THE ABUNDANCES OF NEUTRON-CAPTURE SPECIES IN THE VERY METAL-POOR GLOBULAR CLUSTER M15: A UNIFORM ANALYSIS OF RED GIANT BRANCH AND RED HORIZONTAL BRANCH STARS

By J. Sobeck, R. P. Kraft, C. Sneden, G. Preston, J. Cowan, Graeme H. Smith, I. Thompson, S. Shectman, G. Burley. 2011

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The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Δ(RHB − RGB) ≈ 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.

Subfields: Astronomy and Astrophysics, Instrumentation, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/887325297a7143a620fe6d4dd4a43378c9da2cd7

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Citations in the corpus

DETAILED CHEMICAL ABUNDANCES IN THE r-PROCESS-RICH ULTRA-FAINT DWARF GALAXY RETICULUM 2 (2016, methodology): “We compute Fe abundances from Fe i and Fe ii lines using a recent version of the spectrum analysis code MOOG (Sneden 1973; Sobeck et al. 2011), which assumes local thermodynamic equilibrium (LTE) for the line-forming layers of the atmosphere.”
The GALAH survey: scientific motivation (2015, methodology): “MNRAS 449, 2604–2617 (2015) at A ustralian A stronom ical O bservatory on M ay 2, 2015 http://m nras.oxfordjournals.org/ D ow nloaded from The measured EWs were used to derive spectroscopic parameters for the solar spectra using the 2012 version of the MOOG code (Sneden 1973; Sobeck et al. 2011).”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, methodology): “We refer the reader to Cayrel et al. (2004) and Sobeck et al. (2011) for a discussion regarding the importance of Raleigh scattering (Griffin et al. 1982) at blue wavelengths in metal-poor stars.”
A SEARCH FOR STARS OF VERY LOW METAL ABUNDANCE. VI. DETAILED ABUNDANCES OF 313 METAL-POOR STARS (2014, methodology): “The current version of MOOG includes Rayleigh scattering from neutral H atoms in the source function (Sobeck et al. 2011).”
The SUMO project: a SUrvey of Multiple pOpulations in globular clusters (2013, background): “In NGC 7078CN-CH, C-N, and Na-O anticorrelations have been observed (Sneden et al. 1997; Cohen et al. 2005; Kayser et al. 2008; Pancino et al. 2010) and also a spread in the slow neutroncapture elements (Sneden et al. 1997, 2000; Sobeck et al. 2011).”