1998A&A...336..662C

We present images of the N4 region in the Large Magellanic Cloud obtained with ISOCAM on board ISO through broad band filters centered at 6.75 and 15µm. Far from the three HII regions contained in the map, the emission at both wavelengths is due to the Unidentified Infrared Bands and associated continuum and originates in the external layers of a molecular cloud complex. The ratio between the intensities at 15 and 6.75µm is ≃0.6-0.7 comparable to the 0.55-0.85 ratio found in our Galaxy. Closer to the HII regions, this ratio increases when the ultraviolet radiation density reaches ≃10³ times the radiation density near the Sun, due to the contribution of very small grains to the flux near 15µm. The emission at both wavelengths is maximum in the direction of an interface between the main HII region N4A and the molecular cloud, a region very similar to the classical interface of M17 in our Galaxy. We have detected at both mid-IR wavelengths the emission of a M supergiant present in the field.