NGC 6124: a young open cluster with anomalous- and fast-rotating giant stars

Abstract We present the results of a chemical analysis of fast and anomalous rotator giants members of the young open cluster NGC 6124. For this purpose, we carried out abundances of the mixing sensitive species such as Li, C, N, Na and 12C/13C isotopic ratio, as well as other chemical species for a sample of four giants among the seven observed ones. This study is based on standard spectral analysis technique using high-resolution spectroscopic data. We also performed an investigation of the rotational velocity (v sin i) once this sample exhibit abnormal values – giant stars commonly present rotational velocities of few km s−1. In parallel, we have been performed a membership study, making use of the third data release from ESA Gaia mission. Based on these data, we estimated a distance of d = 630 pc and an age of 178 Myr through isochrone fitting. After that procedure, we matched all the information raised and investigated the evolutionary stages and thermohaline mixing model through of spectroscopic Teff and log g and mixing tracers, as 12C/13C and Na, of the studied stars. We derived a low mean metallicity of [Fe/H] = −0.13 ±0.05 and a modest enhancement of the elements created by the s-process such as Y, Zr, La, Ce, and Nd, which is in agreement of what has already been reported in the literature for young clusters. The giants analyzed have homogeneous abundances, except for lithium abundance [log ε(Li)NLTE = 1.08±0.42] and this may be associated to a combination of mechanisms that act increasing or decreasing lithium abundances in stellar atmospheres.

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Main-sequence and sub-giant stars in the globular cluster NGC 6397: The complex evolution of the lithium abundance

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310004217 ◽

2009 ◽

Vol 5 (S268) ◽

pp. 257-261

Author(s):

J. I. González Hernández ◽

P. Bonifacio ◽

E. Caffau ◽

M. Steffen ◽

H.-G. Ludwig ◽

...

Keyword(s):

Globular Cluster ◽

Main Sequence ◽

3D Models ◽

Stellar Atmospheres ◽

Evolutionary Status ◽

Thermodynamical Equilibrium ◽

Lithium Abundance ◽

Giant Stars ◽

Effective Temperatures ◽

Hydrodynamical Simulations

AbstractThanks to the high multiplex and efficiency of Giraffe at the VLT we have been able for the first time to observe the Li I doublet in the Main Sequence stars of a globular cluster. At the same time we observed Li in a sample of Sub-Giant stars of the same B-V colour.Our final sample is composed of 84 SG stars and 79 MS stars. In spite of the fact that SG and MS span the same temperature range we find that the equivalent widths of the Li I doublet in SG stars are systematically larger than those in MS stars, suggesting a higher Li content among SG stars. This is confirmed by our quantitative analysis carried out making use of 1D hydrostatic plane-parallel models and 3D hydrodynamical simulations of the stellar atmospheres.We derived the effective temperatures of stars in our the sample from Hα fitting. Theoretical profiles were computed using 3D hydrodynamical simulations and 1D ATLAS models. Therefore, we are able to determined 1D and 3D-based effective temperatures. We then infer Li abundances taking into account non-local thermodynamical equilibrium effects when using both 1D and 3D models.We find that SG stars have a mean Li abundance higher by 0.1 dex than MS stars. This result is obtained using both 1D and 3D models. We also detect a positive slope of Li abundance with effective temperature, the higher the temperature the higher the Li abundance, both for SG and MS stars, although the slope is slightly steeper for MS stars. These results provide an unambiguous evidence that the Li abundance changes with evolutionary status.The physical mechanisms responsible for this behaviour are not yet clear, and none of the existing models seems to describe accurately these observations. Based on these conclusions, we believe that the cosmological lithium problem still remains an open question.

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TYC 8327-1678-1: a new super lithium-rich K giant

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2271 ◽

2020 ◽

Vol 498 (1) ◽

pp. 77-83

Author(s):

N Holanda ◽

N A Drake ◽

C B Pereira

Keyword(s):

Spectral Synthesis ◽

Isotopic Ratio ◽

Rotational Velocity ◽

Mean Value ◽

High Resolution Spectroscopy ◽

Evolutionary Stage ◽

Chemical Abundances ◽

Lithium Abundance ◽

Red Giant ◽

Width Measurements

ABSTRACT In this work, we show that TYC 8327-1678-1 is a low-mass red giant star with a super lithium abundance in its atmosphere. For this, we used high-resolution spectroscopy to determine atmospheric parameters, the chemical abundances of the light elements and the isotopic ratio 12C/13C using the spectral synthesis techniques and the equivalent width measurements. Also, we used theoretical evolutionary tracks to find out the mass and the evolutionary stage of TYC 8327-1678-1. The lithium abundance was determined using the Li i resonance doublet at 6708 Å and the subordinate line at 6104 Å that yielding a mean value of $\log \, \epsilon {\rm (Li)_{NLTE}}\, =\, 3.48$. The projected rotational velocity ($v\, \sin \, i$) has been determined using spectral synthesis based on the isolated Fe i lines. Our results show that TYC 8327-1678-1 has a mass of $M\, =\, 1.60$ $\pm \, 0.20\, {\rm M}_{\odot }$, a low rotational velocity ($v\, \sin \, i$ = 2.35 ± 0.24 km s−1) and metallicity of [Fe/H] = +0.23 ± 0.09. Finally, we discuss the possibility that TYC 8327-1678-1 became a lithium-rich star after a merging event involving a red giant and a helium white dwarf.

