Papers produced by group members

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  1. We present our models of the effect of binaries on high-resolution spectroscopic surveys. We want to determine how many binary stars will be observed, whether unresolved binaries will contaminate measurements of chemical abundances, and how we can use spectroscopic surveys to better constrain the population of binary stars in the Galaxy. Using a rapid binary-evolution algorithm that enables modelling of the most complex binary systems we generate a series of large binary populations in the Galactic disc and evaluate the results. As a first application we use our model to study the binary fraction in APOGEE giants. We find tentative evidence for a change in binary fraction with metallicity.
  2. Context. The pattern of chemical abundance ratios in stellar populations of the Milky Way is a fingerprint of the Galactic chemical history. In order to interpret such chemical fossils of Galactic archaeology, chemical evolution models have to be developed. However, despite the complex physics included in the most recent models, significant discrepancies between models and observations are widely encountered.
    Aims: The aim of this paper is to characterise the abundance patterns of five iron-peak elements (Mn, Fe, Ni, Cu, and Zn) for which the stellar origin and chemical evolution are still debated.
    Methods: We automatically derived iron peak (Mn, Fe, Ni, Cu, and Zn) and α element (Mg) chemical abundances for 4666 stars, adopting classical LTE spectral synthesis and 1D atmospheric models. Our observational data collection is composed of high-resolution, high signal-to-noise ratios HARPS and FEROS spectra, which were previously parametrised by the AMBRE project.
    Results: We used the bimodal distribution of the magnesium-to-iron abundance ratios to chemically classify our sample stars into different Galactic substructures: thin disc, metal-poor and high-α metal rich, high-α, and low-α metal-poor populations. Both high-α and low-α metal-poor populations are fully distinct in Mg, Cu, and Zn, but these substructures are statistically indistinguishable in Mn and Ni. Thin disc trends of [Ni/Fe] and [Cu/Fe] are very similar and show a small increase at supersolar metallicities. Also, both thin and thick disc trends of Ni and Cu are very similar and indistinguishable. Yet, Mn looks very different from Ni and Cu. [Mn/Fe] trends of thin and thick discs actually have noticeable differences: the thin disc is slightly Mn richer than the thick disc. The [Zn/Fe] trends look very similar to those of [α/Fe] trends. The typical dispersion of results in both discs is low (≈0.05 dex for [Mg, Mn, and Cu/Fe]) and is even much lower for [Ni/Fe] (≈0.035 dex).
    Conclusions: It is clearly demonstrated that Zn is an α-like element and could be used to separate thin and thick disc stars. Moreover, we show that the [Mn/Mg] ratio could also be a very good tool for tagging Galactic substructures. From the comparison with Galactic chemical evolutionary models, we conclude that some recent models can partially reproduce the observed Mg, Zn, and, Cu behaviours in thin and thick discs and metal-poor sequences. Models mostly fail to reproduce Mn and Ni in all metallicity domains, however, models adopting yields normalised from solar chemical properties reproduce Mn and Ni better, suggesting that there is still a lack of realistic theoretical yields of some iron-peak elements. The very low scatter (≈0.05 dex) in thin and thick disc sequences could provide an observational constrain for Galactic evolutionary models that study the efficiency of stellar radial migration. Based on observations collected at ESO telescopes under the AMBRE programme. Full Table 5 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/A22
  3. Table 5 contains Chemical abundances of iron-peak elements and magnesium in the solar neighbourhood. (1 data file).
  4. High-resolution spectral analysis is performed for the first time in evolved stars of two young open clusters: NGC 4609 and NGC 5316, of about 80 and 100 Myr in age, respectively, and turn-off masses above 5 M. Stellar evolution models predict an extra-mixing event in evolved stars, which follows the first dredge-up and happens later on the red giant branch. However, it is still not understood how this process affects stars of different masses. In this study, we determine abundances of the mixing sensitive elements carbon and nitrogen, carbon isotope 12C/13C ratios, as well as 20 other elements produced by different nucleosynthetic processes (O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu). We compared our results with the latest theoretical models of evolutionary mixing processes. We find that the obtained 12C/13C and C/N ratios and [Na/Fe] agree quite well with the model which takes into account thermohaline- and rotation-induced mixing but within error limits also agree with the standard first dredge-up model. Comparison of oxygen, magnesium, and other α-elements with theoretical models of Galactic chemical evolution revealed that both clusters follow the thin disc α-element trends. Neutron-capture element abundances in NGC 4609 are apparently reflecting its birthplace in the thin disc, while NGC 5316 has marginally higher abundances, which would indicate its birthplace in an environment more enriched with neutron-capture elements.
  5. We present the current status of CNO abundance investigations in evolved stars of Galactic open clusters observed in the currently ongoing Gaia-ESO survey. The spectra were observed with the VLT UVES spectrograph and analysed using a differential model atmosphere method. The C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolutionary models. For the corresponding stellar turn-off masses from 1.15 to 3.3 M, the observed C/N ratio values are close to the predictions of standard first dredge-up and thermohaline extra-mixing models. The recent model in which the thermohaline- and rotation-induced extra-mixing act together seems to provide C/N values that are too low.

  6. Aims: Our main aim is to determine carbon-to-nitrogen and carbon isotope ratios for evolved giants in the open clusters NGC 2324, NGC 2477, and NGC 3960, which have turn-off masses of about 2 M, and to compare them with predictions of theoretical models.
    Methods: High-resolution spectra were analysed using a differential synthetic spectrum method. Abundances of carbon were derived using the C2 Swan (0, 1) band heads at 5135 and 5635.5 Å. The wavelength interval 7940-8130 Å with strong CN features was analysed to determine nitrogen abundances and carbon isotope ratios. The oxygen abundances were determined from the [O i] line at 6300 Å.
    Results: The mean values of the CNO abundances are [C/Fe] = -0.35 ± 0.06 (s.d.), [N/Fe] = 0.28 ± 0.05, and [O/Fe] = -0.02 ± 0.10 in seven stars of NGC 2324; [C/Fe] = -0.26 ± 0.02, [N/Fe] = 0.39 ± 0.04, and [O/Fe] = -0.11 ± 0.06 in six stars of NGC 2477; and [C/Fe] = -0.39 ± 0.04, [N/Fe] = 0.32 ± 0.05, and [O/Fe] = -0.19 ± 0.06 in six stars of NGC 3960. The mean C/N ratio is equal to 0.92 ± 0.12, 0.91 ± 0.09, and 0.80 ± 0.13, respectively. The mean 12C /13C ratio is equal to 21 ± 1, 20 ± 1, and 16 ± 4, respectively. The 12C /13C and C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolution models.
