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Astron. Astrophys. 348, 768-782 (1999)

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3. Observations and data reduction of the K band mosaic

We are in the process of mapping the central 2[FORMULA] of the Nuclear Bulge and selected areas further out in the H and K band ([FORMULA] 1.65 and 2.2 µm) using the IRAC 2B camera with the ESO-MPG 2.2m telescope on La Silla, Chile. The IRAC 2B camera uses a NICMOS3 chip with 2562 pixels. The pixel scale can be changed between [FORMULA] and [FORMULA] using lenses A to E, respectively (Lidman et al. 1996). For the chosen lens B we have a pixel scale of [FORMULA]. This produces images of size [FORMULA]. The image shown here in Fig. 1a and b is part of a K band mosaic which - when finished - will cover an area of size [FORMULA]. An observing technique has been selected which allows us to recover an extended background emission using a nearby dark cloud as reference point (see also Table 2). 494 images were used to construct the K band mosaic image of the central [FORMULA] shown in Fig. 1a and discussed in this paper (see Appendix A and B for a more detailed discussion of observing and data processing techniques. Appendix C deals specifically with problems associated with K band source counts). Since IRS 7, one of the strongest individual sources in all of our NIR images, is variable on time-scales of months (we measured [FORMULA] Jy in 1995 and [FORMULA] Jy in 1996) we used the IR star SA 109-71 as flux density calibrator. In the UKIRT Faint Standard Star List this star is designated FS 28 with flux densities [FORMULA] mJy and [FORMULA] mJy.


Table 2. Characteristics of the K band Mosaic [FORMULA] approximately centered on Sgr A*.
1 Eq. (1)
2 Cox & Mezger, 1989
3 Mezger & Pauls, 1979

The [FORMULA] 1.2 mm bolometer observations were made using the 7- through 37-channel bolometer arrays developed by E. Kreysa and coworkers of the MPIfR (Kreysa et al., 1996) with the IRAM 30m-MRT. Uranus and Mars were used as flux density calibrators. Extinction caused by the atmosphere was measured using SKYDIPS. The observing and reduction procedures will be detailed in a forthcoming paper. In Fig. 1b the surface brightness of the dust emission is overlaid as a contour map on the K band mosaic shown in Fig. 1a.

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199