arXiv subjects

Gražina Tautvaišienė

Publications and source records attributed to Gražina Tautvaišienė.

At least 19 recordsLinked to original sources

arXiv2026

A More Complex Than Expected Formation History of the Milky Way's Last Major Merger

The Gaia$-$Sausage$-$Enceladus (GSE) structure, widely recognized as the most recent major accretion event experienced by our Galaxy, is traditionally interpreted as the remnant of a single ancient merger that played a significant role in building the Milky Way's inner halo. Most previous studies have characterized the GSE as a kinematically coherent population that originated from either a single progenitor or a recent infall event. Here, we present evidence for a more complex origin, based on data from the DESI and a novel unsupervised clustering algorithm, GS$^3$ Hunter. Applying this method to local halo stars near the solar neighborhood, we identify 17 structures, including known systems such as Sequoia and GSE, as well as several previously unrecognized structures/stellar streams. A more detailed analysis incorporating chronological, dynamical, and chemical dimensions reveals four distinct substructures within the GSE region, herein designated GSE$-$GSH1 (12 Gyr), GSE$-$GSH2 (10 Gyr), GSE$-$GSH3 (8 Gyr), and GSE$-$GSH4 (7 Gyr). Although all four are broadly consistent with the overall phase$-$space distribution and abundance patterns of the GSE, they display markedly distinct orbital actions and chemical abundances relative to previously reported results. This finding reveals an unprecedented level of internal complexity in the GSE's formation history and supports a scenario in which the GSE is not the remnant of a single accretion event, but rather a composite structure assembled through multiple, sequential merger episodes during the early Milky Way.

astro-ph.GA↗

arXiv2026

Stellar Population Astrophysics (SPA) with the TNG. CNO abundances in 28 open clusters

Aims. Our main aim with this work was to enlarge the pool of open clusters with determined carbon, nitrogen, and oxygen abundances in evolved giants to further advance chemical clocks in stellar age determinations. Methods. High-resolution spectra were analysed using a differential model atmosphere method. Carbon abundances were derived using spectral synthesis of the C2 band heads at 5135 and 5635.5 Å. The CN features at 6470-6490 Å were analysed to determine the abundances of nitrogen. The oxygen abundances were determined from the [O I] line at 6300 Å. Results. We provide abundances of C, N, and O for 88 giants in 28 open clusters and in two stars of the association Theia 1214. The results were compared with theoretical predictions and used for the analysis of the [C/N] relations with age, and we investigated the origin of the two Theia 1214 stars. Conclusions. Precise age dating requires separate age calibrations of [C/N] ratios for the first-ascent giants of the lower part of the red giant branch and for the red clump stars to account for the additional abundance alterations during the post-red giant branch luminosity bump evolution. In the first-ascent giant stars with larger turn-off masses, the observed C/N ratios are slightly higher than those predicted by standard models, and the obtained [C/N] versus age relation is flatter in the young age regime than in previous studies. We doubt that the two stars we investigated in the Theia 1214 association belong to the tail of NGC 752. Most probably, they are field stars.

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arXiv2026

Observational constraints on the origin of the elements. X. Combining NLTE and machine learning for chemical diagnostics of 4 million stars in the 4MIDABLE-HR survey

We present the 4MOST-HR resolution Non-Local Thermal Equilibrium (NLTE) Payne artificial neural network (ANN), trained on $404\,793$ new FGK spectra with 16 elements computed in NLTE. This network will be part of the Stellar Abundances and atmospheric Parameters Pipeline (SAPP), which will analyse 4 million stars during the five year long 4MOST consortium 4: 4MOST MIlky way Disc And BuLgE High-Resolution (4MIDABLE-HR) survey. A fitting algorithm using this ANN is also presented that is able to fully-automatically and self-consistently derive both stellar parameters and elemental abundances. The ANN is validated by fitting 121 observed spectra of low-mass FGKM type stars, including main-sequence dwarf, subgiant and giant stars down to [Fe/H] $\approx -3.3$ degraded to 4MOST-HR resolution of $R\approx20\,000$, and comparing the derived abundances with the output of the classical radiative transfer code TSFitPy. We are able to recover all 18 elemental abundances with a bias~$<0.13$ and spread~$<0.16$\,dex, although the typical values are $<0.09$ dex for most elements. These abundances are compared to the OMEGA+ Galactic Chemical Evolution model, showcasing for the first time, the expected performance and results obtained from high-resolution spectra of the quality expected to be obtained with 4MOST. The expected Galactic trends are recovered, and we highlight the potential of using many chemical elements to constrain the formation history of the Galaxy.

