Lithium in Stellar Atmospheres: Observations and Theory

Lyubimkov, L. S.

doi:10.1007/s10511-016-9446-5

Cited by 24 publications

(41 citation statements)

References 61 publications

(125 reference statements)

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“…Here about a dozen of the stars have the lithium abundance logε(Li)  1.5. Table 2 shows that the observed abundances of the isotopes of hydrogen and helium, i.e., deuterium, 4 He, and 3 He, are in very good agreement with the SMBB calculations. The situation is utterly different for lithium: the observed abundance log( 7 Li)  2.2 is smaller than the theoretically predicted value of 2.7 by 0.5.…”

Section:      supporting

confidence: 62%

“…. This is an order of magnitude greater than the "relict" value Modern models of the chemical evolution of the universe give an answer to this question [3]. The interstellar medium has been enriched in lithium (isotope 7 Li) through outflow or ejection of matter from stars of the following types: low-mass red giants (up to 40%), AGB (asymptotic giants branch), and novae.…”

Section: Features Of the Abundances Of Lithium Beryllium And Boron mentioning

confidence: 99%

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Light Chemical Elements in Stars: Mysteries and Unsolved Problems

Lyubimkov

2018

Astrophysics

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them were initially synthesized in the Big Bang. The primordial abundances of these elements calculated using the Standard Model of the Big Bang (SMBB) are presented in this review. The good agreement between the SMBB and observations of the primordial abundances of the isotopes of hydrogen and helium, D, 3 He, and 4 He, is noted, but there is a difference of ~0.5 dex for lithium (the isotope 7 Li) between the SMBB and observations of old stars in the galactic halo that has not yet been explained. The abundances of light elements in stellar atmospheres depends on the initial rotation velocity, so the typical rotation velocities of young Main Sequence (MS) stars are examined. Since the data on the adundances of light elements in stars are very extensive, the main emphasis in this review is on several unsolved problems. The helium abundance He/H in early B-type MS stars shows an increment with age; in particular, for the most massive B stars with masses M 12 19 M  , He/H increases by more than a factor of two toward the end of the MS. Theoretical models of stars with rotation cannot explain such a large increase in He/H. For early B-and late O-types MS stars that are components of close binary systems, He/H undergoes a sharp jump in the middle of the MS stage that is a mystery for the theory. The anomalous abundance of helium (and lithium) in the atmospheres of chemically peculiar stars (types He-s, He-w, HgMn, Ap, and Am) is explained in terms of the diffusion of atoms in surface layers of the stars, but this hypothesis cannot yet explain all the features of the chemical composition of these stars. The abundances of lithium, beryllium, and boron in FGK-dwarfs manifest a trend with decreasing effective temperature T eff as well as a dip at T eff ~ 6600 K in the Hyades and other old clusters. These two effects are among the unsolved problems. In the case of lithium, there is special interest in FGK-giants and supergiants that are rich in lithium (they have log ε(Li) > 2 ). Most of them cannot be explained in terms of the standard theory of stellar evolution, so nonstandard hypotheses are invoked: the recent synthesis of lithium in a star and the engulfment by a star of a giant planet with mass equal to that of Jupiter or greater. An analysis of the abundances of carbon, nitrogen, and oxygen in early B-and late O-type MS stars indicates that the C II, N II, and O II ions are overionized in their atmospheres. For early B-type MS stars, good agreement is found between observations of the N/O ratio and model calculations for rotating stars. A quantitative explanation of the well-known "nitrogen-oxygen" anticorrelation in FGK-giants and supergiants is found. It reflects the dependence of the anomalies in N and C on the initial rotation velocity V 0 . The stellar rotation models which yield successful explanations for C, N. and O cannot, however, explain the observed increased helium enrichment in early B-type MS stars.

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Section:      supporting

confidence: 62%

Section: Features Of the Abundances Of Lithium Beryllium And Boron mentioning

confidence: 99%

Light Chemical Elements in Stars: Mysteries and Unsolved Problems

Lyubimkov

2018

Astrophysics

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“…They definitely indicate that all three stars have already passed the DCM phase. The proof is the very low (compared to the sun and young stars) ratio of the carbon isotopes, 12 C/ 13 C = 10 -18 (for the sun 12 C/ 13 C = 89), as well as a substantially reduced ratio of the oxygen isotopes, 16 quantitatively the long known "nitrogen-oxygen" anticorrelation for AFG-supergiants [37], as well as the observed change in the N/O ratio at the end of the MS stage for B-stars with masses from 5 to 20 ¤ M [38]. These effects depend significantly on the mass M and on the initial rotation velocity V 0 .…”

Section: Discussionmentioning

confidence: 99%

“…It should be noted that in the BSD the acceleration of gravity was found using the formula defining this quantity, i.e., 2…”

