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Title: THE DETAILED CHEMICAL PROPERTIES OF M31 STAR CLUSTERS. I. Fe, ALPHA AND LIGHT ELEMENTS

Abstract

We present ages, [Fe/H] and abundances of the α elements Ca I, Si I, Ti I, Ti II, and light elements Mg I, Na I, and Al I for 31 globular clusters (GCs) in M31, which were obtained from high-resolution, high signal-to-noise ratio >60 echelle spectra of their integrated light (IL). All abundances and ages are obtained using our original technique for high-resolution IL abundance analysis of GCs. This sample provides a never before seen picture of the chemical history of M31. The GCs are dispersed throughout the inner and outer halo, from 2.5 kpc < R {sub M31} < 117 kpc. We find a range of [Fe/H] within 20 kpc of the center of M31, and a constant [Fe/H] ∼ – 1.6 for the outer halo clusters. We find evidence for at least one massive GC in M31 with an age between 1 and 5 Gyr. The α-element ratios are generally similar to the Milky Way GC and field star ratios. We also find chemical evidence for a late-time accretion origin for at least one cluster, which has a different abundance pattern than other clusters at similar metallicity. We find evidence for star-to-star abundance variations in Mg, Na, and Al in the GCs in ourmore » sample, and find correlations of Ca, Mg, Na, and possibly Al abundance ratios with cluster luminosity and velocity dispersion, which can potentially be used to constrain GC self-enrichment scenarios. Data presented here were obtained with the HIRES echelle spectrograph on the Keck I telescope.« less

Authors:
;  [1];  [2]
  1. The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101 (United States)
  2. Palomar Observatory, Mail Stop 105-24, California Institute of Technology, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
22364834
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 797; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALUMINIUM; CALCIUM; CHEMICAL PROPERTIES; CORRELATIONS; ELEMENT ABUNDANCE; IRON; LUMINOSITY; MAGNESIUM; METALLICITY; MILKY WAY; RESOLUTION; SIGNAL-TO-NOISE RATIO; STAR ACCRETION; STAR CLUSTERS; STARS; TELESCOPES; TITANIUM; VISIBLE RADIATION

Citation Formats

Colucci, Janet E., Bernstein, Rebecca A., and Cohen, Judith G., E-mail: jcolucci@obs.carnegiescience.edu. THE DETAILED CHEMICAL PROPERTIES OF M31 STAR CLUSTERS. I. Fe, ALPHA AND LIGHT ELEMENTS. United States: N. p., 2014. Web. doi:10.1088/0004-637X/797/2/116.
Colucci, Janet E., Bernstein, Rebecca A., & Cohen, Judith G., E-mail: jcolucci@obs.carnegiescience.edu. THE DETAILED CHEMICAL PROPERTIES OF M31 STAR CLUSTERS. I. Fe, ALPHA AND LIGHT ELEMENTS. United States. doi:10.1088/0004-637X/797/2/116.
Colucci, Janet E., Bernstein, Rebecca A., and Cohen, Judith G., E-mail: jcolucci@obs.carnegiescience.edu. Sat . "THE DETAILED CHEMICAL PROPERTIES OF M31 STAR CLUSTERS. I. Fe, ALPHA AND LIGHT ELEMENTS". United States. doi:10.1088/0004-637X/797/2/116.
@article{osti_22364834,
title = {THE DETAILED CHEMICAL PROPERTIES OF M31 STAR CLUSTERS. I. Fe, ALPHA AND LIGHT ELEMENTS},
author = {Colucci, Janet E. and Bernstein, Rebecca A. and Cohen, Judith G., E-mail: jcolucci@obs.carnegiescience.edu},
abstractNote = {We present ages, [Fe/H] and abundances of the α elements Ca I, Si I, Ti I, Ti II, and light elements Mg I, Na I, and Al I for 31 globular clusters (GCs) in M31, which were obtained from high-resolution, high signal-to-noise ratio >60 echelle spectra of their integrated light (IL). All abundances and ages are obtained using our original technique for high-resolution IL abundance analysis of GCs. This sample provides a never before seen picture of the chemical history of M31. The GCs are dispersed throughout the inner and outer halo, from 2.5 kpc < R {sub M31} < 117 kpc. We find a range of [Fe/H] within 20 kpc of the center of M31, and a constant [Fe/H] ∼ – 1.6 for the outer halo clusters. We find evidence for at least one massive GC in M31 with an age between 1 and 5 Gyr. The α-element ratios are generally similar to the Milky Way GC and field star ratios. We also find chemical evidence for a late-time accretion origin for at least one cluster, which has a different abundance pattern than other clusters at similar metallicity. We find evidence for star-to-star abundance variations in Mg, Na, and Al in the GCs in our sample, and find correlations of Ca, Mg, Na, and possibly Al abundance ratios with cluster luminosity and velocity dispersion, which can potentially be used to constrain GC self-enrichment scenarios. Data presented here were obtained with the HIRES echelle spectrograph on the Keck I telescope.},
doi = {10.1088/0004-637X/797/2/116},
journal = {Astrophysical Journal},
number = 2,
volume = 797,
place = {United States},
year = {Sat Dec 20 00:00:00 EST 2014},
month = {Sat Dec 20 00:00:00 EST 2014}
}
  • We present absorption line indices measured in the integrated spectra of globular clusters both from the Galaxy and from M31. Our samples include 41 Galactic globular clusters, and more than 300 clusters in M31. The conversion of instrumental equivalent widths into the Lick system is described, and zero-point uncertainties are provided. Comparison of line indices of old M31 clusters and Galactic globular clusters suggests an absence of important differences in chemical composition between the two cluster systems. In particular, CN indices in the spectra of M31 and Galactic clusters are essentially consistent with each other, in disagreement with several previousmore » works. We reanalyze some of the previous data, and conclude that reported CN differences between M31 and Galactic clusters were mostly due to data calibration uncertainties. Our data support the conclusion that the chemical compositions of Milky Way and M31 globular clusters are not substantially different, and that there is no need to resort to enhanced nitrogen abundances to account for the optical spectra of M31 globular clusters.« less
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  • We present the abundance analysis of 97 nearby metal-poor (-3.3 < [Fe/H] <-0.5) stars having kinematic characteristics of the Milky Way (MW) thick disk and inner and outer stellar halos. The high-resolution, high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg, Si, Ca, and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres. By assigning membership of the sample stars to the thick disk, inner halo, or outer halo components based on their orbital parameters, we examine abundancemore » ratios as a function of [Fe/H] and kinematics for the three subsamples in wide metallicity and orbital parameter ranges. We show that, in the metallicity range of -1.5 < [Fe/H] {<=}-0.5, the thick disk stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter. In contrast, the inner and the outer halo stars show lower mean values of these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe], and [Ca/Fe] for the inner and the outer halo stars also show weak decreasing trends with [Fe/H] in the range [Fe/H] >-2. These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars, while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales.« less
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