Electronographic photometry of star clusters in the Magellanic Clouds - VI. The colour-magnitude diagram of Hodge 11

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 $$6 \times 10^8\enspace\text {yr}$$, but with a giant branch which is displaced blueward by about $$\Delta (B-V)_0 = 0.4$$ 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.