The Lithium Abundances of a Large Sample of Red Giants

Liu, Y. J.; Tan, Kefeng; Wang, Liang; Zhao, Gang; Sato, Bun’ei; Takeda, Yoichi; N., Li, H.

doi:10.1088/0004-637x/785/2/94

Cited by 61 publications

(70 citation statements)

References 48 publications

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“…We could achieve satisfactory convergence for most cases, though the solutions failed for the cases where the Li line feature is too weak and undetectable (8 out of Since all the 239 stars in the former sample are included in Liu et al's (2014) extensive Li abundance analysis for red giants, we can compare our results (LTE Li abundances and non-LTE corrections) with theirs as displayed in figure 19a,b. We can see from figure 19a that our Li abundances are quite consistent with those of Liu et al (2014) as far as the Li i 6708 line is sufficiently strong (group A1). However, as the line becomes weaker (group A2), their abundances tend to be systematically larger than our results.…”

Section: Appendix 2 LI Abundances Of Normal Red Giantssupporting

confidence: 76%

“…However, as the line becomes weaker (group A2), their abundances tend to be systematically larger than our results. The non-LTE corrections adopted by Liu et al (2014), for which they invoked Lind et al's (2009) tables, are slightly (by a few hundredths dex) smaller than ours (figure 19b), though the differences are quantitatively insignificant.…”

Section: Appendix 2 LI Abundances Of Normal Red Giantscontrasting

confidence: 73%

“…That is, this element generally suffers considerable deficiency in the atmosphere of these evolved stars, due to (1) destruction of Li atoms at the hot stellar interior of T > ∼ 2.5 × 10 6 K and (2) efficient evolution-induced mixing at the red-giant stage causing Li dilution in the outer envelope, by which the observable Li line is considerably weakened and its abundance determination becomes rather difficult (see e.g., Liu et al 2014 and the references therein for representative Li abundance studies of red giants in general published so far).…”

Section: Introductionmentioning

confidence: 99%

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On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants

Takeda

Tajitsu²

2017

Publications of the Astronomical Society of Japan

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While lithium is generally deficient in the atmosphere of evolved giant stars because of the efficient mixing-induced dilution, a small fraction of red giants show unusually strong Li lines indicative of conspicuous abundance excess. With an aim to shed light on the origin of these peculiar stars, we carried out a spectroscopic study on the observational characteristics of selected 20 bright giants already known to be Li-rich from past studies, in comparison with the reference sample of a large number of normal late G -early K giants. Our special attention was paid to clarifying any difference between the two samples from a comprehensive point of view (i.e., with respect to stellar parameters, rotation, activity, kinematic properties, 6 Li/ 7 Li ratio, and the abundances of Li, Be, C, O, Na, S, and Zn). Our sample stars are roughly divided into "bump/clump group" and "luminous group" according to the positions on the HR diagram. Regarding the former group (1.5 < ∼ log(L/L ⊙ ) < ∼ 2 and M ∼1.5-3 M ⊙ ), Li-enriched giants and normal giants appear practically similar in almost all respect except for Li, suggesting that surface Li enhancement in this group may be a transient episode which normal giants undergo at certain evolutionary stages in their lifetime. Meanwhile, those Li-rich giants belonging to the latter group (log(L/L ⊙ ) ∼ 3 and M ∼3-5 M ⊙ ) appear more anomalous in the sense that they tend to show higher rotation as well as higher activity, and that their elemental abundances (especially those derived from high-excitation lines) are apt to show apparent overabundances, though this might be due to a spurious effect reflecting the difficulty of abundance derivation in stars of higher rotation and activity. Our analysis confirmed considerable Be deficiency as well as absence of 6 Li as the general characteristics of Li-rich giants under study, which implies that engulfment of planets is rather unlikely for the origin of Li-enrichment.

