Abstract
High-resolution observations of the C-band and L-band radio continuum of the hypercompact H II region G9.62+0.20E conducted with the e-MERLIN interferometric array are presented. A flux density of 2.25±0.20 mJy and an angular size of 127±22 mas were measured for the C-band continuum. At L band, an upper limit of on the integrated flux density was calculated at the continuum's position. The surrounding sources C and D were detected at levels consistent with previous detections. The results for source E requires a steeper spectrum at L band than previous observations extrapolated from higher frequencies. This can be explained with a truncated inverse square law density distribution model. We obtain a C-band peak brightness temperature of about 4000 K, which assuming an electron temperature of 104K translates to an optical depth of 0.5, indicating the continuum is optically thin at C band going thick at L band. These results therefore place firm constraints on H II region models in source E. The periodic variability of methanol masers, as seen in G9.62+0.20E, has been explained with the pulsating star, accretion disc, and colliding wind binary models. Some models predict a hypercompact H II region can provide pumping for methanol masers. In the colliding wind binary model context maser variability is attributed to seed photon modulation. Hence, future H II models matching our observations could test predictions of these models in terms of the variability profiles of the 1.6 GHzOH and 6.7 GHz methanol masers.
Original language | English |
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Pages (from-to) | 3277-3283 |
Number of pages | 7 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 536 |
Issue number | 4 |
DOIs | |
Publication status | Published - 1 Feb 2025 |
Keywords
- (ISM:) H ii regions
- masers
- radio continuum: stars
- stars: formation
- stars: massive