Nitrogen is an important element in various fields of stellar and Galactic astronomy, and the solar nitrogen abundance is crucial as a yardstick for comparing different objects in the cosmos. In order to obtain a precise and accurate value for this abundance, we carried out N i line formation calculations in a 3D radiative-hydrodynamic STAGGER model solar atmosphere, in full 3D non-local thermodynamic equilibrium (non-LTE), using a model atom that includes physically-motivated descriptions for the inelastic collisions of N i with free electrons and with neutral hydrogen. We selected five N i lines of high excitation energy to study in detail, based on their strengths and on their being relatively free of blends. We found that these lines are slightly strengthened from non-LTE photon losses and from 3D granulation effects, resulting in negative abundance corrections of around $-0.01$ dex and $-0.04$ dex respectively. Our advocated solar nitrogen abundance is $\logε_{\mathrm{N}} = 7.77$, with the systematic $1σ$ uncertainty estimated to be $0.05$ dex. This result is consistent with earlier studies after correcting for differences in line selections and equivalent widths.
The solar chemical abundances studied in considerable detail because of discrepant values of solar metallicity inferred from different indicators, where in the present work we have used 28 suitable atomic spectral solar nitrogen lines, relying on new equivalent widths measurements for determining the nitrogen abundance. Corresponding to 28 solar neutral nitrogen lines, we derived a solar abundance of nitrogen using the Holweger and Muller solar model and the measured equivalent widths from the literature. Our study reported the solar nitrogen abundance result to be of 8.05 (sigma = 0.09) using…
Carbon, nitrogen, and oxygen are the fourth, sixth, and third most abundant elements in the Sun. Their abundances remain hotly debated due to the so-called solar modelling problem that has persisted for almost $20$ years. We revisit this issue by presenting a homogeneous analysis of $408$ molecular lines across $12$ diagnostic groups, observed in the solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic model solar photosphere and LTE (local thermodynamic equilibrium) line formation, we find $\logε_{C} = 8.47\pm0.02$, $\logε_{N} = 7.89\pm0.04$, and $\logε_{O} = 8.70\pm0.04$. Th…
Two distinct halo populations were found in the solar neighborhood by a series of works. They can be clearly separated by [alpha\Fe] and several other elemental abundance ratios including [Cu/Fe]. Very recently, a non-local thermodynamic equilibrium (non-LTE) study revealed that relatively large departures exist between LTE and non-LTE results in copper abundance analysis. We aim to derive the copper abundances for the stars from the sample of Nissen et al (2010) with both LTE and non-LTE calculations. Based on our results, we study the non-LTE effects of copper and investigate whether the hig…
We present three-dimensional (3D) non-local thermodynamic equilibrium (non-LTE) radiative transfer calculations for silicon in the solar photosphere, using an extensive model atom that includes recent, realistic neutral hydrogen collisional cross-sections. We find that photon losses in the SiI lines give rise to slightly negative non-LTE abundance corrections of the order -0.01 dex. We infer a 3D non-LTE based solar silicon abundance of 7.51 dex. With silicon commonly chosen to be the anchor between the photospheric and meteoritic abundances, we find that the meteoritic abundance scale remains…
Spectroscopic measurements of iron abundances are prone to systematic modelling errors. We present 3D non-LTE calculations across 32 STAGGER-grid models with effective temperatures from 5000 K to 6500 K, surface gravities of 4.0 dex and 4.5 dex, and metallicities from $-$3 dex to 0 dex, and study the effects on 171 Fe I and 12 Fe II optical lines. In warm metal-poor stars, the 3D non-LTE abundances are up to 0.5 dex larger than 1D LTE abundances inferred from Fe I lines of intermediate excitation potential. In contrast, the 3D non-LTE abundances can be 0.2 dex smaller in cool metal-poor stars …
We investigate the feasibility of the Si I infrared (IR) lines as Si abundance indicators for giant stars. We find that Si abundances obtained from the Si I IR lines based on the local thermodynamic equilibrium (LTE) analysis show large line-to-line scatter (mean value of 0.13dex), and are higher than those from the optical lines. However, when the non-LTE effects are taken into account, the line-to-line scatter reduces significantly (mean value of 0.06dex), and the Si abundances are consistent with those from the optical lines. The typical average non-LTE correction of [Si/Fe] for our sample …
