  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,DDO51
photometric system allows us to remove the background M31/M33 giants from our
CMD and more clearly define the dwarf star feature, which has an MSTO near M ~
20.5. The corresponding stellar population shows little density variation over
the 12 X 6 square degree area of the sky sampled and is of very low surface
brightness, >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).

Astrophysics