Aims. We study the abundances of Na, Mg, and K in the atmospheres of 32 red giant branch (RGB) stars in the Galactic globular cluster (GGC) 47 Tuc, with the goal to investigate the possible existence of Na-K and Mg-K correlations/anti-correlations, similar to those that were recently discovered in two other GGCs, NGC 2419 and 2808. Methods. The abundances of K, Na, and Mg were determined using high-resolution 2dF/HERMES spectra obtained with the Anglo-Australian Telescope (AAT). The one-dimensional (1D) NLTE abundance estimates were obtained using 1D hydrostatic ATLAS9 model atmospheres and spectral line profiles synthesized with the MULTI package. We also used three-dimensional (3D) hydrodynamical CO 5 BOLD and 1D hydrostatic LHD model atmospheres to compute 3D-1D LTE abundance corrections, ∆ 3D−1D LTE , for the spectral lines of Na, Mg, and K used in our study. These abundance corrections were used to understand the role of convection in the formation of spectral lines, as well as to estimate the differences in the abundances obtained with the 3D hydrodynamical and 1D hydrostatic model atmospheres.Results. The average element-to-iron abundance ratios and their RMS variations due to star-to-star abundance spreads determined in our sample of RGB stars were [Na/Fe] 1D NLTE = 0.42± 0.13, [Mg/Fe] 1D NLTE = 0.41± 0.11, and [K/Fe] 1D NLTE = 0.05± 0.14. We found no statistically significant relations between the abundances of the three elements studied here. Also, there were no abundance trends with the distance from the cluster center, nor any statistically significant relations between the abundance/abundance ratios and absolute radial velocities of individual stars. All these facts suggest the similarity of K abundance in stars that belong to different generations in 47 Tuc which, in turn, may hint that evolution of K in this particular cluster was unrelated to the nucleosynthesis of Na and/or Mg.
Abstract. We derive photometric metallicities for 56 intermediate-age and old star clusters in the Large Magellanic Cloud from the slopes of their red-giant branches in near-infrared colormagnitude diagrams (CMDs). The cluster sample covers the LMC bar and disk to a distance of ∼ 2 kpc from the LMC center. The derived cluster metallicity distribution spans a range of [Fe/H] = +0.0...1.4 and is similar to the metallicity distribution of field stars. We find that the average cluster metallicities in certain fields of the LMC bar and disk may be different, but there seems to be no compelling evidence for a global cluster metallicity gradient in the LMC.
Abstract. Seven-color photometry in the Vilnius system has been obtained for 420 stars down to V = 16 mag in the area containing the overlapping open clusters NGC 1750 and NGC 1758 in Taurus. Spectral and luminosity classes, color excesses, interstellar extinctions and distances are given for 287 stars. The classi cation of stars is based on their reddening-free Q-parameters. 18 stars observed photoelectrically were used as standards. The extinction vs. distance diagram exhibits the presence of one dust cloud at a distance of 175 pc which almost coincides with a distance of other dust clouds in the Taurus complex. The clusters NGC 1750 and NGC 1758 are found to be at the same distance of 760 pcand may penetrate each other. Their interstellar extinction A V is 1.06 mag which corresponds to E B;V = 0.34 mag. (1992, hereafter Paper I). Photoelectric photometry of 116 stars down to 13th magnitude has revealed that the clusters are at 510 and 680 pc distances, respectively. Interstellar reddeningE B;V of both clusters was found to beclose to 0.4 mag. The distance of the dust layer responsible for the reddening was found to be at 175 pc. The reality of the clusters was veri ed by their photometric distances and proper motions of the cluster members.Paper I has increased the interest in this pair of clusters. In a series of papers Galadi-Enriquez et al. (1998a,b,c) have con rmed the reality of the two clusters. Their investigation was based on stellar photometry in the UBVRI photometric system by CCD and photographic techniques down to 18{20 mag and on the proper motions of stars based on a plate collection covering a broad range of epochs (from 1891 to 1994). The lists of NGC 1750 and NGC 1758 members down to V = 15 mag were composed containing 79 and 57 stars respectively. For bothclusters the reddening E B;V = 0.34 mag, based on the member stars measured by Strai zys et al. (1992) in the Vilnius system and by the authors in the Str omgren system. The distances to the clusters were found to be630 pc and 760 pc. Another proper motion study in the area was published by Tian et al. (1998).Trying to obtain an independent criterion of membership to both clusters, based on photometric classi cation of stars in terms of MK spectral and luminosity classes, we have started a new investigation of the cluster area in the Vilnius system by CCD photometry, extending photometric classi cation down to a fainter limit in comparison to Paper I. Although the preliminary results of the present study were known already in 1995{1996, the publication was delayed due to problems of at-elding and CCD non-linearity.
