Search for TeV γ-ray emission from the open star cluster Berkeley 87

Abstract

Observations of the nearby young open star cluster Berkeley 87 (distance=0.9 kpc) have been carried out in the TeV energy range with the system of imaging air Cherenkov telescopes of the HEGRA collaboration. Berkeley 87, with its dense interstellar medium, many young stars and especially the Wolf-Rayet Star WR–142 producing stellar winds of approximately 5200 km/s, is the most promising candidate among the known open clusters for the acceleration of cosmic rays. The EGRET source 2EG J2019+3719 has been associated with Berkeley 87, thus giving further motivation for VHE observations of this source with the HEGRA telescopes. No evidence for emission of TeV γ-rays has been found. The derived upper limit ΦU.L.90%(E>0.8 TeV)=3×10−12 cm−2 s−1 on the integral flux constrains the possible contribution of young open clusters to the observed flux of charged Galactic cosmic rays and makes a significant contribution seem unlikely.