Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-02-19
Astrophys.J. 604 (2004) L105-L108
Astronomy and Astrophysics
Astrophysics
12 pages, 3 figures
Scientific paper
10.1086/386282
We present high angular resolution ($\sim0\rlap.{''}1$-$0\rlap.{''}4$) VLA observations at 2 and 6 cm made in 1983, 1986, and 1995 toward the ultracompact bipolar H II region NGC 7538 IRS1. We find, at both wavelengths, clear evidence of a decrease in the emission from the lobes. This decrease, of orden 20-30%, has not been observed previously in any ultracompact H II region. Most likely, it is due to recombination of the ionized gas in the lobes as a result of a decrease in the available ionizing photon flux. It is unclear if this decrease in the ionizing photon flux is due to an intrinsic change in the exciting star or to increased absorption of ionizing photons in the optically-thick core of the nebula.
Franco-Hernández Ramiro
Rodr{\'ı}guez Luis F.
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