Star clusters in the dwarf irregular galaxy Leo A

Abstract

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 $\sim$10 Myr to $\sim$10 Gyr. So far, only one star cluster has been discovered in this galaxy. Our aim is to search for star cluster candidates in the Leo A galaxy. 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. 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 ($\sim$20 Myr; overlapping with HII regions) and low in mass ($\gtrsim$400 M$_\odot$ and $\gtrsim$150 M$_\odot$), the other three clusters are older ($\gtrsim$100 Myr) and also of low mass ($\gtrsim$300 M$_\odot$). These rough estimates are made assuming the isochrones of a metallicity derived for HII regions ($Z=0.0007$). Colour-magnitude diagrams of the stars residing in the circular areas of a 2.5arcsec radius around the clusters and integrated aperture photometry results of the clusters are presented.