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Using high-resolution spectroscopy, we provide a determination of [Fe/H] and[Ca/H] for confirmed red-giant branch member stars of the Hercules dwarfspheroidal galaxy. Based on this we explore the ages of the prevailing stellarpopulations in Hercules, and the enrichment history from supernovae.Additionally, we provide a new simple metallicity calibration for Stromgrenphotometry for metal-poor, red giant branch stars. We find that the red-giantbranch stars of the Hercules dSph galaxy are more metal-poor than estimated inour previous study that was based on photometry alone. Additionally, we find anabundance trend such that [Ca/Fe] is higher for more metal-poor stars, andlower for more metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe]trend suggests an early rapid chemical enrichment through supernovae of typeII, followed by a phase of slow star formation dominated by enrichment throughsupernovae of type Ia. A comparison with isochrones indicates that the redgiants in Hercules are older than 10 Gyr.

An abundance study of red-giant-branch stars in the Hercules dwarf spheroidal galaxy