Helium-burning evolutionary phases in population II stars. I Breathing pulses in horizontal branch stars

Castellani, V.; Chieffi, A.; Tornambé, Amedeo; Pulone, L.

doi:10.1086/163437

Cited by 117 publications

(124 citation statements)

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“…The mechanism is the analog of the breathing pulses occurring in low mass stars (see e.g. Sweigart & Demarque 1972Castellani et al 1985). Figure 2 shows, for a 7 M model, the effects on the blue loop extension of variations in the helium and metal contents within the uncertainties of these quantities (cases from I to IV of Table 1).…”

Section: Effects Of the Chemical Composition Uncertaintiesmentioning

confidence: 83%

“…During the central He burning phase our code implements the classical semi-convection criterion (see e.g. Castellani et al 1985) at the border of the Schwarzschild convective core (which is driven by mechanical overshooting at the convective core boundary), while breathing pulses (see e.g. Castellani et al 1985;Dorman & Rood 1993) are suppressed following the procedure described by Caputo et al (1989).…”

Section: Overshootingmentioning

confidence: 99%

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Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

Valle

Marconi²,

Degl’Innocenti

et al. 2009

A&A

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Context. With their period-luminosity relation, "classical Cepheids" (CC) are the most common primary distance indicators within the Local Group, also providing an absolute calibration of important secondary distance indicators. However, the predicted position of these pulsators in the HR diagram, along the so called blue loop, that is the expected distribution of Cepheids within the instability strip is affected by several model inputs, reflecting upon the predicted PL relation. Aims. The aim of this work is to quantitatively evaluate the effects on the theoretical PL relation of current uncertainties on the chemical abundances of Cepheids in the Large Magellanic Cloud (LMC) and on several physical assumptions adopted in the evolutionary models. We will separately analyse how the different factors influence the evolutionary and pulsational observables and the resulting PL relation. Methods. To achieve this goal we computed new sets of updated evolutionary and pulsational models. Results. As a result, we find that present uncertainties on the most relevant H and He burning reaction rates do not influence in a relevant way the loop extension in temperature. On the contrary, current uncertainties on the LMC chemical composition significantly affect the loop extension and also reflect in the morphology of the instability strip; however their influence on the predicted pulsational parameters is negligible. We also discussed how overshooting and mass loss, sometimes suggested as possible solutions for the long-standing problem of the Cepheid mass discrepancy, influence the ML relation and the pulsational parameters. Conclusions. In summary, the present uncertainties on the physical inputs adopted in the evolutionary codes and in the LMC chemical composition are negligible for the prediction of the main pulsational properties. On the other hand, the inclusion of overshooting in the previous hydrogen burning phase and/or of mass loss is expected to significantly change the resulting theoretical pulsational scenario for Cepheids, as well as the calibration of their distance scale. These systematic effects are expected to influence the theoretical Cepheid calibration of the secondary distance indicators and in turn the resulting evaluation of the Hubble constant.

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Section: Effects Of the Chemical Composition Uncertaintiesmentioning

confidence: 83%

Section: Overshootingmentioning

confidence: 99%

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

Valle

Marconi²,

Degl’Innocenti

et al. 2009

A&A

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“…The extension of the semiconvective region varies with stellar mass, being important in low-and intermediate-mass stars up to about 5 M , and negligible in more massive stars. We followed the scheme of Castellani et al (1985), as described in Bressan et al (1993).…”