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arXiv2026

A method to derive self-consistent NLTE astrophysical parameters for 4 million high-resolution 4MOST stellar spectra in half a day with invertible neural networks

Modern spectroscopic surveys obtain spectra for millions of stars. However, classical spectroscopic methods can often be computationally expensive, rendering them impractical for the analysis of large datasets. We introduce a novel simulation-based deep-learning approach for the efficient analysis of high-resolution stellar spectra to be obtained with the upcoming high-resolution 4MOST spectrograph. We used a suite of synthetic non-local thermodynamic equilibrium (NLTE) spectra generated with Turbospectrum to mimic 4MOST observations and trained a conditional invertible neural network (cINN) for the purpose of predicting self-consistently stellar surface parameters and chemical abundances. The cINN is a neural network architecture that estimates full posterior distributions for the target stellar properties, providing an intrinsic uncertainty estimate. We evaluated the predictive performance of the trained cINN model on both synthetic data and observed spectra of stars. We found that our new cINN trained on NLTE synthetic spectra is capable of recovering stellar parameters with average errors ($σ$) of $33$ K for $T_\mathrm{eff}$, $0.16$ dex for $\log(g)$, and $0.12$ dex for [Fe/H], $0.1$ dex for [Ca/Fe], $0.11$ for [Mg/Fe], and $0.51$ dex for [Li/Fe], respectively, at a signal to noise ratio of 250 per Angstrom. From the analysis of the observed spectra of Gaia-ESO / 4MOST / PLATO benchmark stars, we verified that our NLTE estimates for stellar parameters and abundances are consistent with results obtained with the independent code TSFitPy. We conclude that the NLTE cINN is robust and can, theoretically, evaluate 4 million high-resolution 4MOST spectra in less than a day, using GPU acceleration.

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arXiv2025

Mapping the Ages of Stars with Chemistry

Chemical clocks, based on age-sensitive stellar abundance ratios, offer a powerful and scalable approach to reconstruct the formation history of the Milky Way. This white paper outlines how wide-field, high-resolution spectroscopy can transform chemical clocks into precise and broadly applicable stellar age estimators when combined with astrometry and asteroseismology. We summarize the current limitations, including calibration across Galactic environments and the impact of internal stellar evolution, and define the observational requirements needed to overcome them. The Wide-field Spectroscopic Telescope (WST), with its large field of view, high multiplex, and broad wavelength coverage at high spectral resolution, is uniquely suited to deliver the homogeneous datasets required to map the age structure of the Galaxy at unprecedented scale. Such a capability will enable decisive progress in Galactic archaeology and stellar evolution studies.

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arXiv2025

Transients as Determinants of Habitability

Stellar magnetic activity, manifested through spots (faculae and flares), fundamentally shapes the exoplanets' environments. For low-mass stars in particular, where most habitable-zone planets reside, the variable magnetic phenomena can dominate atmospheric chemistry, surface radiation levels, long-term atmospheric escape, and ultimately habitability. However, physical characteristics of these transients (e.g. energy and temperature) and their spectra remain ill-constrained due to limitations in cadence and magnitude access of current spectroscopic facilities. A next-generation 12-m class ground-based observatory equipped with integral-field spectroscopy (IFS) and multi-object spectroscopy (MOS) at R$\sim$4,000 and $\sim$40,000 offers a transformational opportunity to characterize stellar activity in the time domain across large samples of exoplanet host stars. Such a facility would enable simultaneous monitoring of continuum variability, chromospheric and coronal line diagnostics, and particle-accelerated flare signatures, resolving the physics driving space weather and quantifying its impact on planetary atmospheres.

astro-ph.IM↗

arXiv2023

The role of radial migration in open cluster and field star populations with Gaia dr3

