Star clusters in the dwarf irregular galaxy Leo A

Abstract

Context. Leo A is an isolated gas-rich dwarf irregular galaxy of low stellar mass and metallicity residing at the outskirts of the Local Group. Ages of the stellar populations in Leo A range from ∼10 Myr to ∼10 Gyr. So far, only one star cluster has been discovered in this galaxy. Aims. Our aim is to search for star cluster candidates in the Leo A galaxy. Methods. We performed photometry of star-like objects on HST ACS archive observation frames in the F475W and F814W passbands and studied the spatial clustering of the Leo A stars down to the turn-off point of the old stellar populations. Results. We report the discovery of four star clusters in the Leo A galaxy. This means that now a sample of five star clusters is known in Leo A. Two clusters are of a young age (∼20 Myr; overlapping with H II regions) and low in mass (≳400 M⊙ and ≳150 M⊙), the other three clusters are older (≳100 Myr) and also of low mass (≳300 M⊙). These rough estimates are made assuming the isochrones of a metallicity derived for H II regions (Z = 0.0007). Colour–magnitude diagrams of the stars residing in the circular areas of a 2.5″ radius around the clusters and integrated aperture photometry results of the clusters are presented.