Chandra Observations of the Massive Star-Forming Region Onsala 2
  Previous radio and infrared observations have revealed an obscured region of
high-mass star formation in Cygnus known as Onsala 2 (ON 2). Within this region
lies the optically-revealed young stellar cluster Berkeley 87 which contains
several OB stars and the rare oxygen-type Wolf-Rayet star WR 142. Previous
radio studies of ON 2 have also discovered masers and several H II regions
excited by embedded OB stars. Radio and GAIA parallaxes have now shown that the
H II regions are more distant than Berkeley 87. We summarize two Chandra X-ray
observations of ON 2 which detected more than 300 X-ray sources. Several
optically-identified stars in Berkeley 87 were detected including massive OB
stars and WR 142, the latter being a faint hard source whose X-ray emission
likely arises in hot thermal plasma. Intense X-ray emission was detected near
the compact H II regions G75.77+0.34 and G75.84+0.40 consisting of numerous
point sources and diffuse emission. Heavily-absorbed X-ray sources and their
near-IR counterparts that may be associated with the exciting OB stars of the H
II regions are identified. Shocked winds from embedded massive stars offer a
plausible explanation of the diffuse emission. Young stellar object candidates
in the ON 2 region are identified using near-IR colors, but surprisingly few
counterparts of X-ray sources have near-IR excesses typical of classical T
Tauri stars.
