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

2018 ◽  
Vol 618 ◽  
pp. A16 ◽  
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.

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

2021 ◽  
Author(s):  
N Holanda ◽  
N Drake ◽  
W J B Corradi ◽  
F A Ferreira ◽  
F Maia ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
Rotational Velocity ◽  
Open Cluster ◽  
Chemical Species ◽  
Stellar Atmospheres ◽  
Lithium Abundance ◽  
Giant Stars ◽  
Analysis Technique ◽  
Young Open Cluster ◽  
Fast Rotating

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.

scholarly journals A detailed study of lithium in 107 CHEPS dwarf stars

2018 ◽  
Vol 611 ◽  
pp. A27 ◽  
Author(s):  
Ya. V. Pavlenko ◽  
J. S. Jenkins ◽  
O. M. Ivanyuk ◽  
H. R. A. Jones ◽  
B. M. Kaminsky ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
Small Sample Size ◽  
Small Sample ◽  
Thermodynamical Equilibrium ◽  
Lithium Abundance ◽  
Dwarf Stars ◽  
Upper Limits ◽  
Resonance Doublet ◽  
Non Local ◽  
Local Thermodynamical Equilibrium

Context. We report results from lithium abundance determinations using high resolution spectral analysis of the 107 metal-rich stars from the Calan-Hertfordshire Extrasolar Planet Search programme. Aims. We aim to set out to understand the lithium distribution of the population of stars taken from this survey. Methods. The lithium abundance taking account of non-local thermodynamical equilibrium effects was determined from the fits to the Li I 6708 Å resonance doublet profiles in the observed spectra. Results. We find that a) fast rotators tend to have higher lithium abundances; b) log N(Li) is higher in more massive and hot stars; c) log N(Li) is higher in stars of lower log g; d) stars with the metallicities >0.25 dex do not show the lithium lines in their spectra; e) most of our planet hosts rotate slower; and f) a lower limit of lithium isotopic ratio is 7Li/6Li > 10 in the atmospheres of two stars with planets (SWP) and two non-SWP stars. Conclusions. Measurable lithium abundances were found in the atmospheres of 45 stars located at distances of 20−170 pc from the Sun, for the other 62 stars the upper limits of log N(Li) were computed. We found well defined dependences of lithium abundances on Teff, V sin i, and less pronounced for the log g. In case of V sin i we see two sequences of stars: with measurable lithium and with the upper limit of log N(Li). About 10% of our targets are known to host planets. Only two SWP have notable lithium abundances, so we found a lower proportion of stars with detectable Li among known planet hosts than among stars without planets. However, given the small sample size of our planet-host sample, our analysis does not show any statistically significant differences in the lithium abundance between SWP and stars without known planets.

scholarly journals Rotational evolution of solar-type protostars during the star-disk interaction phase

2019 ◽  
Vol 632 ◽  
pp. A6 ◽  
Author(s):  
F. Gallet ◽  
C. Zanni ◽  
L. Amard
Keyword(s):  
Stellar Wind ◽  
Main Sequence ◽  
Stellar Winds ◽  
Stellar Rotation ◽  
Solar Mass ◽  
Stellar Envelope ◽  
Spin Evolution ◽  
Rotational Evolution ◽  
Solar Type ◽  
The Impact

