Isolated dwarf irregular galaxies are good laboratories to study the star formation history as well as the evolution of galaxies in the absence of external triggers and without the influence of large-scale internal triggers like density waves (see Hunter 1997, for a review). Understanding local dwarfs constrains the models which were developed for a description of the large population of sub-luminous, irregular systems at medium redshifts (see Babul & Ferguson 1996; Ferguson & Babul 1998). Very nearby galaxies of this type are best suited for detailed analysis of their star formation histories as they can be resolved into individual stars (see e.g. Gallart et al. 1996, their Table 1, and Greggio 1994 and references in these papers). Inside the Local Group (distance up to roughly 1 Mpc), ground-based deep images under excellent seeing conditions can be used for this type of investigation while for more distant galaxies (up to about roughly 5-10 Mpc), HST data are essential (e.g. Schulte-Ladbeck et al. 1998). For galaxies in this distance range, radial velocities are very crude distance estimators as the peculiar velocities are in the order of or larger than the Hubble flow. A quick and in-expensive method to reject more distant interlopers from the 10 Mpc sample is the identification of the brightest stars which can be done with ground-based images of good seeing (see the discussion by Karachentsev & Tikhonov 1993, K&T hereafter), and Rozanski & Rowen-Robinson 1994, R&RR). Further, the ground based images indicate the regions of recent high star formation activities (HII regions, star clusters), thus allowing a pre-selection for the pointing of the HST or adaptive optic observations with their rather small field of view.
UGC 685 (=CGCG0104.7+1625), which belongs to the 10 Mpc sample of Kran-Korteweg & Tammann (1979), was classified as a late type dwarf galaxy (Sm). Kran-Korteweg & Tammann could not associate UGC 685 to one of their groups and therefore called it a field galaxy. This indicates that at least the recent evolution and star formation history of UGC 685 was free of important triggers by interaction, albeit small mass HI companions as found in several cases by Taylor et al. (1996) can not be ruled out. The available optical data as recently compiled by Schmidt & Boller (1992a,b) indicate a rather normal and absolutely faint dwarf galaxy at a systemic velocity (corrected for the local group flow) of 377 km s-1. The galaxy was included in various HI surveys which indicate an amount of in neutral gas and a ratio of neutral gas to blue luminosity of 0.6 (Schmidt & Boller 1992a,b), also rather normal for its type. As this dwarf galaxy appears relatively regular on survey plates and was indicated to be nearby, I selected it for a kinematic study of its stars and its ionized gas as well as for a study of its chemical abundances through optical long slit spectroscopy.
Only a radial velocity exists as distance indicator for UGC 685. Surface photometry which is necessary for the analysis of kinematic data is still missing. Finally, no colors or other values which hint at the star formation history, are published yet. I therefore included this dwarf galaxy in photometric CCD observations with the Calar Alto 3.5 m and 2.2 m telescopes to obtain multi-color surface photometry of the galaxy, its structural parameters and HII morphology and to resolve the brightest supergiants. These can yield an independent distance estimate, following the recent update of the calibration for the brightest blue supergiants by K&T and R&RR. The limitation and error budget of this techniques has been discussed in detail by R&RR.
The observations and their reductions are described in Sect. 2. The structure and HII morphology, the color-magnitude diagram of the resolved stars and the distance estimate are presented in Sect. 3 and I conclude in Sect. 4.
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