Results of the digital co-addition of thirteen Schmidt films of the Virgo cluster of galaxiesA. C. Katsiyannis, S. N. Kemp, D. S. Berry and J. MeaburnAstron. Astrophys. Suppl. Ser., 132 3 (1998) 387-399DOI: https://doi.org/10.1051/aas:1998302