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Chemical analysis of giant stars in the young open cluster NGC 3114

Astronomy and Astrophysics ◽

10.1051/0004-6361/201220252 ◽

2013 ◽

Vol 554 ◽

pp. A2 ◽

Cited By ~ 25

Author(s):

O. J. Katime Santrich ◽

C. B. Pereira ◽

N. A. Drake

Keyword(s):

Chemical Analysis ◽

Open Cluster ◽

Giant Stars ◽

Young Open Cluster

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Bimodality and Lithium Abundance on the Upper Main Sequence of the Open Cluster NGC 752

Symposium - International Astronomical Union ◽

10.1017/s0074180900035518 ◽

1988 ◽

Vol 132 ◽

pp. 473-476

Author(s):

J E Beckman ◽

R. Rebolo

Keyword(s):

Main Sequence ◽

Rotational Velocity ◽

Open Cluster ◽

Lithium Abundance ◽

Evolved Stars

Spectra of resolution λ/Δλ∼2 ×104 and good S:N ratio are presented in the range containing the 7Li doublet at 6707 Å for 9 main sequence or slightly evolved stars in NGC 752 (age ∼2 ×109 years). We investigate the suggested main sequence bimodality using spectroscopic indications of binarity and high rotational velocity, as well as the Li abundance to supplement previous photometry.

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Period–luminosity relations of fast-rotating B-type stars in the young open cluster NGC 3766

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stx346 ◽

2017 ◽

Vol 467 (4) ◽

pp. 3864-3873 ◽

Cited By ~ 8

Author(s):

H. Saio ◽

S. Ekström ◽

N. Mowlavi ◽

C. Georgy ◽

S. Saesen ◽

...

Keyword(s):

Open Cluster ◽

Young Open Cluster ◽

Fast Rotating

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Impact of the convective mixing-length parameter α on stellar metallicity

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937110 ◽

2020 ◽

Vol 635 ◽

pp. A176 ◽

Cited By ~ 1

Author(s):

N. Song ◽

S. Alexeeva ◽

T. Sitnova ◽

L. Wang ◽

F. Grupp ◽

...

Keyword(s):

Open Cluster ◽

Synthesis Method ◽

Stellar Atmospheres ◽

High Signal ◽

Mixing Length ◽

Dwarf Stars ◽

Giant Stars ◽

Spectrum Synthesis ◽

Mixing Length Theory ◽

The Impact

Context. Mixing-length theory is used to treat stellar convection. As a simulation in one-dimensional stellar atmospheres models, the mixing-length parameter α is calibrated from the Sun and then applied to other stars. However, there is no strong evidence to suggest that α should be the same for stars of different evolutionary stages. Aims. We evaluate the impact of the α value on the metallicity of different types of stars and investigate the correlation between the metallicity discrepancy (Δ[Fe∕H]) and stellar parameters (Teff, log g). Methods. We selected ten well-studied field stars and one open cluster of nine members for which high-resolution and high signal-to-noise spectra are available. The model atmospheres were calculated with the code MAFAGS-OS. We derived iron abundances from Fe I and Fe II lines both under local thermodynamic equilibrium and non-LTE conditions using a spectrum synthesis method. After deriving [Fe/H] for each line, we calculated Δ[Fe∕H] with two different α values, fixed solar-calibrated α, and α obtained for each star individually. Finally, we investigated the correlation between Δ[Fe∕H] caused by revised α with stellar parameters. Results. For FGK dwarf stars, the Δ[Fe∕H] caused by the α correction is less than 0.02 dex, while for turn-off and giant stars, the Δ[Fe∕H] values are no more than 0.03 dex, which are lower than typical uncertainties in metallicity. For main-sequence stars, Δ[Fe∕H] versus Teff and Δ[Fe∕H] versus log g are well fit by linear relations.

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3D non-LTE corrections for Li abundance and 6Li/7Li isotopic ratio in solar-type stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832852 ◽

2018 ◽

Vol 618 ◽

pp. A16 ◽

Cited By ~ 7

Author(s):

G. Harutyunyan ◽

M. Steffen ◽

A. Mott ◽

E. Caffau ◽

G. Israelian ◽

...

