Distribution and Studies of the Infrared Stellar Population in the Galaxy - Part Three - Baade's Window Photometry

Details Distribution and Studies of the Infrared Stellar Population in the Galaxy - Part Three - Baade's Window Photometry Distribution and Studies of the Infrared Stellar Population in the Galaxy - Part Three - Baade's Window Photometry

Apr 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26as...93...61f&link_type=abstract

Astronomy and Astrophysics Supplement, Vol.93, NO. 1/APR, P. 61, 1992

Astronomy and Astrophysics

Astrophysics

13

Galaxy (The): Bulge Of, Galaxy (The): General, Galaxy (The): Stellar Content Of, Infrared Radiation, Photometry

Scientific paper

An infrared scan of the Baade Window (BW) (l ˜ 0.0, b ˜ -4°) area is obtained. The Cumulative K-Counts Function (hereafter CCF is the No. of sources per sq. degree down to K ˜ +13.5) is formed by combining 1.9 m (74") telescope scans with Anglo Australian Telescope (AAT) scans. With the aid of a theoretical exponential disk model (see Jones et a'. 1981, Ruelas-Mayorga 1991 a, b) and observations at l = 20, b = 5 and l = 10, b = -5, we decompose the observed CCF into disk-CCF and components. The bulge-CCF is steeper than the disk-CCF in the range +5.0 < K < +11.0 showing a relative depletion of high mass stars with respect to the disk. The contribution of the bulge component towards BW is significant only at K ˜ +8.0 or fainter magnitudes; the bright end of the 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 population of the bulge may be similar in age and perhaps metallicity characteristics to the stellar population in globular clusters. Photometric studies of a bright-K subs ample (˜ 165) of the 578 sources found in BW down to K ˜ +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) = 0.45 obtained by optical techniques. In an HR diagram most of the sources in our photometric subsample lie above the giant branch tips of ω-Cen, 47 Tuc and M92 if the giant branches (GB) of these clusters are extrapolated to higher K brightnesses, a sizable fraction of our sample would lie between them. This also suggests that their metallicity may 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 magnitudes brighter than K = +8.5, an even higher metallicity is required. However, on the basis of the CCF results mentioned above, the brighter sources should be predominantly disk members, so their high metal content should not be surprising

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