The extinction law inside the 30 Doradus nebula

We have studied the interstellar extinction in a field of ~3' x 3' at the core of the 30 Doradus nebula, including the central R136 cluster, in the Large Magellanic Cloud. Observations at optical and near-infrared wavelengths, obtained with the WFC3 camera on board the Hubble Space Telescope, show that the stars belonging to the red giant clump are spread across the colour-magnitude diagrams because of the considerable and uneven levels of extinction in this region. Since these stars share very similar physical properties and are all at the same distance, they allow us to derive the absolute extinction in a straightforward and reliable way. Thus we have measured the extinction towards about 180 objects and the extinction law in the range 0.3 - 1.6 micron. At optical wavelengths, the extinction curve is almost parallel to that of the diffuse Galactic interstellar medium. Taking the latter as a template, the value of Rv = 4.5 +/- 0.2 that we measure indicates that in the optical there is an extra grey component due to a larger fraction of large grains. At wavelengths longer than ~1 micron, the contribution of this additional component tapers off as lambda^-1.5, like in the Milky Way, suggesting that the nature of the grains is otherwise similar to those in our Galaxy, but with a ~2.2 times higher fraction of large grains. These results are consistent with the addition of "fresh" large grains by supernova explosions, as recently revealed by Herschel and ALMA observations of SN 1987A.Comment: 14 pages, 11 figures, accepted for publication in MNRAS. Updated reference

Stellar populations in the Magellanic Clouds: looking through the dust

We present the first results of our study of stellar populations in the Large and Small Magellanic Clouds based on multi-band WFPC2 observations of "random" fields taken as part of the "pure parallel" programme carried out with the HST as a service to the community.Comment: Two pages, one figure, to appear in the proceedings of IAU Symposium 241 "Stellar Populations as Building Blocks of Galaxies", eds. A. Vazdekis and R. Peletie