VLT/UVES spectroscopy of individual stars in three globular clusters in the Fornax dwarf spheroidal galaxy

Abstract

We present a high resolution (R ∼ 43 000) abundance analysis of a total of nine stars in three of the five globular clusters associated with the nearby Fornax dwarf spheroidal galaxy. These three clusters (1, 2 and 3) trace the oldest, most metal-poor stellar populations in Fornax. We determine abundances of O, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y, Ba, Nd and Eu in most of these stars, and for some stars also Mn and La. We demonstrate that classical indirect methods (isochrone fitting and integrated spectra) of metallicity determination lead to values of [Fe/H] which are 0.3 to 0.5 dex too high, and that this is primarily due to the underlying reference calibration typically used by these studies. We show that Cluster 1, with [Fe /H] = −2.5, now holds the record for the lowest metallicity globular cluster. We also measure an over-abundance of Eu in Cluster 3 stars that has only been previously detected in a subgroup of stars in M 15. We find that the Fornax globular cluster properties are a global match to what is found in their Galactic counterparts; including deep mixing abundance patterns in two stars. We conclude that at the epoch of formation of globular clusters both the Milky Way and the Fornax dwarf spheroidal galaxy shared the same initial conditions, presumably pre-enriched by the same processes, with identical nucleosynthesis patterns.

Searching for chemical inhomogeneities in open clusters

“…Similar features have been reported in extragalactic GCs (e.g. Letarte et al 2006;Mucciarelli et al 2009). Several main-sequence (MS) turn-offs or anomalous spreads in this region have been observed in intermediate-age and young massive clusters in the Magellanic Clouds (e.g.…”

Chemical abundance analysis of the open clusters Cr 110, NGC 2099 (M 37), NGC 2420, NGC 7789, and M 67 (NGC 2682)

“…The most interesting property of the chemical anomalies, is that they have never been found outside globular clusters. They are not present in the field populations of the Milky Way and its surrounding dwarf galaxies, and they have only more recently been found in Fornax and LMC clusters (Letarte et al 2006;Johnson et al 2006;Mucciarelli et al 2009). Dedicated searches for anticorrelations in OC include that of Martell & Smith (2009), on the strength of CH and CN bands in NGC 188, NGC 2158, and NGC 7789, that of Smiljanic et al (2009), based on high resolution spectroscopy of C, N, O, Na, and 12 C/ 13 C and that of De Silva et al (2009), which compiles and homogenizes literature Na-O high resolution data.…”

A high-resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy

“…There have also been high-resolution UVES studies of 9 individual stars in 3 of the globular clusters associated with Fornax (Letarte et al 2006). One of the globular clusters was observed to have a mean metallicity of [Fe/H] = −2.5 and all of them (see also, Strader et al 2003) have metallicities quite distinctly lower than the majority of the field stellar population, although Fornax field also host a low-level metal-poor tail extending down to −2.8 (B06).…”