arXiv subjects

L. Mashonkina

Publications and source records attributed to L. Mashonkina.

At least 19 recordsLinked to original sources

arXiv2025

Understanding an origin of palladium in metal-poor stars based on the non-LTE analysis of Pd~I lines

Palladium is one of poorly observed neutron-capture elements. Abundance determinations for stellar samples covering a broad metallicity range are needed for better understanding the mechanisms of Pd synthesis during the Galaxy evolution. We aim to obtain accurate abundances of Pd for the Sun and the sample of metal-poor stars based on the non-local thermodynamic equilibrium (non-LTE) line formation for Pd~I. We present a new, comprehensive model atom of Pd~I. Abundances of Pd, Sr, Ba, and Eu were derived for 48 stars from the non-LTE analyses of high resolution and high signal-to-noise ratio spectra provided by the ESO archives. Non-LTE leads to weakened Pd~I lines and positive non-LTE abundance corrections growing from 0.2~dex for the solar lines up to 0.8~dex for the lines in the most luminous star of the sample. Depending on a treatment of inelastic collisions with hydrogen atoms, the solar non-LTE abundance amounts to log eps = 1.61+-0.02 to 1.70+-0.02 and agrees within the error bars with the meteoritic abundance log eps_met = 1.65. Non-LTE largely removes the discrepancies in the LTE abundances between the giant and dwarf stars of similar metallicities. Palladium tightly correlates with Eu in the -1.71 < [Fe/H] < -0.56 range indicating the r- and s-process contributions to Pd synthesis of approximately 70% and 30%, respectively. Palladium is of pure r-process origin in our two r-II stars, and a dominant contribution of the r-process to the Pd abundances is found for another two very metal-poor (VMP, [Fe/H] < -2) stars. The two VMP stars, which are strongly enhanced with Sr relative to Ba and Eu, reveal also enhancements with Pd. We propose that the source of extra Sr and Pd in these stars are VMP, fast rotating massive stars. Non-LTE is essential for obtaining the observational constraints to future models of the Galactic Pd evolution.

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arXiv2024

Extremely metal-poor stars in the Fornax and Carina dwarf spheroidal galaxies

We present our analysis of VLT/UVES and X-shooter observations of six very metal-poor stars, including four stars at [Fe/H]$\approx$$-3$ in the Fornax and Carina dwarf spheroidal (dSph) galaxies. To date, this metallicity range in these two galaxies has not yet been investigated fully, or at all in some cases. The chemical abundances of 25 elements are presented, based on 1D and local thermodynamic equilibrium (LTE) model atmospheres. We discuss the different elemental groups, and find that $α$- and iron-peak elements in these two systems are generally in good agreement with the Milky Way halo at the same metallicity. Our analysis reveals that none of the six stars we studied exhibits carbon enhancement, which is noteworthy given the prevalence of carbon-enhanced metal-poor stars without s-process enhancement (CEMP-no) in the Galaxy at similarly low metallicities. Our compilation of literature data shows that the fraction of CEMP-no stars in dSph galaxies is significantly lower than in the Milky Way, and than in ultra-faint dwarf galaxies. Furthermore, we report the discovery of the lowest metallicity, [Fe/H]=$-2.92$, r-process rich (r-I) star in a dSph galaxy. This star, fnx_06_019, has $\rm[Eu/Fe]=+0.8$, and also shows enhancement of La, Nd, and Dy, $\rm[X/Fe]>+0.5$. Our new data in Carina and Fornax help populate the extremely low metallicity range in dSph galaxies, and add to the evidence of a low fraction of CEMP-no stars in these systems.

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arXiv2023

Influence of departures from LTE on determinations of the scandium abundances in A-B type stars

We developed a comprehensive model atom of Sc II-Sc III. Abundances of scandium for a sample of eight unevolved A9-B3 type stars with well-determined atmospheric parameters were determined based on the non-local thermodynamic equilibrium (NLTE) line formation for Sc II-Sc III and high-resolution observed spectra. For the Sc II lines, the abundance differences between NLTE and LTE grow rapidly with increasing effective temperature (Teff), from slightly negative at Teff = 7250 K to positive ones of up to 0.6 dex at Teff = 10400 K. For Sc III in $ι$ Her, NLTE reduces the line-to-line scatter substantially compared to the LTE case. The NLTE abundances of Sc in our five superficially normal stars are consistent within the error bars with the solar system Sc abundance, while the LTE abundances of the late B-type stars are greatly subsolar. NLTE reduces, but does not remove a deficiency of Sc in the Am stars HD 72660 and Sirius. Based on our own and the literature data, the Ca/Sc abundance ratios of the sample of 16 Am stars were found to be close together, with [Ca/Sc] = 0.6-0.7. We propose the Ca/Sc abundance ratio, but not abundances of individual Ca and Sc elements to be used for classifying a star as Am and for testing the diffusion models. We provide the NLTE abundance corrections for ten lines of Sc II in a grid of model atmospheres appropriate for A to late B-type stars.