The survival time of a star cluster depends on its total mass, density, and thus size, as well as on the environment in which it was born and in which lies. Its dynamical evolution is influenced by various factors such as gravitational effects of the Galactic bar, spiral structures, and molecular clouds. Overall, the factors that determine the longevity of a cluster are complex and not fully understood. This study aims to investigate if open clusters and field stars respond differently to the perturbations that cause radial migration. In particular, we aim at understanding the nature of the oldest surviving clusters. We compared the time evolution of the kinematic properties of two Gaia DR3 samples: the first sample is composed of $\sim$40 open clusters and the second one of $\sim$66,000 MSTO field stars. Both selected samples are composed of stars selected with the same quality criterion, belonging to the thin disc, in a similar metallicity range, located in the same Galactocentric region [7.5-9 kpc] and with ages >1 Gyr. We performed a statistical analysis comparing the properties of the samples of field stars and of open clusters. A qualitative comparison of kinematic and orbital properties reveals that clusters younger than 2-3 Gyr are more resistant to perturbations than field stars and they move along quasi-circular orbits. Conversely, clusters older than approximately 3 Gyr have more eccentric and inclined orbits than isolated stars in the same age range. Such orbits lead them to reach higher elevations on the Galactic plane, maximising their probability to survive several Gyr longer. A formal statistical analysis reveals that there are differences among the time evolution of most of the kinematic and orbital properties of field stars and open clusters. Our results suggest that oldest survived clusters are usually more massive and move on orbits with higher eccentricity.

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arXiv2021

Abundances of neutron-capture elements in thin- and thick-disc stars in the solar neighbourhood

The aim of this work is to determine abundances of neutron-capture elements for thin- and thick-disc F, G, and K stars in several sky fields near the north ecliptic pole and to compare the results with the Galactic chemical evolution models, to explore elemental gradients according to stellar ages, mean galactocentric distances, and maximum heights above the Galactic plane. The observational data were obtained with the 1.65m telescope at the Moletai Astronomical Observatory and a fibre-fed high-resolution spectrograph. Elemental abundances were determined using a differential spectrum synthesis with the MARCS stellar model atmospheres and accounting for the hyperfine-structure effects. We determined abundances of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu for 424 thin- and 82 thick-disc stars. The sample of thick-disc stars shows a clearly visible decrease in [Eu/Mg] with increasing [Fe/H] compared to the thin-disc stars, bringing more evidence of a different chemical evolution in these two Galactic components. Abundance correlation with age slopes for the investigated thin-disc stars are slightly negative for the majority of s-process dominated elements, while r-process dominated elements have positive correlations. Our sample of thin-disc stars with ages spanning from 0.1 to 9 Gyrs give the [Y/Mg]=0.022 ($\pm$0.015)-0.027 ($\pm$0.003)*age [Gyr] relation. For the thick-disc stars, when we also took data from other studies into account, we found that [Y/Mg] cannot serve as an age indicator. The radial [El/Fe] gradients in the thin disc are negligible for the s-process dominated elements and become positive for the r-process dominated elements. The vertical gradients are negative for the light s-process dominated elements and become positive for the r-process dominated elements. In the thick disc, the radial [El/Fe] slopes are negligible, and the vertical slopes are predominantly negative.

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arXiv2020

High-resolution Spectroscopic Study of Dwarf Stars in the Northern Sky: Lithium, Carbon, and Oxygen Abundances

Abundances of lithium, carbon, and oxygen have been derived using spectral synthesis for a sample of 249 bright F, G, and K Northern Hemisphere dwarf stars from the high-resolution spectra acquired with the VUES spectrograph at the Moletai Astronomical Observatory of Vilnius University. The sample stars have metallicities, effective temperatures, and ages between -0.7 and 0.4 dex; 5000 and 6900 K; 1 and 12 Gyr, accordingly. We confirm a so far unexplained lithium abundance decrease at supersolar metallicities - $A$(Li) in our sample stars, which drop by 0.7 dex in the [Fe/H] range from +0.10 to +0.55 dex. Furthermore, we identified stars with similar ages, atmospheric parameters, and rotational velocities, but with significantly different lithium abundances, which suggests that additional specific evolutionary factors should be taken into account while interpreting the stellar lithium content. Nine stars with predominantly supersolar metallicities, i.e. about 12 % among 78 stars with C and O abundances determined, have the C/O number ratios larger than 0.65, thus may form carbon-rich rocky planets. Ten planet-hosting stars, available in our sample, do not show a discernible difference from the stars with no planets detected regarding their lithium content.

