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Hayashi et al. have studied high-mass star formation in the HII region W28A2 by
investigating the molecular clouds surrounding the central stars using
carbon monoxide (CO) spectral line data taken with the NANTEN2 and Mopra telescopes.
The highest CO intensity is detected
where high-mass stars with the spectral types of O6.5–B0.5 (labelled A to D in the image above)
are embedded.
Comparisons of the radio continuum emission and 8 µm infrared emission
suggest physical associations between the gas and the exciting sources.
Similar gas properties are found in other Galactic massive star clusters, RCW 38 and
NGC 6334, where an early stage of molecular cloud collision to trigger the star formation has been suggested.
Based on these results, Hayashi et al. discuss the possibility of the formation of high-mass stars in the
W28A2 region triggered by a cloud-cloud collision.
The paper will be published in Publications of the Astronomical Society of Japan.
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