W. Herschel in November 1787, respectively, and are known to be members of the M31 subgroup. Together with NGC205, they are the most luminous dSphs in the Local Group and are located at an angular distance of approximately $12^\circ$ from the Andromeda nebula (van den Bergh [@vanbergh]; Corradi [@corr]). According to van den Bergh ([@vanbergh]), they are separated by only 58on the sky without any indication of interaction (Battinelli & Demers [@batti_a]; Geha et al. [@geha]). Although these galaxies appear fairly similar concerning their colour-magnitude diagrams (CMDs), some differences can be found in their star formation histories (SFHs), most notably for recent epochs ($<$1Gyr see Mateo [@mateo]). Because there are no main-sequence turn-off stars with $M_{V}$$<$$-1$, Han et al. ([@han]) mentioned that the most recent large-scale star-forming activity in occurred at least 1Gyr in the past. According to broad-band near-infrared CMDs of Riebel ([@riebel]), this event happened $\approx$3Gyr ago and Dolphin ([@dolphin]) derived 4Gyr using HST images. That there are no signs of dust and gas (Young and Lo [@yolo], Sage [@sage]) in this galaxy, which could serve as building material for new stars, also supports the idea that star formation ceased long ago. Using the relation between the $K$-magnitude 