On a Rapid Lithium Enrichment and Depletion of K Giant Stars

Reza, R. de la; Драке, Н. А.; Silva, L. da; Torres, C. A. O.; Martín, E. L.

doi:10.1086/310685

Cited by 86 publications

(106 citation statements)

References 17 publications

(20 reference statements)

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“…In agreement with this, Kraft et al (1999) De la Reza et al (1996Reza et al ( , 1997 proposed a different scenario for the Li production along the RGB, associated with short episodes of mass loss occurring just after each extra-mixing event. In this way, some fresh Li would be produced when convection penetrates close to the H-burning shell, which might occur at the RGB bump or brighter.…”

Section: Circumstellar Materials and Infrared Excessmentioning

confidence: 82%

“…The thin layer containing fresh Li would be quickly carried to the surface (and observed) but would be lost by the star immediately afterwards. Observational support of this scenario was given by the detection of infrared excess in some Li-rich giant stars (Gregorio-Hetem et al 1993;De la Reza et al 1996, 1997Castilho et al 1998).…”

Section: Circumstellar Materials and Infrared Excessmentioning

confidence: 93%

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Li-rich red giant branch stars in the Galactic bulge

Gonzalez

Zoccali²,

Monaco

et al. 2009

A&A

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Aims. We present lithium abundance determination for a sample of K giant stars in the Galactic bulge. The stars presented here are the only 13 stars with a detectable lithium line (6767.18 Å) among ∼400 stars for which we have spectra in this wavelength range, half of them in Baade's Window (b = −4 • ) and half in a field at b = −6 • . Methods. The stars were observed with the GIRAFFE spectrograph of FLAMES mounted on VLT, with a spectral resolution of R ∼ 20 000. Abundances were derived from spectral synthesis and the results are compared with those of stars with similar parameters, but no detectable Li line. Results. We find 13 stars with a detectable Li line, among which 2 have abundances A(Li) > 2.7. No clear correlations were found between the Li abundance and those of other elements. With the exception of the two most Li rich stars, the others follow a fairly tight A(Li) − T eff correlation. Conclusions. There is strong indication of a Li production phase during the red giant branch (RGB), acting either on a very short timescale, or selectively only in some stars. That the proposed Li production phase is associated with the RGB bump cannot be excluded, although our targets are significantly brighter than the predicted RGB bump magnitude for a population at 8 kpc.

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Section: Circumstellar Materials and Infrared Excessmentioning

confidence: 82%

Section: Circumstellar Materials and Infrared Excessmentioning

confidence: 93%

Li-rich red giant branch stars in the Galactic bulge

Gonzalez

Zoccali²,

Monaco

et al. 2009

A&A

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“…Exploring the RGB hypothesis further, de la Reza et al (1997) argue that, at a certain point in the life of a giant, an abrupt mixing mechanism can lead to a rapid surface injection of material with fresh internal 7 Be, which is rapidly transformed to 7 Li. The same mechanism would then enable the formation of a circumstellar shell of gas and dust that is later ejected in the interstellar medium.…”

Section: Discussionmentioning

confidence: 99%

The Be-test in the Li-rich star #1657 of NGC 6397: evidence for Li-flash in RGB stars?

