Physics and Astronomy Calendar

The Hercules Thick Disk Cloud (Larsen et al. 2009) was first initially
discovered as an excess in the number of faint blue stars between
quadrants I and IV of the Galaxy. The field stars responsible for the
excess, are between 2 and 4 kiloparsecs from the Sun, 1.2 kpc above the
Galactic plane, and the asymmetry feature or Cloud is kiloparsecs in
length -- a major substructure in the Galaxy. The origin of the Cloud
could be an interaction with the disk bar, a triaxial thick disk or a
merger remnant or stream. To better map the spatial extent of the Cloud
along the line of sight, we have obtained multi-color UBVR photometry
for 1.2 million stars in 67 fields of approximately 1 square degree
each. Our analysis of fields beyond the apparent boundaries of the
excess rule out a triaxial thick disk as a possible explanation for the
Cloud (Larsen et al., accepted). In this talk we present our results
for the counts over all of our fields and characterize the size of the
excess. Over the entire 500 square degrees of sky containing the Cloud,
we estimate about a quarter of a million F/G type stars, bringing the
estimated mass of the Cloud to over a million solar masses.
Additionally, one of our quadrant IV fields contains a blue horizontal
branch feature that implies that a large number of stars are clumped in
a small range of distances. We have tentatively identified this clump
with the Cetus Tidal Stream of Newberg et al. (2009).