# Chandra Observations of the Massive Star-Forming Region Onsala 2

## TL;DR

This study uses Chandra X-ray observations to analyze the massive star-forming region Onsala 2, revealing numerous X-ray sources, including massive stars, Wolf-Rayet stars, and diffuse emission, providing new insights into its stellar population and structure.

## Contribution

First detailed X-ray analysis of Onsala 2 revealing its stellar content, diffuse emission, and the nature of embedded massive stars and young stellar objects.

## Key findings

- Over 300 X-ray sources detected, including massive OB stars and WR 142.
- Diffuse X-ray emission associated with H II regions and shocked stellar winds.
- Few X-ray sources show near-IR excesses typical of classical T Tauri stars.

## Abstract

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.