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Register a new userChemical Study of the Metal-rich Globular Cluster NGC 5927
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Globular Clusters (GCs) are natural laboratories where stellar and chemical evolution can be studied in detail. In addition, their chemical patterns and kinematics can tell us wich Galactic structure (Disk, Bulge, Halo or extragalactic) the cluster belongs to. NGC 5927 is one of most metal-rich GCs in the Galaxy and its kinematics links it to the Thick Disk. We present abundance analysis based on high resolution spectra of 7 giant stars. The data were obtained using FLAMES/UVES spectrograph mounted on UT2 telescope of the European Southern Observatory. The principal motivation of this work is to perform a wide and detailed chemical abundance analysis of the cluster and look for possible Multiple Populations (MPs). We determined stellar parameters and measured 22 elements corresponding to light (Na, Al), alpha (O, Mg, Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and heavy elements (Y, Zr, Ba, Ce, Nd, Eu). We found a mean iron content of [Fe/H]=-0.47 $pm$0.02 (error on the mean). We confirm the existence of MPs in this GC with an O-Na anti-correlation, and moderate spread in Al abundances. We estimate a mean [$alpha$/Fe]=0.25 $pm$0.08. Iron-peak elements shows no significant spread. The [Ba/Eu] ratios indicate a predominant contribution from SNeII for the formation of the cluster.
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We present the first spectroscopic abundance determination of iron, alpha-elements (Si, Ca and Ti) and sodium for the Mira variable V1 in the metal-rich globular cluster NGC 5927. We use high-resolution (R~ 28,000), high signal-to-noise ratio (~200) spectra collected with WINERED, a near-infrared (NIR) spectrograph covering simultaneously the wavelength range 0.91--1.35 micron. The effective temperature and the surface gravity at the pulsation phase of the spectroscopic observation were estimated using both optical (V) and NIR time-series photometric data. We found that the Mira is metal-rich ([Fe/H]=-0.55 pm 0.15) and moderately alpha-enhanced ([alpha/Fe]=0.15 pm 0.01, sigma=0.2). These values agree quite well with the mean cluster abundances based on high-resolution optical spectra of several cluster red giants available in the literature ([Fe/H]=-0.47 pm 0.06, [alpha/Fe]=+0.24 pm 0.05). We also found a Na abundance of +0.35 pm 0.20 that is higher than the mean cluster abundance based on optical spectra (+0.18 pm 0.13). However, the lack of similar spectra for cluster red giants and that of corrections for departures from local-thermodynamical equilibrium prevents us from establishing whether the difference is intrinsic or connected with multiple populations. These findings indicate a strong similarity between optical and NIR metallicity scales in spite of the difference in the experimental equipment, data analysis and in the adopted spectroscopic diagnostics.
We present the abundance analysis for a sample of 18 red giant branch stars in the metal-poor globular cluster NGC 4147 based on medium and high resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, Ba, and Eu. We find a metallicity of [Fe/H]=-1.84+-0.02 and an alpha-enhancement of +0.38+-0.05 (errors on the mean), typical of halo globular clusters in this metallicity regime. A significant spread is observed in the abundances of light elements C, N, O, Na, and Al. In particular we found a Na-O anti-correlation and Na-Al correlation. The cluster contains only 15% of stars that belong to the first generation (Na-poor and O-rich). This implies that it suffered a severe mass loss during its lifetime. Its [Ca/Fe] and [Ti/Fe] mean values agree better with the Galactic Halo trend than with the trend of extragalactic environments at the cluster metallicity. This possibly suggests that NGC 4147 is a genuine Galactic object at odd with what claimed by some author that proposed the cluster to be member of the Sagittarius dwarf galaxy. A anti-relation between the light s-process element Y and Na may also be present.
Low resolution spectra have been used to measure individual metal abundances of RR Lyrae stars in NGC 6441, a Galactic globular cluster known to have very unusual horizontal branch morphology and periods of the RR Lyrae stars for its high metallicity. We find an average metal abundance of [Fe/H]=-0.69 +/- 0.06 (r.m.s.=0.33 dex) and [Fe/H]=-0.41 +/- 0.06 (r.m.s.=0.36 dex) on Zinn & West and Carretta & Gratton metallicity scales, respectively, consistent with the cluster metal abundance derived by Armandroff & Zinn. Most of the metallicities were extrapolated from calibration relations defined for [Fe/H] < -1; however, they are clearly high and contrast with the rather long periods of the NGC 6441 variables, thus confirming that the cluster does not fit in the general Oosterhoff classification scheme. The r.m.s. scatter of the average is larger than observational errors (0.15-0.16 dex) possibly indicating some spread in metallicity. However, even the metal poor variables, if confirmed to be cluster members, are still more metal rich than those commonly found in the Oosterhoff type II globular clusters.
We present chemical abundances for 17 elements in a sample of 11 red giant branch stars in NGC 6362 from UVES spectra. NGC 6362 is one of the least massive globulars where multiple populations have been detected, yet its detailed chemical composition has not been investigated so far. NGC 6362 turns out to be a metal-intermediate ([Fe/H]=-1.07pm0.01 dex) cluster, with its alpha- and Fe-peak elements content compatible with that observed in clusters with similar metallicity. It also displays an enhancement in its s-process element abundances. Among the light elements involved in the multiple populations phenomenon, only [Na/Fe] shows star-to-star variations, while [Al/Fe] and [Mg/Fe] do not show any evidence for abundance spreads. A differential comparison with M4, a globular cluster with similar mass and metallicity, reveals that the two clusters share the same chemical composition. This finding suggests that NGC 6362 is indeed a regular cluster, formed from gas that has experienced the same chemical enrichment of other clusters with similar metallicity.
With a high value of heliocentric radial velocity, a retrograde orbit, and being suspected to have an extragalactic origin, NGC 3201 is an interesting globular cluster for kinematical studies. Our purpose is to calculate the relative proper motions (PMs) and membership probability for the stars in the wide region of globular cluster NGC 3201. Proper motion based membership probabilities are used to isolate the cluster sample from the field stars. The membership catalogue will help address the question of chemical inhomogeneity in the cluster. Archive CCD data taken with a wide-field imager (WFI) mounted on the ESO 2.2m telescope are reduced using the high-precision astrometric software developed by Anderson et al. for the WFI images. The epoch gap between the two observational runs is $sim$14.3 years. To standardize the $BVI$ photometry, Stetsons secondary standard stars are used. The CCD data with an epoch gap of $sim$14.3 years enables us to decontaminate the cluster stars from field stars efficiently. The median precision of PMs is better than $sim$0.8 mas~yr$^{-1}$ for stars having $V<$18 mag that increases up to $sim$1.5 mas~yr$^{-1}$ for stars with $18<V<20$ mag. Kinematic membership probabilities are calculated using proper motions for stars brighter than $Vsim$20 mag. An electronic catalogue of positions, relative PMs, $BVI$ magnitudes and membership probabilities in $sim$19.7$times$17 arcmin$^2$ region of NGC 3201 is presented. We use our membership catalogue to identify probable cluster members among the known variables and $X$-ray sources in the direction of NGC 3201.
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