Time Scales of Stars during the Crossing of the Cepheid Strip

Lauterborn, D.; Refsdal, S.; Roth, Manfred

doi:10.1017/s0252921100032759

Cited by 27 publications

(53 citation statements)

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“…4 (point e) as soon as the maximum energy production layer of the H-burning shell touches the abundance discontinuity. Lauterborn et al (1971a) discovered a similar effect before.…”

Section: Properties Of Evolution Modelssupporting

confidence: 53%

“…Firstly, helium exhaustion in the stellar core can terminate the blue loop, as pointed out by Lauterborn et al (1971a) and Fricke et al (1971). Secondly, when the center of the H-burning shell touches the abundance discontinuity in our CNO models as shown in Fig.…”

Section: Discussion On Some Factors Of the Blue Loopmentioning

confidence: 66%

“…Kippenhahn & Weigert (1990) considered the formation of the blue loop as a result of the Hburning shell moving outward through an increasing hydrogen abundance profile. They introduced an effective core potential (Lauterborn et al 1971a), ϕ = hM C /R C , to measure the distance of a model from the Hayashi line on the HRD, and found that a blue loop occurred when ϕ < ϕ cr . They assumed that h was proportional to the mass fraction of helium just above the shell source in the chemical profile.…”

Section: Introductionmentioning

confidence: 99%

“…The decrease of metal abundance, which leads to the decrease of opacity, sometimes produces more extended blue loops but sometimes not (Castellani et al 1990;Alongi et al 1991;Schaller et al 1992;Bono et al 2000). Mass loss in the red-giant phase is a strong effect to suppress the blue loop (Lauterborn et al 1971a;Lauterborn & Siquig 1974;Bertelli et al 1985;Bono et al 2000), but massive stars sometimes develop extended blue loops when strong mass loss is taken into account (Bertelli et al 1985;Salasnich et al 1999). It is well known that the shape and extension of the blue loop are different with different opacity tables (Fricke et al 1971;Carson & Stothers 1976;Bressan et al 1993;Stothers & Chin 1968, 1991bCassisi et al 1994).…”

Section: Introductionmentioning

confidence: 99%

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Blue loops of intermediate mass stars

HY(许海云)

2004

A&A

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Abstract.We investigate the effects of the CNO cycles on the formation of the blue loop for intermediate mass stars of solarlike metallicity. By use of two ways to treat the CNO cycles, we find that the models adopting the CNO bi-cycles (CNO models) develop extensive blue loops while those only considering the CN cycle (CN models) do not. We compare the properties of the CN and CNO models to explore the triggering mechanism of the blue loop. We notice that during the blue loop the increase of luminosity is determined by the nuclear energy production in the stellar core while the increase of effective temperature measures how far the stellar envelope can expand for a given luminosity at its base. We find that the stellar envelope obeys the virial theorem to a very high accuracy. Thus in a convection-dominated envelope, the extra heat from its base will lead to more developed convective motion and the decrease of temperature, and the star evolves up along the RGB. However in a radiationdominated envelope, the increase of luminosity requires the increase of temperature to enlarge the radiation transfer efficiency, and the star develops a blue loop. We introduce an envelope convective ratio η, which is defined by the envelope convection mass divided by the total envelope mass, to measure the development of convection in the stellar envelope. It is found that the critical value, η crit , for a star to develop a blue loop is between 0.3 and 0.45, and η crit shows a weak dependence on the stellar mass. On the other hand, we find that the enhancement of the energy production rate in the H-burning shell is responsible for the increase of the stellar luminosity during the blue loop phase. The increasing central He-burning rate increases the temperature of the H-burning shell, while the movement of the H-burning shell along the chemical profile enhances its energy production efficiency. We find that higher 14 N abundance in the H-burning shell plays a crucial role in the formation of the blue loop for the CNO models. It makes the H-burning shell not only move quickly toward the lower temperature region in the pre-loop phase to decrease the stellar luminosity and η, but also place the hydrogen discontinuity closer to the shell source to increase the stellar luminosity during the blue loop phase by adding higher abundant hydrogen into the H-burning shell. We find that overshooting from the convective core makes the abundance discontinuity layer displace farther from the stellar core, which makes the energy production of the H-burning shell less efficient and the blue loop more difficult to be formed. The opacity enhancement of the OPAL over the LAOL leads to stronger convective motion in the stellar envelope and thus makes the blue loop more difficult to form.