Non-local thermodynamic equilibrium (non-LTE) line formation for Ca I-Ca II, Ti I-Ti II, and Fe I-Fe II is considered in model atmospheres of giant stars with an effective temperature of 4000 K $\le$ Teff $\le$ 5000 K and a metal abundance of -4 $\le$ [Fe/H] $\le$ 0. The departures from LTE are analyzed depending on atmospheric parameters. We present the non-LTE abundance corrections for 28 lines of Ca I, 42 lines of Ti I, 54 lines of Ti II, and 262 lines of Fe I and a three-dimensional interpolation code to obtain the non-LTE correction online (http://spectrum.inasan.ru/nLTE/) for an individu…
We evaluate non-local thermodynamical equilibrium (non-LTE) line formation for neutral sodium in model atmospheres of the 79 red giants using the model atom that incorporates the best available atomic data. The non-LTE abundances of Na were determined from Na I 6154, 6161 Å for the 38 stars of the thin disk (15 of them the BaII stars), 15 stars of the thick disk, 13 stars of Hercules stream and 13 transition stars which can be identified with neither thin disk nor thick disk. For Na I 6154, 6161 Å non-LTE abundance corrections amount to -0.06 to -0.24 dex depending on stellar parameters. We fo…
The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. We carried out three-dimensional (3D) non-LTE radiative transfer calculations for CI and OI, and 3D LTE radiative transfer calculations for FeII, across the STAGGER-grid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as $-0.3$ dex for CI lines in low-metallicity F dwarfs, and $-0.6$ dex for OI lines in high-metallicity F dwarfs…
We study the solar photospheric abundance of singly ionized neodymium (Nd II) using high resolution spectroscopic data obtained by Fourier transform spectrograph (FTS). Based on the Local Thermodynamical Equilibrium (LTE) assumption, a new value of Nd abundance is derived. We succeed to select of 51 solar Nd II lines with accurate transition probabilities measured experimentally by Den Hartog et al. (2003) and with accurate damping parameters are determined from literature. Relying on atomic data of Opacity Distribution Function (ODF), we construct theoretical photospheric solar model. The mea…
In the aim of determining accurate iron abundances in stars, this work is meant to empirically calibrate H-collision cross-sections with iron, where no quantum mechanical calculations have been published yet. Thus, a new iron model atom has been developed, which includes hydrogen collisions for excitation, ionization and charge transfer processes. We show that collisions with hydrogen leading to charge transfer are important for an accurate non-LTE modeling. We apply our calculations on several benchmark stars including the Sun, the metal-rich star α Cen A and the metal-poor star HD140283.
Older GCE models predict [K/Fe] ratios as much as 1 dex lower than those inferred from stellar observations. Abundances of potassium are mainly based on analyses of the 7698 $Å$ resonance line, and the discrepancy between models and observations is in part caused by the LTE assumption. We study the statistical equilibrium of KI, focusing on the non-LTE effects on the $7698 \ Å$ line. We aim to determine how non-LTE abundances of K can improve the analysis of its chemical evolution, and help to constrain the yields of models. We construct a model atom that employs the most up-to-date data. In p…
It is well known that cool star atmospheres depart from local thermodynamic equilibrium (LTE). Accurate abundance determination requires taking those effects into account, but the necessary non-LTE calculations are often lacking. Our goal is to provide detailed estimates of NLTE effects for FGK type stars for all spectral lines from the ultraviolet to the infrared that are potentially useful as abundance diagnostics. The first paper in this series focusses on the light elements Na, Mg and Al. The code PySME is used to compute curves-of-growth for 2158 MARCS model atmospheres in a wide paramete…
A non-LTE (NLTE) abundance analysis was carried out for three extreme helium stars (EHes): BD+10 2179, BD-9 4395, and LS IV+6 002, from their optical spectra with NLTE model atmospheres. NLTE TLUSTY model atmospheres were computed with H, He, C, N, O, and Ne treated in NLTE. Model atmosphere parameters were chosen from consideration of fits to observed He I line profiles and ionization equilibria of C and N ions. The program SYNSPEC was then used to determine the NLTE abundances for Ne as well as H, He, C, N, and O. LTE neon abundances from Ne I lines in the EHes: LSE 78, V1920 Cyg, HD 124448,…
Medium resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE calculations are presented to investigate the influence of NLTE on the formation of silicon lines in the J-band spectra of red supergiants. Substantial effects are found resulting in significantly stronger absorption lines of neutral silicon in non-LTE. As a consequence, silicon abundances determined in non-LTE are significantly smalle…