Section: Helium Semiconvectionmentioning

confidence: 99%

Scaled solar tracks and isochrones in a large region of theZ–Yplane

Bertelli¹,

Nasi²,

Girardi³

et al. 2009

A&A

252

348

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We extend our theoretical computations for low-mass stars to intermediate-mass and massive stars, for which few databases exist in the literature. Evolutionary tracks and isochrones are computed for initial masses 2.50−20 M for a grid of 37 chemical compositions with metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.40 to enable users to obtain isochrones for ages as young as about 10 7 years and to simulate stellar populations with different helium-to-metal enrichment laws. The Padova stellar evolution code is identical to that used in the first paper of this series. Synthetic TP-AGB models allow stellar tracks and isochrones to be extended until the end of the thermal pulses along the AGB. We provide software tools for the bidimensional interpolation (in Y and Z) of the isochrones from very old ages down to about 10 7 years. This lower limit depends on chemical composition. The extension of the blue loops and the instability strip of Cepheid stars are compared and the Cepheid mass-discrepancy is discussed. The location of red supergiants in the H-R diagram is in good agreement with the evolutionary tracks for masses from 10 to 20 M . Tracks and isochrones are available in tabular form for the adopted grid of chemical compositions in the extended plane Z − Y in three photometric systems. An interactive web interface allows users to obtain isochrones of any chemical composition inside the provided Z − Y range and also to simulate stellar populations with different Y(Z) helium-to-metal enrichment laws.

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“…Induced overshooting and semiconvection during the He-central burning phase 1 The EOS code is made publicly available at ftp://astroftp.phys.uvic.ca under the GNU General Public License (GPL). are accounted for following Castellani et al (1985). The thermal gradient in the superadiabatic regions is determined according to the mixing length theory, whose free parameter has been calibrated by computing a solar standard model.…”

Section: The Theoretical Frameworkmentioning

confidence: 99%

The Red Giant Branch luminosity function bump

Riello

Cassisi

Piotto

et al. 2003

A&A

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Abstract. We present observational estimates of the magnitude difference between the luminosity function red giant branch bump and the horizontal branch (∆F555W bump HB ), and of star counts in the bump region (R bump ), for a sample of 54 Galactic globular clusters observed by the HST. The large sample of stars resolved in each cluster, and the high photometric accuracy of the data allowed us to detect the bump also in a number of metal poor clusters. To reduce the photometric uncertainties, empirical values are compared with theoretical predictions obtained from a set of updated canonical stellar evolution models which have been transformed directly into the HST flight system. We found an overall qualitative agreement between theory and observations. Quantitative estimates of the confidence level are hampered by current uncertainties on the globular cluster metallicity scale, and by the strong dependence of ∆F555W bump HB on the cluster metallicity. In case of the R bump parameter, which is only weakly affected by the metallicity, we find a very good quantitative agreement between theoretical canonical models and observations. For our full cluster sample the average difference between predicted and observed R bump values is practically negligible, and ranges from −0.002 to −0.028, depending on the employed metallicity scale. The observed dispersion around these values is entirely consistent with the observational errors on R bump . As a comparison, the value of R bump predicted by theory in case of spurious bump detections due to Poisson noise in the stellar counts would be ∼0.10 smaller than the observed ones. We have also tested the influence on the predicted ∆F555W bump HB and R bump values of an He-enriched component in the cluster stellar population, as recently suggested by D' Antona et al. (2002). We find that, under reasonable assumptions concerning the size of this He-enriched population and the degree of enrichment, the predicted ∆F555W bump HB and R bump values are only marginally affected.Key words. Galaxy: globular clusters: general -stars: luminosity function, mass function -stars: evolution -stars: statistics IntroductionStellar evolution models supply fundamental tools that enable one to constrain the structure of the Milky Way, the properties of extragalactic stellar systems, and the early evolution of the universe. During the last few years the substantial increase in the spatial resolution provided by the Hubble Space TelescopeSend offprint requests to: M. Riello, e-mail: riello@pd.astro.it Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555, and on observations retrieved with the ESO ST-ECF Archive.(HST), as well as the advent of wide field imagers in groundbased telescopes provided homogeneous and accurate photometry for large samples of stars in Galactic Globular Clusters (GGCs). This has made possible a thorough comparison between theoretical models of low mass s...

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Helium-burning evolutionary phases in population II stars. I Breathing pulses in horizontal branch stars

Cited by 117 publications

References 0 publications

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

Scaled solar tracks and isochrones in a large region of theZ–Yplane

The Red Giant Branch luminosity function bump

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