Pasquini¹,

Koch²,

Smiljanić³

et al. 2014

A&A

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Context. The Li-rich turn-off star recently discovered in the old, metal-poor globular cluster NGC 6397 could represent the smoking gun for some fundamental, but very rare episode of Li enrichment in globular clusters and in the early Galaxy. Aims. We aim to understand the nature of the Li enrichment by performing a spectroscopic analysis of the star, in particular of its beryllium (Be) abundance, and by investigating its binary nature.Methods. We used the VLT/UVES spectrograph to observe the near UV region where the Be ii resonance doublet and the NH bands are located. We also re-analyzed an archival Magellan/MIKE spectra for C and O abundance determination.Results. We could not detect the Be ii lines and derive an upper limit of log(Be/H) < −12.2 that is consistent with the Be observed in other stars of the cluster. We could detect a weak G-band, which implies a mild carbon enhancement [C/Fe]+0.4 ± 0.2. We could not detect the UV NH band, showing that this star is less N-enhanced than other stars of the cluster, and we derive an upper limit [N/Fe] < 0.0. For oxygen we could not convincingly detect any of the near UV OH lines, which implies that oxygen cannot be strongly enhanced in this star. This is consistent with the detection of the strongest line of the O i triplet at 777 nm, which is contaminated by telluric absorptions but is consistent with [O/Fe] ∼ 0.5. Combining the UVES and Mike data, we could not detect any variation in the radial velocity greater than 0.95 kms −1 over 8 years.Conclusions. The chemical composition of the star strongly resembles that of "first generation" NGC 6397 stars, with the huge Li as the only deviating abundance. Not detecting Be rules out two possible explanations of the Li overabundance: capture of a substellar body and spallation caused by a nearby type II SNe. Discrepancies are also found with respect to other accretion scenarios, except for contamination by the ejecta of a star that has undergone the RGB Li-flash. This is at present the most likely possibility for explaining the extraordinary Li enrichment of this star.

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“…when the stars evolve out of the main sequence; but this scenario should suggest that lithium-rich K-giants may have spotted lithium-rich Ap progenitors, a new scenario that needs more detailed analysis in the future. The discovery of this large number of lithium-rich giants adds more than 40% to the known ones (40 quoted by de la Reza et al 1997b; 15 quoted by Pereyra et al 2006, and some other dispersed in the literature). Our results reinforce those of Fekel & Balachandran (1994), who found that 58% of single active giants have high lithium abundance (36% for the giants in binary systems) and are also in line with a 50% of lithium-rich stars among rapidly-rotating K-giants found by Drake et al (2002).…”

Section: Lithium-rich Giantsmentioning

confidence: 92%

A spectroscopic survey of the youngest field stars in the solar neighbourhood

Guillout¹,

Klutsch²,

Frasca

et al. 2009

A&A

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Aims. We present the first results of an ambitious ground-based observation programme conducted on 1-4 meter class telescopes. Our sample consists of 1097 active and presumably young stars, all of them being optical (Tycho Catalogue) counterparts of ROSAT All-Sky Survey X-ray sources in the northern hemisphere. In this paper, we concentrate on the optically brightest (V T 9. m 5) candidates (704 objects). We acquired high-resolution optical spectroscopy in the Hα and/or lithium spectral regions for 426 of such stars without relevant data in the literature. We describe the star sample and the observations and we start to discuss the physical properties of the investigated stars. Methods. We used a cross-correlation technique and other tools developed by us to derive accurate radial and rotational velocities and to perform an automatic spectral classification for both single stars and double-lined systems. The spectral subtraction technique was used to derive chromospheric activity levels and lithium abundances. We estimated the fraction of young single stars and multiple systems in stellar soft X-ray surveys and the contamination by more evolved systems, like RS CVn binaries. We classified stars on the basis of their lithium abundance and give a glimpse of their sky distribution.Results. The sample appears to be a mixture of quite young Pleiades-like and Hyades-like stars plus an older lithium-poor population probably born within the last 1-2 Gyr. Seven stars with a lithium abundance compatible with the age of IC 2602 (about 30 Myr) or even younger were detected as well, although two appear to be lithium-rich giants.The discovery of a large number of highly or moderately lithium-rich giants is another outcome of the present survey. Conclusions. The contamination of soft X-ray surveys by old systems in which the activity level is enhanced by tidal synchronisation is not negligible, especially for K-type stars. Five stars with lithium content close to the primordial abundance are probably associated with already known moving groups in the solar neighbourhood. Some of them are good post-T Tauri candidates according to their positions in the HR diagram.

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On a Rapid Lithium Enrichment and Depletion of K Giant Stars

Cited by 86 publications

References 17 publications

Li-rich red giant branch stars in the Galactic bulge

Li-rich red giant branch stars in the Galactic bulge

The Be-test in the Li-rich star #1657 of NGC 6397: evidence for Li-flash in RGB stars?

A spectroscopic survey of the youngest field stars in the solar neighbourhood

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