Images of the six observed irregular
dwarf galaxies are reproduced from the Digital POSS in Fig. 1 (click here). We performed
observations of the galaxies in March 10, 1994 at the prime focus of
the 6 meter telescope (scale 8.6 arcsec/mm). A CCD chip of 
pixels was used with a readout noise of 12 e and a pixel size of
microns, which yielded a total field of 
arcsec.
For each of the galaxies we obtained B and V frames with a typical
exposure 
s under a seeing of FWHM = 1.3 - 1.5 arcsec. The frames
were calibrated using the equatorial standard stars from Landolt (1992).
Figure 1: Reproductions from the Digital POSS-I of the six irregular galaxies.
Each chart is 
arcmin. North at top, East at left
Figure 2: The V frames of NGC 4163, NGC 4190, UGC 7298, UGC 7577, UGC 8308,
and UGC 8320 after a subtraction of a smoothed frame. North and
East are indicated by arrows. The brightest stars from Table 1 (click here)
are marked. Tick marks are given for every 5 arcsec
After the initial processing of the frames we made aperture photometry of stars using the PC VISTA package (Treffers & Richmond 1990) and the UMAG package of Georgiev (1995), which allows us to reduce the inhomogeneity of the local background around the measured stars.
The V images of the observed galaxies are presented in Fig. 2 (click here). To show
the structure of the central part as well as of the periphery of each galaxy, we
subtracted a frame smoothed with a window of 
. Based on the
results of our photometry the Colour-Magnitude diagrams were
derived for the brightest stars of the galaxies. We reproduce them in
Fig. 3 (click here), where star-like objects are indicated with filled squares and
slightly diffuse ones with open squares. The brightest blue (B- V < 0.4)
and red (B - V > 1.6) stars are marked in Fig. 2 (click here). Their apparent
B magnitudes and B - V colours are presented in Table 1 (click here). The complete
tables of the photometric data are accessible via FTP address: ntik@sao.ru.
Figure 3: Colour-Magnitude diagrams for the six dwarf galaxies. Dark squares
are star-like objects, open squares are slightly diffuse ones,
crosses are the blue stars which have been used for distance determination
| star | B | B - V | star | B | B - V |
| NGC 4163 | UGC 7577 | ||||
| B0 | 18.76 | 0.05 | B1 | 20.26 | -0.17 |
| B1 | 20.01 | -0.10 | B2 | 20.48 | -0.19 |
| B2 | 20.37 | 0.09 | B3 | 20.56 | 0.12 |
| B3 | 20.65 | -0.21 | (R1) | 22.49 | 1.58 |
| NGC 4190 | UGC 8308 | ||||
| B1 | 19.84 | 0.13 | B1 | 20.60 | 0.04 |
| B2 | 20.02 | -0.09 | B2 | 21.07 | 0.08 |
| B3 | 20.64 | -0.01 | B3 | 21.19 | -0.13 |
| R1 | 21.80 | 1.67 | R1 | 22.16 | 1.87 |
| UGC 7298 | UGC 8320 | ||||
| B1 | 21.93 | 0.20 | B1 | 19.37 | 0.17 |
| B2 | 22.45 | 0.11 | B2*) | 20.21 | (0.21) |
| B3 | 22.47 | 0.07 | B3 | 20.76 | 0.08 |
| R1 | 23.33 | 1.60 | B4 | 21.10 | 0.00 |
| B5 | 21.40 | 0.12 | |||
| R1 | 22.97 | 2.30 | |||
| *) The star No 44 from Hopp & Schulte-Ladbeck | |||||
| is situated outside our CCD frame. | |||||