THE DUST DISTRIBUTION INSIDE THE LARGE MAGELLANIC CLOUD

The distribution of the interstellar dust inside the LMC has been inve stigated on the basis of UBV photometry and spectral classifications o f 1507 luminous O-A type stars. The mean internal reddening has been f ound to be rather high with E(B-V) = 0.(m)16. The frequency distributi on of the reddenings is strongly asymmetric, so that it is useless to give an error of the mean. Reddenings up to 0.(m)8 have been observed. A strong selection effect is caused by the restricted visibility of s trongly reddened stars. The intrinsically faint stars (V-0 > 13.(m)3) of our sample show no or low reddening E(B-V) < 0.(m)2 Stars of interm ediate brightness (12.(m)3 < V-0 less than or equal to 13.(m)3) are re ddened by up to more than 0.(m)3. Reddenings between 0.(m)4 and 0.(m)8 occur for the intrinsically brightest stars (V-0 less than or equal t o 12.(m)3) only. According to the luminosity function the completeness limit of our sample has been found to be about 12.(m). To determine t he reddening without bias, all intrinsically fainter stars have to be rejected. A comparison of the positions of highly reddened stars with E(B-V) > 0.3 with those of molecular clouds detected by Cohen et al. ( 1988) shows few coincidences. Contrary to the dark cloud catalogues of Hedge (1972) and van den Bergh (1974) we detect highly reddened stars almost everywhere in the LMC. The frequency distribution of the redde nings can be fitted by a two cloud model. The mean reddenings caused b y small and large dark clouds are 0.(m)04 +/- 0.(m)01 and 0.(m)40 +/- 0.(m)10, respectively. In the LMC, dust cloud properties are quite sim ilar to those in the Galaxy. The number of small clouds on line of sig ht in comparison to that of large clouds is, however, higher than in t he Milky Way. For the LMC we observe a number ratio of 45 +/- 10 which may be compared with the galactic value of 9 +/- 1. Finally we have d etermined a map of the internal reddening in the LMC. It shows overall agreement with that of Isserstedt & Kohl (1984), but gives higher abs olute values, dominated by 30 Dor and the supershell LMC 2. Rather hig h reddenings have been found in the HII region N 11 and around the sup ershell LMC 6, too. Our map shows the same structure of the interstell ar medium in the LM as the HI map derived by Luks & Rohlfs (1992) and the IR emission maps derived by Israel & Schwering (1986).