Astron. Astrophys. Suppl. Ser. 134, 21-37

The Local Group dwarf irregular galaxy IC 1613

I.The young stellar content

L. Georgiev¹ - J. Borissova² - M. Rosado¹ - R. Kurtev³ - G. Ivanov³ - G. Koenigsberger¹

Send offprint request: J. Borissova

1 - Instituto de Astronomía, Universidad Nacional Autónoma de México, México
e-mail: georgiev@astroscu.unam.mx, margarit@astroscu.unam.mx and gloria@astroscu.unam.mx
2 - Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko chaussèe, BG-1784 Sofia, Bulgaria
e-mail: jura@haemimont.bg
3 - Department of Astronomy, Sofia University, BG-1164 Sofia, Bulgaria
e-mail: kurtev@phys.uni-sofia.bg and ivanov@phys.uni-sofia.bg

Received March 26; accepted July 1, 1998

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 IC1613 - 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 (IMF) for blue stars is $\Gamma = -2.0\pm0.1$ 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 IC1613, which confirms the original suggestion of Baade that IC1613 contains no bright globular clusters.

Key words: galaxies: individual: IC1613 -- galaxies: stellar content -- galaxies: star clusters and associations