An upper main sequence ( MS ) and main-sequence turn-off ( MSTO ) feature appears in the color-magnitude diagram ( CMD ) of a large area photometric survey of the southern half of M31 stretching to M33 .
Imaging in the Washington M,T _ { 2 } ,DDO 51 system allows us to remove the background M31/M33 giants from our CMD and more clearly defined the dwarf star feature , which has an MSTO near M \sim 20.5 .
The corresponding stellar population shows little density variation over the 12 ^ { \circ } \times 6 ^ { \circ } area of the sky sampled and is of very low surface brightness , \Sigma > 32 mag arcsec ^ { -2 } .
We show that this feature is not the same as a previously identified , MS+MSTO in the foreground of the Andromeda Galaxy that has been associated with the tidal stream ringing the Milky Way disk at less than half the distance .
Thus , the new stellar system is a separate , more distant entity , perhaps a segment of tidal debris from a disrupted satellite galaxy .
It is most likely related to the structure with similar distance , location and density uniformity seen as an excess of K and M giants in the Two Micron All-Sky Survey reported in the companion paper by Rocha-Pinto et al .
( 2004 ) .