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arXiv2023

1D non-LTE corrections for chemical abundance analyses of very metal-poor stars

Detailed chemical abundances of very metal-poor (VMP, [Fe/H] < -2) stars are important for better understanding the First Stars, early star formation and chemical enrichment of galaxies. Big on-going and coming high-resolution spectroscopic surveys provide a wealth of material that needs to be carefully analysed. For VMP stars, their elemental abundances should be derived based on the non-local thermodynamic equilibrium (non-LTE = NLTE) line formation because low metal abundances and low electron number density in the atmosphere produce the physical conditions favorable for the departures from LTE. The galactic archaeology research requires homogeneous determinations of chemical abundances. For this purpose, we present grids of the 1D-NLTE abundance corrections for the Na I, Mg I, Ca I, Ca II, Ti II, Fe I, Zn I, Zn II, Sr II, and Ba II lines, which are used in the galactic archaeology research. The range of atmospheric parameters represents VMP stars on various evolutionary stages and covers effective temperatures from 4000 to 6500~K, surface gravities from log g = 0.5 to log g = 5.0, and metallicities $-5.0 \le$ [Fe/H] $\le -2.0$. The data is publicly available, and we provide the tools for interpolating in the grids online.

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arXiv2023

The Pristine Inner Galaxy Survey (PIGS) VII: a discovery of the first inner Galaxy CEMP-r/s star

Well-studied very metal-poor (VMP, [Fe/H] < -2 ) stars in the inner Galaxy are few in number, and they are of special interest because they are expected to be among the oldest stars in the MilkyWay. We present high-resolution spectroscopic follow-up of the carbon-enhanced metal-poor (CEMP) star Pristine_184237.56-260624.5 (hereafter Pr184237) identified in the Pristine Inner Galaxy Survey. This star has an apocentre of about 2 kpc. Its atmospheric parameters (Teff = 5100 K, log g = 2.0, [Fe/H] = -2.60) were derived based on the non-local thermodynamic equilibrium (NLTE) line formation. We determined abundances for 32 elements, including 15 heavy elements beyond the iron group. The NLTE abundances were calculated for 13 elements from Na to Pb. Pr184237 is strongly enhanced in C, N, O, and both s- and r-process elements from Ba to Pb; it reveals a low carbon isotope ratio of 12C/13C = 7. The element abundance pattern in the Na-Zn range is typical of halo stars. With [Ba/Eu] = 0.32, Pr184237 is the first star of the CEMP-r/s subclass identified in the inner Galaxy. Variations in radial velocity suggest binarity. We tested whether a pollution by the s- or i-process material produced in the more massive and evolved companion can form the observed abundance pattern and find that an i-process in the asymptotic giant branch star with a progenitor mass of 1.0-2.0 Msun can be the solution.

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arXiv2023

BD+30$^\circ$549: young helium-weak silicon star in NGC 1333 star-forming region

We present results of the spectroscopic study of the chemically peculiar star BD+30$^\circ$549 which is bona-fide member of young NGC 1333 star forming region. We found that the star possesses negligible rotation and helium-weak spectroscopic pattern with strongly enhanced Si II and Si III lines. The fundamental parameters of the star $T_{eff}$=13100~K and $\log (L/L_{\odot})$=2.1 indicate its age of about 2.7 Myr and position on the Hertzsprung-Russell diagram at the end of the Pre-Main Sequence evolutionary track, close to the Zero Age Main Sequence. Abundance analysis reveals the modest deficit of almost all elements with exception of Si, Fe, Ca and P which are overabundant. We performed the non-LTE calculations for Si II/Si III, Mg II and Ca II in order to check the influence of departures from LTE on line formation. Non-LTE calculations lead to much better reproduction of individual silicon line profiles, but does not completely remove the abundance discrepancy between Si II and Si III lines. We also investigate the effects of possible chemical stratification in BD+30$^\circ$549. We suspect that the "Si II/Si III anomaly", observed in BD+30$^\circ$549 spectrum arises under the combined action of the vertical and horizontal abundance gradients and non-LTE effects. We suppose that evolutionary status and phenomena observed in BD+30$^\circ$549 indicate that conditions favorable for the selective diffusion and formation of the surface chemical composition peculiarities (slow rotation and stabilization of the atmosphere) can be built up already at the Pre-Main Sequence phase.