As one of the most important elements in astronomy, iron abundance determinations need to be as accurate as possible. We investigate the accuracy of spectroscopic iron abundance analyses using archetypal metal-poor stars. We perform detailed 3D non-LTE radiative transfer calculations based on 3D hydrodynamic Stagger model atmospheres, and employ a new model atom that includes new quantum-mechanical neutral hydrogen collisional rate coefficients. With the exception of the red giant HD122563, we find that the 3D non-LTE models achieve Fe i/Fe ii excitation and ionization balance as well as not h…
We performed non-LTE calculations for O I with the plane-parallel model atmospheres for a set of stellar parameters corresponding to A-K type stars. The model atom of Przybilla et al. (2000) was updated using the best theoretical and experimental atomic data available so far. Non-LTE leads to strengthening the O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The departures from LTE grow toward higher effective temperature and lower surface gravity. In the entire temperature range and log g = 4, the non-LTE correction does not exceed 0.05 de…
We present the non-local thermodynamic equilibrium (non-LTE) calculations for O I with the updated model atom that includes quantum-mechanical rate coefficients for O I + H I inelastic collisions from the recent study of Barklem (2018). The non-LTE abundances from the O I lines were determined for the Sun and 46 FG stars in a wide metallicity range, -2.6 < [Fe/H] < 0.2. An application of accurate atomic data leads to larger departures from LTE and lower oxygen abundances compared to that for the Drawin's theoretical approximation. For the infrared O I 7771-5 A triplet lines, the change in the …
We perform non-LTE calculations of lithium in late-type stars for a wide range of stellar parameters, including quantum mechanical cross-sections for collisions with neutral hydrogen and the negative hydrogen ion. Non-LTE abundance corrections for the lithium resonance line at 670.7nm and the subordinate line at 610.3nm, are calculated using 1D MARCS model atmospheres spanning a grid Teff=[4000,8000]K, log(g)=[1.0,5.0], and [Fe/H]=[0.0,-3.0], for lithium abundances in the range A(Li)=[-0.3,4.2]. The competing effects of ultraviolet over-ionization and photon losses in the resonance line govern…
Oxygen abundance measurements are important for understanding stellar structure and evolution. Measured in Cepheids, they further provide clues on the metallicity gradient and chemo-dynamical evolution in the Galaxy. However, most of the abundance analyses of Cepheids to date have been based on one-dimensional (1D) hydrostatic model atmospheres. Here, we test the validity of this approach for the key oxygen abundance diagnostic, the \ion{O}{I} $777\,\mathrm{nm}$~triplet lines. We carry out 2D non-LTE radiative transfer clculations across two different 2D radiation hydrodynamics simulations of …
Non-LTE calculations for Mg I in red supergiant stellar atmospheres are presented to investigate the importance of non-LTE for the formation of Mg I lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated that technique is a very promising tool to investigate the chemical composition of the young stellar population in star forming galaxies. As in previous work, where non-LTE effects were studied for iron, titanium and silicon, substantial effects are found resulting in significantly stronger Mg …
Open cluster members are coeval and share the same initial bulk chemical compositions. Consequently, differences in surface abundances between members of a cluster that are at different evolutionary stages can be used to study the effects of mixing and internal chemical processing. We carry out an abundance analysis of seven elements (Li, O, Na, Mg, Al, Si, Fe) in 66 stars belonging to the open cluster M67, based on high resolution GALAH spectra, 1D MARCS model atmospheres, and, for the first time for a large sample of M67 stars, non-local thermodynamic equilibrium (non-LTE) radiative transfer…
The non-local thermodynaic equilibrium (non-LTE) line formation for the two ions of zirconium is considered through a range of spectral types when the Zr abundance varies from the solar value down to [Zr/H] = -3. The model atom was built using 148 energy levels of Zr I, 772 levels of Zr II, and the ground state of Zr III. It was shown that the main non-LTE mechnism for the minority species Zr I is ultraviolet overionization. Non-LTE leads to systematically depleted total absorption in the Zr I lines and positive abundance corrections, reaching to 0.33 dex for the solar metallicity models. The …
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.…