Section: Determining the Acceleration Of Gravity Logg And Mass Mmentioning

confidence: 99%

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Three Nearby K-Giants with Planets: Accurate Determination of Basic Parameters, Including an Analysis of Metallicity Based on Fe I Lines

2019

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Fundamental parameters, including the effective temperature T eff , surface gravity logg, mass M, luminosity L, radius R, and age t, are determined for three bright, nearby K-giants, β Gem (K0 III), μ Leo (K2 III), and α Tau (K5 III). It is notable that around all three stars the giant planets have been found. Our results are compared with published high-precision data for benchmark stars included in the Gaia project. Very good agreement was obtained for all three giants with these data for the basic parameters T eff , logg, and M, although our technique of their determination was simpler. Special attention was devoted to analy-sis of the Fe I lines which are the basis of a simultaneous determination of the metallicity index [Fe/H] and microturbulent parameter V t . The equivalent widths W of the Fe I lines are automatically measured from published spectra for the benchmark stars. An analysis of Fe I lines from the list of "golden lines" selected in a study of benchmark stars led to the conclusion that the excitation potential E l of the low level of the lines plays an substantial role in determining [Fe/H] and V t . It is shown that in the case of the early K-giants β Gem and μ Leo with temperatures T eff between 4400 and 4900 K for lines in the range of W from 100 to 300 mÅ there is a dependence of the [Fe/H] and V t values on E l . This dependence was not taken into account earlier is studies of the K-giants, in particular in the Fe I lines analysis of the benchmark stars. It is shown that a correct accounting for it leads an ambiguity in the determination of [Fe/H] and V t for β Gem and μ Leo. In the case of the coolest K-giant α Tau (Aldebaran) with a temperature T eff = 3920K, this effect seems to be less pronounced. Recommendations are given for the Crimean Astrophysical Observatory, RAN, Russia;Fe I lines selection for [Fe/H] and V t determination. It is sonfirmed for the example of the three stars studied here that the non-LTE effects in the Fe I lines for the K-giants with normal metallicity are very minor, so they cannot be the reason of the revealed ambiguity in [Fe/H] and V t . values. The low ratios of the carbon 12 C/ 13 C and oxygen 16 O/ 17 O isotopes confirm that all three giants passed the phase of deep convective mixing.

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Fundamental parameters and non‐local thermodynamic equilibrium abundances of key light elements for nine bright and nearby K giants

et al. 2021

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For nine bright K giants within 100 pc of the sun, the fundamental parameters and the non-local thermodynamic equilibrium (LTE) abundances of three key light elements (Li, C, and O) are accurately determined. These stars are of special interest due to the planets detected around them. Their fundamental parameters are found to be typical for K giants; in particular, these stars have effective temperatures T eff = 3,920-4,830 K, surface gravities log g = 1.20-2.85, masses M = 1.2-2.8 M ⊙ , and ages t = 0.4-5.4 Gyr (the pronounced anticorrelation between ages t and masses M exists). The microturbulent parameter V t derived from Fe I lines varies between 1.2 and 1.9 km s −1 ; the metallicity index [Fe/H] forfive stars is close to the normal (zero) value, for other four stars it varies between −0.3 and −0.4 dex. All the giants are on the red giant branch stage and passed the first-dredge-up (FDU) phase. This conclusion is confirmed by the published low isotope ratios 12 C/ 13 C and 16 O/ 17 O. Basing on the non-LTE analysis of Li I, C I, and O I lines, we determined abundances of lithium, carbon, and oxygen, three tracers of stellar evolution. The carbon deficiency −0.3 dex is found for the giants, which is quite expectable for these post-FDU objects.The oxygen abundance is likely to be unchanged, whereas for the C/O ratio we obtained (after correction due to galactic chemical evolution) the mean value [C/O] cor = −0.22 ± 0.10 that is in very good agreement with the theory. The lithium abundance is not detected for seven of nine program giants; this result is quite expectable for the post-FDU stars. We determined the Li abundance with the confidence only for two giants, namely, log ϵ(Li) = 0.92 for β Gem and log ϵ(Li) = 0.45 for μ Leo; this result contradicts the standard theory. Hypothetical engulfment by a star of a giant planet could solve the problem.

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Lithium in Stellar Atmospheres: Observations and Theory

Cited by 24 publications

References 61 publications

Light Chemical Elements in Stars: Mysteries and Unsolved Problems

Light Chemical Elements in Stars: Mysteries and Unsolved Problems

Three Nearby K-Giants with Planets: Accurate Determination of Basic Parameters, Including an Analysis of Metallicity Based on Fe I Lines

Fundamental parameters and non‐local thermodynamic equilibrium abundances of key light elements for nine bright and nearby K giants

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