The Local Group dwarf irregular galaxy IC 1613

Abstract

Abstract. We obtained U -band photometry of 1500 stars and BV -band photometry of 3100 stars in a field centred on the HII regions of the northeast sector of the dwarf irregular galaxy IC 1613 -a member of the Local Group. The ages of the stellar populations were determined from the ((B − V ) 0 , M V ) color-magnitude using the isochrones from Padua's library. The stellar populations were split into three groups: the group of the youngest stars with ages of between 5 and 20 Myr, the group of intermediate stars with ages of 200−300 Myr and the group of old stars with ages up to 10 Gyr. The slope of the Stellar Initial Mass Function (IM F ) for blue stars is Γ = −2.0 ± 0.1 which is similar to that of other nearby galaxies. We investigated the stellar content of nine Hodge associations as well as that of seven new OB associations determined by cluster analysis. The total U , B and V magnitudes of eight Hodge open clusters and two new cluster candidates are given and there are six new possible nonstellar objects reported. The latter are most probably distant galaxies visible through the disk of IC 1613, which confirms the original suggestion of Baade that IC 1613 contains no bright globular clusters.

The young stellar population of IC 1613

“…The associations we have found follow the same distribution as Hodge (1978)'s, but our code breaks them into many smaller ones. Georgiev et al (1999) observed the same effect in their results for the bubble area of the galaxy, and pointed out that their associations are the bright cores of Hodge's. We also find new associations both at the core of IC 1613 and the periphery.…”

“…The youngest stars (age ∼ 10 Myr) are patchily arranged on the uniform underlying distribution of red stars (Freedman 1988;Battinelli et al 2007). In the bubble region, the young population can be split into 2 age groups of 5-20 Myr and 200-300 Myr (Georgiev et al 1999). The red supergiant stars in the region are massive (20-25 M ) and belong to the younger age group (Borissova et al 2000).…”

“…The first one was made from visual inspection of plates and published by Hodge (1978). More recent works by Ivanov (1996) (catalogue not public), Georgiev et al (1999) and Borissova et al (2004) have used an automatic procedure very similar to ours. Our work has produced the largest catalogue: a total of 164 stellar groups, almost tripling the 60 associations found by Borissova et al Hodge (1978) listed 20 associations andIvanov (1996) only found 6.…”

“…Our work has produced the largest catalogue: a total of 164 stellar groups, almost tripling the 60 associations found by Borissova et al Hodge (1978) listed 20 associations andIvanov (1996) only found 6. Georgiev et al (1999) studied a smaller field.…”

“…The associations found by Georgiev et al (1999) are provided on detector coordinates or plotted over a poor quality image, and since the same team studied a wider field in Borissova et al (2004) we preferred the latter for comparison. We use the coordinates and radius of the associations in their Table 1 to compare with ours (see Fig.…”