The OI 777 nm lines are among the most commonly used diagnostics for the oxygen abundances in the atmospheres of FGK-type stars. However, they form in conditions that are far from local thermodynamic equilibrium (LTE). We explore the departures from LTE of atomic oxygen, and their impact on OI lines, across the Stagger-grid of three-dimensional hydrodynamic model atmospheres. For the OI 777 nm triplet we find significant departures from LTE. These departures are larger in stars with larger effective temperatures, smaller surface gravities, and larger oxygen abundances. We present grids of pred…
Neutral sodium is a minority species in the atmospheres of late-type stars, and line formation in local thermodynamic equilibrium (LTE) is often a poor assumption, in particular for strong lines. We present an extensive grid of non-LTE calculations for several NaI lines in cool stellar atmospheres, including metal-rich and metal-poor dwarfs and giants. For the first time, we constructed a Na model atom that incorporates accurate quantum mechanical calculations for collisional excitation and ionisation by electrons as well as collisional excitation and charge exchange reactions with neutral hyd…
In this review we discuss possible systematic errors inherent in classical 1D LTE abundance analyses of late-type stars for the light elements (here: H, He, Li, Be and B). The advent of realistic 3D hydrodynamical model atmospheres and the availability of non-LTE line formation codes place the stellar analyses on a much firmer footing and indeed drastically modify the astrophysical interpretations in many cases, especially at low metallicities. For the Teff-sensitive hydrogen lines both stellar granulation and non-LTE are likely important but the combination of the two has not yet been fully e…
We present a preliminary local thermodynamic equilibrium (LTE) abundance analysis of the template halo red giant HD122563 based on a realistic, three-dimensional (3D), time-dependent, hydrodynamical model atmosphere of the very metal-poor star. We compare the results of the 3D analysis with the abundances derived by means of a standard LTE analysis based on a classical, 1D, hydrostatic model atmosphere of the star. Due to the different upper photospheric temperature stratifications predicted by 1D and 3D models, we find large, negative, 3D-1D LTE abundance differences for low-excitation OH and…
The aim of this study is to analyse and determine elemental abundances for a large sample of distant B stars in the outer Galactic disk in order to constrain the chemical distribution of the Galactic disk and models of chemical evolution of the Galaxy. Here, we present preliminary results on a few stars along with the adopted methodology based on securing simultaneous O and Si ionization equilibria with consistent NLTE model atmospheres.
We performed the non-local thermodynamic equilibrium (non-LTE) calculations for Ti I-II with the updated model atom that includes quantum-mechanical rate coefficients for inelastic collisions with hydrogen atoms. We have calculated for the first time the rate coefficients for bound-bound transitions in inelastic collisions of titanium atoms and ions with hydrogen atoms and for the charge-exchange processes: Ti I + H <-> Ti II + H- and Ti II + H <-> Ti III + H-. The influence of these data on non-LTE abundance determinations has been tested for the Sun and four metal-poor stars. For Ti I and Ti…
Context. The pursuit of more realistic spectroscopic modelling and consistent abundances has led us to begin a new series of papers designed to improve current solar and stellar abundances of various atomic species. To achieve this, we have began updating the three-dimensional (3D) non-local thermodynamic equilibrium (non-LTE) radiative transfer code, Multi3D, and the equivalent one-dimensional (1D) non-LTE radiative transfer code, MULTI. Aims. We examine our improvements to these codes by redetermining the solar barium abundance. Barium was chosen for this test as it is an important diagnosti…
The dominant form of nitrogen provided to most solar system bodies is currently unknown, though available measurements show that the detected nitrogen in solar system rocks and ices is depleted with respect to solar abundances and the interstellar medium. We use a detailed chemical/physical model of the chemical evolution of a protoplanetary disk to explore the evolution and abundance of nitrogen-bearing molecules. Based on this model we analyze how initial chemical abundances, provided as either gas or ice during the early stages of disk formation, influence which species become the dominant …
Photospheric nitrogen abundances for a sample of 26 Be stars and 16 normal B stars were found using high-resolution spectra from the Magnetism in Massive Stars (MiMeS) spectroscopic survey. Nitrogen abundances were obtained using non-LTE equivalent widths and line profiles, and Monte Carlo simulation was used to determine the error bounds of the measured nitrogen abundances due to uncertainties in the adopted stellar parameters, continuum normalization, and atomic data. In addition, the effects of the gravitational darkening and disk contamination on the measured Be star nitrogen abundances we…