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arXiv2022

Scandium abundances of F-G-K dwarf stars in a wide metallicity range

A new model atom of Sc II was constructed using the most up-to-date atomic data. For the testing purpose, the non-local thermodynamic equilibrium (non-LTE) calculations were carried out for three stars with reliably determined atmospheric parameters: the Sun, HD~61421 (Procyon), and HD~84937. Accounting for deviations from LTE leads to smaller abundance errors compared with the LTE case and consistent within the error bars abundances obtained from different Sc II lines. Solar non-LTE abundance log eps_Sun = 3.12+-0.05 exceeds the meteoritic abundance recommended by Lodders (2021), by 0.08~dex. But agreement within 0.02~dex with the meteoritic abundance is obtained for Procyon. Using high-resolution spectra, we determined the scandium LTE and non-LTE abundances for 56 stars in the metallicity range -2.62 <= [Fe/H] <= 0.24. The dependence of [Sc/Fe] on [Fe/H] demonstrates a similarity with the behavior of the alpha-process elements: scandium is enhanced relative to iron ([Sc/Fe] ~ 0.2) for [Fe/H] < -1, and [Sc/Fe] decreases with increasing [Fe/H] for the higher metallicity. There is a hint of a tight relation between abundances of scandium and titanium. The results obtained provide observational constraints to the scenarios of scandium origin.

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arXiv2022

Detailed abundances of the wide pairs of stars with and without planets: the binary systems 16 Cyg and HD 219542

We present results of the comparative analysis of the two wide binary systems -- 16 Cyg, with a giant gas planet orbiting around 16 Cyg B, and HD 219542 without planet detected. Atmospheric parameters of the binary components and the Sun were determined using their high-resolution spectra and the SME tools for automatic spectral analysis. By applying the synthetic spectrum method, we derived abundances of 29 and 23 chemical elements in 16 Cyg and HD 219542, respectively. For 19 of these elements, our results are based on the non-local thermodynamic equilibrium (NLTE) line formation. For both 16 Cyg and HD 219542, we obtained a small abundance difference between the A and B components: +0.019$\pm$0.012 and -0.014$\pm$0.019, respectively, suggesting only a weak influence of the giant gas planet formation on chemical composition of the host star atmosphere. For HD 219542 A and B, trends of the relative-to-solar abundances with the dust condensation temperature are similar to the literature data for the solar analogues without detected planets. The components of 16 Cyg reveal very similar behaviour of [X/H] with the condensation temperature, however, it is different from that for HD 219542. This indicates a specific chemical composition of the cloud from which the 16 Cyg binary system formed.

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arXiv2022

Non-LTE analysis of the Si II lines in iota Her with various atomic data sets

This study shows that the statistical equilibrium of Si II in the atmosphere of a B3 IV type star iota Her is extremely sensitive to a variation in photoionization cross-sections for the Si II levels. The difference in abundances derived from absorption lines of Si II between applying the data from two equal accuracy sources, namely, the Opacity Project (OP) and the NORAD database, amounts to 0.18 dex, on average. Using the hydrogenic approximation for photoionization cross-sections, we obtain the departure coefficients for the Si II \eu{4s}{2}{S}{}{} level, the source function for Si II 6371 A, and the abundance derived from this line, which are very similar to the corresponding values computed by Takeda (2022). We suppose that close-to-solar abundance obtained by Takeda (2022) from Si II 6371 A in iota Her is due to using the hydrogenic photoionization cross-sections for the Si II levels. However, emission lines of Si II observed in iota Her can only be reproduced with the OP photoionization cross-sections. Photoionization cross-sections for the Si II levels need further improvements.

