British and Irish contexts

Stancliffe, Clare; DeGregorio, Scott

doi:10.1017/ccol9780521514958.005

Cited by 19 publications

(7 citation statements)

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“…In the present case the production of 7 Li is significant, and the surface N(Li) reaches a value of ∼0.9 (then the star has a total luminosity Log(L/L ⊙ ) between ∼3.0 and 3.6). We thus confirm, but this time at solar metallicity, the finding by Stancliffe (2010) that thermohaline mixing does increase the surface Li abundance in low-mass TP-AGB stars. Whether these Li-rich objects can simultaneously be carbon-rich will require further investigation of the TP-AGB phase including parametric convective overshoot as mentioned before.…”

Section: Predictions On the Agbsupporting

confidence: 85%

Thermohaline instability and rotation-induced mixing. I - Low- and intermediate-mass solar metallicity stars up to the end of the AGB

Charbonnel,

Lagarde

2010

Preprint

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Context. Numerous spectroscopic observations provide compelling evidence for non-canonical processes that modify the surface abundances of low-and intermediate-mass stars beyond the predictions of standard stellar theory. Aims. We study the effects of thermohaline instability and rotation-induced mixing in the 1-4 M ⊙ range at solar metallicity. Methods. We present evolutionary models by considering both thermohaline and rotation-induced mixing in stellar interior. We discuss the effects of these processes on the chemical properties of stars from the zero age main sequence up to the end of the second dredge-up on the early-AGB for intermediate-mass stars and up to the AGB tip for low-mass stars. Model predictions are compared to observational data for lithium, 12 C/ 13 C, [N/C], [Na/Fe], 16 O/ 17 O, and 16 O/ 18 O in Galactic open clusters and in field stars with well-defined evolutionary status, as well as in planetary nebulae. Results. Thermohaline mixing simultaneously accounts for the observed behaviour of 12 C/ 13 C, [N/C], and lithium in low-mass stars that are more luminous than the RGB bump, and its efficiency is increasing with decreasing initial stellar mass. On the TP-AGB, thermohaline mixing leads to lithium production, although the 7 Li yields remain negative. Although the 3 He stellar yields are much reduced thanks to this process, we find that solar-metallicity, low-mass stars remain net 3 He producers. Rotation-induced mixing is found to change the stellar structure so that in the mass range between ∼ 1.5 and 2.2 M ⊙ the thermohaline instability occurs earlier on the red giant branch than in non-rotating models. Finally rotation accounts for the observed star-to-star abundance variations at a given evolutionary status, and is necessary to explain the features of CN-processed material in intermediate-mass stars. Conclusions. Overall, the present models account for the observational constraints very well over the whole mass range presently investigated.

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Section: Predictions On the Agbsupporting

confidence: 85%

Thermohaline instability and rotation-induced mixing. I - Low- and intermediate-mass solar metallicity stars up to the end of the AGB

Charbonnel,

Lagarde

2010

Preprint

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“…On the other hand, we also showed in Paper I that rotationinduced mixing on the main sequence changes the stellar structure so that it slightly re-enforces the effects of the thermohaline instability in low-mass stars and explains the observed features of CN-processed material in more massive evolved stars that do not undergo thermohaline mixing on the RGB. Last but not least, in Paper I thermohaline mixing was found to lead to additional 3 He depletion associated to Li production in all the solar-metallicity models that we computed along the thermal pulse phase on the asymptotic giant branch (TP-AGB), confirming the previous findings by Stancliffe (2010) for low-metallicity low-mass stars. This accounts beautifully for the Li behaviour in Galactic oxygen-rich AGB variables.…”

Section: Introductionsupporting

confidence: 89%

“…After the second dredge-up, 3 He remains in sufficient quantity to drive thermohaline mixing during the TP-AGB in stars that do not undergo hot-bottom burning (i.e., with initial mass below ∼ 3 M ⊙ ). As discussed in Paper I (see also Cantiello & Langer 2010;Stancliffe 2010), this leads to even greater (although modest) depletion of 3 He associated to 7 Li production during that phase. This is depicted in Fig.…”

Section: Tp-agbmentioning

confidence: 75%

Thermohaline instability and rotation-induced mixing II- Yields of 3He for low- and intermediate-mass stars

Lagarde,

Charbonnel,

Decressin

et al. 2011

Preprint

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Context. The 3 He content of Galactic HII regions is very close to that of the Sun and the solar system, and only slightly higher than the primordial 3 He abundance as predicted by the standard Big Bang nucleosynthesis. However, the classical theory of stellar evolution predicts a high production of 3 He by low-mass stars, implying a strong increase of 3 He with time in the Galaxy. This is the well-known " 3 He problem". Aims. We study the effects of thermohaline and rotation-induced mixings on the production and destruction of 3 He over the lifetime of low-and intermediate-mass stars at various metallicities. Methods. We compute stellar evolutionary models in the mass range 1 to 6 M ⊙ for four metallicities, taking into account thermohaline instability and rotation-induced mixing. For the thermohaline diffusivity we use the prescription based on the linear stability analysis, which reproduces Red Giant Branch (RGB) abundance patterns at all metallicities. Rotation-induced mixing is treated taking into account meridional circulation and shear turbulence. We discuss the effects of these processes on internal and surface abundances of 3 He and on the net yields. Results. Over the whole mass and metallicity range investigated, rotation-induced mixing lowers the 3 He production, as well as the upper mass limit at which stars destroy 3 He. For low-mass stars, thermohaline mixing occuring beyond the RGB bump is the dominant process in strongly reducing the net 3 He yield compared to standard computations. Yet these stars remain net 3 He producers. Conclusions. Overall, the net 3 He yields are strongly reduced compared to the standard framework predictions.

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“…45 While this was arguably in-line with Theodore's views early in his career as archbishop, the elderly archbishop seems to have moderated his views while in Britain and adopted a more pragmatic stance. 46 In contrast, Wilfrid did not. His authoritarian approach will arguably have alarmed large numbers of Northumbria's clergy and alienated Ecgfrith's Scottish, Pictish and British tributaries.…”

Section: Theodore Ecgfrith and The Northmentioning

confidence: 98%