High resolution infrared spectra of NGC 6342 and NGC 6528: two moderately reddened Bulge Globular Clusters (original) (raw)
Related papers
Monthly Notices of The Royal Astronomical Society, 2005
Using the Near Infrared Spectrometer (NIRSPEC) spectrograph at Keck II, we have obtained infrared (IR) echelle spectra covering the range 1.5 –1.8 μm for the moderately reddened bulge globular clusters NGC 6342 and 6528, finding [Fe/H]=−0.60 and −0.17 dex, respectively. We measure an average α-enhancement of ≈+0.33 dex in both clusters, consistent with previous measurements on other metal-rich bulge clusters, and favouring the scenario of a rapid bulge formation and chemical enrichment. We also measure very low 12C/13C isotopic ratios (≈5 in NGC 6342 and ≈8 in NGC 6528), suggesting that extra-mixing mechanisms resulting from cool bottom processing are at work during evolution along the red giant branch (RGB).
Monthly Notices of The Royal Astronomical Society, 2005
Using the SofI imager at ESO/NTT and NIRSPEC spectrograph at KeckII, we have obtained J,K images and echelle spectra covering the range 1.5 - 1.8 micron for the intermediate metallicity Bulge globular clusters NGC6539 and UKS1. We find [Fe/H]=-0.76 and -0.78, respectively, and an average alpha-enhancement of +0.44 dex and +0.31 dex, consistent with previous measurements of metal rich Bulge clusters, and favoring the scenario of rapid chemical enrichment. We also measure very low 12C/13C=4.5 +/-1 isotopic ratios in both clusters, suggesting that extra-mixing mechanisms due to cool bottom processing are at work during the evolution along the Red Giant Branch. Finally, we measure accurate radial velocities of <v_r>=+31 +/-4Km/s and <v_r>=+57 +/-6Km/s and velocity dispersion of about 8 Km/s and 11 Km/s for NGC6539 and UKS1, respectively.
Near-infrared photometry of four metal-rich bulge globular clusters: NGC 6304, 6569, 6637 and 6638
Monthly Notices of The Royal Astronomical Society, 2005
We present high-quality near-infrared (near-IR) photometry of four bulge metal-rich globular clusters, namely NGC 6304, 6569, 6637 and 6638. By using the observed colour-magnitude diagrams we derived photometric estimates of the cluster reddening and distance. We performed a detailed analysis of the red giant branch (RGB), presenting a complete description of its morphologic parameters and evolutionary features (bump and tip). Photometric estimates of the cluster metallicity were obtained using the updated data set (published by our group) linking metal abundance to a variety of near-IR indices measured along the RGB. The detection of the RGB bump and tip is also presented and briefly discussed.
High resolution infrared spectroscopy of the old open cluster NGC6791
2006
We report abundance analysis for 6 M giant members of the old open cluster NGC6791, based on infrared spectroscopy (1.5-1.8 micron) at R=25,000, using the NIRSPEC spectrograph at the Keck II telescope. We find the iron abundance <[Fe/H]>= +0.35 +/- 0.02$, confirming the super solar metallicity of this cluster derived from optical medium-high resolution spectroscopy. We also measure C, O and other alpha element abundances, finding roughly solar [alpha/Fe] and <[C/Fe]> = -0.35. Our approach constrains [O/Fe] especially well, based on the measurement of a number of OH lines near 1.6micron; we find [O/Fe]=-0.07 +/-0.03. The Solar alpha enhancement is in contrast to the composition of similar stars in the Galactic bulge. We also find low 12C/13C~10, confirming the presence of extra-mixing processes during the red giant phase of evolution, up to super solar metallicities.
Astronomy & Astrophysics, 2003
A detailed abundance analysis of 5 giants of the metal-rich bulge globular cluster NGC 6553 was carried out using high resolution infrared spectra in the H band, obtained at the Gemini-South 8m telescope. JK photometry collected at ESO and VI photometry from the Hubble Space Telescope are used to derive effective temperatures. The present analysis provides a metallicity [Fe/H] = -0.20±0.10. An overabundance of oxygen of [O/Fe] = +0.20 is found from IR OH lines.
High-resolution abundance analysis of red giants in the globular cluster NGC 6522
Astronomy & Astrophysics, 2014
Context. The [Sr/Ba] and [Y/Ba] scatter observed in some galactic halo stars that are very metal-poor and in a few individual stars of the oldest known Milky Way globular cluster NGC 6522 have been interpreted as evidence of early enrichment by massive fastrotating stars (spinstars). Because NGC 6522 is a bulge globular cluster, the suggestion was that not only the very-metal poor halo stars, but also bulge stars at [Fe/H] ∼−1 could be used as probes of the stellar nucleosynthesis signatures from the earlier generations of massive stars, but at much higher metallicity. For the bulge the suggestions were based on early spectra available for stars in NGC 6522, with a medium resolution of R ∼ 22 000 and a moderate signal-to-noise ratio. Aims. The main purpose of this study is to re-analyse the NGC 6522 stars reported previously by using new high-resolution (R ∼ 45 000) and high signal-to-noise spectra (S /N > 100). We aim at re-deriving their stellar parameters and elemental ratios, in particular the abundances of the neutron-capture s-process-dominated elements such as Sr, Y, Zr, La, and Ba, and of the r-element Eu. Methods. High-resolution spectra of four giants belonging to the bulge globular cluster NGC 6522 were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph in FLAMES-UVES configuration. The spectroscopic parameters were derived based on the excitation and ionization equilibrium of Fe i and Fe ii. Results. Our analysis confirms a metallicity [Fe/H] = −0.95 ± 0.15 for NGC 6522 and the overabundance of the studied stars in Eu (with +0.2 < [Eu/Fe] < +0.4) and alpha-elements O and Mg. The neutron-capture s-element-dominated Sr, Y, Zr, Ba, and La now show less pronounced variations from star to star. Enhancements are in the range 0.0 < [Sr/Fe] < +0.4, +0.23 < [Y/Fe] < +0.43, 0.0 < [Zr/Fe] < +0.4, 0.0 < [La/Fe] < +0.35, and 0.05 < [Ba/Fe] < +0.55. Conclusions. The very high overabundances of [Y/Fe] previously reported for the four studied stars is not confirmed with the new high-quality spectra. The moderate enhancement in [Sr/Fe] previously reported for one of the re-studied stars is confirmed, but the strong enhancements of this ratio for the other two stars are not confirmed. Despite the moderate enhancements found for the neutroncapture s-element-dominated species, none of the four stars studied here show positive values for all [Sr/Ba], [Y/Ba] and [Zr/Ba] ratios. The re-studied stars are now compatible not only with the interpretation that the s-process enhancements in these very old stars are due to spinstars, but also with alternative models such as mass transfer from s-process-rich AGB stars. Note, however, that when our results are interpreted in the context of more extended datasets from the literature, the spinstar scenario still seems to be favoured.
