| Abstract | Detailed surface photometry in blue light of the SA(s)d galaxy NGC 7793, the faintest of the five major members of the Sculptor group, is obtained from photoelectrically calibrated Mount Stromlo and McDonald photographs. The luminosity distribution is dominated by an exponential disk of effective radius αe = 2'.11 = 1.92 kpc contributing 98.6% of the total luminosity BT = 9.51 ± 0.06. The corrected face-on magnitude BT0 = 9.13 corresponds to MT0 = -18.35 at the revised distance ∆ = 3.1 Mpc (Appendix C). The spheroidal component visible only in the vicinity of the nucleus can be represented by an r1/4 law of effective radius rIe = 6".0 = 91 pc and total magnitude BTI = 14.13 or 1.4% of the total luminosity of the galaxy. The position angle of the major axis is 97°, the mean axis ratio is q = b/a = 0.61, and the inclination = 53°. The concentration indices C21 = 1.68 and C32 = 1.48 are consistent with the Sd classification. The integrated colors from UBV aperture photometry are essentially constant at = 0.56 ± 0.02, = -0.07 ± 0.02, the corrected face-on colors are (B - V)T0 = 0.46, (U - B)T0 = -0.15 in close agreement with the colors of M33 and the mean values for type Scd. A decomposition of the disk into an underlying old component and a young arm component shows that 65.570 of the total luminosity comes from the old component which has a corrected central luminosity μcα(0) = 21.06 and an effective radius re = 1'.76 = 1.60 kpc. The neutral H I mass MH = 0.67 × 109 Msun corresponds to a hydrogen-luminosity ratio MH/LB = 0.14 which is less than half the average for the morphological type and luminosity class of NGC 7793. The large number of H ii regions and the strength of the Hα emission in the disk suggest that a large fraction of the hydrogen is ionized. The integrated magnitude of the brightest superassociation (Hodge Nr 20) B, = 16.0 ± 0.1 is derived in Appendix A. The effect of resolution on the apparent peak brightness is illustrated in Appendix B. A revised distance modulus μ0 = 27.48 ± 0.25 (∆ = 3.13 ± 0.38 Mpc) is derived from five indicators in Appendix C. |