    Conclusions: The mean values of the 12C /13C and C/N ratios in NGC 2324 and NGC 2477 agree well with the first dredge-up and thermohaline-induced extra-mixing models, which are similar for intermediate turn-off mass stars. The 12C /13C ratios in the investigated clump stars of NGC 3960 span from 10 to 20. The mean carbon isotope and C/N ratios in NGC 3960 are close to predictions of the model in which the thermohaline- and rotation-induced (if rotation velocity at the zero-age main sequence was 30% of the critical velocity) extra-mixing act together. Based on observations collected at ESO telescopes under programmes 072.D-0550 and 074.D-0571.
  7. We provide CNO and Fe abundance investigations for a sample of up to 45 NGC 1851 giants. High-resolution spectra were obtained with the VLT UVES spectrograph in the framework of the Gaia-ESO Survey. The stars in our sample can be separated into two groups with a difference of 0.1 dex in the mean metallicity, 0.3 dex in the mean C/N, and no significant difference in the mean values of C+N+O.
  8. The Gaia-ESO Survey was designed to target all major Galactic components (i.e. bulge, thin and thick discs, halo and clusters), with the goal of constraining the chemical and dynamical evolution of the Milky Way. This paper presents the methodology and considerations that drive the selection of the targeted, allocated and successfully observed Milky Way field stars. The detailed understanding of the survey construction, specifically the influence of target selection criteria on observed Milky Way field stars is required in order to analyse and interpret the survey data correctly. We present the target selection process for the Milky Way field stars observed with Very Large Telescope/Fibre Large Array Multi Element Spectrograph and provide the weights that characterize the survey target selection. The weights can be used to account for the selection effects in the Gaia-ESO Survey data for scientific studies. We provide a couple of simple examples to highlight the necessity of including such information in studies of the stellar populations in the Milky Way.
  9. 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 C2 Swan (0, 1) band head at 5635.5 Å. The wavelength interval 7940-8130 Å, 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 Å.
    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 12C /13C 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 12C /13C and C/N ratios are 8 ± 2 and 1.67 ± 0.21, respectively.
    Conclusions: The 12C /13C 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 12C /13C 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 M. 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. Based on observations collected at ESO telescopes under Guaranteed Time Observation programmes 071.D-0065, 072.D-0019, and 076.D-0220.
  10. Asymptotic giant branch stars play an important role in enriching galaxies by s-process dominated elements. Recent studies showed that their role in producing neutron-rich elements in the Galactic disk was underestimated and should be reconsidered. We have derived abundances of neutron-capture elements in seven Galactic open clusters to further expand an observational dataset necessary for theoretical modelling of the Galactic chemical evolution. We present elemental enrichment patterns of the Galaxy, based on accurate ages, galactocentric distances and chemical composition of open clusters determined in this and other recent studies.
  11. Observations were conducted with the FLAMES (Fiber Large Array Multi-Element Spectrograph) multi-fiber facility in spring of 2012 and 2013. Spectra of high-resolving power (R~47000) were obtained with UVES (Ultraviolet and Visual Echelle Spectrograph) The spectra were exposed onto two CCDs, resulting in a wavelength coverage of 4700-6840Å with a gap of about 50Å in the centre. (6 data files).
  12. It has been suspected already more than thirty year ago that NGC 1851 is not chemically homogeneous. By now, it is clear that NGC 1851 has two distinct subgiant branches, however explanations of their origin so far lack consensus. Some authors explain them by two generations of stars, the first being primordial, while the second one being born from the ejecta of a fraction of the stars of the earlier one. There are suggestions that NGC 1851 might be the result of a merger of two globular clusters, or originated as the nucleus of a dwarf galaxy that was captured by the Milky Way. In this presentation, we provide a crucial missing information on CNO abundances determined in a homogeneous way for a large sample of NGC 1851 giants. High-resolution spectra were obtained with the VLT UVES spectrograph in a framework of the Gaia-ESO Survey. From the investigated stars we clearly see that the two NGC 1851 populations have by about 0.2 dex difference in metallicity, the sums of C+O+N differ by about 0.1 dex, the mean C/N ratio values differ by about 0.5 dex, chemical elements that are insensitive to internal stellar mixing show normal Galactic abundances of the corresponding metallicities. This leads us to the conclusion that NGC 1851 is a binary cluster. We provide interpretations of these and other results of the study.
  13. Determinations of carbon and nitrogen abundances in red giants provide useful diagnostic data for testing of mixing processes in stellar atmospheres. Observations already have provided proves not only of the first dredge-up, which brings the CN-processed material up to the surfaces of low-mass stars when they reach the bottom of the red giant branch, but also show evidence of extra-mixing, which happens later on the giant branch. Theoretical models of thermohaline- and rotation-induced extra-mixing currently are in most intense development. The influence of thermohaline mixing and rotation is different in stars of various masses and still needs more observational data in order to be robustly treated. We present new observational data of C and N abundances and carbon isotope ratios in giants and clump stars of ten open clusters with different turn-off masses. Taken together with results of our previous studies, they are used to evaluate the theoretical models of extra-mixing.
  14. We obtained high-resolution spectra of the programme and comparison stars with the Fibre-fed Echelle Spectrograph on the Nordic Optical 2.5 m telescope (NOT) during 2008, 2011, and 2012. (2 data files).
  15. Context. A combined study of kinematics and chemical composition of stars is one of the most promising tools of research in Galaxy formation. The main goal in this field of research is to reconstruct the formation history of our Galaxy, to reveal the origin of the thick disc, and to find remnants of ancient mergers.
    Aims: We determine detailed elemental abundances in stars belonging to the so-called Group 1 of the Geneva-Copenhagen survey (GCS) and compare the chemical composition with the Galactic thin- and thick-disc stars, with the GCS Group 2 and Group 3 stars, as well as with several kinematic streams of similar metallicities. The aim is to search for chemical signatures that might give information about the formation history of this kinematic group of stars.
    Methods: High-resolution spectra were obtained with the Fibre-fed Echelle Spectrograph 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.
    Results: The average value of [Fe/H] for the 37 stars of Group 1 is -0.20 ± 0.14 dex. Investigated Group 1 stars can be separated into three age subgroups. Along with the main 8- and 12-Gyr-old populations, a subgroup of stars younger than 5 Gyr can be separated as well. Abundances of oxygen, α-elements, and r-process dominated elements are higher than in Galactic thin-disc dwarfs. This elemental abundance pattern has similar characteristics to that of the Galactic thick disc and differs slightly from those in Hercules, Arcturus, and AF06 stellar streams.