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Section: Appendix 2 LI Abundances Of Normal Red Giantssupporting

confidence: 76%

Section: Appendix 2 LI Abundances Of Normal Red Giantscontrasting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

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On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants

Takeda

Tajitsu²

2017

Publications of the Astronomical Society of Japan

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“…The absence of lithium is explained by its depletion in the shell into which it is transferred by the red giant's extensive convective envelope. The presence of lithium in the atmospheres of some giants is associated with their activity (Fekel & Balachandran 1994), a high rotation velocity (Fekel & Balachandran 1993;Carlberg et al 2013), and even the presence of planets (Liu et al 2014). Active RS CVn stars, to which the star PZ Mon being investigated belongs, generally exhibit a lithium overabundance (Liu et al 1993;Morel et al 2003).…”

Section: Discussionmentioning

confidence: 99%

Overabundance of s-process elements in the atmosphere of the active red giant PZ Mon

Pakhomov

2015

Astron. Lett.

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Based on high-resolution (R=60 000) spectra taken with the NES spectrograph (the 6-m BTA telescope, the Special Astrophysical Observatory of the Russian Academy of Science), we have determined the abundances of 26 elements, from lithium to europium, in the atmosphere of the active red giant PZ Mon which belongs to the class of RS CVn variable stars, by the method of model stellar atmospheres. We have taken into account the hyperfine splitting, the isotopic shift, and the departure from local thermodynamic equilibrium. Analysis of our data has revealed an overabundance of lithium and neutron-capture elements compared to normal red giants. For lithium, this is explained by the activity of the star, while the overabundance of s-elements is presumably similar in nature to that in moderate barium stars.

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“…In addition to 15 new Lirich K giants, another 25 were included from the literature following the criterion suggested by Charbonnel & Balachandran (2000). The Li abundance data for the entire Li-rich sample was taken from Kumar et al (2011), Liu et al (2014, Adamow et al (2014), and references therein. Of the 25 Li-rich K giants taken from the literature 22 belong to the thin disk component, one to the thick disk component and one to the halo.…”

Section: Sample Selection and Datamentioning

confidence: 99%

Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss

Kumar

Reddy

Muthumariappan

et al. 2015

A&A

Self Cite

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Context. A small group of red giant branch (RGB) stars are known to have anomalous Li enhancement whose origin is still not well understood. Some studies have proposed that the Li enhancement in RGB stars is correlated to their far-IR excess, a result of mass loss. Studies to confirm such a correlation have a significant bearing on our understanding of the Galactic Li enhancement. Aims. We searched for a correlation between the two anomalous properties of K giants: Li enhancement and IR excess from an unbiased survey of a large sample of RGB stars. Methods. A sample of 2000 low-mass K giants with accurate astrometry from the Hipparcos catalog was chosen for which Li abundances have been determined from low-resolution spectra. Far-IR data were collected from the WISE and IRAS catalogs. To probe the correlation between the two anomalies, we supplemented 15 Li-rich K giants discovered from this sample with 25 known Li-rich K giants from other studies. Dust shell evolutionary models and spectral energy distributions were constructed using the code DUSTY to estimate different dust shell properties, such as dust evolutionary time scales, dust temperatures, and mass-loss rates. Results. Among 2000 K giants, we found about two dozen K giants with detectable far-IR excess, and surprisingly, none of them are Li-rich. Similarly, the 15 new Li-rich K giants that were identified from the same sample show no evidence of IR excess. Of the total 40 Li-rich K giants, only 7 show IR excess. Important is that K giants with Li enhancement and/or IR excess begin to appear only at the bump on the RGB. Conclusions. Results show that K giants with IR excess are very rare, similar to K giants with Li enhancement. This may be due to the rapid differential evolution of dust shell and Li depletion compared to RGB evolutionary time scales. We also infer from the results that during the bump evolution, giants probably undergo some internal changes, which are perhaps the cause of mass-loss and Li-enhancement events. However, the available observational results do not ascertain that these properties are correlated. That a few Li-rich giants have IR excess seems to be pure coincidence.

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The Lithium Abundances of a Large Sample of Red Giants

Cited by 61 publications

References 48 publications

On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants

On the observational characteristics of lithium-enhanced giant stars in comparison with normal red giants

Overabundance of s-process elements in the atmosphere of the active red giant PZ Mon

Far-infrared study of K giants in the solar neighborhood: Connection between Li enrichment and mass-loss

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