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arXiv2019

High-resolution spectroscopic study of dwarf stars in the northern sky: Na to Zn abundances in two fields with radii of 20 degrees

New space missions, such as NASA TESS or ESA PLATO, will focus on bright stars, which have been largely ignored by modern large surveys, especially in the northern sky. Spectroscopic information is of paramount importance in characterising the stars and analysing planets possibly orbiting them, and in studying the Galactic disc evolution. The aim of this work was to analyse all bright (V < 8 mag) F, G, and K dwarf stars using high-resolution spectra in the selected sky fields near the northern celestial pole. The observations were carried out with the 1.65 m diameter telescope at the Molėtai Astronomical Observatory and a fibre-fed high-resolution spectrograph covering a full visible wavelength range (400-850 nm). The atmospheric parameters were derived using the classical equivalent width approach while the individual chemical element abundances were determined from spectral synthesis. For both tasks the one-dimensional plane-parallel LTE MARCS stellar model atmospheres were applied. Results. We determined the main atmospheric parameters, kinematic properties, orbital parameters, and stellar ages for 109 newly observed stars and chemical abundances of 23 chemical species for 249 F, G, and K dwarf stars observed in the present study and in our previous study. The [MgI/FeI] ratio was adopted to define the thin-disc ($α$-poor) and thick-disc ($α$-rich) stars in our sample. We explored the behaviour of 21 chemical species in the [El/FeI] versus [FeI/H] and [El/FeI] versus age planes, and compared the results with the latest Galactic chemical evolution models. We also explored [El/FeI] gradients according to the mean Galactocentric distances and maximum height above the Galactic plane.

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arXiv2019

Spectroscopy of Dwarf Stars Around the North Celestial Pole

New space missions (e.g., NASA-TESS and ESA-PLATO) will perform an analysis of bright stars in large fields of the celestial sphere searching for extraterrestrial planets. Asteroseismic observations will search for exoplanet-hosting stars with solar-like oscillations. In order to achieve all the goals, a full characterization of the stellar objects is important. However, accurate atmospheric parameters are available for less than 30% of bright dwarf stars of the solar neighborhood. In this study we observed high-resolution (R = 60,000) spectra for all bright (V < 8 mag) and cooler than F5 spectral class dwarf stars in the northern-most field of the celestial sphere with radius of 20° from the α(2000) = 161$^\circ$03 and δ(2000) = 86$^\circ$60 that is a center of one of the preliminary ESO-PLATO fields. Spectroscopic atmospheric parameters were determined for 140 slowly rotating stars, for 73% of them for the first time. The majority (83%) of the investigated stars are in the TESS object lists and all of them are in the preliminary PLATO field. Our results have no systematic differences when compared with other recent studies. Comparing our results for 39 stars with previous high-resolution spectral determinations, we find only a 7 $\pm$ 73 K difference in effective temperatures, 0.02 $\pm$ 0.09 in log g, and -0.02 $\pm$ 0.09 dex in metallicities. We also determined basic kinematic and orbital parameters for this sample of stars. From the kinematical point of view, almost all our stars belong to the thin disk substructure of the Milky Way. The derived galactocentric metallicity gradient is -0.066 $\pm$ 0.024 dex/kpc (2.5σ significance) and the vertical metallicity gradient is -0.102 $\pm$ 0.099 dex/kpc (1σ significance) that comply with the latest inside-out thin disk formation models, including those with stellar migration taken into account.

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arXiv2018

Variability analysis of δ Scuti candidate stars

The Hipparcos catalog contains stars suspected to be δ Scuti variables for which extensive ground-based observations and characterization of variability are necessary. Our aim was to characterize variability of 13 candidates to δ Scuti type stars. We obtained 24 215 CCD images and analyzed stellar light curves using the Period04 program. Twelve δ Scuti candidate stars have been characterized as pulsating with frequencies intrinsic to δ Scuti stars: HIP 2923, HIP 5526, HIP 5659, HIP 11090, HIP 17585, HIP 74155, HIP 101473, HIP 106219, HIP 107786, HIP 113487, HIP 115093, HIP 115856. Five of them (HIP 2923, HIP 5526, HIP 11090, HIP 115856 and HIP 106219) may be hybrid δ Scuti-γ Doradus pulsators. One more candidate, HIP 106223, is a variable star with longer periods of pulsations which are intrinsic to γ Doradus.