    Conclusions: The similar chemical composition of stars in Group 1, as well as in Group 2 and 3, with that in stars of the thick disc might suggest that their formation histories are linked. The chemical composition pattern together with the kinematic properties and ages of stars in the investigated GCS groups provide evidence of their common origin and possible relation to an ancient merging event. A gas-rich satellite merger scenario is proposed as the most likely origin. Tables 4 and 5 are available in electronic form at http://www.aanda.org
  16. Context. The Gaia-ESO Public Spectroscopic Survey will observe a large sample of clusters and cluster stars, covering a wide age-distance-metallicity-position-density parameter space.
    Aims: We aim to determine C, N, and O abundances in stars of Galactic open clusters of the Gaia-ESO survey and to compare the observed abundances with those predicted by current stellar and Galactic evolution models. In this pilot paper, we investigate the first three intermediate-age open clusters.
    Methods: High-resolution spectra, observed with the FLAMES-UVES spectrograph on the ESO VLT, were analysed using a differential model atmosphere method. Abundances of carbon were derived using the C2 band heads at 5135 and 5635.5 Å. The wavelength interval 6470-6490 Å, with CN features, was analysed to determine nitrogen abundances. Oxygen abundances were determined from the [O i] line at 6300 Å.
    Results: The mean values of the elemental abundances in Trumpler 20 as determined from 42 stars are: [ Fe/H ] = 0.10 ± 0.08 (s.d.), [ C/H ] = -0.10 ± 0.07, [ N/H ] = 0.50 ± 0.07, and consequently C/N = 0.98 ± 0.12. We measure from five giants in NGC 4815: [ Fe/H ] = -0.01 ± 0.04, [ C/H ] = -0.17 ± 0.08, [ N/H ] = 0.53 ± 0.07, [ O/H ] = 0.12 ± 0.09, and C/N = 0.79 ± 0.08. We obtain from 27 giants in NGC 6705: [ Fe/H ] = 0.0 ± 0.05, [ C/H ] = -0.08 ± 0.06, [ N/H ] = 0.61 ± 0.07, [ O/H ] = 0.13 ± 0.05, and C/N = 0.83 ± 0.19. The C/N ratios of stars in the investigated open clusters were compared with the ratios predicted by stellar evolutionary models. For the corresponding stellar turn-off masses from 1.9 to 3.3 M, the observed C/N ratio values are very close to the predictions of standard first dredge-up models as well as to models of thermohaline extra-mixing. They are not decreased as much as predicted by the recent model in which the thermohaline- and rotation-induced extra-mixing act together. The average [O/H] abundance ratios of NGC 4815 and NGC 6705 are compared with the predictions of two Galactic chemical evolution models. The data are consistent with the evolution at the solar radius within the errors.
    Conclusions: The first results of CNO determinations in open clusters show the potential of the Gaia-ESO Survey to judge stellar and Galactic chemical evolution models and the validity of their physical assumptions through a homogeneous and detailed spectral analysis. Based on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey, PIs G. Gilmore and S. Randich).
  17. We have started a study of chemical composition of a new kinematically identified group of stars in the Galactic disc. Based on dynamical properties those stars were suspected to belong to a disrupted satellite. The main atmospheric parameters and chemical composition were determined for thirty-two stars from high resolution spectra obtained at the Nordic Optical Telescope with the spectrograph FIES. In this contribution the preliminary results of chemical composition study are presented. The metallicity of the investigated stars lie in the interval -0.2 < [Fe/H] < -0.6, their abundances of oxygen and alpha-elements are overabundant in comparison to the Galactic thin disc dwarfs at this metallicity range. This provides further evidences of their common and possibly extragalactic origin.

  18. Aims: Until recently, most high-resolution spectroscopic studies of the Galactic thin and thick discs were mostly confined to objects in the solar vicinity. Here we aim at enlarging the volume in which individual chemical abundances are used to characterise the thin and thick discs, using the first internal data release of the Gaia-ESO survey (GES iDR1).
    Methods: We used the spectra of around 2000 FGK dwarfs and giants from the GES iDR1, obtained at resolutions of up to R ~ 20 000 with the FLAMES/GIRAFFE spectrograph. We derive and discuss the abundances of eight elements (Mg, Al, Si, Ca, Ti, Fe, Cr, Ni, and Y).
    Results: We show that the trends of these elemental abundances with iron are very similar to those in the solar neighbourhood. We find a natural division between α-rich and α-poor stars, best seen in the bimodality of the [Mg/M] distributions in bins of metallicity, which we attribute to thick- and thin-disc sequences, respectively. This separation is visible for most α-elements and for aluminium. With the possible exception of Al, the observed dispersion around the trends is well described by the expected errors, leaving little room for astrophysical dispersion. Using previously derived distances from the first paper from this series for our sample, we further find that the thick-disc is more extended vertically and is more centrally concentrated towards the inner Galaxy than the thin-disc, which indicates a shorter scale-length. We derive the radial (4 to 12 kpc) and vertical (0 to 3.5 kpc) gradients in metallicity, iron, four α-element abundances, and aluminium for the two populations, taking into account the identified correlation between RGC and | Z |. Similarly to other works, a radial metallicity gradient is found in the thin disc. The positive radial individual [α/M] gradients found are at variance from the gradients observed in the RAVE survey. The thin disc also hosts a negative vertical metallicity gradient in the solar cylinder, accompanied by positive individual [α/M] and [Al/M] gradients. The thick-disc, on the other hand, presents no radial metallicity gradient, a shallower vertical metallicity gradient than the thin-disc, an α-elements-to-iron radial gradient in the opposite sense than that of the thin disc, and positive vertical individual [α/M] and [Al/M] gradients. We examine several thick-disc formation scenarii in the light of these radial and vertical trends. Based on observations collected at ESO telescopes under Gaia-ESO survey programme.Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A33
  19. Table2 contains chemical abundances of 1916 stars from GES DR1. (1 data file).
  20. Context. From correlations between orbital parameters, several new coherent groups of stars were recently identified in the Galactic disc and suggested to correspond to remnants of disrupted satellites. To reconstruct their origin at least three main observational parameters - kinematics, chemical composition and age - must be known.
    Aims: We determine detailed elemental abundances in stars belonging to the so-called Group 2 of the Geneva-Copenhagen Survey and compare the chemical composition with Galactic thin- and thick-disc stars, as well as with the Arcturus and AF06 streams (Arifyanto & Fuchs 2006, A&A, 449, 533). The aim is to search for chemical signatures that might give information about the formation history of this kinematic group of stars.
    Methods: 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.
    Results: The average value of [Fe/H] for the 32 stars of Group 2 is - 0.42 ± 0.10 dex. The investigated group consists mainly of two 8- and 12-Gyr-old stellar populations. Abundances of oxygen, α-elements, and r-process-dominated elements are higher than in Galactic thin-disc dwarfs. This elemental abundance pattern has similar characteristics as that of the Galactic thick-disc.
