Chandra Detects the Rare Oxygen-type Wolf-Rayet Star WR 142 and OB Stars in Berkeley 87

Kimberly R. Sokal$^1$, Stephen L. Skinner$^1$, Svetozar A. Zhekov$^{2,3}$, Manuel G"{u}del$^4$, and Werner Schmutz$^5$

1-CASA, Univ. of Colorado, Boulder, CO, USA 80309-0389; 2-JILA, Univ. of Colorado, Boulder, CO, USA 80309-0440; 3-On leave from Space Research Institute, Sofia, Bulgaria; 4-Dept. of Astronomy, Univ. of Vienna, T"{u}rkenschanzstr. 17, A-1180 Vienna, Austria; 5-Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center (PMOD/WRC), Dorfstrasse 33, CH-7260 Davos Dorf, Switzerland

We present first results of a {em Chandra} X-ray observation of the rare oxygen-type Wolf-Rayet star WR 142 (= Sand 5 = St 3) harbored in the young, heavily-obscured cluster Berkeley 87. Oxygen type WO stars are thought to be the most evolved of the WRs and progenitors of supernovae or gamma ray bursts. As part of an X-ray survey of supposedly single Wolf-Rayet stars, we observed WR 142 and the surrounding Berkeley 87 region with {em Chandra} ACIS-I. We detect WR 142 as a faint, yet extremely hard X-ray source. Due to weak emission, its nature as a thermal or nonthermal emitter is unclear and thus we discuss several emission mechanisms. Additionally, we report seven detections and eight non-detections by {em Chandra} of massive OB stars in Berkeley 87, two of which are bright yet soft X-ray sources whose spectra provide a dramatic contrast to the hard emission from WR 142.

Reference: ApJ
Status: Manuscript has been accepted