Fundamental parameters of the highly reddened young open clusters Westerlund 1 and 2

We study the compact open clusters Westerlund 1 (BH 197) and Westerlund 2. We present CCD integrated spectroscopy for both clusters, and CCD imaging in the V and I bands for the former one. So far, Westerlund 1 is possibly the most reddened open cluster studied in detail ($A_{v} \approx 13.0$). It has an age of 8 ± 3 Myr and a distance from the Sun of $d_\odot \approx 1.0 \pm 0.4$ kpc. For Westerlund 2 we derive a visual absorption $A_{V}\approx 5.0$ mag, an age of 2-3 Myr, and $d_\odot=5.7\pm 0.3$ kpc. From luminosity and structural arguments we conclude that Westerlund 1, although young and compact, it is a massive cluster, in contrast to Westerlund 2.