Spectroscopic analysis of the candidate globular clusters NGC 1928 and 1939 in the Large Magellanic Cloud

Abstract

The integrated spectral properties in the range 3600±6700 Å of the candidate old clusters NGC 1928 and 1939 in the LMC bar are compared with those of old-and intermediate-age reference LMC clusters, the properties of which are better established. It has been possible to infer the age of the sample clusters by means of absorption features and the continuum distribution, in particular in the plane WM x WB (where WB is the average of Hδ, Hγ and Hβ equivalent widths, and WM that of Ca II K, G band and Mg I). The results indicate that NGC 1928 and 1939 are compatible with old clusters. The metallicity is derived with respect to galactic globular cluster templates: [Fe/H]~~ - 1.2 and - 2.0 for NGC 1928 and 1939, respectively. We also discuss the census of Population II clusters in the LMC, their spatial distribution and the possibility of a LMC core and a transient morphological classification for interacting late-type disc galaxies.