The stellar content and distance to the nearby blue compact dwarf galaxy NGC 6789^*

¹ Astronomical Institute, St.-Petersburg State University, Petrodvoretz 198904, Russia
² Special Astrophysical Observatory, N.Arkhyz, Karachai-Circassian Rep. 357147, Russia

Send offprint request to: I. Drozdovsky; e-mail: dio@astro.spbu.ru

Received: 21 August 1998
Accepted: 19 October 1999

Abstract

In this paper we present the results of a detailed B, V, R, I, and Hα study of the isolated nearby blue compact dwarf (BCD) galaxy NGC 6789. The observed galaxy has not yet been resolved into stars up to now. On CCD frames obtained with 6 m BTA telescope and 2.5 m Nordic telescope the galaxy is well resolved. Its colour-magnitude diagram confirms the two component (core-halo) galaxy morphology, which consists of two stellar populations distinct in structure and colour: an inner high surface-brightness young population within 150 pc from the center of the galaxy, and a relatively low surface-brightness intermediate-age population extending out to at least 600 pc. The distance to the galaxy, estimated from the tip of the red giant branch (TRGB) is 2.1 Mpc which places NGC 6789 close to the Local Group. From the mean colour of the RGB, the mean metal abundance of the halo population is estimated as [Fe/H]  dex.