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arXiv2021

The Pristine survey -- XV. A CFHT ESPaDOnS view on the Milky Way halo and disc populations

We present a one-dimensional, local thermodynamic equilibrium (1D-LTE) homogeneous analysis of 132 stars observed at high-resolution with ESPaDOnS. This represents the largest sample observed at high resolution (R$\sim$40,000) from the Pristine survey. This sample is based on the first version of the Pristine catalog and covers the full range of metallicities from [Fe/H]$\sim -3$ to $\sim +0.25$, with nearly half of our sample (58 stars) composed of very metal-poor stars ([Fe/H] $\le$ $-$2). This wide range of metallicities provides the opportunity of a new detailed study of the Milky Way stellar population. Because it includes both dwarf and giant stars, it also enables the analysis of any potential bias induced by the Pristine selection process. Based on Gaia EDR3, the orbital analysis of this Pristine$-$Espadons sample shows that it is composed of 65 halo stars and 67 disc stars. After a general assessment of the sample chemical properties with the $α$-elements Mg and Ca, we focus on the abundance of carbon and the neutron capture elements Ba and Sr. While most of our very metal-poor subsample is carbon normal, we also find that 14 stars out of the 38 stars with [Fe/H] $\leq$ $-$2 and measured carbon abundances turn out to be carbon enhanced metal-poor (CEMP) stars. We show that these CEMP stars are nearly exclusively (i.e. 12 stars out of 14) in the regime of low luminosity, unevolved, dwarf stars, which we interpret as the consequence of bias of the Pristine filter against C-rich giants. Among the very metal-poor (VMP) stars, we identify 2 CEMP stars with no enhancement in neutron-capture process elements (CEMP-no) and another one enriched in s-process element (CEMP-s). Finally, one VMP star is found with a very low [Sr/Fe] abundance ratio for its metallicity, as expected if it had been accreted from an ultra-faint dwarf galaxy.

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arXiv2021

The formation of the Milky Way halo and its dwarf satellites: A NLTE-1D abundance analysis. V. The Sextans galaxy

We present a homogeneous set of accurate atmospheric parameters for a sample of eleven very metal-poor (-3.32 <= [Fe/H] <= -2.61) stars in the Sextans dwarf spheroidal galaxy (dSph) and the non-local thermodynamic equilibrium (NLTE) abundances of, at least, seven chemical elements based on high-resolution UVES/VLT and HDS/Subaru spectra. For each star, its effective temperature and surface gravity were derived from the spectral energy distribution and the known distance, and the Fe abundance was obtained as the average from lines of Fe I and Fe II. Based on abundances of Mg, Ca, and Ti, we show that all the investigated stars reveal alpha-enhancements of 0.4~dex to 0.2~dex, and there is a hint of a decline in alpha/Fe for [Fe/H] > -2.8. The Sextans stars are deficient in Ba. The new result is an extremely tight relation between Ba and Mg, suggesting their common origin in massive stars and Ba synthesis in the r-process events on the timescales of standard supernovae. The exception is a C-enhanced star S 15-19 which is strongly enhanced in Ba. This star is unlikely to be a CEMP-s star because of low abundances of Sr and Y ([Y/Fe] < -1) that are produced in the s-process as efficiently as Ba and a non-detection of variation in the radial velocity. No distinctions from the Milky Way halo and the Sculptor and Ursa Minor dSphs were found in a history of early enrichment in Na and Ni, namely, the Sextans stars are deficient in Na and have close-to-solar Ni/Fe.

