2 Observations

The DENIS instrument is mounted at the Cassegrain focus of the 1-m ESO telescope (La Silla - Chile). It contains three cameras: a Tektronix CCD with $1024\times1024$ pixels and two NICMOS infrared detectors with $256\times256$ pixels. The array of the camera has four quadrants to reduce the read-out time, and each quadrant, especially in the I band, presents different image characteristics and must be treated separately. The pixel sizes are $1\hbox{$^{\prime\prime}$ }$ in Iand $3\hbox{$^{\prime\prime}$ }$ in J and $K_{\rm s}$, respectively. The total integration time is 9 s for each image. The sampling of the image is $1\hbox{$^{\prime\prime}$ }$ in all three wave bands. The J and $K_{\rm s}$ images are dithered to a $1\hbox{$^{\prime\prime}$ }$ pseudo-resolution, using a microscanning mirror. They consist of a set of 9 frames each obtained in 1 s integration time, shifted by $\pm 1/3$ pixel in right ascension (RA) plus $\pm 7/3$ pixel in declination (DEC).

The DENIS strategy is to divide the sky into three declination zones and scan each in strips of $30\hbox{$^\circ$ }$ in DEC and $12\hbox{$^\prime$ }$ in RA. The overlap in RA between consecutive strips is $2\hbox{$^\prime$ }$. Each strip consists of 180 images of $12\hbox{$^\prime$ }\times12\hbox{$^\prime$ }$ with an overlap of $2\hbox{$^\prime$ }$ between each image. The observation of a photometric standard star consists of 8 sub-images shifted according to a circular pattern in order to have the star always at a different position on the chip. One I standard is observed before the observation of a strip and one J and $K_{\rm s}$ standard afterwards. On average 6 to 8 strips per night are observed.

Data on the MCs were taken during observing seasons from August to March, the first centered on December 1995, and the last one on December 1998. The two clouds, LMC and SMC, were covered by 119 and 88 strips, respectively.