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Astron. Astrophys. 358, L9-L12 (2000)

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2. The data

Our morphological study of the Magellanic Cloud is based on a sample of stars extracted from the DCMC catalogue (Cioni et al. 2000). The sample includes all sources detected in both I and J, irrespective of detection in [FORMULA]. The DCMC catalogue contains sources detected in at least two of the three DENIS bands (I: [FORMULA]m, J: [FORMULA]m and [FORMULA]: [FORMULA]m) within a surface area of [FORMULA] square degrees centered on [FORMULA],[FORMULA] toward the LMC and [FORMULA] square degrees centered on [FORMULA],[FORMULA] toward the SMC; J2000 coordinates are used throughout this paper. The observations have been performed with the DENIS instrument (Epchtein et al. 1997) on the 1m-ESO telescope.

We have used the ([FORMULA], I) colour-magnitude diagrams (Fig. 1 for the LMC only) to select three classes of objects in each Cloud. Sources labelled (A) with [FORMULA] represent the youngest population in the Magellanic Clouds: the brightest dwarf stars, blue-loop stars and supergiants (third vertical sequence from the left), together with an unrelated foreground component of dwarfs and giants (first two vertical sequences from the left). Sources labelled (B) with [FORMULA], located above the tip of the red giant branch (TRGB - Cioni et al. 2000a) are mainly asymptotic giant branch stars (AGB). Sources labelled (C) with [FORMULA] located below the TRGB are mostly red giant branch stars (RGB) and represent the oldest population in the Clouds. For the sake of clarity, we have plotted in Fig. 1 only those sources that were detected in all three wave bands and that occur in the very central part of the Cloud. Sources detected only in I and J predominantly populate the lower part of the diagram. The position of the TRGB is indicated by a horizontal line. The I, J and [FORMULA] sensitivity limits are 18, 16 and 14 mag respectively. Photometric errors widen the sequences towards fainter magnitudes.

[FIGURE] Fig. 1. Colour-Magnitude Diagram ([FORMULA],I) of sources detected simultaneously in I, J and [FORMULA] towards the LMC ([FORMULA]). The horizontal line marking the position of the TRGB (Cioni et al. 2000a), and the slanted line at [FORMULA] define the classes A, B, and C discussed in the text.

For each class of objects in each of the two Clouds, we show their distribution in the plane of the sky by counting the sources in bins of [FORMULA], applying a light smoothing to the resulting structure (Figs. 2-7); the contour values increase logarithmically. Regions corresponding to missing data (strips at constant RA indicated by diamonds) were filled in by interpolation. Their effect is mostly negligible except in Fig. 4 where strips of possibly lower photometric quality may be causing discontinuities in the outermost contours.

[FIGURE] Fig. 2. Star count of the LMC - class A (Fig. 1); contours are at: 100, 125, 150, 200, 300, 400, 500, 800 per 0.04 deg2.

[FIGURE] Fig. 3. Star count of the LMC - class B (Fig. 1); contours are at: 3, 5, 7, 10, 20, 30, 50, 100, 150 per 0.04 deg2.

[FIGURE] Fig. 4. Star count of the LMC - class C (Fig. 1); contours are at: 100, 150, 200, 250, 350, 500, 600, 800, 1000, 1200 per 0.04 deg2.

[FIGURE] Fig. 5. Star count of the SMC - class A; contours are at: 20, 30, 45, 60, 75, 100, 125, 150, 200, 250 per 0.04 deg2.

[FIGURE] Fig. 6. Star count of the SMC - class B; contours are at: 2, 5, 10, 15, 20, 25, 50 per 0.04 deg2.

[FIGURE] Fig. 7. Star count of the SMC - class C; contours are at: 50, 60, 75, 100, 125, 150, 200, 225 per 0.04 deg2.

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© European Southern Observatory (ESO) 2000

Online publication: June 26, 2000