Context. The early pre-main sequence phase during which solar-mass stars are still likely surrounded by an accretion disk represents a puzzling stage of their rotational evolution. While solar-mass stars are accreting and contracting, they do not seem to spin up substantially. Aims. It is usually assumed that the magnetospheric star-disk interaction tends to maintain the stellar rotation period constant (“disk-locking”), but this hypothesis has never been thoroughly verified. Our aim is to investigate the impact of the star-disk interaction mechanism on the stellar spin evolution during the accreting pre-main sequence phases. Methods. We devised a model for the torques acting on the stellar envelope based on studies of stellar winds, and we developed a new prescription for the star-disk coupling founded on numerical simulations of star-disk interaction and magnetospheric ejections. We then used this torque model to follow the long-term evolution of the stellar rotation. Results. Strong dipolar magnetic field components up to a few kG are required to extract enough angular momentum so as to keep the surface rotation rate of solar-type stars approximately constant for a few Myr. Furthermore an efficient enough spin-down torque can be provided by either one of the following: a stellar wind with a mass outflow rate corresponding to ≈10% of the accretion rate, or a lighter stellar wind combined with a disk that is truncated around the corotation radius entering a propeller regime. Conclusions. Magnetospheric ejections and accretion powered stellar winds play an important role in the spin evolution of solar-type stars. However, kG dipolar magnetic fields are neither uncommon or ubiquitous. Besides, it is unclear how massive stellar winds can be powered while numerical models of the propeller regime display a strong variability that has no observational confirmation. Better observational statistics and more realistic models could contribute to help lessen our calculations’ requirements.

scholarly journals Temperatura efectiva en estrellas de tipo solar

2019 ◽  
pp. 81-86
Keyword(s):  
Quantum Theory ◽  
Space Physics ◽  
Stellar Atmospheres ◽  
Line Profiles ◽  
Carnegie Institution ◽  
Santa Barbara ◽  
University Of Texas ◽  
Spectral Profiles ◽  
Solar Type ◽  
The University

Temperatura efectiva en estrellas de tipo solar D. Cornejo, I. Ramírez, P. Barklem, W. Guevara Dirección de Astrofísica, Comisión Nacional de Investigación y Desarrollo Aeroespacial - CONIDA, Luis Felipe Villarán 1069, San Isidro, Lima, Perú. The Observatories of the Carnegie Institution for Science; 813 Santa Barbara Street, Pasadena, CA 91101, USA. Department of Astronomy and Space Physics, Uppsala University, Box 515, 751-20 Uppsala, Sweden DOI: https://doi.org/10.33017/RevECIPeru2011.0027/ RESUMEN Este trabajo consiste en determinar la temperatura efectiva de una muestra de 62 estrellas de tipo solar mediante el método de ajuste de perfiles teóricos a la linea espectral Hα (6562.8 A). Las estrellas analizadas han sido observadas usando el Telescopio Harlan J. Smith de 2.7 m del Observatorio McDonald de la Universidad de Texas mientras que los perfiles teóricos se basan en modelos de atmósferas estelares y teoría cuántica mas recientes. Nuestros resultados poseen un margen de error interno de ≈ 20 K, lo cual nos permite comparar nuestras temperaturas con aquellas determinadas usando otros métodos y especular sobre el origen de las diferencias observadas. Descriptores: Perfiles de lineas espectrales, atmósferas estelares. ABSTRACT The effective temperature for a sample of 62 solar-type stars has been determined fitting theoretical spectral profiles to observed Hα lines (6562.8 A). The stars analyzed has been observed using the 2.7 m Harlan J. Smith telescope at the McDonald Observatory of the University of Texas. The theoretical profiles are based on recent models of stellar atmospheres and quantum theory. The calculated temperatures have internal errors of ≈ 20 K with other techniques and speculate about the origin of the observed differences. Keywords: Spectral line profiles, Stellar Atmospheres.

scholarly journals Non-Local Convection Models for Stellar Atmospheres and Envelopes

2003 ◽  
Vol 210 ◽  
pp. 143-156
Author(s):  
F. Kupka
Keyword(s):  
Numerical Simulations ◽  
Main Sequence ◽  
Stellar Atmospheres ◽  
Surface Velocity ◽  
Line Profiles ◽  
Main Sequence Stars ◽  
Solar Type ◽  
Non Local ◽  
Stress Models ◽  
Do So

