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G. De Marchi (ESA), N. Panagia, V. Kozhurina-Platais (STScI), M. Romaniello (ESO)
We have started a study of the stellar populations in the Large and Small Magellanic Clouds using data (U, B, V, I and H-alpha imaging) collected as part of the WFPC2 pure parallel programme. In our first step, we have considered four fields in the LMC and three in the SMC, which comprise stellar populations with ages ranging from a few Myr to a few Gyr and in which pre-main-sequence objects are clearly identified. In addition to the properties of these populations, we have studied the characteristics and distribution of the dust present in these fields. Using the properties of the red giant branch in the various colour--magnitude diagrams, we have determined the extinction law in each field. We find that not only the amount of extinction but also its wavelength dependence varies considerably from site to site, indicating that the physical properties of the absorbing dust are not uniform across the Clouds. This analysis has allowed us to determine the relative three-dimensional distribution of the different populations as well as their location with respect to the absobing dust clouds. We find that, among young stars, those less massive than 2 solar masses are spatially more spread over each field than massive B-type stars, whereas old stars are quite uniformly distributed. The data also reveal that young stars, which appear to be spatially associated with the nebular emission, are physically confined within a small range of distances, whereas old stars are uniformly distributed at all depths along the line of sight. An important corollary of our investigation is that unaccounted patchy absorption or a variable extinction law are likely to contribute significantly to the present discrepancies between various distance indicators for the LMC.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.