VLBA+Y27 Images of the Formaldehyde Masers in NGC 7538 and G29.96-0.02

Details VLBA+Y27 Images of the Formaldehyde Masers in NGC 7538 and G29.96-0.02 VLBA+Y27 Images of the Formaldehyde Masers in NGC 7538 and G29.96-0.02

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aspc..340..347h&link_type=abstract

Future Directions in High Resolution Astronomy: The 10th Anniversary of the VLBA, ASP Conference Proceedings, Vol. 340. Edited

Astronomy and Astrophysics

Astronomy

Scientific paper

We present the first VLBI detections of formaldehyde (H2CO) masers. Using the VLBA+Y27, we have imaged the 6 cm H2CO masers in the H II regions NGC 7538 and G29.96-0.02 using phase-referencing. Our images include a 15 mJy source which is the weakest Galactic maser to be imaged with VLBI techniques. We find the angular sizes of the NGC 7538 masers to be ˜ 10 mas (30 AU) and the G29.96-0.02 masers to be ˜ 20 mas (130 AU). These sizes correspond to brightness temperatures ˜ 107-8 K, several orders of magnitude above theoretical expectations. We detect no formaldehyde emission in the 2 cm line, indicating the lack of a 2 cm maser and placing limits on the 6 cm excitation process. A pronounced velocity gradient of 28 km s-1 arcsecond-1 (1900 km s-1 pc-1) is detected in the NGC 7538 maser gas.

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