The lithium abundance in stars

Michaud, G.; Charbonneau, Paul

doi:10.1007/bf00195950

Cited by 81 publications

(62 citation statements)

References 106 publications

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“…log N(Li) 1 2 10). Such high abundances are a qualitative, but not a quantitative, indication of stellar youth: The relationship between lithium and age is more complex than previously assumed (Michaud & Charbonneau 1991). Two stars in the sample have , and a third (HD 97334) may be lithium poor, log N(Li) !…”

Section: Rotation Calcium Emission and Lithiummentioning

confidence: 90%

Nearby Young Solar Analogs. I. Catalog and Stellar Characteristics

Gaidos

1998

PUBL ASTRON SOC PAC

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ABSTRACT. We present a catalog of 38 young solar analogs within 25 pc, stars that are uniquely well suited for observations of their circumstellar environments to improve our understanding of conditions within the solar system during the Hadean/early Archean eons (prior to 3.8 Gyr ago). These G and early K stars were selected from the Hipparcos astrometric catalog based on lack of known stellar companions within 800 AU, bolometric luminosities close to that of the zero-age Sun and consistent with the zero-age main sequence, and ROSAT X-ray luminosities commensurate with the higher rotation rate and level of dynamo-driven activity in solar-mass stars less than 0.8 Gyr old. While many of these objects have been previously identified, this sample is novel in two respects: The selection criteria specifically consider the planetary environment, and the selection is uniform and all-sky. The X-ray emission from these young analogs is spectrally soft and consistent with a coronal origin. Calcium H and K emission, rotation periods, lithium abundances, and kinematics support an age range of 0.2-0.8 Gyr for most of these stars. Three stars have exceptionally high space motions with respect to the local standard of rest and may be old disk or halo stars that are anomalously X-ray luminous.

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Section: Rotation Calcium Emission and Lithiummentioning

confidence: 90%

Nearby Young Solar Analogs. I. Catalog and Stellar Characteristics

Gaidos

1998

PUBL ASTRON SOC PAC

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“…At the cool end of the Fm star domain, the well documented Li dip, first observed in the Hyades open cluster (Boesgaard & Tripicco 1986), has challenged theoretical astronomers for decades (Michaud 1986;Vauclair 1988;Michaud & Charbonneau 1991;Talon & Charbonnel 2005). The lithium abundance has also been observed in many other open clusters (e.g.…”

Section: Astrophysical Contextmentioning

confidence: 97%

“…The shoulder on the cold side of the gap obtained in the present calculations matches the curve they obtained with Z 0 = 0.02 within 20 It has been suggested to revise these observations upwards by up to 0.4 dex (see the discussion in Sect. 2.1.2 of Michaud & Charbonneau 1991;and Boesgaard & King 2002). The maximum depletion encountered in the deepest part of the gap might so be closer to a factor of 50.…”

Section: Lithium Gapmentioning

confidence: 99%

“…9, if we had chosen Z 0 = 0.03 ([Fe/H] = +0.18), some of the 150 K difference would have been recuperated as the gap minimum would have been shifted toward cooler temperatures by 50-80 K. There is also a ±50−100 K uncertainty on the observed potition of the gap (see discussion in Sect. 2.1.2 of Michaud & Charbonneau 1991). The uncertainty on the age of the Hyades (from 625 to 783 Myr, see Sect.…”

Section: Lithium Gapmentioning

confidence: 99%

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AmFm and lithium gap stars

Vick

Michaud

Richer

et al. 2010

A&A

102

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Aims. A thorough study of the effects of mass loss on internal and surface abundances of A and F stars is carried out in order to constrain mass loss rates for these stars, as well as further elucidate some of the processes which compete with atomic diffusion. Methods. Self-consistent stellar evolution models of 1.3 to 2.5 M stars including atomic diffusion and radiative accelerations for all species within the OPAL opacity database were computed with mass loss and compared to observations as well as previous calculations with turbulent mixing. Results. Models with unseparated mass loss rates between 5 × 10 −14 and 10 −13 M yr −1 reproduce observations for many cluster AmFm stars as well as Sirius A and o Leonis. These models also explain cool Fm stars, but not the Hyades lithium gap. Like turbulent mixing, these mass loss rates reduce surface abundance anomalies; however, their effects are very different with respect to internal abundances. For most of the main-sequence lifetime of an A or F star, surface abundances in the presence of such mass loss depend on separation which takes place between log ΔM/M * = −6 and −5. Conclusions. The current observational constraints do not allow us to conclude that mass loss is to be preferred over turbulent mixing (induced by rotation or otherwise) in order to explain the AmFm phenomenon. Internal concentration variations which could be detectable through asteroseismic tests should provide further information. If atomic diffusion coupled with mass loss are to explain the Hyades Li gap, the wind would need to be separated.

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“…Michaud & Charbonneau 1991) predicts a strong reduction in the Li surface abundance after the first dredge up to values log (Li) < 1.5, or even less if depletion effects on the main sequence are considered. Most giants for which a Li abundance has been determined (see a summary by Michaud & Charbonneau 1991) agree with this result.…”

Section: Introductionmentioning

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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The lithium abundance in stars

Cited by 81 publications

References 106 publications

Nearby Young Solar Analogs. I. Catalog and Stellar Characteristics

Nearby Young Solar Analogs. I. Catalog and Stellar Characteristics

AmFm and lithium gap stars

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

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