Mid-infrared imaging and spectroscopy of the enigmatic cocoon stars in the Quintuplet Clusters

In an attempt, to determine the nature of the enigmatic cocoon stars in the Quintuplet Cluster, we have analyaed mid-infrared imaging and spectroscopy of the cluster obtained with the CAM and SWS instruments on ISO. We find no spectral line or feature that could elucidate the nature of these sources. Detailed modeling of the 9.7 mum silicate feature shows that it is best reproduced by the mu Cep profile with tau (sil) similar or equal to 2.9, consistent with the adopted extinction of A(V) similar or equal to 30 mag. The energy distributions are dereddened with a new reddening law specific to the Galactic Center, and are characterised by temperatures of 750-925 K, somewhat cooler than determined from near IR data alone. Models of optically thin and geometrically thick dust shells reproduce the observed SEDs from 4 to 17 mum, and imply shell luminosities of log(L/L-circle dot) similar or equal to 4.5-4.9.