A moderately deep survey of stellar maser sources toward the Galactic center has been made in the SiO J=1-0 v=1 and v=2 transitions (∼ 43 GHz) with the Nobeyama 45-m telescope of a beam size of about 40. At the Galactic center (Sgr A*), 7 (4 new) SiO maser sources were detected in one beam. In order to investigate the spatial distribution of SiO maser sources, we have also observed the offset p...

We have used the Australia Telescope Compact Array (ATCA) to make a sensitive (5-σ ≃ 100 mJy) search for maser emission from the 4765-MHz 2Π1/2 F=1→0 transition of OH. Fifty five star formation regions were searched and maser emission with a peak flux density in excess of 100 mJy was detected toward fourteen sites, with ten of these being new discoveries. In addition we observed the 4750-MHz 2Π...

We report on the first multi-epoch, phase referenced VLBI observations of the H2O maser emission in a high-mass protostar associated with a disk-jet system. The source under study, IRAS 20126+4104, has been extensively investigated in a large variety of tracers, including H2O maser VLBA data acquired by us three years before the present observations. The new findings fully confirm the interpret...

We used the Submillimeter Array to map the angular distribution of the H30α recombination line (231.9 GHz) in the circumstellar region of the peculiar star MWC349A. The resolution was 1. 2, but because of high signal-to-noise ratio we measured the positions of all maser components to accuracies better than 0. 01, at a velocity resolution of 1 km s. The two strongest maser components (called hig...

Recent observations show that the OH 1720 MHz maser is a powerful probe of the shocked region where a supernova remnant strikes a molecular cloud. We perform a thorough study of the pumping of this maser and find tight constraints on the physical conditions needed for its production. The presence of the maser implies moderate temperatures (50 – 125 K) and densities (∼ 10 cm), and OH column dens...

We present the results of 22 GHz H2O maser observations of a sample of 85 post-Asymptotic Giant Branch (post-AGB) candidate stars, selected on the basis of their OH 1612 MHz maser and far-infrared properties. All sources were observed with the Tidbinbilla 70-m radio telescope and 21 detections were made. 86 GHz SiO Mopra observations of a subset of the sample are also presented. Of the 21 H2O d...

The OH 1667 MHz maser in the circumstellar shell around the Mira variable U Her has been observed with the NRAO Very Long Baseline Array (VLBA) at 6 epochs, spread over 4 years. Using phase referencing techniques the position of the most blue-shifted maser spot was monitored with respect to two extra-galactic radio sources. The absolute radio positions of the maser can be compared with the stel...

We present the first 6.7 GHz methanol maser linear polarization map of the extended filamentary maser structure around the compact H region W3(OH). The methanol masers show linear polarization up to ∼ 8 per cent and the polarization angles indicate a magnetic field direction along the North-South maser structure. The polarization angles are consistent with those measured for the OH masers, ta...

We report the detection of a new H 2 CO maser in the massive star forming region G23.71−0.20 (IRAS 18324−0820), i.e., the fifth region in the Galaxy where H 2 CO maser emission has been found. The new H 2 CO maser is located toward a compact H II region, and is coincident in velocity and position with 6.7 GHz methanol masers and with an IR source as revealed by Spitzer/IRAC GLIMPSE data. The co...

Aims. We characterize the molecular environment of candidate massive young stellar objects (MYSOs) signposted by methanol masers. Methods. Single pixel observations of 10 transitions of HCO, CO and CS isotopomers were carried out, using the IRAM 30 m telescope. We studied a sample of 28 targets for which the 6.7 GHz maser emission positions are known with a sub-arcsecond accuracy. Results. The ...