    Conclusions: The similarity in chemical composition of stars in Group 2 with that in stars of the thick-disc might suggest that their formation histories are linked. The chemical composition together with the kinematic properties and ages of stars in the stars investigated provides evidence of their common origin and possible relation to an ancient merging event. A gas-rich satellite merger scenario is proposed as the most likely origin. Groups 2 and 3 of the Geneva-Copenhagen Survey might have originated in the same merging event. Tables 4 and 5 are available in electronic form at http://www.aanda.org
  21. We study the chemical composition of two kinematically identified groups of stars in the Galactic disc. Based on dynamical properties these stars were suspected to belong to disrupted satellites. Using high resolution spectra obtained with the spectrograph FIES at the Nordic Optical Telescope, La Palma, we determine detailed elemental abundances of elements and look for possible chemical signatures that might give information about the formation history of these possibly accreted kinematic groups of stars. Our results reveal that abundances of chemical elements produced mainly by the r-process are overabundant and those mainly produced by the s-process are the same as in Galactic thin-disc dwarfs and models. The similar elemental abundance patterns were observed in the Galactic thick-disc stars. Similar chemical composition of project stars and the thick-disc stars might suggest that their formation histories are linked. The homogeneous chemical composition inside each of the groups together with their kinematic properties provide additional evidences of their common origin and possible relation to ancient merging events.
  22. In order to investigate how magnetic activity influences a stellar evolution, we undertake a detailed study of photospheric abundances in a sample of RS CVn stars. Using the Nordic Optical Telescope we investigate abundances of more than 20 chemical elements, including carbon isotopes, nitrogen and other mixing-sensitive species. In this presentation we report on current results of the analysis, among which there are first evidences that extra-mixing processes may start acting in low-mass chromospherically active stars below a bump of the luminosity function of red giants.
  23. Context. 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.
    Aims: We determine detailed elemental abundances of s- and r-process elements in stars belonging to Group 3 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.
    Methods: 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.
    Results: 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.
    Conclusions: The chemical composition together with the kinematic properties and ages of stars in Group 3 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 Group 3 and the thick-disc stars might suggest that their formation histories are linked.
  24. In this work we present the main atmospheric parameters, carbon, nitrogen and oxygen abundances, and 12C/13C ratios determined in a sample of 28 Galactic clump stars. Abundances of carbon were studied using the C2 band at 5086.2 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. The mean abundances of C, N and O abundances in the investigated clump stars support our previous estimations that, compared to the Sun and dwarf stars of the Galactic disc, carbon is depleted by about 0.2 dex, nitrogen is enhanced by 0.2 dex and oxygen is close to abundances in dwarfs. The 12C/13C and C/N ratios for galactic red clump stars analysed were compared to the evolutionary models of extra-mixing. The steeper drop of 12C/13C ratio in the model of thermohaline mixing by Charbonnel & Lagarde better reflects the observational data at low stellar masses than the more shallow model of cool bottom processing by Boothroyd & Sackmann. For stars of about 2 M masses a modelling of rotationally induced mixing should be considered with rotation of about 250 km s-1 at the time when a star was at the hydrogen-core-burning stage.
  25. Context. Galactic archeology is a powerful tool for investigating the formation and evolution of the Milky Way. We use this technique to study kinematic groups of F- and G-stars in the solar neighbourhood. From correlations between orbital parameters, three new coherent groups of stars were recently identified and suggested to correspond to remnants of disrupted satellites.
    Aims: We determine detailed elemental abundances in stars belonging to one of these groups and compare their chemical composition with Galactic disc stars. The aim is to look for possible chemical signatures that might give information about the history of this kinematic group of stars.
    Methods: High-resolution spectra were obtained with the FIES spectrograph at the Nordic Optical Telescope, La Palma, and analysed with a differential model atmosphere method. Comparison stars were observed and analysed with the same method.
    Results: The average value of [Fe/H] for the 20 stars investigated in this study is -0.69 ± 0.05 dex. Elemental abundances of oxygen and α-elements are overabundant in comparison with Galactic thin-disc dwarfs and thin-disc chemical evolution models. This abundance pattern has similar characteristics as the Galactic thick-disc.
    Conclusions: The homogeneous chemical composition together with the kinematic properties and ages of stars in the investigated Group 3 of the Geneva-Copenhagen survey provides evidence of their common origin and possible relation to an ancient merging event. The similar chemical composition of stars in the investigated group and the thick-disc stars might suggest that their formation histories are linked. Table 3 is available in electronic form at http://www.aanda.org
  26. 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 C2 Swan (0, 1) band head at 5635.5 Å (FEROS spectra) and the C2 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 12C/13C isotope ratios. The oxygen abundances were determined from the [O i] line at 6300 Å.
    Results: The average value of 12C/13C isotope ratios of Cr 261 is equal to 18 ± 2 in four giants and to 12 ± 1 in two clump stars; it is equal to 16 ± 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 ± 0.06 and 1.37 ± 0.09, respectively.
    Conclusions: The 12C/13C 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. Based on observations collected at ESO telescopes under programmes 65.N-0286, 169.D-0473.
  27. We present detailed analysis of two groups of F- and G- type stars originally found to have similarities in their orbital parameters. The distinct kinematic properties suggest that they might originate from ancient accretion events in the Milky Way. From high resolution spectra taken with the spectrograph FIES at the Nordic Optical Telescope, La Palma, we determined abundances of oxygen, alpha- and r-process elements. Our results indicate that the sample of investigated stars is chemically homogeneous and the abundances of oxygen, alpha and r-process elements are overabundant in comparison with Galactic disk dwarfs. This provides the additional evidence that those stellar groups had the common formation and possible origin from disrupted satellites.
  28. The carbon and nitrogen abundances, C/N and especially carbon isotope ratios 12C / 13C are key tools for stellar evolution studies. In this presentation we overview available up to date analyses of C and N abundances in red clump stars of open clusters along with our recent results obtained for the open clusters NGC 6134 and IC 4651. The clump stars have accumulated all chemical composition changes, which have happened during their evolution along the giant branch and during the helium flash, thus are very trustful sources of information. A comparison of the observational data with theoretical models of stellar evolution shows that processes of extra-mixing in stars of 2-3 M turn-off masses are larger than predicted.
  29. We present the preliminary results of a project aimed at high resolution spectral analysis of stars in a kinematically identified stellar group, suspected to belong to a remnant of a disrupted satellite galaxy. The 16 stars analysed by now have a metallicity around - 0. 7 dex, an average isochrone age of about 12 Gyr, their chemical composition is homogeneous and distinct from the Galactic disk dwarfs. This provides further evidence of their common and maybe extragalactic origin.
