Blue loops of intermediate mass stars

HY(许海云), Xu; Y, Li

doi:10.1051/0004-6361:20040024

Cited by 29 publications

(39 citation statements)

References 43 publications

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“…Brunish et al 1990;Renzini et al 1992;Sestito et al 2002;Xu & Li 2004a;Weiss et al 2005), and have shown that the loop morphology is sensitive to variations of the adopted cross sections.…”

Section: Dependence Of the Loop Extension On The Uncertainties On Thementioning

confidence: 99%

“…producing effects that are not yet completely understood (see e.g. Xu & Li 2004a;Stothers & Chin 1994;Brunish et al 1990). In this context, a detailed comparison of evolutionary and pulsational models with the observations can provide insight into the physics of stellar evolution and pulsation.…”

Section: Article Published By Edp Sciencesmentioning

confidence: 99%

“…Several authors (see e.g. Sestito et al 2002;Xu & Li 2004a) showed that the 12 C(α, γ) 16 O cross section is related to the efficiency of the envelope contraction and thus to the loop extension.…”

Section: C(α γ) 16 O Cross Sectionmentioning

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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“…Brunish et al 1990;Renzini et al 1992;Sestito et al 2002;Xu & Li 2004a;Weiss et al 2005), and have shown that the loop morphology is sensitive to variations of the adopted cross sections.…”

Section: Dependence Of the Loop Extension On The Uncertainties On Thementioning

confidence: 99%

Section: Article Published By Edp Sciencesmentioning

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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show abstract

“…There may well be a region in the uppermass regime of RSG where stars have lost a significant fraction (but not all) of their H envelopes prior to exploding. Some models suggest that such stars could undergo "blue loops" on the HRD, during which they experience temporary blueward excursions (e.g., Xu & Li 2004), and it is possible that some of these stars could even explode during these brief migrations. This would give their progenitors characteristics consistent with hotter supergiant stars, e.g., yellow supergiants (YSG) or, even, blue supergiants (BSG).…”

Section: Sn Classification Stellar Evolution and Zeroth-order Prmentioning

confidence: 99%

On the progenitors of core-collapse supernovae

Leonard

2010

Astrophys Space Sci

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Theory holds that a star born with an initial mass between about 8 and 140 times the mass of the Sun will end its life through the catastrophic gravitational collapse of its iron core to a neutron star or black hole. This core collapse process is thought to usually be accompanied by the ejection of the star's envelope as a supernova. This established theory is now being tested observationally, with over three dozen core-collapse supernovae having had the properties of their progenitor stars directly measured through the examination of high-resolution images taken prior to the explosion.Here I review what has been learned from these studies and briefly examine the potential impact on stellar evolution theory, the existence of "failed supernovae", and our understanding of the core-collapse explosion mechanism.

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“…In a previous paper (Xu & Li 2004, hereafter referred to as Paper I), we have made extensive investigations on the formation of the blue loop for stellar models of solar-like composition. We found that the blue loop evolution depends closely on the development of the envelope convection and nuclear energy production in the H-burning shell.…”

Section: Introductionmentioning

confidence: 99%

Blue loops of intermediate mass stars

2004

A&A

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Abstract. Based on the results of the blue loop formation for models of solar-like metallicity, we have explored the blue loop evolution of metal-poor stars. Three series of models with a wide range of metallicity and the initial helium abundance were calculated. An important parameter, η c , defined as the envelope convection mass divided by the total envelope mass at the bottom of the RGB, was introduced as a criterion to determine the formation of the blue loop. We have found that the low-Z models will develop extensive blue loops when η c is lower than a critical value η crit . The physical explanation for this result could be as follows. Lower Z reduces the envelope opacity and leads to a hotter stellar envelope and a bluer RGB. Thus the model will have a smaller η a at the top and an even smaller η c at the bottom of the RGB. When η c is lower than the critical value η crit , the envelope is radiation-dominated. Under this condition and the constraint of the virial theorem, the response of the star to the increase of the stellar luminosity is to contract to increase the thermal conductivity coefficient in the stellar envelope and to form a blue loop. Compared with the high-Z models, we have confirmed that the development of convection in the stellar envelope is a crucial factor to determine the formation of the blue loop, but the low-Z models reach low η c values in a different way from the high-Z models, in which the modulation of the nuclear reaction rates by higher 14 N abundance in the H-burning shell is responsible for the stars to get small η c values. It has been found that η crit depends not only on the stellar mass, but also on metallicity and the initial helium abundance. Our numerical results show that η crit decreases with Z while slowly increases with Y.

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Blue loops of intermediate mass stars

Cited by 29 publications

References 43 publications

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

Uncertainties on the theoretical predictions for classical Cepheid pulsational quantities

On the progenitors of core-collapse supernovae

Blue loops of intermediate mass stars

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