Electronographic photometry of star clusters in the Magellanic Clouds - VI. The colour-magnitude diagram of Hodge 1 1

Electronographic magnitudes and colours of 78 stars in the cluster Hodge 11 in the Large Magellanic Cloud have been measured to V = 21.5 on electrographs taken with a Spectracon image-converter attached to the focus of the 1.5-m (60-inch) Cerro Tololo reflector. The zero point of the electronographic photometry was provided by photoelectric observations of four stars in the cluster field using the same telescope. The colour-magnitude diagram of the cluster consists of an evolved main sequence, whose termination point corresponds to an age of about 6 × 10⁸ yr, but with a giant branch which is displaced blueward by about Δ(B-V)₀ = 0.4 from the positions of the giant branches of open clusters of similar age in our Galaxy. This displacement probably results from a very low metal abundance, similar to that in the most metal-poor globular clusters such as M92. However, an enriched He content cannot presently be ruled out as a contributing factor. Hodge 11 thus appears to be similar to the Large Magellanic Cloud cluster NGC 2209, but is somewhat younger than this cluster and possesses a more abnormal chemical composition.