  30. Hipparcos data have allowed the identification of a large number of clump stars in the solar neighbourhood. We discuss our present knowledge of their distributions of metallicities, CNO abundances, carbon isotope ratios and memberships of the first ascent giants and helium-core-burning stars.
  31. The detailed chemical composition of the atmosphere AY Cet (HD 7672) is determined from a high-resolution spectrum in the optical region. The main atmospheric parameters and the abundances of 22 chemical elements, including key species such as 12C, 13C, N, and O, are determined. A differential line analysis gives T_eff=5080 K, log g=3.0, [Fe/H]=-0.33, [C/Fe]=-0.17, [N/Fe]=0.17, [O/Fe]=0.05, C/N=1.58, and 12C/13C=21. Despite the high chromospheric activity, the optical spectrum of AY Cet provides a chemical composition typical for first ascent giants after the first dredge-up.
  32. In this study we present abundances of 12C, 13C, 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 C2 Swan (0,1) band head at 5635.5 Å. The wavelength interval 7940-8130 Å, 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 Å. 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 12C/13C ratios are lowered to 1.25 ± 0.27 and 11 ± 3, respectively.
  33. 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 (Teff, log g, vt and [Fe/H]) were determined in our previous study by Carretta et al. In this study, we present abundances of C, N, O and up to 24 other chemical elements. Abundances of carbon were derived using the C2 Swan (0, 1) band head at 5635.5 Å. The wavelength interval 7980-8130 Å, with strong CN features, was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. 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 0.3 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 12C/13C ratios are lowered to 16 ± 2. Other investigated chemical elements have abundance ratios close to the solar ones. a Star numbers, V and B-V from Lindoff (1972).
  34. The paper presents the design and development of English-Lithuanian-English dictionarylexicon tool and lexicon database management system for MT. The system is oriented to support two main requirements: to be open to the user and to describe much more attributes of speech parts as a regular dictionary that are required for the MT. Programming language Java and database management system MySql is used to implement the designing tool and lexicon database respectively. This solution allows easily deploying this system in the Internet. The system is able to run on various OS such as: Windows, Linux, Mac and other OS where Java Virtual Machine is supported. Since the modern lexicon database managing system is used, it is not a problem accessing the same database for several users.
  35. This article overviews the current state of the English-Lithuanian-English machine translation system. The first part of the article describes the problems that system poses today and what actions will be taken to solve them in the future. The second part of the article tackles the main issue of the translation process. Article briefly overviews the word sense disambiguation for MT technique using Google.
  36. Abundances of 22 chemical elements, including the key elements and isotopes such as 12C, 13C, N and O, are investigated in the spectrum of 33 Psc, a single-lined RS CVn-type binary of low magnetic activity. The high resolution spectra were observed on the Nordic Optical Telescope and analyzed with the MARCS model atmospheres. The following main parameters have been determined: T eff = 4750 K, log g = 2.8, [Fe/H] = -0.09, [C/Fe] = -0.04, [N/Fe] = 0.23, [O/Fe] = 0.05, C/N = 2.14, 12C/13C = 30, which show the first-dredge-up mixing signatures and no extra-mixing.
  37. The Hipparcos orbiting observatory has revealed a large number of helium-core-burning ‘clump’ stars in the Galactic field. These low-mass stars exhibit signatures of extra mixing processes that require modelling beyond the first dredge-up of standard models. The 12C/13C ratio is the most robust diagnostic of deep mixing because it is insensitive to the adopted stellar parameters. In this paper we present 12C/13C determinations in a sample of 34 Galactic clump stars as well as abundances of nitrogen, carbon and oxygen. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. Compared with the Sun and 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 enhanced by 0.2 dex and oxygen is close to abundances in dwarfs. Comparisons to evolutionary models show that the stars fall into two groups: one is of first ascent giants with carbon isotope ratios altered according to the first dredge-up prediction and the other is of helium-core-burning stars with carbon isotope ratios altered by extra mixing. The stars investigated fall to these groups in approximately equal numbers.
  38. The main atmospheric parameters and abundances of the iron-group elements (vanadium, chromium, iron, cobalt and nickel) are determined for 62 red giant `clump' stars revealed in the Galactic field by the Hipparcos orbiting observatory. The stars form a homogeneous sample with the mean value of temperature Teff = 4750 +/- 160K, of surface gravity log g = 2.41 +/- 0.26 and the mean value of metallicity [Fe/H] = -0.04 +/- 0.15dex. A Gaussian fit to the [Fe/H] distribution produces the mean <[Fe/H]> = -0.01 and dispersion σ[Fe/H] = 0.08. The near-solar metallicity and small dispersion of σ[Fe/H] of clump stars of the Galaxy obtained in this paper confirm the theoretical model of the Hipparcos clump by Girardi & Salaris. This suggests that nearby clump stars are (in the mean) relatively young objects, reflecting mainly the near-solar metallicities developed in the local disc during the last few Gyr of its history. We find iron-group element to iron-abundance ratios in clump giants to be close to solar.
  39. We present an analysis of high-resolution spectra of six core-helium-burning `clump' stars in the open cluster NGC 6134. Atmospheric parameters (Teff, logg, vt 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 C2 Swan (0,1) band head at 5635.5 Å (FEROS spectra) and the C2 Swan (1,0) band head at 4737 Å (UVES spectra). The wavelength interval 7980-8130 Å, with strong CN features, was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [OI] line at 6300 Å. Compared to 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 oxygen is underabundant by about 0.1 dex. This has the effect of lowering the mean C/N ratio to 1.2 +/- 0.2. The mean 12C/13C ratios are lowered to 9 +/- 2.5. Concerning other chemical elements, the analysis of sodium and magnesium lines, lines of other α-elements, iron-group and heavier chemical elements gave abundance ratios close to the solar ones. Based on observations collected at ESO telescopes under programmes 65.N-0286 and in part 169.D-0473 E-mail: sarunas.mikolaitis@tfai.vu.lt
  40. Hipparcos orbiting observatory has revealed a large number of helium-core- burning “clump” stars of the Galactic field. These low-mass stars exhibit signatures of extra-mixing processes that require modeling beyond the standard stellar theory. In this contribution we overview available results of 12C, 13C, N and O abundances obtained by high-resolution spectra for clump stars and discuss them in the light of current predictions of stellar evolution models.
  41. From high resolution spectra taken with the spectrograph FIES on the Nordic Optical Telescope, La Palma, we measure abundances of oxygen and α-elements in order to characterize stars which from their dynamical properties are suspected to have originated in disrupted satellites. We find that the chemical composition of investigated stars is homogeneous and distinct from Galactic disk dwarfs, which is providing further evidence of their extragalactic origin.
