Stellar population of the blue compact dwarf galaxy SBS 1415+437

Abstract

The stellar population of the blue compact dwarf galaxy SBS 1415+437 is investigated us- ing the archive database of the Hubble space telescope. The color index-magnitude diagram for stars reaches a magnitude of 29 m in the V and I bands. It comprises young main-sequence stars, blue and red supergiants, and the old population of red giant branch and asymptotic giant branch. The tip of the red giant branch (TRGB) was used to calculate the distance modulus, which turned out to be m-M = 30.65 0.08 m . The corresponding distance to the galaxy is D = 13.5 1.0 Mpc. The youngest stars are distributed irregularly near the bright H II region in the southwest part of SBS 1415+437. The old popu- lation occupies a larger area, it is distributed more evenly and forms the galactic halo. The spatial distri- bution of young stars shows that the star formation in the galaxy spread in the direction from northeast to southwest over the last 5 10 7 yr with an average rate of 60 km/s. The TRGB of SBS 1415+437 was found to be appreciably shifted to the blue range: (V - I)TRGB 1.30. The galaxy age turns out to be not smaller than the age of Galactic globular clusters (about 10 10 yr), provided that the galaxy originally had a very low metallicity (our photometric estimate is (Fe/H) = -2.4). If the metallicity of SBS 1415+437 changed almost not at all in the course of evolution and was equal to (Fe/H) = -1.3 (as estimated from the emission lines of ionized gas), the galaxy age is no more than 2 10 9 yr.