Abstract:
The integrated magnitudes and colors of 163 DDO "dwarf" galaxies in the UBV system are derived from 542 photoelectric observations with four telescopes between 1976 and 1980. Total (asymptotic) magnitude B_T, mean color indices (B-V), (U-B), effective aperture diameter Aₑ, and mean effective surface brightness m'ₑ are derived for 150 objects, all but two late-type (T≥6) systems. The total magnitudes are in the range 11.1 ≤ B_T ≤ 15.8. The mean surface brightness m'e is in the range 22.3 ≤ m'ₑ ≤ 25.9 mag arcsec^-2; it is in all cases fainter than the night sky (22.2) and, in the mean, fainter than in the (non-DDO) late-type galaxies in the Second Reference Catalogue of Bright Galaxies (RC2), for which 20 < m'ₑ < 24. The accidental errors in the photometry, discussed in Appendix B, are correspondingly larger. The luminosity distributions follow closely the standard magnitude-aperture curves for the appropriate types and are characteristic of exponential disks with vanishingly small spheroidal components. The color-aperture relations indicate a slight bluing with increasing aperture, contrary to earlier findings for the brighter (non-DDO) late-type systems in RC2. There is no clear indication of a dependence of color on axis ratio (i.e., inclination) or surface brightness. Mean colors corrected to the standard effective aperture and for galactic extinction are calculated. The magnitude estimates of Fisher and Tully are reduced to the B_T system. Their systematic errors depend on mean surface brightness, diameter, and axis ratio. The corrected magnitudes so derived for 244 objects have mean errors of ˜0.5 mag and may be used as first approximations for the 79 objects not yet measured by us. The physical properties of the DDO sample will be discussed in Paper II.