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arXiv2021

The Pristine survey XIV: chemical analysis of two ultra-metal-poor stars

Elemental abundances of the most metal-poor stars reflect the conditions in the early Galaxy and the properties of the first stars. We present a spectroscopic follow-up of two ultra metal-poor stars ([Fe/H]<-4.0) identified by the survey {\em Pristine}: Pristine 221.8781+9.7844 and Pristine 237.8588+12.5660 (hereafter Pr 221 and Pr 237, respectively). Combining data with earlier observations, we find a radial velocity of -149.25 $\pm$ 0.27 and -3.18 $\pm$ 0.19 km/s for Pr 221 and Pr 237, respectively, with no evidence of variability between 2018 and 2020. From a one-dimensional (1D) local thermodynamic equilibrium (LTE) analysis, we measure [Fe/H]$_{\rm LTE}$=-4.79 $\pm$ 0.14 for Pr 221 and [Fe/H]$_{\rm LTE}$=-4.22 $\pm$ 0.12 for Pr 237, in good agreement with previous studies. Abundances of Li, Na, Mg, Al, Si, Ca, Ti, Fe, and Sr were derived based on the non-LTE (NLTE) line formation calculations. When NLTE effects are included, we measure slightly higher metallicities: [Fe/H]$_{\rm NLTE}$=-4.40 $\pm$ 0.13 and [Fe/H]$_{\rm NLTE}$=-3.93 $\pm$ 0.12, for Pr 221 and Pr 237, respectively. Analysis of the G-band yields [C/Fe]$_{\rm 1D-LTE} \leq$ +2.3 and [C/Fe]$_{\rm 1D-LTE} \leq$ +2.0 for Pr 221 and Pr 237. Both stars belong to the low-carbon band. Upper limits on nitrogen abundances are also derived. Abundances for other elements exhibit good agreement with those of stars with similar parameters. Finally, to get insight into the properties of their progenitors, we compare NLTE abundances to theoretical yields of zero-metallicity supernovae. This suggests that the supernovae progenitors had masses ranging from 10.6 to 14.4 M$_{\odot}$ and low-energy explosions with 0.3-1.2 $\times$ 10$^{51}$ erg.

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arXiv2020

Chemical diversity among A-B stars with low rotational velocities: non-LTE abundance analysis

We present accurate element abundance patterns based on the non-local thermodynamic equilibrium (non-LTE, NLTE) line formation for 14 chemical elements from He to Nd for a sample of nine A9 to B3 type stars with well determined atmospheric parameters and low rotational velocities. We constructed new model atom of Zr II-III and updated model atoms for Sr II and Ba II by implementing the photoionization cross sections from calculations with the Dirac B-spline R-matrix method. The NLTE abundances of He to Fe in the stars HD~17081, HD~32115, HD~160762, and HD~209459 are found to be consistent with the solar abundances, and HD~73666 being a Blue Struggler does not reveal deviations from chemical composition of the Praesepe cluster. Three of these stars with an effective temperature of lower than 10500~K have supersolar abundances of Sr, Zr, Ba, and Nd, and our results suggest the presence of a positive correlation between stellar effective temperature and abundance. For each star, enhancement of Ba is higher than that for any other heavy element. We propose that the solar Ba abundance is not representative of the galactic Ba abundance at modern epoch. The status of HD~145788 was not clarified: this star has solar abundances of C to Si and enhancements of Sr to Ba similar to that for superficially normal stars of similar temperature, while overabundant Ca, Ti, and Fe. The NLTE abundances of Vega support its status of a mild lambda~Bootis star.

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arXiv2017

Program package for the analysis of high resolution high signal-to-noise stellar spectra

The program package SME (Spectroscopy Made Easy), designed to perform an analysis of stellar spectra using spectral fitting techniques, was updated due to adding new functions (isotopic and hyperfine splittins) in VALD and including grids of NLTE calculations for energy levels of few chemical elements. SME allows to derive automatically stellar atmospheric parameters: effective temperature, surface gravity, chemical abundances, radial and rotational velocities, turbulent velocities, taking into account all the effects defining spectral line formation. SME package uses the best grids of stellar atmospheres that allows us to perform spectral analysis with the similar accuracy in wide range of stellar parameters and metallicities - from dwarfs to giants of BAFGK spectral classes.

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arXiv2017

The formation of the Milky Way halo and its dwarf satellites; a NLTE-1D abundance analysis. II. Early chemical enrichment

We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, -4 < [Fe/H] < -2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in PaperI. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [alpha/Fe] ~ 0.3 for each of the alpha-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in alpha/Fe with increasing metallicity in the BootesI ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is well correlated with Mg suggesting a strong link to massive stars and that its production is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs: BootesI, UMaII, and LeoIV are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg] ~ -1.3 and [Ba/Mg] ~ -1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H] < -2, is the strongest.