astro-ph.SR↗

arXiv2018

Chemical composition of giant stars in the open cluster IC 4756

Context: Homogeneous investigations of red giant stars in open clusters contribute to studies of internal evolutionary mixing processes inside stars, which are reflected in abundances of mixing-sensitive chemical elements like carbon, nitrogen, and sodium, while alpha- and neutron-capture element abundances are useful in tracing the Galactic chemical evolution. Aims: The main aim of this study is a comprehensive chemical analysis of red giant stars in the open cluster IC 4756, including determinations of 12C/13C and C/N abundance ratios, and comparisons of the results with theoretical models of stellar and Galactic chemical evolution. Methods: We used a classical differential model atmosphere method to analyse high-resolution spectra obtained with the FEROS spectrograph on the 2.2m MPG/ESO Telescope. The carbon, nitrogen, and oxygen abundances, 12C/13C ratios, and neutron-capture element abundances were determined using synthetic spectra, and the main atmospheric parameters and abundances of other chemical elements were determined from equivalent widths of spectral lines. Results: We have determined abundances of 23 chemical elements for 13 evolved stars and 12C/13C ratios for six stars of IC 4756. The mean metallicity of this cluster, as determined from nine definite member stars, is very close to solar - [Fe/H] = -0.02 +/- 0.01. Abundances of carbon, nitrogen, and sodium exhibit alterations caused by extra-mixing: the mean 12C/13C ratio is lowered to 19 +/- 1.4, the C/N ratio is lowered to 0.79 +/- 0.05, and the mean [Na/Fe] value, corrected for deviations from the local thermodynamical equilibrium encountered, is enhanced by 0.14 +/- 0.05 dex. We compared our results to those by other authors with theoretical models.

astro-ph.SR↗

arXiv2016

The extent of mixing in stellar interiors: the open clusters Collinder 261 and Melotte 66

Context: Determining carbon and nitrogen abundances in red giants provides useful diagnostics to test mixing processes in stellar atmospheres. Aims: Our main aim is to determine carbon-to-nitrogen and carbon isotope ratios for evolved giants in the open clusters Collinder 261 and Melotte 66 and to compare the results with predictions of theoretical models. Methods: High-resolution spectra were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C_2 Swan (0,1) band head at 5635.5 A. The wavelength interval 7940-8130 A, which contains CN features, was analysed to determine nitrogen abundances and carbon isotope ratios. The oxygen abundances were determined from the [O_I] line at 6300 A. Results: The mean values of the elemental abundances in Collinder 261, as determined from seven stars, are: [C/Fe]=-0.23 +- 0.02 (s.d.), [N/Fe]=0.18 +- 0.09, [O/Fe]=-0.03 +- 0.07. The mean 12^C/13^C ratio is 11 +- 2, considering four red clump stars and 18 for one star above the clump. The mean C/N ratios are 1.60 +- 0.30 and 1.74, respectively. For the five stars in Melotte 66 we obtained: [C/Fe]=-0.21 +- 0.07 (s.d.), [N/Fe]=0.17 +- 0.07, [O/Fe]=0.16 +- 0.04. The 12^C/13^C and C/N ratios are 8 +- 2 and 1.67 +- 0.21, respectively. Conclusions: The 12^C/13^C and C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolution models. The mean values of 12^C/13^C ratios in Collinder 261 and Melotte 66 agree well with models of thermohaline-induced extra-mixing for the corresponding stellar turn-off masses of about 1.1 - 1.2 Msun. The mean C/N ratios are not decreased as much as predicted by the model in which the thermohaline- and rotation-induced extra-mixing act together.

