[show abstract][hide abstract] ABSTRACT: As part of the Selected Areas Starcount Survey (SASS), a CCD survey to V>21, we have obtained VI photometry of two fields at b=+-40 aligned roughly with an extrapolation of the major axis of the Sagittarius (Sgr) dwarf spheroidal galaxy. Comparison of the color-magnitude diagram (CMD) for some of these fields to the CMDs of fields reflected about the Galactic l=0 meridian reveals an excess of stars at V_o=17.85 and 0.9 < (V-I)_o < 1.1 in the (l,b) = (11,-40) field. The excess stars have colors consistent with the Sgr red clump, and deeper CMD imaging in these locations shows evidence of a main-sequence turnoff at V=21 with the main-sequence extending to the limit of our data (V=24). The surface brightnesses we derive from either the potential excess of red clump stars or the apparent excess of MSTO stars are consistent with each other and with the results of other surveys at this latitude. No similar excess appears in our northern Galactic hemisphere fields near l=353, b=+41 field. We have obtained spectroscopy of all 30 candidate red clump stars in the range 0.9 < (V-I)_o < 1.1 and 17.75 < V_o < 17.95. The radial velocity distribution of the stars, while dissimilar from expectations of Galactic structure models, does not show a contribution by stars near the Galactocentric radial velocity seen in other studies near the Sgr core. It is difficult to reconcile a photometric result that is consistent with other explorations of the Sagittarius stream with a radial velocity distribution that is apparently inconsistent. In a companion paper (Johnston et al. 1999), we discuss how some of the discrepancies are resolved if ur potential Sgr detection corresponds to a different Sgr tidal streamer than that detected by most other surveys. Comment: 26 pages, including 8 figures, accepted to Astronomical Journal
The Astronomical Journal 01/1999; 118(4):1709-1718. · 4.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: 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=+/- 40(deg) . Comparison of the field star color-magnitude diagram (CMD) for these fields to the CMDs of fields reflected about the Galactic l=0(deg) 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(deg) , b=-40(deg) 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(deg) , b=+41(deg) 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.