We present deep and accurate optical photometry of the Local Group starburst galaxy IC10 .
The photometry is based on two sets of images collected with the Advanced Camera for Surveys and with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope .
We provide new estimates of the Red Giant Branch tip ( TRGB ) magnitude , m _ { F 814 W } ^ { TRGB } = 21.90 \pm 0.03 , and of the reddening , E ( B-V ) = 0.78 \pm 0.06 , using field stars in the Small Magellanic Cloud ( SMC ) as a reference .
Adopting the SMC and two globulars , \omega Cen and 47 Tuc , as references we estimate the distance modulus to IC10 : independent calibrations give weighted average distances of \mu = 24.51 \pm 0.08 ( TRGB ) and \mu = 24.56 \pm 0.08 ( RR Lyrae ) .
We also provide a new theoretical calibration for the TRGB luminosity , and using these predictions we find a very similar distance to IC10 ( \mu \approx 24.60 \pm 0.15 ) .
These results suggest that IC10 is a likely member of the M31 subgroup .