Keyword(s):

Spectral Synthesis ◽

Isotopic Ratio ◽

Stellar Atmospheres ◽

Line Profiles ◽

Solar Mass ◽

Lithium Abundance ◽

Dwarf Stars ◽

Link Type ◽

Solar Type ◽

The Impact

Context. Convective motions in solar-type stellar atmospheres induce Doppler shifts that affect the strengths and shapes of spectral absorption lines and create slightly asymmetric line profiles. One-dimensional (1D) local thermodynamic equilibrium (LTE) studies of elemental abundances are not able to reproduce this phenomenon, which becomes particularly important when modeling the impact of isotopic fine structure, like the subtle depression created by the 6Li isotope on the red wing of the Li I resonance doublet line. Aims. The purpose of this work is to provide corrections for the lithium abundance, A(Li), and the 6Li/7Li isotopic ratio that can easily be applied to correct 1D LTE lithium abundances in G and F dwarf stars of approximately solar mass and metallicity for three-dimensional (3D) and non-LTE (NLTE) effects. Methods. The corrections for A(Li) and 6Li/7Li are computed using grids of 3D NLTE and 1D LTE synthetic lithium line profiles, generated from 3D hydro-dynamical CO5BOLD and 1D hydrostatic model atmospheres, respectively. For comparative purposes, all calculations are performed for three different line lists representing the Li I λ670.8 nm spectral region. The 3D NLTE corrections are then approximated by analytical expressions as a function of the stellar parameters (Teff, log ℊ, [Fe/H], ν sin i, A(Li), 6Li/7Li). These are applied to adjust the 1D LTE isotopic lithium abundances in two solar-type stars, HD 207129 and HD 95456, for which high-quality HARPS observations are available. Results. The derived 3D NLTE corrections range between −0.01 and +0.11 dex for A(Li), and between −4.9 and −0.4% for 6Li/7Li, depending on the adopted stellar parameters. We confirm that the inferred 6Li abundance depends critically on the strength of the Si I 670.8025 nm line. Our findings show a general consistency with recent works on lithium abundance corrections. After the application of such corrections, we do not find a significant amount of 6Li in any of the two target stars. Conclusions. In the case of 6Li/7Li, our corrections are always negative, showing that 1D LTE analysis can significantly overestimate the presence of 6Li (up to 4.9% points) in the atmospheres of solar-like dwarf stars. These results emphasize the importance of reliable 3D model atmospheres combined with NLTE line formation for deriving precise isotopic lithium abundances. Although 3D NLTE spectral synthesis implies an extensive computational effort, the results can be made accessible with parametric tools like the ones presented in this work.

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The Gaia-ESO Survey: impact of extra mixing on C and N abundances of giant stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732433 ◽

2018 ◽

Vol 621 ◽

pp. A24 ◽

Cited By ~ 17

Author(s):

N. Lagarde ◽

C. Reylé ◽

A. C. Robin ◽

G. Tautvaišienė ◽

A. Drazdauskas ◽

...

Keyword(s):

Stellar Evolution ◽

Globular Clusters ◽

Chemical Elements ◽

Isotopic Ratio ◽

Current Model ◽

Chemical Species ◽

Open Clusters ◽

Giant Stars ◽

C And N ◽

The Impact

Context. The Gaia-ESO Public Spectroscopic Survey using FLAMES at the VLT has obtained high-resolution UVES spectra for a large number of giant stars, allowing a determination of the abundances of the key chemical elements carbon and nitrogen at their surface. The surface abundances of these chemical species are known to change in stars during their evolution on the red giant branch (RGB) after the first dredge-up episode, as a result of the extra mixing phenomena. Aims. We investigate the effects of thermohaline mixing on C and N abundances using the first comparison between the Gaia-ESO survey [C/N] determinations with simulations of the observed fields using a model of stellar population synthesis. Methods. We explore the effects of thermohaline mixing on the chemical properties of giants through stellar evolutionary models computed with the stellar evolution code STAREVOL. We include these stellar evolution models in the Besançon Galaxy model to simulate the [C/N] distributions determined from the UVES spectra of the Gaia-ESO survey and to compare them with the observations. Results. Theoretical predictions including the effect of thermohaline mixing are in good agreement with the observations. However, the field stars in the Gaia-ESO survey with C and N abundance measurements have a metallicity close to solar, where the efficiency of thermohaline mixing is not very large. The C and N abundances derived by the Gaia-ESO survey in open and globular clusters clearly show the impact of thermohaline mixing at low metallicity, which explains the [C/N] value observed in lower mass and older giant stars. Using independent observations of carbon isotopic ratio in clump field stars and open clusters, we also confirm that thermohaline mixing should be taken into account to explain the behaviour of 12C/13C as a function of stellar age. Conclusions. Overall, the current model including thermohaline mixing is able to reproduce very well the C and N abundances over the whole metallicity range investigated by the Gaia-ESO survey data.

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