  42. We present a gridified stellar energy flux modelling software SYNTSPEC for stellar spectra analysis. It is an example of data- and compute-intensive application running on the testbed of the Enabling Grids for E-sciencE (EGEE) Grid compatible infrastructure, which brings the new quality to the research in astrophysics. The multi job application is running within the GRIDCOM system - a user friendly interface that allows a virtual work of a physically spread scientific group. The SYNTSPEC software calculates stellar energy fluxes and normalized to the continuum spectra that are applied for stellar classification and determination of chemical compositions, effective temperatures, surface gravities and other parameters of stars. The SYNTSPEC application benefits from usage of large computing resources, which makes possible calculations of synthetic stellar spectra for significant wavelength ranges and numbers of stellar parameter combinations. The specific energy flux modelling will be used for the analysis of data, which will be produced by the European Space Agency`s Gaia space observatory.
  43. Photospheric parameters and chemical composition are determined for the single-lined chromospherically active RS CVn-type star 29 Draconis (HD 160538). From the high resolution spectra obtained on the Nordic Optical Telescope, abundances of 22 chemical elements, including the key elements such as 12C, 13C, N and O, were investigated. The differential line analysis with the MARCS model atmospheres gives T eff = 4720 K, log g = 2.5, [Fe/H] = --0.20, [C/Fe] = --0.14, [N/Fe] = 0.08, [O/Fe] = --0.04, C/N = 2.40, 12C/13C = 16. The low value of the 12C/13C ratio gives a hint that extra mixing processes in low-mass chromospherically active stars may start earlier than the theory of stellar evolution predicts.
  44. Photospheric parameters and chemical composition are determined for the single-lined chromospherically active RS CVn-type star λ And (HD 222107). From the high resolution spectra obtained on the Nordic Optical Telescope, abundances of 22 chemical elements and isotopes, including such key elements as 12C, 13C, N and O, were investigated. The differential line analysis with the MARCS model atmospheres gives T eff=4830 K, log g=2.8, [Fe/H]=-0.53, [C/Fe]=0.09, [N/Fe]=0.35, [O/Fe]=0.45, C/N=2.21, 12C/13C = 14. The value of 12C/13C ratio for a star of the RS CVn-type is determined for the first time, and its low value gives a hint that extra-mixing processes may start acting in low-mass chromospherically active stars below the bump of the luminosity function of red giants.
  45. Not Available
  46. E-infrastructure in Baltic States currently is rapidly developing. A large impact in this area is given by the European Commission FP6 project "Baltic Grid". A review of progress in this field as well as currently developed grid applications in astrophysics are presented.
  47. Among the most interesting applications of the VLT and ELT are high-resolution spectral investigations of stars in Local Group galaxies. It is of paramount importance to determine detailed abundances of a variety of chemical elements in these stellar systems to explore their chemical evolution and search for its dependence on global parameters like mass and morphological type. In this contribution we give a short overview of the outstanding observational tasks of the VLT and ELT in the next decades.
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  49. Chemical abundances in three M supergiants in the Local Group dwarf irregular galaxy IC 1613 have been determined using high-resolution spectra obtained with the UVES spectrograph on the ESO 8.2 m Kueyen telescope. A detailed synthetic-spectrum analysis has been used to determine the atmospheric parameters and abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Fe, Co, Ni, La, and Eu. We find the overall metallicity of the stars to be [Fe/H] = -0.67 ± 0.09 and the age 9-13 Myr, which is in excellent agreement with the present-day values in the age-metallicity relationship model of IC 1613 by Skillman et al. We have found that the three supergiants investigated have a mean [α/Fe] equal to about -0.1, which is lower than seen in Galactic stars at the same metallicity and is in agreement with the results obtained in other dwarf irregular galaxies. The oxygen abundances are in agreement with the upper values of the nebular oxygen determinations in IC 1613. The abundance ratios of s- and r-process elements to iron are enhanced relative to solar by about 0.3 dex. The abundance pattern of the elements studied is similar to that of the Small Magellanic Cloud, except for Co and Ni, which are underabundant in the SMC. The observed elemental abundances are generally in very good agreement with the recent chemical evolution model of Yuk and Lee. Based on observations collected with the Very Large Telescope and the 2.2 m Telescope of the European Southern Observatory within the Observing Programs 70.B-0361(A) and 072.D-0113(D).
  50. Not Available
  51. The most recently discovered Galactic component - thick disk - still needs high-resolution spectral investigations since its origin and evolution is not understood enough. Elemental abundance ratios in the metallicity range -0.68 ≤ [Fe/H] ≤ -0.10 were determined in a sample of 10 thick-disk dwarfs and compared with results of other stars investigated as well as with models of thin disk chemical evolution.
  52. In this contribution we present the results based on high-resolution spectra of 45 clump stars of the Galactic field. The main atmospheric parameters and abundances of 12C, 13C, N, O and other mixing sensitive chemical elements were investigated. Elemental ratios in the sample of field stars are compared to the results available for evolved stars in open clusters and to the theoretical prediction of extra mixing in stellar interiors.
  53. Not Available
  54. High-resolution spectra of six giants and three core-helium-burning “clump” stars in the open cluster NGC 7789 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 20 chemical elements. Abundances of carbon were studied using the C2 Swan (0, 1) band head at 5635.5 Å. The wavelength interval 7980 8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. The overall metallicity of evolved stars in the cluster was found to be close to solar ([Fe/H]=-0.04±0.05). Compared with the Sun and other dwarf stars of the Galactic disk, mean abundances in the investigated giant stars suggest that carbon is depleted by about 0.2 dex, and nitrogen and oxygen are close to solar. In the clump stars investigated, carbon is depleted by about 0.2 dex, the mean abundance of nitrogen is enhanced by 0.26 dex and oxygen is lower by 0.14 dex. This has the effect of lowering the mean C/N ratios to the value of 1.9±0.5 in the giant stars and to the value of 1.3±0.2 in the clump stars. The mean 12C/13C ratios are lowered to about the same value of 9±1 in the giants and clump stars investigated. Concerning other chemical elements an overabundance of sodium is noticeable and of silicon and calcium one is suspected. Abundances of iron-group and heavier chemical elements in all nine stars were found to be close to solar. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?A+A/431/933 Based on observations made with the Nordic Optical Telescope, which is operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.
  55. Not Available
  56. Not Available
  57. The spectra were obtained at the Nordic Optical Telescope (NOT) with the SOFIN echelle spectrograph in July of 2001. (1 data file).
