Chemical composition of the young massive cluster NGC 1569-B

Abstract

We present a detailed chemical abundance analysis of the young massive cluster (YMC) NGC 1569-B. The host galaxy, NGC~1569, is a dwarf irregular starburst galaxy at a distance of 3.36$\pm$0.20 Mpc. We determined the abundance ratios from the analysis of an optical integrated-light spectrum of NGC 1569-B, obtained with the HIRES echelle spectrograph on the Keck I telescope. We considered different red-to-blue supergiant ratios, namely: the ratio obtained from a theoretical isochrone, the ratio obtained from a resolved colour-magnitude diagram of the YMC, and the ratio that minimises the ${\chi }^2$ when comparing our model spectra with the observations. We adopted the latter ratio for our resulting chemical abundances. The derived iron abundance is sub-solar with [Fe/H] = $-0.74\pm 0.05$. In relation to the scaled solar composition, we find enhanced $\alpha$-element abundances, $\text{[<Mg,Si,Ca,Ti>/Fe]}=+0.25\pm$0.11, with a particularly high Ti abundance of +0.49$\pm$0.05. Other super-solar elements include $\text{[Cr/Fe]}=+0.50\pm$0.11, $\text{[Sc/Fe]}=+0.78\pm$0.20, and $\text{[Ba/Fe]}=+1.28\pm$0.14, while other Fe-peak elements are close to scaled solar abundances: ($\text{[Mn/Fe]}=-0.22\pm$0.12 and $\text{[Ni/Fe]}=+0.13\pm$0.11). The composition of NGC 1569-B resembles the stellar populations of the YMC NGC 1705-1, located in a blue compact dwarf galaxy. The two YMCs agree with regard to $\alpha$-elements and the majority of the Fe-peak elements, except for Sc and Ba, which are extremely super-solar in NGC~1569-B -- and higher than in any YMC studied so far. The blue part of the optical spectrum of a young population is still a very challenging wavelength region to analyse using IL spectroscopic studies. This is due to the uncertain contribution to the light from blue supergiant stars, which can be difficult to disentangle from turn-off stars, even when resolved photometry is available.

18 pages, 9 figures. Accepted for publication in A&A

References in corpus (17)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• The effect of massive binaries on stellar populations and supernova progenitors
• A high resolution VLT/FLAMES study of individual stars in the centre of the Fornax dwarf spheroidal galaxy
• Age as a Major Factor in the Onset of Multiple Populations in Stellar Clusters
• Chemical composition and constraints on mass loss for globular clusters in dwarf galaxies: WLM and IKN
• The Araucaria Project. VLT spectra of blue supergiants in WLM: classification and first abundances
• The search for multiple populations in Magellanic Clouds clusters - V. Correlation between cluster age and abundance spreads
• Anatomy of a Young Massive Star Cluster: NGC 1569-B
• A New Hubble Space Telescope Distance to NGC 1569: Starburst Properties and IC 342 Group Membership
• Stellar Metallicity of the Extended Disk and Distance of the Spiral Galaxy NGC 3621
• A New Method for Measuring Metallicities of Young Super Star Clusters
• The chemical composition of globular clusters in the Local Group
• A homogeneous comparison between the chemical composition of the Large Magellanic Cloud and the Sagittarius dwarf galaxy
• Young stellar population gradients in central cluster galaxies from NUV and optical spectroscopy
• The Massive M31 Cluster G1: Detailed Chemical Abundances from Integrated Light Spectroscopy
• Searching for globular cluster chemical anomalies on the main sequence of a young massive cluster

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