We present new ultra-metal-poor (UMP) stars parameters with [Fe/H]<-4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameter and show that they can grow up to ~1.0 dex in [Fe/H], 150K in Teff and 0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being signifcantly higher, are the first step to eventually providing full NLTE abundance patterns that …
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. 1D 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. The purpose of this work is to provide corrections for the lithium abundance, A(Li), and the 6Li/7Li ratio that can easily be applied t…
Although oxygen is an important tracer of the early Galactic evolution, its abundance trends with metallicity are still relatively poorly known at [Fe/H] < -2.5. This is in part due to a lack of reliable oxygen abundance indicators in the metal-poor stars, in part due to shortcomings in 1D LTE abundance analyses. In this study we determined the oxygen abundance in the metal-poor halo giant HD 122563 using a 3D hydrodynamical CO5BOLD model atmosphere. Our main goal was to understand whether a 3D LTE analysis may help to improve the reliability of oxygen abundances determined from OH UV lines in…
We checked consistency between the copper abundance derived in six metal-poor stars using UV Cu II lines (which are assumed to form in LTE) and UV Cu I lines (treated in NLTE). Our program stars cover the atmosphere parameters which are typical for intermediate temperature dwarfs (effective temperature is in the range from approximately 5800 to 6100 K, surface garvity is from 3.6 to 4.5, metallicity is from about -1 to -2.6 dex). We obtained a good agreement between abundance from these two sets of the lines, and this testifies about reliability of our NLTE copper atomic model. We confirmed th…
This is the second paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to enable further constraints on the early evolution of massive stars. We investigate the NIV lambda4058 emission line formation, provide nitrogen abundances for a substantial O-star sample in the LMC, and compare our findings with recent predictions from stellar evolutionary models. Stellar and wind parameters are determined by line profile fitting of hydrogen, helium and nitrogen lines, based on synthetic spectra calculated by FASTWIND. We derive nitrogen abundances for 20 O- and 5 B-stars, by…
A five-dimensional interpolation method and corresponding computer program are developed for using published calculations to determine the non-LTE correction {Δ\}NLTE to the lithium abundance logε(Li) derived from the Li I 6707.8 Å line. The {Δ\}NLTE values is determined from the following five parameters: {Δ\}NLTE the effective temperature Teff, the acceleration of gravity logg, the metallicity index [Fe/H], the microturbulent velocity Vt, and the LTE Li abundance log ε(Li). The program is used to calculate values of {Δ\}NLTE and the non-LTE Li abundance for 91 single bright giants from the l…
We investigated the copper abundances for $64$ late-type stars in the Galactic disk and halo with effective temperatures from $5400$ K to $6700$ K and [Fe/H] from $-1.88$ to $-0.17$. For the first time, the copper abundances are derived using both local thermodynamic equilibrium (LTE) and non-local thermodynamic equilibrium (non-LTE) calculations. High resolution ($R > 40,000$), high signal-to-noise ratio ($S/N > 100$) spectra from the FOCES spectrograph are used. The atmospheric models are calculated based on the MAFAGS opacity sampling code. All the abundances are derived using the spectrum …
Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C i lines, one of the main abundance diagnostics, are sensitive to departures from local thermodynamic equilibrium (LTE). We present a model atom for non-LTE analyses of C i lines, that uses a new, physically-motivated recipe for the rates of neutral hydrogen impact excitation. We analyse C i lines in the solar spectrum, employing a three-dimensional (3D) hydrodynamic model solar atmosphere and 3D non-LTE radiative transfer. We find negative non-LTE abundance corrections for C i lines in the sola…
Accurate spectroscopic lithium abundances are essential in addressing a variety of open questions, such as the origin of a uniform lithium content in the atmospheres of metal-poor stars (Spite plateau) or the existence of a correlation between the properties of extra-solar planetary systems and the lithium abundance of their host stars. We have developed a tool that allows the user to improve the accuracy of standard lithium abundance determinations based on 1D model atmospheres and the assumption of Local Thermodynamic Equilibrium (LTE) by applying corrections that account for hydrodynamic (3…
