/LRIS multiobject spectroscopic observations, our results indicate that 0.8 M ⊙ population II main-sequence stars evolving today form 0.53 ± 0.01 M ⊙ white dwarfs. We discuss the implications of this result as it relates to our understanding of stellar structure and evolution of population II stars and for the age of the Galactic halo, as measured with white dwarf cooling theory.

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“…of clusters and nearby galaxies, while the observed chemical composition of its members is useful to investigate the chemical evolution of galaxies (e.g., see Girardi & Salaris 2001;Catelan 2009;Nidever et al 2014).…”

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confidence: 99%

Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump

Bossini

Miglio

Salaris

et al. 2015

Mon. Not. R. Astron. Soc.

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Low-mass stars in the He-core-burning phase (HeCB) play a major role in stellar, galactic, and extragalactic astrophysics. The ability to predict accurately the properties of these stars, however, depends on our understanding of convection, which remains one of the key open questions in stellar modelling. We argue that the combination of the luminosity of the AGB bump (AGBb) and the period spacing of gravity modes (∆Π 1 ) during the HeCB phase, provides us with a decisive test to discriminate between competing models of these stars. We use the MESA, BaSTI, and PARSEC stellar evolution codes to model a typical giant star observed by Kepler. We explore how various near-core-mixing scenarios affect the predictions of the above-mentioned constraints, and we find that ∆Π 1 depends strongly on the prescription adopted. Moreover we show that the detailed behaviour of ∆Π 1 shows the signature of sharp variations in the Brunt-Väisälä frequency, which could potentially give additional information about near-core features. We find evidence for the AGBb among Kepler targets, and a first comparison with observations shows that, even if standard models are able to reproduce the luminosity distribution, no standard model can account for satisfactorily the period spacing of HeCB stars. Our analysis allows us to outline a candidate model to describe simultaneously the two observed distributions: a model with a moderate overshooting region characterized by an adiabatic thermal stratification. This prescription will be tested in the future on cluster stars, to limit possible observational biases.

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The ages of stars: The horizontal branch

Abstract: Abstract. Horizontal branch (HB) stars play a particularly important role in the "age debate," since they are at the very center of the long-standing "second parameter" problem. In this review, I discuss some recent progress in our understanding of the nature and origin of HB stars.

Cited by 5 publications

References 47 publications

New parsec data base of α-enhanced stellar evolutionary tracks and isochrones – I. Calibration with 47 Tuc (NGC 104) and the improvement on RGB bump

New parsec data base of α-enhanced stellar evolutionary tracks and isochrones – I. Calibration with 47 Tuc (NGC 104) and the improvement on RGB bump

The Masses of Population Ii White Dwarfs

Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump

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