Lithium-Rich Giants in Globular Clusters*

Kirby, Evan N.; Guhathakurta, Puragra; Zhang, Andrew J.; Hong, Jerry; Guo, Michelle; Guo, Ruiqian; Cohen, Judith G.; Cunha, Kátia

doi:10.3847/0004-637x/819/2/135

Cited by 79 publications

(112 citation statements)

References 139 publications

(224 reference statements)

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“…The Li-rich star in our sample corresponds to the star with id M30-132 in the sample of Kirby et al (2016). The Li enhancement we derive for the star is 0.27 dex lower than derived by Kirby et al (2016) but can fully be explained by the difference in stellar parameters (see Table 6) and the low signalto-noise ratio of our spectrum, which does not allow us to derive accurate abundances besides Li. The detection of Li-rich stars in M30 adds to the ever-growing list of globular clusters that host Li-rich stars.…”

Section: A Li-rich Subgiantmentioning

confidence: 66%

“…Two Li-rich stars were discovered in M30 by Kirby et al (2016). The Li-rich star in our sample corresponds to the star with id M30-132 in the sample of Kirby et al (2016).…”

Section: A Li-rich Subgiantmentioning

confidence: 82%

“…When we include a typical error in effective temperature (50-100 K), which is the most influential stellar parameter, we can explain a spread in Li abundances of 0.10-0.12 dex, and thus we conclude that the observed Li abundances on the TOP and RGB plateau are compatible with zero scatter among the first-generation stars. Kirby et al (2016).…”

Section: As Tracer For Multiple Populations?mentioning

confidence: 99%

“…These clusters are M3 (Kraft et al 1999), M5 (Carney et al 1998), M30 (Kirby et al 2016), M68 (Ruchti et al 2011;Kirby et al 2016), NGC 362 (Smith et al 1999;D'Orazi et al 2015), NGC 5053 (Kirby et al 2016), and NGC 5897 (Kirby et al 2016). While until recently, only one giant had been found to reside close to the RGB bump (D'Orazi et al 2015), Kirby et al (2016) now added four more Li-rich stars that have not yet evolved beyond the second dredge-up. Our Li-rich star in M30 is the least evolved star (V = 17.7) to date and forms an important data point in bridging the Li evolution from Li-rich dwarfs to Li-rich giants.…”

Section: A Li-rich Subgiantmentioning

confidence: 99%

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Atomic diffusion and mixing in old stars

Gruyters

Lind

Richard

et al. 2016

A&A

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Context. The prediction of the Planck-constrained primordial lithium abundance in the Universe is in discordance with the observed Li abundances in warm Population II dwarf and subgiant stars. Among the physically best motivated ideas, it has been suggested that this discrepancy can be alleviated if the stars observed today had undergone photospheric depletion of lithium. Aims. The cause of this depletion is investigated by accurately tracing the behaviour of the lithium abundances as a function of effective temperature. Globular clusters are ideal laboratories for such an abundance analysis as the relative stellar parameters of their stars can be precisely determined. Methods. We performed a homogeneous chemical abundance analysis of 144 stars in the metal-poor globular cluster M30, ranging from the cluster turnoff point to the tip of the red giant branch. Non-local thermal equilibrium (NLTE) abundances for Li, Ca, and Fe were derived where possible by fitting spectra obtained with VLT/FLAMES-GIRAFFE using the quantitative-spectroscopy package SME. Stellar parameters were derived by matching isochrones to the observed V vs. V − I colour-magnitude diagram. Independent effective temperatures were obtained from automated profile fitting of the Balmer lines and by applying colour-T eff calibrations to the broadband photometry. Results. Li abundances of the turnoff and early subgiant stars form a thin plateau that is broken off abruptly in the middle of the SGB as a result of the onset of Li dilution caused by the first dredge-up. Abundance trends with effective temperature for Fe and Ca are observed and compared to predictions from stellar structure models including atomic diffusion and ad hoc additional mixing below the surface convection zone. The comparison shows that the stars in M30 are affected by atomic diffusion and additional mixing, but we were unable to determine the efficiency of the additional mixing precisely. This is the fourth globular cluster (after NGC 6397, NGC 6752, and M4) in which atomic diffusion signatures are detected. After applying a conservative correction (T6.0 model) for atomic diffusion, we find an initial Li abundance of A(Li) = 2.48 ± 0.10 for the globular cluster M30. We also detected a Li-rich SGB star with a Li abundance of A(Li) = 2.39. The finding makes Li-rich mass transfer a likely scenario for this star and rules out models in which its Li enhancement is created during the RGB bump phase.

