Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...325..255b&link_type=abstract
Astronomy and Astrophysics, v.325, p.255-268
Astronomy and Astrophysics
Astrophysics
54
Masers, Stars: Formation, Interstellar Medium: Hii Regions, Magnetic Fields, Radio Lines: Ism
Scientific paper
We have undertaken a comprehensive search for 5 cm OH masers in regions visible from Effelsberg with the 100-m telescope (i.e., those with declinations above -29^o^). Our sample is based on bright sources taken from the IRAS Point Source Catalog and/or from previous 18 cm OH and H_ 2_O surveys. Among the 165 sources observed, 16 are new (15 exhibit emission and one source shows both absorption and emission). Two new absorption line sources have been tentatively detected. The general properties of the 5 cm OH sources are presented and discussed. The 6035MHz line is more often detected than the 6031MHz line. Nevertheless, the latter line is frequently present, a fact that is not explained by present OH excitation models. Simple calculations tend to show that there are enough FIR photons to pump the 6035 and 6031MHz masers, and we found that the statistics of the ratio S_ radio_/S_ IR_ at 18, 5 and 6 cm suggest that the maser pumping efficiency decreases with increasing OH excitation. Variability on short (months) or long (years) time-scales is a common feature in many 5 cm OH sources. We also present observations of the 6 GHz satellite lines and report, besides W3(OH), on two certain and perhaps two newly detected weak sources. Some implications on the excitation of OH are briefly discussed. Clearly, there is no efficient maser mechanism for the satellite lines. We derive the percentage of circular polarization in detected 6035 and 6031 MHz emission sources and suggest the identifications of possible Zeeman patterns. We have found several features having > 90 % polarization. Combining our magnetic field measurements with other published results we find that the dominant field alignment is consistent with the direction of the Galactic rotation. However, there is no convincing correlation of the field direction with the Galactic spiral pattern, and it is possible that the field direction is not preserved in the star formation process.
Baudry Alain
Cohen Richard J.
Desmurs J.-F.
Wilson Thomas L.
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