Search

Twenty-four bright, steep-spectrum far-infrared IRAS point sources, which were originally discussed by Hughes & MacLeod, have been searched for hydroxyl, water, and methanol masers and for formaldehyde absorption features. Distances and spectral types for the stars exciting these masers were estimated using radio continuum, IRAS spectra, and maser velocity data. It is found that 21 of the 24 sources are regions of massive star formation containing stars earlier than type B2. We report the discovery of five new OH masers, one new 6.7 GHz CH3OH maser, and two new 12.2 GHz CH3OH masers toward these IRAS sources. By contrast, no 4.765 GHz excited-OH masers were found toward these sources. This sample contains only star-forming regions; there are no planetary or reflection nebulae or extragalactic sources present, as seen in samples with less extreme IRAS colors.

After an extensive monitoring program of the water vapour emission originated from W49N we were able to detect very strong eruptions at +28 km/s, −61 km/s and −27 km/s. Here we present the results of the monitoring of these explosions and discuss the possible correlated variability of the events recorded at +28 km/s with one of them, not so intense, that appeared at +62 km/s.

Twenty-four regions of massive star-formation have been searched for OH, H2O, 6.6-GHz and 12.2-GHz CH3OH masers. Chosen from the IRAS Point Source Catalog by their infrared colours, these objects are the coolest objects in the catalog. Masers were detected towards all but two of these IRAS sources. Seven sources were observed in the 12CO (J=1−0) line and all show evidence of molecular outflow. In six of the CO sources we have found maser emission with peaks in both the red and the blue wings of the outflow. We infer that the conditions for masing in these regions are probably produced by the mechanical energy of the outflowing material.

Since the discovery of the 616-523 rotational transition of interstellar water in maser emission, several hundred sources have been discovered. Their profiles are very variable, presenting correlated variability (Gammon, 1976) or anticorrelated variability (Cesaroni, 1990). Several models have been proposed to explain this variabi1ity. Strong Galactic masers, such as W49 and W51 (Kylafis et al. 1991), and also an extremely strong outburst detected by Abraham et al. (1981) in Orion, could not be fully explained based on current models. We have monitored from October 1989 to July 1991 a very strong water vapour eruption in the +28 km s-1 feature, originated from W49N. Here we present the results and discuss the possible correlated variability of this feature with the one that appeared at +62 km s-1.

The H2O maser source in G305.8 - 0.2 was first detected by Haynes et al. (1984). Inspection of the Southern Hemisphere radio surveys did not show any strong compact HII region or water maser placed nearby this source. The IRAS point source catalog (2.0) shows a strong source in the direction of the maser. We analysed the temporal variation and line profile of the H2O maser emission and discussed the nature of its associated IRAS source. These source characteristics seem compatible with the hypothesis that the maser is associated with a protostellar disk around an early-type star of spectral type 07 to 09 surrounded by a spherical shell of gas and dust.

Observations of water vapor and silicon monoxide masers were conducted in the direction of G305.8−0.2. No SiO maser emission above 7 Jy of flux density was detected. The short-time variability of the H 2 O maser together with the absence of compact radio continuum emission suggests that the excitation energy of the maser could originate from an O7-O9 protostar in its earlier evolutionary stages

The first spectra of southern H2O masers obtained with the 14-m Itapetinga radio telescope are described. A new H2O source was found in H2-3 (G345.4–0.9).

WE report here the first results of a nearly complete, high-sensitivity, water vapour survey of galactic H II regions situated in the Southern Hemisphere.

Ammonia was searched in the direction of 46 sources placed in the southern hemisphere where H2CO or H2O was detected previously. Observations were carried out at Itapetinga Radio Observatory, Atibaia, Brazil using a 13.7 m paraboloid. The receiver used for these observations had a K-band ruby travelling wave maser as a preamplifier and the system temperature ranged from 250 to 300K. All sources were observed at least twice, each observation lasting for 30 minutes. The filter bank used consisted of 47 contiguous channels with 100 kHz bandwidth. Results are presented on Table 1 — Positive results and Table 2 — Negative results.

Microwave emission associated with the para form of ammonia, in the (1, 1) line, was searched for in the direction of 46 southern sky positions where strong H/sub 2/CO absorption or strong H/sub 2/O maser emission was observed previously. The results of those observations are presented with 17 new ammonia sources discovered.

An extensive search for water vapor maser emission towards the Large and Small Magellanic Clouds is reported. The 6/sub 16/--5/sub 23/ transition of water molecule was detected in two H II regions in LMC (including N 159, previously was detected) and in two H II regions in SMC. A total of 32 positions was searched in both Clouds. The strength of the sources detected is comparable with galactic masers with luminosities L< or approx. =10/sup -2/L/sub sun/.

Surveys of the Large Magellanic Cloud (LMC), the closest satellite galaxy to our Solar System, for water vapour sources of measurable intensity have so far yielded negative results. These searches, by Johnston et al.1 and Kaufmann et al.2, with detection limits of about 150 and 20 Jy (1 Jy = 10−26 Wm−2 Hz−1), respectively, suggest that any water vapour masers that exist in the LMC are much weaker than the sources recognized in our own Galaxy and in several more distant galaxies3–5. We now report the results of a survey using the 45-ft Itapetinga radio telescope which shows the presence of a water vapour maser in the N159 region of the LMC.