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“…4 (point e) as soon as the maximum energy production layer of the H-burning shell touches the abundance discontinuity. Lauterborn et al (1971a) discovered a similar effect before.…”

Section: Properties Of Evolution Modelssupporting

confidence: 53%

Section: Discussion On Some Factors Of the Blue Loopmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Blue loops of intermediate mass stars

HY(许海云)

2004

A&A

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“…According to Lauterborn et al (1971), the occurrence of 6 We focus our discussion on comparing models with the same ω ini . The trends can differ slightly if we considered for example the same v eq, ini .…”

Section: Blue Loopsmentioning

confidence: 99%

Populations of rotating stars

Georgy

Ekstr

Granada

et al. 2013

A&A

269

382

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AstrophysicsPopulations of rotating stars I. Models from 1.7 to 15 M at Z = 0.014, 0.006, and 0.002with Ω/Ω crit between 0 and 1 , ABSTRACTContext. B-type stars are known to rotate at various velocities, including very fast rotators near the critical velocity as the Be stars. Aims. In this paper, we provide stellar models covering the mass range between 1.7 to 15 M , which includes the typical mass of known Be stars, at Z = 0.014, 0.006, and 0.002 and for an extended range of initial velocities on the zero-age main sequence. Methods. We used the Geneva stellar-evolution code, including the effects of shellular rotation, with a numerical treatment that has been improved so the code can precisely track the variation in the angular momentum content of the star as it changes under the influence of radiative winds and/or mechanical mass loss. Results. We discuss the impact of the initial rotation rate on the tracks in the Hertzsprung-Russell diagram, the main-sequence (MS) lifetimes, the evolution of the surface rotation and abundances, as well as on the ejected masses of various isotopes. Among the new results obtained from the present grid we find that 1) fast-rotating stars with initial masses around 1.7 M present at the beginning of the core hydrogen-burning phase quite small convective cores with respect to their slowly rotating counterparts. This fact may be interesting to keep in mind in the framework of the asteroseismic studies of such stars. 2) The contrast between the core and surface angular velocity is higher in slower rotating stars. Our results are in agreement with the very few values obtained for B-type stars from asteroseismology. 3) At Z = 0.002, the stars in the mass range of 1.7 to 3 M with a mean velocity on the MS of the order of 150 km s −1 show N/H enhancement superior to 0.2 dex at mid-MS, and superior to 0.4 dex at the end of the MS phase. At solar metallicity the corresponding values are below 0.2 dex at any time in the MS.Conclusions. An extended database of stellar models containing 270 evolutionary tracks is provided to the community.

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The Evolution of Massive Stars: The Production of “Single” WR Stars

Chiosi

1982

Symp. - Int. Astron. Union

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In this paper we summarize the basic observational properties of WR stars, and the current status of the evolution of massive stars, giving particular emphasis to those physical mechanisms (mass loss, overshooting, turbulent diffusion…) that may lead O type stars to the WR stage. We consider only those scenarios for WR formation and evolution that have been developed during the last few years and that appear to be sufficiently substanciated by observational and theoretical arguments. Finally, the theoretical results are compared with the observations, pointing out several still unsettled aspects of the problem.

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Time Scales of Stars during the Crossing of the Cepheid Strip

Cited by 27 publications

References 0 publications

Blue loops of intermediate mass stars

Blue loops of intermediate mass stars

Populations of rotating stars

The Evolution of Massive Stars: The Production of “Single” WR Stars

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