Berkeley 87

V. F. Polcaro, Istituto di Astrofisica Spaziale, CNR, Frascati, and Universita 'La Sapienza', Rome; F. Giovannelli, Istituto di Astrofisica Spaziale, CNR, Frascati; R. K. Manchanda, Physics Department, Space Physics Group, AADF, Canberra; L. Norci and C. Rossi, Istituto di Astronomia, Universita 'La Sapienza'; and G. Tessicini, Osservatorio Astronomico, Bologna, write: "We announce the discovery with the Loiano 1.52-m telescope (+ Boller and Chivens 26767 spectrograph + CCD RCA camera) of a strong, diffuse C IV (580.1-581.2 nm) emission in the Berkeley 87 cluster near the WR star ST3 (which shows strong emission from O VI, C IV, and He II). The diffuse emission seems to cover the entire core of Berkeley 87. This young open cluster is embedded in the ON2 molecular clouds complex at the boundary of the Cygnus X region. Its position is fully compatible with the unidentified COS-B source 2GC 075+00. A weak, hard x-ray source, positionally coincident with the cluster, was identified during a slew by the EXOSAT satellite. The UHURU and HEAO-A1 catalogs report sources compatible with the position of Berkeley 87. We can assume that the envelope of ST3 is strongly interacting with the cluster's interstellar medium. In particular, the ON2 association contains the compact HII region G75.77+0.34, whose angular distance from the center of the cluster is on the order of 1'. The density of this cloud was evaluated as 10E5 cmE-3. We suggest that the interaction of the ST3 stellar wind with this cloud generates a shock wave that can accelerate to relativistic velocities the energetic particles emitted by the numerous early-type stars contained in the cluster. This mechanism can originate the high-energy emission. Further observations, mainly at high energies, are needed."