Astron. Astrophys. 358, L9-L12 (2000)
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
. The DCMC catalogue contains sources
detected in at least two of the three DENIS bands (I:
within a surface area of square
degrees centered on
toward the LMC and square degrees
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 (, I)
colour-magnitude diagrams (Fig. 1 for the LMC only) to select
three classes of objects in each Cloud. Sources labelled (A) with
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
, 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
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
sensitivity limits are 18, 16 and 14 mag respectively. Photometric
errors widen the sequences towards fainter magnitudes.
Fig. 1. Colour-Magnitude Diagram (,I) of sources detected simultaneously in I, J and towards the LMC (). The horizontal line marking the position of the TRGB (Cioni et al. 2000a), and the slanted line at 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 , 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.
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.
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.
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.
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.
Fig. 6. Star count of the SMC - class B; contours are at: 2, 5, 10, 15, 20, 25, 50 per 0.04 deg2.
Fig. 7. Star count of the SMC - class C; contours are at: 50, 60, 75, 100, 125, 150, 200, 225 per 0.04 deg2.
© European Southern Observatory (ESO) 2000
Online publication: June 26, 2000