Aims. We determined abundances of Mg and K in the atmospheres of 53 (Mg) and 75 (K) turn-off (TO) stars of the Galactic globular cluster 47 Tuc. The obtained abundances, together with those of Li, O, and Na that we had earlier determined for the same sample of stars, were used to search for possible relations between the abundances of K and other light elements, Li, O, Na, and Mg, as well as the connections between the chemical composition of TO stars and their kinematical properties. Methods. Abundances of Mg and K were determined using archival high resolution VLT FLAMES/GIRAFFE spectra, in combination with the one-dimensional (1D) non-local thermodynamic equilibrium (NLTE) spectral synthesis methodology. Spectral line profiles were computed with the MULTI code, using 1D hydrostatic ATLAS9 stellar model atmospheres. We also utilized three-dimensional (3D) hydrodynamical CO 5 BOLD and 1D hydrostatic LHD model atmospheres for computing 3D-1D LTE abundance corrections for the spectral lines of Mg and K, in order to assess the influence of convection on their formation in the atmospheres of TO stars. Results. The determined average abundance-to-iron ratios and their root mean square (RMS) variations due to star-to-star abundance spreads were [Mg/Fe] 1D NLTE = 0.47 ± 0.12, and [K/Fe] 1D NLTE = 0.39 ± 0.09. Although the data suggest the possible existence of a weak correlation in the [K/Fe]-[Na/Fe] plane, its statistical significance is low. No statistically significant relations between the abundance of K and other light elements were detected. Also, we did not find any significant correlations or anti-correlations between the [Mg/Fe] and [K/Fe] ratios and projected distance from the cluster center. Similarly, no relations between the absolute radial velocities of individual stars and abundances of Mg and K in their atmospheres were detected. The 3D-1D abundance corrections were found to be small (≤ 0.1 dex) for the lines of Mg and K used in this study, thus indicating that the influence of convection on their formation is small.
Aims. We investigate possible relations between the abundances of zinc and the light elements sodium, magnesium, and potassium in the atmospheres ofred giant branch (RGB) stars of the Galactic globular cluster 47 Tuc and study connections between the chemical composition and dynamical properties of the cluster RGB stars. Methods. The abundance of zinc was determined in 27 RGB stars of 47 Tuc using 1D local thermal equilibrium (LTE) synthetic line profile fitting to the high-resolution 2dF/HERMES spectra obtained with the Anglo-Australian Telescope (AAT). Synthetic spectra used in the fitting procedure were computed with the SYNTHE code and 1D ATLAS9 stellar model atmospheres.Results. The average 1D LTE zinc-to-iron abundance ratio and its RMS variations due to star-to-star abundance spread determined in the sample of 27 RGB stars is [Zn/Fe] 1D LTE = 0.11 ± 0.09. We did not detect any statistically significant relations between the abundances of zinc and those of light elements. Neither did we find any significant correlation or anticorrelation between the zinc abundance in individual stars and their projected distance from the cluster center. Finally, no statistically significant relation between the absolute radial velocities of individual stars and the abundance of zinc in their atmospheres was detected. The determined average [Zn/Fe] 1DLTE ratio agrees well with those determined in this cluster in earlier studies and nearly coincides with that of Galactic field stars at this metallicity. All these results suggest that nucleosynthesis of zinc and light elements proceeded in separate, unrelated pathways in 47 Tuc.
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