EDP Sciences
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Volume 394, Number 1, October IV 2002
Page(s) 107 - 113
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021097

A&A 394, 107-113 (2002)
DOI: 10.1051/0004-6361:20021097

Discovery of new highly excited OH sources in regions of high-mass star formation

A. Baudry1 and J. F. Desmurs1, 2

1  Observatoire de l'Université de Bordeaux 1, BP 89, 33270 Floirac, France
2  Observatorio Astronómico Nacional, Apartado 1143, 28800 Alcalá de Henares, Spain

(Received 20 March 2002 / Accepted 29 July 2002)

We have carried out sensitive observations of the highly excited $^2
\Pi_{3\over 2}, J={7\over 2}$ 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 $J={5\over 2}$ OH maser survey of star-forming regions taken from the IRAS point-source catalog. We have observed weak $^2 \Pi_{3\over 2},
J={7\over 2}, F = 4-4$ 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 $J={7\over 2}, F =
3-3$ emission feature lying on the red wing of the 13 435 MHz absorption feature in W3(OH) no $J={7\over 2}, F =
3-3$ 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 $J={5\over 2}$, 6035 MHz maser emission observed in a large number of star-forming regions, $J={7\over 2}$, 13 441 MHz emission is not widespread. This is expected from OH maser theory, and because the involved $J={7\over 2}$ levels are high in the OH energy ladder and not directly connected to the ground-state.

Key words: ISM: HII regions -- ISM: molecules -- masers -- stars: formation

Offprint request: A. Baudry, baudry@observ.u-bordeaux.fr

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