Our source list is mainly based on the Arcetri Atlas of galactic H2O
masers (Comoretto et al. 1990; Palagi et al. 1993;
Brand et al. 1994; Arc),
which covers the declination range , and the
catalog of non stellar H2O/OH masers by Braz & Epchtein (1983, B&E).
From the Arcetri Atlas we selected 174 H2O masers which are associated
with star forming regions. Some Arcetri sources have been included in our
sample even though they are classified as late type stars (STAR) or of
unknown type (UNKN) in Palagi et al. (1993). These sources have been
detected in CS(J=7-6) by Plume et al. (1992) or in NH3(1,1) by
Molinari et al. (1996), and therefore probably are associated with
star forming regions after all. In these cases the Palagi classification is
indicated in brackets in Tables B.1 and B.2 described in Sect. 4.
From B&E we selected 60 H2O masers which have declination . The Arcetri and B&E lists were complemented by sources from the
H2O surveys of Henning et al. (1992, 17 sources),
Scalise et al.
(1989, 7 sources), Jenness et al. (1995, 6 sources),
Braz et al.
(1989, 5 sources) and Wouterloot & Walmsley (1986, 1 source, i.e.
S152 OH2). Altogether the source list contains thus 270 H2O masers. We
started from the sources having H2O maser peak flux densities greater
than 10 Jy. When several observations are listed in the Arcetri Catalogue,
we have taken the maximum of all observing rounds. In the course of the
observations the flux density limit was relaxed in order to fill LST gaps.
Of the selected H2O masers, 55 (20 percent) have flux densities less
than 10 Jy and 78 (29 percent) have flux densities greater than 100
Jy.
Many of the observed H2O masers also exhibit OH and CH3OH maser emission. Nineteen 18-cm OH maser sources without associated H2O emission were included in the sample from B&E (originally from Caswell et al. 1983a,b and Caswell & Haynes 1983a,b) and the survey of Braz et al. (1990).
In addition to the masers, we observed 62 IRAS point sources fulfilling the
colour criteria of ultracompact HII regions (Wood & Churchwell 1989).
Except one (IRAS 18032-2032, SEST No. 145) these sources do not have any
known H2O masers closer than . The southern sources
(32) were selected directly from the IRAS point source catalogue. All except
one are included in the CS survey of Bronfman et al. (1996). The
northern sources were selected from the surveys of
Molinari et al.
(1996, 20 objects), Churchwell et al. (1990, 6 objects), and
Bronfman
et al. (1996, 4 objects).
Eleven dust continuum peaks within from H2O masers
detected in the survey of Jenness et al. (1995) and one location near
the H2O maser source S76E included in the CS(7-6) survey of
Plume et al.
(1992) were observed with Onsala in order to study the extension of SiO
emission in these regions. In addition, during the Onsala runs altogether 6
positions towards the Herbig-Haro complexes HH1-3
(Haschick et al.
1983) and HH290 (Moreira & Yun 1995) were observed.
The total number of observed sources is 369. Three of them were observed with both SEST and Onsala. These sources are Ori KL (SEST No. 3, Onsala No. 40 in Tables B.1 and B.2, respectively), HH1-H2O (SEST 6, Onsala 43) and NGC 2071 (SEST 11, Onsala 58). Our observing strategy was not intended to be unbiased. On the basis of a test survey we decided to start from the most intense H2O masers in order to maximize the probability of detecting SiO, and thereby find suitable sources for further studies of shocked regions. The UC HII regions and OH masers were included to provide comparison material.
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