We present an overview of the concepts underlying advanced non-local Reynolds stress models of turbulent convection and review a comparison of this approach with a series of numerical simulations of fully compressible convection. We then discuss results from applications of the model to complete envelopes of A-type main sequence stars. The non-local model reproduces surface velocities in agreement with the lower limit of observed macro- and microturbulence velocities of A-star photospheres, the asymmetry of the surface velocity field as inferred from spectral line profiles, and the overall structure of the photospheric and subphotospheric convection zones, as predicted by the most recent numerical simulations available for these stars. Traditionally, local models of convection are unable to do so. We conclude with a brief survey of extensions of the model which are interesting for other applications such as atmospheres of solar type stars and overshooting below deep convective envelopes or above the core in massive stars.

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

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.

scholarly journals Evidence for Lithium Destruction and Synthesis in Main-Sequence and Subgiant Stars of about Solar Mass

1968 ◽  
Vol 1 ◽  
pp. 233-236
Author(s):  
M. W. Feast
Keyword(s):  
Main Sequence ◽  
Solar Mass ◽  
Lithium Abundance ◽  
Solar Type ◽  
Subgiant Stars

Herbig’s extensive work on lithium abundances in solar-type stars on and near the main sequence, suggested to him that for these stars the lithium abundance might be some simple, decreasing function of age. If this were the full story we should expect a low lithium abundance in subgiants of about solar mass. However, already in Herbig’s work there were one or two stars with lithium abundance about 10 times the Greenstein-Richardson solar value whose trigonometrical parallaxes showed them to be possible subgiants. Other subgiants with high lithium abundances have been found by Wallerstein and at Pretoria. These results suggest that solar-mass stars are able to synthesise fresh lithium in or just prior to their subgiant phase.

scholarly journals Carbon, isotopic ratio 12C/13C, and nitrogen in solar twins: constraints for the chemical evolution of the local disc

2020 ◽  
Vol 499 (2) ◽  
pp. 2196-2213
Author(s):  
R B Botelho ◽  
A de C Milone ◽  
J Meléndez ◽  
A Alves-Brito ◽  
L Spina ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Spectral Synthesis ◽  
Isotopic Ratio ◽  
Homogeneous Distribution ◽  
The Sun ◽  
Dwarf Stars ◽  
Thin Disc ◽  
Carbon Isotopic ◽  
Wide Range ◽  
C And N

ABSTRACT Abundances of light elements in dwarf stars of different ages are important constraints for stellar yields, Galactic chemical evolution and exoplanet chemical composition studies. We have measured C and N abundances and 12C/13C ratios for a sample of 63 solar twins spanning a wide range in age, based on spectral synthesis of a comprehensive list of CH A-X and CN B-X features using HARPS spectra. The analysis of 55 thin disc solar twins confirms the dependences of [C/Fe] and [N/Fe] on [Fe/H]. [N/Fe] is investigated as a function of [Fe/H] and age for the first time for these stars. Our derived correlation [C/Fe]–age agrees with works for solar-type stars and solar twins, but the [N/Fe]–age correlation does not. The relations [C,N/Fe]–[Fe/H] and [C,N/Fe]–age for the solar twins lay under solar. 12C/13C is found correlated with [Fe/H] and seems to have decreased along the evolution of the local thin disc. Predictions from chemical evolution models for the solar vicinity corroborate the relations [C,N/Fe]–[Fe/H], 12C/13C–age, and [N/O]–[O/H], but do not for the 12C/13C–[Fe/H] and [C/O]–[O/H] relations. The N/O ratio in the Sun is placed at the high end of the homogeneous distribution of solar twins, which suggests uniformity in the N–O budget for the formation of icy planetesimals, watery superearths, and giant planets. C and N had different nucleosynthetic origins along the thin disc evolution, as shown by the relations of [C/N], [C/O], and [N/O] against [O/H] and age. [C/N] and [C/O] are particularly observed increasing in time for solar twins younger than the Sun.

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

2020 ◽  
Vol 635 ◽  
pp. A176 ◽  
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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