Mass loss and luminosities of S and C AGB stars with and without Li

Guandalini, R.; Palmerini, S.; Busso, M.; Maiorca, E.; Uttenthaler, S.

doi:10.1017/s174392131000428x

Cited by 14 publications

(19 citation statements)

References 17 publications

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“…Indeed, stars on the early AGB present on average lower Li abundances than stars at the RGB-bump. Guandalini et al (2009) have interpreted this group of stars as actually lying on the RGB. Their models are unable to interpret super Li-rich stars though.…”

Section: Discussionmentioning

confidence: 99%

Lithium-rich giants in the Galactic thick disk

Monaco

Villanova

Bidin

et al. 2011

A&A

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Context. Lithium is a fragile element, which is easily destroyed in the stellar interior. The existence of lithium-rich giants still represents a challenge for stellar evolution models. Aims. We have collected a large database of high-resolution stellar spectra of 824 candidate thick-disk giants having 2 MASS photometry and proper motions measured by the Southern Proper-Motion Program (SPM). In order to investigate the nature of Li-rich giants, we searched this database for giants presenting a strong Li I resonance line. Methods. We performed a chemical abundance analysis on the selected stars with the MOOG code along with proper ATLAS-9 model atmospheres. The iron content and atmospheric parameters were fixed by using the equivalent width of a sample of Fe lines. We also derive abundances for C, N, and O and measure or derive lower limits on the 12 C/ 13 C isotopic ratios, which is a sensible diagnostic of the stars evolutionary status. Results. We detected five stars with a lithium abundance higher than 1.5, i.e. Li-rich according to the current definition. One of them (SPM-313132) has A(Li) > 3.3 and, because of this, belongs to the group of the rare super Li-rich giants. Its kinematics makes it a likely thin-disk member and its atmospheric parameters are compatible with it being a 4 M star either on the red giant branch (RGB) or the early asymptotic giant branch. This object is the first super Li-rich giant detected at this phase. The other four are likely low-mass thick-disk stars evolved past the RGB luminosity bump, as determined from their metallicities and atmospheric parameters. The most evolved of them lies close to the RGB-tip. It has A(Li) > 2.7 and a low 12 C/ 13 C isotopic ratio, close to the cool bottom processing predictions.

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Section: Discussionmentioning

confidence: 99%

Lithium-rich giants in the Galactic thick disk

Monaco

Villanova

Bidin

et al. 2011

A&A

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“…In the magnetic buoyancy scenario (Guandalini et al 2009), the mixing is thought to arise from magnetic bubbles with locally increased magnetic pressure, thus a decreased density. The magnetic field might be sustained by an α−Ω dynamo produced by a region of rotational shear below the convective envelope.…”

Section: Discussionmentioning

confidence: 99%

Correlation between technetium and lithium in a sample of oxygen-rich AGB variables

Uttenthaler¹,

Lebzelter²

2010

A&A

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Context. The elements technetium and lithium are two important indicators of internal nucleosynthesis and mixing in late-type stars. Studying their occurrence and abundance can give deep insight into the structure and evolution in the late phases of the stellar life cycle. Aims. The aims of this paper are: 1) to revisit the Tc content of a sample of oxygen-rich (M-type) asymptotic giant branch (AGB) variables and 2) to increase the number of such stars for which the Li abundance has been measured to provide constraints on the theoretical models of extra-mixing processes. Methods. To this end, we analysed high-resolution spectra of 18 sample stars for the presence of absorption lines of Tc and Li. The abundance of the latter was determined by comparing the observed spectra to hydrostatic MARCS model spectra. Bolometric magnitudes were established from near-IR photometry and pulsation periods. Results. We correct the classification with respect to the presence of Tc for a number of stars. We reclassify the star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as well as W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, was determined for all of the sample stars. In all stars with Tc we also detected Li. Most of them have a Li content slightly below the solar photospheric value, except for V441 Cyg, which is super-Li rich with ∼1000 times the solar abundance. We also found that, similar to Tc, a lower luminosity limit seems to exist for the presence of Li. Conclusions. We conclude that the higher Li abundance found in the cooler and higher luminosity objects could stem from a Li production mechanism operating on the thermally pulsing AGB. The stellar mass might have a crucial influence on this (extra mixing) production mechanism. Our findings for R Hya and V441 Cyg have some important consequences for these intriguing objects. It was speculated that the declining pulsation period of R Hya is caused by a recent thermal pulse (TP). While not detecting Tc does not rule out a TP, it indicates that the TPs are not strong enough to drive 3DUP in R Hya. The pieces of evidence concerning the mass of V441 Cyg are not entirely conclusive. It could either be a low-mass, intrinsic S-star that produced its large amount of Li by extra-mixing processes, or an intermediate-mass star (M > ∼ 4 M ) undergoing Li production via hot bottom burning.

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“…Indications on the general properties of the phenomenon (velocity, effectiveness and depth) can however be obtained by fitting the observational constraints with physical or parametric models (see e.g. [15,16]). In this way one recognizes that CNO isotopes in evolved stars can be accounted for by various models; on the contrary, more stringent constraints are posed by 26 Al-rich grains (requiring very deep mixing) or by Li-rich giants (requiring mixing mechanisms on time scales shorter than 7 Be-decay).…”

Section: Introductionmentioning

confidence: 99%

“…We show how the use of recent and accurate reaction rates induces considerable differences in the nucleosinthesis results as compared to previous studies. Among the most remarkable novelties we discuss the effects of the new rates for the 14 N(p,γ) 15 O and for p-captures on oxygen isotopes. They jointly provide a much better agreement than before with presolar grain isotopic abundances and allow for a clear determination of the mass of the parent star.…”

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confidence: 99%

Effects of new reaction rates on p-capture nucleosynthesis in Low Mass Stars

Palmerini¹,

Busso²,

Cognata³

et al. 2011

Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI)

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Evolved low-and intermediate-mass stars are important sites for the production of heavy nuclei (through slow n-captures) and of light-and intermediate-mass isotopes (through p-captures). This was revealed by spectroscopy of evolved stars as well as by the chemical analysis of presolar grains of circumstellar origins. The observational basis for these issues has grown considerably over the years, confirming peculiar abundances of 3 He, 7 Li, CNO isotopes and 26 Al. Many studies have been presented in the last thirty years suggesting that the above evidence can be accounted for by non-convective transport mechanisms that link the stellar envelope with the region where pcaptures take place, during the red giant phases. Nucleosynthesis in deep mixing episodes is made uncertain by two series of problems. On one side one has to identify the physical mechanism for the transport. On the other, several reaction rates adopted in the calculations are still uncertain, mainly because hydrogen burning takes place in red giants at typical Gamov-Peak energies of a few tens of keV, where experimental measurements are extremely difficult. We show how the use of recent and accurate reaction rates induces considerable differences in the nucleosinthesis results as compared to previous studies. Among the most remarkable novelties we discuss the effects of the new rates for the 14 N(p,γ) 15 O and for p-captures on oxygen isotopes. They jointly provide a much better agreement than before with presolar grain isotopic abundances and allow for a clear determination of the mass of the parent star.11th Symposium on Nuclei in the Cosmos, NIC XI

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Mass loss and luminosities of S and C AGB stars with and without Li

Cited by 14 publications

References 17 publications

Lithium-rich giants in the Galactic thick disk

Lithium-rich giants in the Galactic thick disk

Correlation between technetium and lithium in a sample of oxygen-rich AGB variables

Effects of new reaction rates on p-capture nucleosynthesis in Low Mass Stars

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