Near-infrared spectroscopy of a young super-star cluster in NGC 6946: chemical abundances and abundance patterns

Using the NIRSPEC spectrograph at Keck II, we have obtained H- and K- band echelle spectra for a young (similar to 10-15 Myr), luminous (M-V similar to - 13.2) super-star cluster in the nearby spiral galaxy NGC 6946. From spectral synthesis and equivalent width measurements we obtain for the first time accurate abundances and abundance patterns in an extragalactic super-star cluster. We find [Fe/H]=- 0.45 +/- 0.08 dex, an average alpha-enhancement of approximate to + 0.22 +/- 0.1 dex, and a relatively low C-12/C-13 approximate to 8 +/- 2 isotopic ratio. We also measure a velocity dispersion of approximate to 9.1 km s(-1), in agreement with previous estimates. We conclude that integrated high-dispersion spectroscopy of massive star clusters is a promising alternative to other methods for abundance analysis in extragalactic young stellar populations.