The metal content of the bulge globular cluster NGC�6528
Astronomy and Astrophysics, 2004
High resolution spectra of five stars in the bulge globular cluster NGC 6528 were obtained at the 8m VLT UT2-Kueyen telescope with the UVES spectrograph. Out of the five stars, two of them showed evidence of binarity. The target stars belong to the horizontal and red giant branch stages, at 4000 < T eff < 4800 K. Multiband V, I, J, H, Ks photometry was used to derive initial effective temperatures and gravities. The main purpose of this study is the determination of metallicity and elemental ratios for this template bulge cluster, as a basis for the fundamental calibration of metal-rich populations. The present analysis provides a metallicity [Fe/H] = −0.1 ± 0.2 and the α-elements O, Mg and Si, show [α/Fe] ≈ +0.1, whereas Ca and Ti are around the solar value or below, resulting in an overall metallicity Z ≈ Z⊙.
Chemical abundances in bright giants of the globular cluster M62 (NGC 6266)
Monthly Notices of the Royal Astronomical Society, 2014
With the exception of Terzan 5, all the Galactic globular clusters that possess significant metallicity spreads, such as ω Cen and M22, are preferentially the more luminous clusters with extended horizontal branches. Here we present radial velocities and chemical abundances for seven bright giants in the globular cluster M62, a previously little-studied cluster. With M V = −9.18, M62 is the ninth most luminous Galactic globular cluster and has an extended horizontal branch. Within our sample, we find (i) no evidence for a dispersion in metallicity, [Fe/H], beyond the measurement uncertainties, (ii) star-to-star abundance variations for C, O, Na and Al with the usual correlations between these elements as seen in other globular clusters, and (iii) a global enrichment for the elements Zr, Ba and La at the level [X/Fe] ≃ +0.4 dex. For elements heavier than La, the abundance ratios are consistent with the scaled-solar r-process distribution. Below La, the abundances are anomalous when compared to the scaledsolar s-process or r-process distributions. For these elements, the abundance signature in M62 is in agreement with predictions of the s-process from fast-rotating massive stars, although the high [Rb/Y] ratio we measure may be a challenge to this scenario.
arXiv (Cornell University), 2023
Previous results in the literature have found the young inner-disk open cluster NGC 6705 to be mildly-enhanced. We examined this possibility via an independent chemical abundance analysis for 11 red-giant members of NGC 6705. The analysis is based on near-infrared APOGEE spectra and relies on LTE calculations using spherical model atmospheres and radiative transfer. We find a mean cluster metallicity of [Fe/H] = +0.13 ± 0.04, indicating that NGC 6705 is metal-rich, as may be expected for a young inner-disk cluster. The mean-element abundance relative to iron is ⟨[ /Fe]⟩ = −0.03 ± 0.05, which is not at odds with expectations from general Galactic abundance trends. NGC 6705 also provides important probes for studying stellar mixing, given its turn-off mass of M∼3.3 M ⊙. Its red giants have low 12 C abundances ([ 12 C/Fe]=−0.16) and enhanced 14 N abundances ([ 14 N/Fe]=+0.51), which are key signatures of the first dredge-up on the red giant branch. An additional signature of dredge-up was found in the Na abundances, which are enhanced by [Na/Fe]=+0.29, with a very small non-LTE correction. The 16 O and Al abundances are found to be near-solar. All of the derived mixing-sensitive abundances are in agreement with stellar models of approximately 3.3 M ⊙ evolving along the red giant branch and onto the red clump. As found in young open clusters with similar metallicities, NGC 6705 exhibits a mild excess in the s-process element cerium, with [Ce/Fe] = +0.13 ± 0.07.
Carolina Digital Repository (University of North Carolina at Chapel Hill), 2006
We report the abundance analysis of one red giant branch star in the metalpoor outer halo globular cluster NGC 5694. We obtain [Fe/H] = −1.93, based on the ionized lines, and our metallicity measurement is in good agreement with previous estimates. We find that [Ca+Ti/2Fe] and [Cu/Fe] of NGC 5694 are about 0.3-0.4 dex lower than other globular clusters with similar metallicities, but similar to some LMC clusters and stars in some dwarf spheroidal galaxies. Differences persist, however, in the abundances of neutron capture elements. The unique chemical abundance pattern and the large Galactocentric distance (30 kpc) and radial velocity (−138.6 ± 1.0 km sec −1) indicate that NGC 5694 had an extragalactic origin.