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Section: A Li-rich Subgiantmentioning

confidence: 66%

“…Two Li-rich stars were discovered in M30 by Kirby et al (2016). The Li-rich star in our sample corresponds to the star with id M30-132 in the sample of Kirby et al (2016).…”

Section: A Li-rich Subgiantmentioning

confidence: 82%

Section: As Tracer For Multiple Populations?mentioning

confidence: 99%

Section: A Li-rich Subgiantmentioning

confidence: 99%

See 2 more Smart Citations

Atomic diffusion and mixing in old stars

Gruyters

Lind

Richard

et al. 2016

A&A

View full text Add to dashboard Cite

show abstract

“…In turn, cool-bottom processes (Wasserburg et al 1995;Sackmann & Boothroyd 1999) below the convection zone may also be capable for transporting material to layers hot enough for the Cameron-Fowler mechanism and then returning to the convection zone. An alternative evolutionary model was proposed by de La Reza et al (1996) in which basically every low-mass K-giant undergoes a short (≈10 5 yr) Lirich phase on the RGB (see also de la Reza et al 1997;Kirby et al 2016). Extra non-axisymmetric mixing that leads to an inhomogeneous super-granulation pattern on the surface in the form of large cool and warm features was invoked to explain super-meteoritic Li abundances in Strassmeier et al (2015).…”

Section: Introductionmentioning

confidence: 99%

Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Orionis

Kővári

Strassmeier

Carroll

et al. 2017

A&A

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Context. Stars with about 1−2 solar masses at the red giant branch (RGB) represent an intriguing period of stellar evolution, i.e. when the convective envelope interacts with the fast-rotating core. During these mixing episodes freshly synthesized lithium can come up to the stellar surface along with high angular momentum material. This high angular momentum may alter the surface rotation pattern. Aims. The single rapidly rotating K-giant V1192 Ori is revisited to determine its surface differential rotation, lithium abundance, and basic stellar properties such as a precise rotation period. The aim is to independently verify the antisolar differential rotation of the star and possibly find a connection to the surface lithium abundance. Methods. We applied time-series Doppler imaging to a new multi-epoch data set. Altogether we reconstructed 11 Doppler images from spectroscopic data collected with the STELLA robotic telescope between 2007-2016. We used our inversion code iMap to reconstruct all stellar surface maps. We extracted the differential rotation from these images by tracing systematic spot migration as a function of stellar latitude from consecutive image cross-correlations. Results. The position of V1192 Ori in the Hertzsprung-Russell diagram suggests that the star is in the helium core-burning phase just leaving the RGB bump. We measure A(Li) NLTE = 1.27, i.e. a value close to the anticipated transition value of 1.5 from Li-normal to Li-rich giants. Doppler images reveal extended dark areas arranged quasi-evenly along an equatorial belt. No cool polar spot is found during the investigated epoch. Spot displacements clearly suggest antisolar surface differential rotation with α = −0.11 ± 0.02 shear coefficient. Conclusions. The surface Li enrichment and the peculiar surface rotation pattern may indicate a common origin.

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Mass loss rates of Li‐rich AGB/RGB stars

Maciel

Costa

2018

Astron Nachr

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Funding Information FAPESP. CNPq.A sample of AGB/RGB stars with an excess of Li abundances is considered in order to estimate their mass loss rates. Our method is based on a correlation between the Li abundances and the stellar luminosity, using a modified version of Reimers formula. We have adopted a calibration on the basis of an empirical correlation between the mass loss rate and some stellar parameters. We conclude that most Li-rich stars have lower mass loss rates compared with the majority of AGB/RGB stars, which show no evidence of Li enhancements, so the Li enrichment process is apparently not associated with an increased mass loss rate.

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Lithium-Rich Giants in Globular Clusters*

Cited by 79 publications

References 139 publications

Atomic diffusion and mixing in old stars

Atomic diffusion and mixing in old stars

Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Orionis

Mass loss rates of Li‐rich AGB/RGB stars

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