Luminosity and colour distribution in the interacting system NGC 7770-71

Detailed surface photometry for the SB(s)a galaxy NGC 7771 has been carried out in the blue spectral band. Isophotes, luminosity profiles, and photometric parameters are obtained from photographs collected with the 74 inch telescope of Kottamia Observatory, Egypt. The total apparent magnitudem_T=13.08 with maximum dimensions 3.6±0.5×2.7±0.5 (at threshold µ_m = 27.38 mag s^–2). The absolute magnitude isM_T=–21.70 if the distance is =90.2 Mpc. The major axis is in position angle =69°.5±1° and the mean axis ratio of the outer regionsq=b/a=0.45 corresponds to an inclinationi=66°. The equivalent effective radiusr_e^*=0.29 and the effective surface brightness µ_e = 22.30 mag s^–2.The equivalent luminosity distribution has been decomposed into two main components, anr^1/4 spheroid and an exponential disk. The total apparent magnitudes of the spheroidal and disk components are 14.36 and 13.48, which correspond to contributions of 31 and 69% to the total blue luminosity, respectively.