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arXiv2017

Influence of inelastic collisions with hydrogen atoms on the non-LTE modelling of Ca I and Ca II lines in late-type stars

We perform the non-local thermodynamic equilibrium (NLTE) calculations for Ca I-II with the updated model atom that includes new quantum-mechanical rate coefficients for Ca I + H I collisions from two recent studies, that is, by Barklem and by Mitrushchenkov, Guitou, Belyaev, Yakovleva, Spielfiedel, and Feautrier, and investigate the accuracy of calcium abundance determinations using the Sun, Procyon, and five metal-poor (MP) stars with well-determined stellar parameters. We show that both collisional recipes lead to very similar NLTE results. When using the subordinate lines of Ca I and the high-excitation lines of Ca II, NLTE provides the smaller line-to-line scatter compared with the LTE case for each star. For Procyon, NLTE removes a steep trend with line strength among strong Ca I lines seen in LTE and leads to consistent [Ca/H] abundances from the two ionisation stages. In the MP stars, the NLTE abundance from Ca II 8498 A agrees well with that from the Ca I subordinate lines. NLTE largely removes abundance discrepancies between the high-excitation lines of Ca I and Ca II 8498 A obtained for our four [Fe/H] < -2 stars under the LTE assumption. We investigate the formation of the Ca I resonance line in the [Fe/H] < -2 stars. Consistent NLTE abundances from the Ca I resonance line and the Ca II lines are found for two hyper metal-poor stars HE0107-5240 and HE1327-2326. We provide the NLTE abundance corrections for 28 lines of Ca I in a grid of model atmospheres suitable for abundance analysis of FGK-type dwarfs and subgiants.

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arXiv2017

The formation of the Milky Way halo and its dwarf satellites, a NLTE-1D abundance analysis. I. Homogeneous set of atmospheric parameters

We present a homogeneous set of accurate atmospheric parameters for a complete sample of very and extremely metal-poor stars in the dwarf spheroidal galaxies (dSphs) Sculptor, Ursa Minor, Sextans, Fornax, Boötes I, Ursa Major II, and Leo IV. We also deliver a Milky Way (MW) comparison sample of giant stars covering the -4 < [Fe/H] < -1.7 metallicity range. We show that, in the [Fe/H] > -3.5 regime, the non-local thermodynamic equilibrium (NLTE) calculations with non-spectroscopic effective temperature (Teff) and surface gravity (log~g) based on the photometric methods and known distance provide consistent abundances of the Fe I and Fe II lines. This justifies the Fe I/Fe II ionisation equilibrium method to determine log g for the MW halo giants with unknown distance. The atmospheric parameters of the dSphs and MW stars were checked with independent methods. In the [Fe/H] > -3.5 regime, the Ti I/Ti II ionisation equilibrium is fulfilled in the NLTE calculations. In the log~g - Teff plane, all the stars sit on the giant branch of the evolutionary tracks corresponding to [Fe/H] = -2 to -4, in line with their metallicities. For some of the most metal-poor stars of our sample, we hardly achieve consistent NLTE abundances from the two ionisation stages for both iron and titanium. We suggest that this is a consequence of the uncertainty in the Teff-colour relation at those metallicities. The results of these work provide the base for a detailed abundance analysis presented in a companion paper.

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arXiv2016

Systematic non-LTE study of the $-2.6 \le$ [Fe/H] $\le 0.2$ F and G dwarfs in the solar neighbourhood. II. Abundance patterns from Li to Eu

For the first time, we present an extensive study of stars with individual non-local thermodynamic equilibrium (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over the $-2.62 \le$ [Fe/H] $\le +0.24$ metallicity range that is suitable for the Galactic chemical evolution research. The star sample has been kinematically selected to trace the Galactic thin and thick disks and halo. We find new and improve earlier results as follows. (i) The element-to-iron ratios for Mg, Si, Ca, and Ti form a MP plateau at a similar height of 0.3~dex, and the knee occurs at common [Fe/H] $\simeq -0.8$. The knee at the same metallicity is observed for [O/Fe], and the MP plateau is formed at [O/Fe] = 0.61. (ii) The upward trend of [C/O] with decreasing metallicity exists at [Fe/H] $< -1.2$, supporting the earlier finding of Akerman et al. (iii) An underabundance of Na relative to Mg in the [Fe/H] $< -1$ stars is nearly constant, with the mean [Na/Mg] $\simeq -0.5$. (iv) The K/Sc, Ca/Sc, and Ti/Sc ratios form well-defined trends, suggesting a common site of the K-Ti production. (v) Sr follows the Fe abundance down to [Fe/H] $\simeq -2.5$, while Zr is enhanced in MP stars. (vi) The comparisons of our results with some widely used Galactic evolution models are given. The use of the NLTE element abundances raises credit to the interpretation of the data in the context of the chemical evolution of the Galaxy.

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