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Session 81 - Dwarf Galaxies.
Display session, Friday, January 09
As part of the Selected Areas Starcount Survey (SASSY), a CCD survey to V=21, we have obtained VI photometry of two fields placed along the major axis of the Sagittarius (Sgr) dwarf spheroidal galaxy at b=\pm 40^\circ. Comparison of the field star color-magnitude diagram (CMD) for these fields to the CMDs of fields reflected about the Galactic l=0^\circ meridian reveals an excess of stars at V=18.1 and 0.98 < V-I < 1.18 -- consistent with expectations for a Sgr red giant clump -- in the l=11^\circ, b=-40^\circ field. The excess appears to be confined to three adjacent 0.13 deg^2 subfields in this direction of the sky. No similar excess appears in our field at l=353^\circ, b=+41^\circ or in two other comparison fields. Deeper CCD imaging at the position of the possible Sgr red giant clump stars reveals an apparent main sequence turn off at 21 < V < 24, also consistent with the presence of the Sgr tidal extension at this Galactic latitude. This detection more than doubles the known extent of the Sgr tidal stream. Our apparent non-detection of Sgr at at b=+40 may indicate a maximum age to the stream of 1500 Myr, but may also be attributable to our northern survey field not being placed precisely along the orbit of Sgr, or a substantially reduced sky density at this large distance from its center.
Program listing for Friday