The nature of VV76 (NGC 4496A,B)

Long-slit optical spectra show that the northern member (NGC 4496A) of the binary galaxy VV 76 has a systemic velocity of cz = 1700 km s-1^, whereas the southern member (NGC 4496B) has the considerably higher velocity of cz = 4510 km s-1^. A series of three narrow-band CCD images confirms the presence of two distinct redshift systems, showing that the galaxies form an optical, rather than a physical, binary. The probability of a chance superposition is roughly 0.006, not so small that the cosmological interpretation of galaxy redshifts need seriously be questioned. We also report the discovery of a probable Type II supernova (SN 1988M) in NGC 4496B, ~ 200-400 days past maximum brightness. If this object were actually at the distance of NGC 4496A, but with a discordant redshift, it should have been quite bright (mV_~ 13.5-14 mag, neglecting extinction) near maximum and, therefore, likely to have been discovered during several active, systematic searches for supernovae. Since SN 1988M was not detected earlier, we conclude that NGC 4496B is indeed much more distant than NGC 4496A.