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arXiv2013

Stellar substructures in the solar neighbourhood. II. Abundances of neutron-capture elements in the kinematic Group 3 of the Geneva-Copenhagen survey

The evolution of chemical elements in a galaxy is linked to its star formation history. Variations in star formation history are imprinted in the relative abundances of chemical elements produced in different supernova events and asymptotic giant branch stars. We determine detailed elemental abundances of s- and r-process elements in stars belonging to Group3 of the Geneva-Copenhagen survey and compare their chemical composition with Galactic disc stars. The aim is to look for possible chemical signatures that might give information about the formation history of this kinematic group of stars, which is suggested to correspond to remnants of disrupted satellites. High-resolution spectra were obtained with the FIES spectrograph at the Nordic Optical Telescope, La Palma, and were analysed with a differential model atmosphere method. Comparison stars were observed and analysed with the same method. Abundances of chemical elements produced mainly by the s-process are similar to those in the Galactic thin-disc dwarfs of the same metallicity, while abundances of chemical elements produced predominantly by the r-process are overabundant. The similar elemental abundances are observed in Galactic thick-disc stars. The chemical composition together with the kinematic properties and ages of stars in Group3 of the Geneva-Copenhagen survey support a gas-rich satellite merger scenario as the most likely explanation for the origin. The similar chemical composition of stars in Group3 and the thick-disc stars might suggest that their formation histories are linked.

astro-ph.GA↗

arXiv2012

C, N, O abundances and carbon isotope ratios in evolved stars of the open clusters Collinder 261 and NGC 6253

Context. Investigations of abundances of carbon and nitrogen in the atmospheres of evolved stars of open clusters may provide comprehensive information on chemical composition changes caused by stellar evolution. Aims. Our main aim is to increase the number of open clusters with determined carbon-to nitrogen and carbon isotope ratios. Methods. High-resolution spectra were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C_2 Swan (0,1) band head at 5635.5 Å (FEROS spectra) and the C_2 Swan (1,0) band head at 4737 Å (UVES spectra). The wavelength interval 7980-8130 Å, with strong CN features was analysed to determine nitrogen abundances and 12^C/13^C isotope ratios. The oxygen abundances were determined from the [Oi] line at 6300 Å. Results. The average value of 12^C/13^C isotope ratios of Cr 261 is equal to 18 \pm 2 in four giants and to 12 \pm 1 in two clump stars; it is equal to 16 \pm 1 in four clump stars of the open cluster NGC 6253. The mean C/N ratios in Cr 261 and NGC 6253 are equal to 1.67 \pm 0.06 and 1.37 \pm 0.09, respectively. Conclusions. The 12^C/13^C and C/N values in Cr 261 and NGC 6253 within limits of uncertainties agree with the theoretical model of thermohaline-induced mixing as well as with the cool-bottom processing model

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arXiv2011

Chemical composition of evolved stars in the open cluster NGC 2506

In this study we present abundances of 12^C, 13^C, N, O and up to 26 other chemical elements in two first ascent giants and two core-helium-burning 'clump' stars of the open cluster NGC 2506. Abundances of carbon were derived using the C_2 Swan (0,1) band head at 5635.5 A. The wavelength interval 7940-8130 A, with strong CN features, was analysed in order to determine nitrogen abundances and carbon isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 A. NGC 2506 was found to have a mean [Fe/H]=-0.24 +- 0.05 (standard deviation). Compared with the Sun and other dwarf stars of the Galactic disc, mean abundances in the investigated clump stars suggest that carbon is depleted by about 0.2 dex, nitrogen is overabundant by about 0.3 dex and other chemical elements have abundance ratios close to solar. The C/N and 12^C/13^C ratios are lowered to 1.25 +- 0.27 and 11 +- 3, respectively.

astro-ph.SR↗

arXiv2011

Chemical composition of evolved stars in the open cluster IC 4651

We present an analysis of high-resolution spectra of three core-helium-burning "clump" stars and two first ascent giants in the open cluster IC 4651. Atmospheric parameters (T_eff, log_g, v_t, and [Fe/H]) were determined in our previous study by Carretta et al. (2004). In this study we present abundances of C, N, O and up to 24 other chemical elements. Abundances of carbon were derived using the C_2 Swan (0,1) band head at 5635.5 A. The wavelength interval 7980-8130 A, with strong CN features, was analysed in order to determine nitrogen abundances and 12^C/13^C isotope ratios. The oxygen abundances were determined from the [O i] line at 6300 A. Compared with the Sun and other dwarf stars of the Galactic disk, mean abundances in the investigated clump stars suggest that carbon is depleted by about 0.3 dex, nitrogen is overabundant by about 0.2 dex and oxygen is close to solar. This has the effect of lowering the mean C/N ratio to 1.36 +- 0.11. The mean 12^C/13^C ratios are lowered to 16 +- 2. Other investigated chemical elements have abundance ratios close to the solar ones.

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