  58. High-resolution spectra of nine stars in the open cluster NGC 7789 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of more than 20 chemical elements including most sensitive to internal stellar processes as carbon nitrogen sodium aluminium and others. Abundances of carbon were studied using the C2 Swan (01) band head at 563.55 nm. The wavelength interval 798-813 nm with strong CN features was analyzed in order to determine nitrogen abundances and carbon isotope ratios. The oxygen abundances were determined from the [OI] line at 630.0 nm. The abundance results are discussed in the light of theories of various mixing episodes that are predicted to occur during stellar evolution.
  59. Chemical abundances in three giants in Terzan 7, a globular cluster associated with the Sagittarius dwarf galaxy, have been determined using high-resolution spectra obtained with the UVES spectrograph on the ESO 8.2 m Kueyen telescope. We find the overall metallicity of the stars to be [Fe/H]=-0.61+/-0.07, which is slightly higher than that previously evaluated from photometry and used for the age determination of this cluster. This metallicity yields an age of about 6 Gyr, which is slightly lower than derived from previous estimates. The relative abundance ratios of various chemical elements to iron lie between those of its host galaxy's metal-poor and metal-rich stars and reveal an intriguing similarity to the pattern seen in the Large Magellanic Cloud.
  60. Not Available
  61. The sensitivity of stellar spectra to C, N, O and α -process element abundances is discussed with the aim of taking this effect into account when selecting a photometric system for the Gaia orbiting observatory. On the basis of a spectrometric, photometric and theoretical study of spectra of evolved first-ascent giants and clump stars in the open cluster NGC 7789 it is demonstrated that evolutionary alterations of carbon and nitrogen abundances can cause noticeable spectral changes and, if not taken into account, may yield misleading photometric [Fe/H] determinations. Carbon features in stellar atmospheres show a particularly complex behavior being dependent on mixing processes in stars, on the stellar surface gravity and on the abundance of oxygen which can also be altered by different reasons. NH bands could serve for the evaluation of mixing processes in stars and the interpretation of carbon dominated spectral regions. Abundances of α -process elements can be evaluated photometrically by using the direct indicators -- Ca II H and K lines and Mg I b triplet.
  62. The sensitivity of stellar spectra to α/Fe abundance changes is investigated with the aim to be detected photometrically and employed for the scientific goals of the GAIA mission. A grid of plane parallel, line blanketed, flux constant, LTE model atmospheres with different [α/Fe] ratios was calculated. As a first step, the modelled stellar energy fluxes for solar-type stars and giants were computed and intercompared. The spectral sensitivity to α/Fe abundance changes is noticeable and has to be taken into account when selecting photometric filters for GAIA. The CaII H and K lines and MgI b triplet are the most sensitive direct indicators of α/Fe abundance changes.
  63. High-resolution spectra of 13 core helium-burning stars in the thick disk of the Galaxy have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 22 chemical elements. Abundances of carbon were studied using the C2 Swan (0, 1) band head at 5635.5 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. Abundances in the investigated stars suggest that carbon is depleted by about 0.3 dex, nitrogen is enhanced by more than 0.4 dex and oxygen is unaltered. The 12C/13C ratios are lowered and lie between values 3 and 7 which is in agreement with ``cool bottom processing'' predictions (Boothroyd & Sackmann 1999). The C/N ratios in the investigated stars are lowered to values between 0.7 and 1.2 which is less than present day theoretical predictions and call for further studies of stellar mixing processes. Abundance ratios of O, Mg, Eu and other heavy chemical elements to iron in the investigated stars show a pattern characteristic of thick disk stars. The results provide evidence that the thick disk population has a distinct chemical history from the thin disk. The onset of the bulk of SN Ia is suggested to appear at [Fe/H] ~ -0.6 dex. Based on observations obtained at the Nordic Optical Telescope, La Palma. Table 1 is only available in electronic at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http:/cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/380/578
  64. High-resolution spectra of 13 core helium-burning stars in the thick disk of the Galaxy have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 22 chemical elements. Abundances of carbon were studied using the C2 Swan (0, 1) band head at 5635.5Å. The wavelength interval 7980-8130Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300Å. Abundances in the investigated stars suggest that carbon is depleted by about 0.3dex, nitrogen is enhanced by more than 0.4dex and oxygen is unaltered. The 12C/13C ratios are lowered and lie between values 3 and 7 which is in agreement with "cool bottom processing" predictions (Boothroyd & Sackmann, 1999ApJ...510..232B). The C/N ratios in the investigated stars are lowered to values between 0.7 and 1.2 which is less than present day theoretical predictions and call for further studies of stellar mixing processes. Abundance ratios of O, Mg, Eu and other heavy chemical elements to iron in the investigated stars show a pattern characteristic of thick disk stars. The results provide evidence that the thick disk population has a distinct chemical history from the thin disk. The onset of the bulk of SN Ia is suggested to appear at [Fe/H]~-0.6dex. (2 data files).
  65. High-resolution spectra of six core helium-burning `clump' stars and three giants in the open cluster M 67 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 25 chemical elements. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5Å. The wavelength interval 7980-8130Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300Å. The overall metallicity of the cluster stars was found to be close to solar ([Fe/H]=-0.03+/-0.03). Compared with the Sun and other dwarf stars of the Galactic disk, as well as with dwarf stars of M 67 itself, abundances in the investigated stars suggest that carbon is depleted by about 0.2dex, nitrogen is enhanced by about 0.2dex and oxygen is unaltered. Among other mixing-sensitive chemical elements an overabundance of sodium may be suspected. The mean C/N and 12C/13C ratios are lowered to the values of 1.7+/-0.2 and 24+/-4 in the giants and to the values of 1.4+/-0.2 and 16+/-4 in the clump stars. These results suggest that extra mixing of CN-cycled material to the stellar surface takes place after the He-core flash. Abundances of heavy chemical elements in all nine stars were found to be almost identical and close to solar. (2 data files).
  66. High-resolution spectra of six core helium- burning `clump' stars and three giants in the open cluster M 67 have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 25 chemical elements. Abundances of carbon were studied using the C2 Swan (0,1) band head at 5635.5 Å. The wavelength interval 7980-8130 Å with strong CN features was analysed in order to determine nitrogen abundances and 12C/13C isotope ratios. The oxygen abundances were determined from the [O I] line at 6300 Å. The overall metallicity of the cluster stars was found to be close to solar ([Fe/H]=-0.03 ± 0.03). Compared with the Sun and other dwarf stars of the Galactic disk, as well as with dwarf stars of M 67 itself, abundances in the investigated stars suggest that carbon is depleted by about 0.2 dex, nitrogen is enhanced by about 0.2 dex and oxygen is unaltered. Among other mixing-sensitive chemical elements an overabundance of sodium may be suspected. The mean C/N and 12C/13C ratios are lowered to the values of 1.7 ± 0.2 and 24 ± 4 in the giants and to the values of 1.4±0.2 and 16±4 in the clump stars. These results suggest that extra mixing of CN-cycled material to the stellar surface takes place after the He-core flash. Abundances of heavy chemical elements in all nine stars were found to be almost identical and close to solar. Based on observations obtained at the Nordic Optical Telescope, La Palma Tables 2 and 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
  67. Abundance anomalies caused by the mixing to the surface of material processed in nuclear reactions inside a star are dependent on parameters of stellar atmospheres (e.g. the effective temperature, gravity and overall metallicity). However, a variety of evolved stars investigated is rather limited. In our study, we present results for 20 cool, metal-abundant stars with a double energy source (helium burning in the centre and hydrogen burning in the shell). High resolution spectroscopic observations of these stars were accomplished on the Nordic Optical Telescope. The main atmospheric parameters and abundances of more than twenty chemical elements, including 12C, 13C, N, O, Na, Mg and Al, were determined and evolutionary effects investigated.
