Mem. S.A.It. Vol. 79, 747 c  SAIt 2008 Memorie della N. Sanna 1,2 , G. Bono 2 , M. Monelli 3 , I. Drozdovsky 3 , G. Giuffrida 1,2 , S. Cassisi 4 , A. Pietrinferni 4 , R. Buonanno 1 , F. Caputo 2 , C. E. Corsi 2 , I. Ferraro 2 , G. Iannicola 2 , and L. Pulone 2 1 Universit` a di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy e-mail: sanna@roma2.infn.it 2 INAF-Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone (RM), Italy 3 IAC-Instituto de Astrofisica de Canarias, Calle Via Lactea, E38200 La Laguna, Tenerife, Spain 4 INAF-Osservatorio Astronomico di Collurania-Teramo, via Maggini, 64100 Teramo, Italy Abstract. We present preliminary results of a photometric investigation on IC10 using F555W and F814W data collected with WFPC2@HST covering two different regions. We provide a new estimate of both distance and reddening by adopting the Tip of the Red Giant Branch (TRGB). We find that the RGB stars in the two regions are located at the same distance, but present different reddening values. In particular, we find DM 0 = 24.75 ± 0.1 and E(B - V ) = 0.44 ± 0.14 for the outer region, and E(B - V ) = 0.60 ± 0.14 for the central fields. Moreover we show that stellar isochrones at fixed metal content, distance and reddening account for both Main Sequence (MS) and evolved stellar components. Key words. Galaxies: dwarf - Galaxies: Local Group - Galaxies: individual (IC10) 1. Introduction IC10 is a dwarf irregular galaxy of the Local Group and it is the unique analogue in the nearby Universe for starburst galaxies. Although several theoretical and empirical in- vestigations have been focused on IC10, cur- rent estimates of distance and reddening are still affected by large uncertainties. This means that we do not know yet whether IC10 is a member of M31 group. Moreover, by using op- Send offprint requests to: N. Sanna tical space (HST) and Near-Infrared ground- based (Keck) data, Vacca, Sheehy & Graham (2007) found a puzzling feature concerning its stellar content. The fit of the young Main Sequence and evolved Red Giant stars would require, at fixed metal abundance (Z = 0.008) and distance modulus (DM 0 = 24.5), two dif- ferent reddening values, E( B - V ) = 0.95 for MS and E( B - V ) = 0.60 for RG stars. 2. Data sets and reduction strategy The data sets consist of two different archival HST/WFPC2 pointings, both observed with