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…
A comprehensive model atom for Fe with more than 3000 energy levels is presented. As a test and first application of this model atom, Fe abundances are determined for the Sun and five stars with well determined stellar parameters and high-quality observed spectra. Non-LTE leads to systematically depleted total absorption in the Fe I lines and to positive abundance corrections in agreement with the previous studies, however, the magnitude of non-LTE effect is smaller compared to the earlier results. Non-LTE corrections do not exceed 0.1 dex for the solar metallicity and mildly metal-deficient s…
Aluminium plays a key role in studies of the chemical enrichment of the Galaxy and of globular clusters. However, strong deviations from LTE (non-LTE) are known to significantly affect the inferred abundances in giant and metal-poor stars. We present NLTE modeling of aluminium using recent and accurate atomic data, in particular utilizing new transition rates for collisions with hydrogen atoms, without the need for any astrophysically calibrated parameters. For the first time, we perform 3D NLTE modeling of aluminium lines in the solar spectrum. We also compute and make available extensive gri…
The titanium abundances of late-type stars are important tracers of Galactic formation history. However, abundances inferred from Ti I and Ti II lines can be in stark disagreement in very metal-poor giants. Departures from local thermodynamic equilibrium (LTE) have a large impact on the minority neutral species and thus influences the ionisation imbalance, but satisfactory non-LTE modelling for both dwarfs and giants has not been achieved in previous literature. The reliability of titanium abundances is reassessed in benchmark dwarfs and giants using a new non-LTE model and one-dimensional (1D…
CONTEXT: In recent years, the solar chemical abundances have been studied in considerable detail because of discrepant values of solar metallicity inferred from different indicators, i.e., on the one hand, the "sub-solar" photospheric abundances resulting from spectroscopic chemical composition analyses with the aid of 3D hydrodynamical models of the solar atmosphere, and, on the other hand, the high metallicity inferred by helioseismology. AIMS: After investigating the solar oxygen abundance using a CO5BOLD 3D hydrodynamical solar model in previous work, we undertake a similar approach studyi…
We have composed a sample of 68 massive stars in our galaxy whose projected rotational velocity, effective temperature and gravity are available from high-precision spectroscopic measurements. The additional seven observed variables considered here are their surface nitrogen abundance, rotational frequency, magnetic field strength, and the amplitude and frequency of their dominant acoustic and gravity mode of oscillation. Multiple linear regression to estimate the nitrogen abundance combined with principal components analysis, after addressing the incomplete and truncated nature of the data, r…
We present a new determination of the solar nitrogen abundance making use of 3D hydrodynamical modelling of the solar photosphere, which is more physically motivated than traditional static 1D models. We selected suitable atomic spectral lines, relying on equivalent width measurements already existing in the literature. For atmospheric modelling we used the co 5 bold 3D radiation hydrodynamics code. We investigated the influence of both deviations from local thermodynamic equilibrium (non-LTE effects) and photospheric inhomogeneities (granulation effects) on the resulting abundance. We also co…
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 h…
We report the detection of an Al II line at 2669.155 Angstroms in 11 metal-poor stars, using ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive Al abundances from this line using a standard abundance analysis, assuming local thermodynamic equilibrium (LTE). The mean [Al/Fe] ratio is -0.06 +/- 0.04 (sigma = 0.22) for these 11 stars spanning -3.9 < [Fe/H] < -1.3, or [Al/Fe] = -0.10 +/- 0.04 (sigma = 0.18) for 9 stars spanning -3.0 < [Fe/H] < -1.3 if two carbon-enhanced stars are excluded. We use these abundances to perform an…
We present non-LTE oxygen abundances for a sample of B stars in the Orion association. The abundance calculations included non-LTE line formation and used fully blanketed non-LTE model atmospheres. The stellar parameters were the same as adopted in the previous study by Cunha & Lambert (1994). We find that the young Orion stars in this sample of 10 stars are described by a single oxygen abundance with an average value of A(O)=8.78 and a small dispersion of +/- 0.05 dex, which is of the order of the uncertainties in the analysis. This average oxygen abundance compares well with the average oxyg…
