Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...394..107b&link_type=abstract
Astronomy and Astrophysics, v.394, p.107-113 (2002)
Astronomy and Astrophysics
Astrophysics
14
Ism: Hii Regions, Ism: Molecules, Masers, Stars: Formation
Scientific paper
We have carried out sensitive observations of the highly excited 2Pi3/2, J=7/2 state of OH (290 K above the ground-level) at 13,441 MHz (F=4-4) and 13,435 MHz (F = 3-3) in both right and left circular polarizations with the Effelsberg 100-m telescope. Our sample included 27 compact or ultra-compact HII regions. Most of them have been selected from our previous J=5/2 OH maser survey of star-forming regions taken from the IRAS point-source catalog. We have observed weak 2Pi3/2, J=7/2, F = 4-4 and 3-3 absorption in 7 sources and discovered 3 new weak F = 4-4 maser sources at 13,441 MHz in addition to W3(OH). The new sources, 20081+3122 (ON1), 21413+5442 and G11.90-0.14, are 50 to 100 times or more weaker than the 13,441 MHz peak flux density observed in W3(OH). 21413+5442 and G11.90-0.14 exhibit extremely narrow velocity extents of the order of 0.4 km s-1. However, in ON1 there are two groups of narrow velocity features separated by about 14 km s-1; these two groups are also observed in lower rotational levels and suggest complex kinematics in the envelope of the young ultra-compact HII region. Apart from a very weak, polarized, and narrow J=7/2, F = 3-3 emission feature lying on the red wing of the 13,435 MHz absorption feature in W3(OH) no J=7/2, F =3-3 emission was discovered. We conclude that the 13,441 MHz OH maser emission from W3(OH) remains exceptionally strong but not unique. In contrast with the J=5/2, 6035 MHz maser emission observed in a large number of star-forming regions, J=7/2, 13,441 MHz emission is not widespread. This is expected from OH maser theory, and because the involved J=7/2 levels are high in the OH energy ladder and not directly connected to the ground-state.
Baudry Alain
Desmurs J.-F.
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