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: email@example.com.
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|
|NGC 4190||UGC 8308|
|UGC 7298||UGC 8320|
|*) The star No 44 from Hopp & Schulte-Ladbeck|
|is situated outside our CCD frame.|