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We derive the first detailed chemical abundances of three star clusters in the Large Magellanic Cloud (LMC), NGC 1831 (436 ± 22 Myr), NGC 1856 (350 ± 18 Myr), and [SL63]268 (1230 ± 62 Myr) using integrated-light spectroscopic observations obtained with the Magellan Echelle spectrograph on Magellan Baade telescope. We derive [Fe/H], [Mg/Fe], [Ti/Fe], [Ca/Fe], [Ni/Fe], [Mn/Fe], [Cr/Fe], and [Na/Fe] for the three clusters. Overall, our results match the LMC abundances obtained in the literature as well as those predicted by detailed chemical evolution models. For clusters NGC 1831 and NGC 1856, the [Mg/Fe] ratios appear to be slightly depleted compared with [Ca/Fe] and [Ti/Fe]. This could be hinting at the well-known Mg–Al abundance anti-correlation observed in several Milky Way globular clusters. We note, however, that higher signal-to-noise observations are needed to confirm such a scenario, particularly for NGC 1831. We also find a slightly enhanced integrated-light [Na/Fe] ratio for cluster [SL63]268 compared with those from the LMC field stars, possibly supporting a scenario of intracluster abundance variations. We stress that detailed abundance analysis of individual stars in these LMC clusters is required to confirm the presence or absence of multiple stellar populations.

In this third paper of a series on the precision of obtaining ages of stellar populations using the full-spectrum fitting technique, we examine the precision of this technique in deriving possible age spreads within a star cluster. We test how well an internal age spread can be resolved as a function of cluster age, population, mass fraction, and signal-to-noise ratio (S/N). For this test, the two ages (Age (SSP1) and Age (SSP2)) are free parameters along with the mass fraction of SSP1. We perform the analysis on 118 800 mock star clusters covering all ages in the range 6.8 < log (age/yr) < 10.2, with mass fractions from 10 per cent to 90 per cent for two age gaps (0.2 and 0.5 dex). Random noise is added to the model spectra to achieve S/N ratios between 50 and 100 per wavelength pixel. We find that the mean of the derived Age (SSP1) generally matches the real Age (SSP1) to within 0.1 dex up to ages around log (age/yr) = 9.5. The precision decreases for log (age/yr) > 9.6 for any mass fraction or S/N, due to the similarity of SED shapes for those ages. In terms of the recovery of age spreads, we find that the derived age spreads are often larger than the real ones, especially for log(age/yr) $\lesssim$ 8.0 and high mass fractions of SSP1. Increasing the age gap in the mock clusters improves the derived parameters, but Age (SSP2) is still overestimated for the younger ages.

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