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  69. Observations by the Hipparcos satellite clearly demonstrated that a population of He-core burning stars is a prominent feature of the colour-magnitude diagram of stars in the solar neighbourhood. However this class of evolved stars, being hardly identified in the Galactic field, so far is barely investigated by means of high-resolution spectroscopy. Identification of metal abundant He-core burning stars is especially difficult since their main atmospheric parameters are very similar to those of ordinary giants. The open cluster M 67 is a very good exhibitor of metal abundant He-core burning stars. We have observed 9 stars of this cluster on the Nordic Optical Telescope and determined abundances of more than 20 chemical elements in their atmospheres. In our contribution we will present the results of the analysis.
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  71. High-dispersion spectra of 10 red horizontal branch (RHB) stars of the galactic field were obtained on the 6-m Special Astrophysical Observatory (SAO) telescope to investigate abundances of up to 22 chemical elements. This constitutes the largest single high-resolution abundance study of RHB stars located in the galactic field. Abundance trends in the range of -1.9<=[Fe/H]<=-0.2 are compared with results for dwarfs and red giants, as well as with theoretical trends. For five metal-deficient stars of the sample, a slight overabundance of oxygen is revealed. The results for alpha-process elements match theoretical predictions; only [Mg/Fe], for almost all stars, is below the theoretical trend. Almost all stars of the sample closely follow the solar [Na/Fe] ratio; only for the two most metal-abundant stars is sodium overabundant by 0.2-0.3dex. A comparison of the available abundances of atmospheres for the RHB stars with those for giants and dwarfs shows a good fit for the iron group elements and for other heavier elements; thus, RHB stars may also serve for Galactic chemical evolution studies.
  72. A brief review is presented on the current progress of the photometric identification of the field red horizontal-branch stars (RHB) in the UBV, Geneva, Stromgren, Vilnius and DDO photometric systems. Stars of this type have been identified in most of structural components of the Galaxy: bulge, thin disk, thick disk and halo. However, the number of these stars and the available data about them are not sufficient for an investigation of the morphology of their color-magnitude diagram and their space density.
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  74. The photometric observations and three-dimensional classification in the Vilnius system have been carried out for 13 of the red horizontal branch (RHB) stars in the Galactic thick disk identified by Rose (1985). The photometric spectral types, metallicities [Fe/H], effective temperatures, surface gravities and absolute magnitudes are determined. The age of about 10--12 Gyr is evaluated for this group of stars from comparison with model isochrones, indicating that the age of the thick disk is intermediate between the disk globular and the oldest open clusters.
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  77. A new semiempirical surface gravity calibration of the intrinsic color indices U-P and U-X of the Vilnius photometric system is presented. It is applicable for giants of all metallicities with temperatures from 4200 K to 5500 K and log g from 0.5 dex to 3.0 dex. The standard deviation of the observed minus predicted log g residuals is about +/- 0.3 dex. The U-P color index is found to be a very good surface gravity indicator, and it can be used for log g determination even when other atmospheric parameters (temperature and metallicity) are poorly known. The main atmospheric parameters for 93 red metal-deficient giants are determined from color indices of the Vilnius system and compared with the evolutionary isochrones.
  78. Not Available
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  81. High dispersion spectra obtained using the 6-m telescope of the Special Astrophysical Observatory were used to determine the atmosphere parameters and chemical composition of 11 G - K giants of differing metallicity, and four stars were reanalyzed on the basis of the equivalent line widths given in the literature. It was found that the content of the light metals Na, Mg, Ca and Ti is enriched in relation to Fe in giants of the galactic halo. The sodium content is elevated in giants of the disk as well. The ratios of the Sc, V, Cr, Co, Ni and Zn to Fe contents do not exhibit appreciable departures from the solar values. In halo giants, [Mn/Fe] is slightly reduced. A substantial overdeficit of Cu was detected. An "odd/even" effect was found for the elements of the iron group. The [Y/H] and [Ba/H] ratios are reduced in halo giants, while the [Ce/H], [Nd/H] and [Sm/H] remain at roughly their solar values.
  82. Not Available
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  85. Effective temperatures, surface gravities and chemical composition parameters [Fe/H] and [Ca/H] are derived for 43 G and K giants of various metallicities by means of medium dispersion spectra obtained with a multichannel spectrophotometer of the 6-meter telescope and photoelectric photometry in the Vilnius seven-color photometric system. Calcium is overabundant with respect to iron by 0.5±0.2 dex for stars with [Fe/H] < -1 and there is a tendency of increase of this overabundance with decreasing metallicity.
  86. Color indices of the Vilnius photometric system are calibrated in effective temperatures Te and surface gravities g for 110 metal-deficient field G and K giants. Positions of these stars in the log g, log Te diagram are compared with evolutionary tracks and isochrones, as well as with giant sequences of globular clusters. This diagram can be used to estimate the evolutionary stage of stars having only photometric data.
  87. Not Available
  88. The atmospheric extinction coefficients for the color indices of the Stromgren uvby medium-band photometric system are analyzed by the method of numerical integration. It is shown that the extinction coefficients for the color indices u-y and the indices a(1) depend in a complicated way on the spectral class and luminosity of the star and on its interstellar reddening. Neglect of this dependence leads to inconstancy of the color system of indices c(1) and to systematic errors, reaching 0.04 mag at a zenith distance of 60 deg. To allow for this effect, it is proposed to use atmospheric extinction coefficients not dependent on interstellar reddening, calculated through photometric parameters Q that are not dependent on interstellar reddening.
  89. A method for metallicity determination of G-K giants using spectra of 50 Å/mm dispersion is proposed. It is based on theoretical interpretation of central intensities of strong Fe I lines using model stellar atmospheres. Temperatures and metallicities for 20 G-K metal-deficient giants and 7 normal giants are determined.