DISTRIBUTION AND STUDIES OF THE INFRARED STELLAR POPULATION IN THE GALAXY .3. BAADE WINDOW PHOTOMETRY

An infrared scan of the Baade Window (BW) (l approximately 0.0, b appr oximately -4-degrees) area is obtained. The Cumulative K-Counts Functi on (hereafter CCF is the N-degrees. of sources per sq. degree down to K approximately +13.5) is formed by combining 1.9 m (74") telescope sc ans with Anglo Australian Telescope (AAT) scans. With the aid of a the oretical exponential disk model (see Jones et al. 1981, Ruelas-Mayorga 1991a, b) and observations at l = 20, b = 5 and l = 10, b = -5, we de compose the observed CCF into disk-CCF and bulge-CCF components. The b ulge-CCF is steeper than the disk-CCF in the range +5.0 < K < +11.0 sh owing a relative depletion of high mass stars with respect to the disk . The contribution of the bulge component towards BW is significant on ly at K approximately +8.0 or fainter magnitudes; the bright end of th e CCF is dominated by the disk. The bulge-CCF is compared with derived CCF's for the globular clusters 47 Tuc, M92, M3 and M13 and with that of the open cluster M67. The similarity of the slope of the bulge-CCF to those of the globular clusters suggests that the stellar populatio n of the bulge may be similar in age and perhaps metallicity character istics to the stellar population in globular clusters. Photometric stu dies of a bright-K subsample (approximately 165) of the 578 sources fo und in BW down to K approximately +11.0 are made. Several sources with mild IR-Excesses are found and later, by spectroscopy, are confirmed as Mira variables. The majority of the sources lie along the reddening line at E(J - K) = 0.27 from the solar neighbourhood intrinsic giant sequence. The reddening agrees very well with the value E(B - V) = 0.4 5 obtained by optical techniques. In an HR diagram most of the sources in our photometric subsample lie above the giant branch tips of omega -Cen, 47 Tuc and M92 if the giant branches (GB) of these clusters are extrapolated to higher K brightnesses, a sizeable fraction of our samp le would lie between them. This also suggests that their metallicity m ay lie in the range between that of M92 and 47 Tuc. For those sources with redder J - K colours than the 47 Tuc Giant Branch (GB) and with m agnitudes brighter than K = +8.5, an even higher metallicity is requir ed. However, on the basis of the CCF results mentioned above, the brig hter sources should be predominantly disk members, so their high metal content should not be surprising.