We describe the proper motion measurements of water masers in the massive-star forming region W 51A and the analysis of the 3-D kinematics in three maser clusters of W 51A. We found a systematic expanding motion in one of the clusters named W 51 North, while no systematic motion was detected in other two clusters named W 51 Main and South. The 3-D motions of the clusters relative to the position reference feature in W 51 North indicate a separating motion between the W 51 North and the W 51 Main/South clusters. We estimated the distance to W 51 North as to be 6.7±2.1 kpc on basis of the statistical parallax and the model fitting methods.

It has been reported that the 22 GHz water maser in the star forming region Orion-KL has started an outburst in rate 1997 (Omodaka et al. 1998, IAUC 6893). Using Mizusawa radio telescope we started a monitoring observation of the bursting maser. We measured the linear polarization of the maser after the burst, during a phase of rapid flux density decrease. We find that the total flux density of 2.4 × 106 Jy (December 1998) exhibits about 46% linear polarization. Over the next six months we find that the total intensity decrease about two orders of magnitude while the fractional linear polarization gradually fell to 30%. These results suggest that the present bursting phenomenon has an origin similar to the super maser event starting in 1979, and the phenomenon of the extremely bright masers in this region is geometric in nature and related to the strong magnetic field.

We have studied the superfine structure of the active H2O maser region in Orion KL with an angular resolution of ≤ 0.3 × 0.7 mas. The high level of H2O maser emission from 1979-1988 was due to an accretion disk, which is divided into five groups of protoplanetary rings. The peak brightness temperatures of the structures was Tpeak = 1013-14 K. The region is located in the OMC-1 molecular cloud, VLSR ⋍ 7.74 km/s. The cloud amplifies by more than two orders of magnitude the emission from the structures, whose radial velocities are within the maser window ±0.3 km/s. Due to this, the velocity of the H2O super maser emission is constant. In the quiescent period of 1995 a 6 AU jet was discovered, PA = −32°, Tb ⋍ 1011K. In 1998 the jet's brightness temperature increased by more than 3 orders of magnitude. Initially the jet's position angle was PA = −45°, and then changed to PA = −38°. During the period of decreasing emission in 1999 the jet had changed its form and became a helix, that suggests the precession of the rotation axes. In the central part of the jet there is a compact bright source - “the ejector” - with Tejc = 1017 K.

VLBA observations of water masers toward the region of NGC1333 near SVS13, the driving source for the well-known Herbig-Haro objects HH7-11, are reported. Maser emission was observed over four epochs spaced by three weeks during late 1998. SVS13 is associated with the millimeter continuum SED Class I source SSV13A1. High resolution CO observations have secured the association of the flow with the continuum object on arc-second scales. A 1998 Aug 12 VLA observation places the blueshifted masers within 80 AU (0.2) of the 2.7 mm position for A1 reported from BIMA. We report observations of two groups of masers, one redshifted by about 6 km s−1 and one blueshifted by about 2-3 km s−1, separated by about 100 AU in projected distance along position angle 21 degrees. Redshifted masers were present only in the latter two epochs. During all epochs, an arclike structure was present with similar morphology; over time this structure moved relative to the southernmost blue maser toward the southeast, roughly along the position angle defined by the Herbig-Haro objects, with a proper motion of about 13 km s−1. Both redshifted and blueshifted masers are clearly part of the same lobe of the flow; their observed Doppler shifts are artifacts of the opening angle of the flow. Our data suggest that the opening angle is about 10°. We measure lower expansion velocities and a wider opening angle than has been found in some other flows near Class 0 SED objects, perhaps indicating that the flows open and slow as they age.

We report on the first space-VLBI observations of the OH masers in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The maps of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature 6 × 1012 K was obtained. The masers seem to be located in the direction of low interstellar scattering.

We have used the Australia Telescope Compact Array (ATCA) to make a sensitive search for maser emission from the 4765-MHz transition of OH towards a sample of 55 star formation regions. Maser emission with peak flux densities in excess of 100 mJy were detected in 14 sites, with 10 of these being new discoveries. Unlike the ground-state OH transitions the 4765-MHz transition is not predicted to be circularly polarised and none of the masers observed have detectable levels of linear, or circular polarisation. Combining our results with those of previous high resolution observations of other OH transitions we are able to investigate various theoretical models for the pumping of OH masers.

We report a search for masers from the A-doublet of the ground-state of OH at 18cm, carried out with the Jodrell Bank Lovell Telescope and with the 25m Dwingeloo telescope. All objects north of δ = −20° which appear in the IRAS Point Source Catalog with fluxes > 1000 Jy at 60μm and 100μm were observed in all four lines and both circular polarisations over the required velocity range. Preliminary results of 52 maser sources are reported here.

During the spectacular 4765 MHz excited OH maser flaring episodes observed in Mon R2 from 1994 to 1998 (Smits et al. 1998), observations were made at the line frequencies of other OH transitions. No excited OH lines were detected, nor were any 1612 or 1720 MHz OH masers found in Mon R2. 1665 and 1667 MHz OH masers were present and underwent small changes. With a peak flux of ∼ 75 Jy, the null detections and small variations at other wavelengths put strong constraints on models of OH masers.

The asymmetric rotor molecule methanol (CH3OH) has hundreds of transitions at centimeter-, millimeter-, and submillimeter wavelengths. Many of these are excited in the hot (T ≳ 150 K), dense (n ≳ 106 cm−3) molecular cloud cores surrounding newly formed massive stars or protostars. The high temperatures in these cores cause evaporation of icy grain mantles, releasing copious amounts of complex molecules, such as methanol, in the gas phase, which in hot cores has abundances (up to 10−6 relative to H2) that are two or more orders of magnitude higher than in cold dark clouds.

Methanol masers occuring in thirteen star-forming regions at both 6.7 and 12.2 GHz were monitored for a year at one to two week intervals using the 26-m Hartebeesthoek telescope. Correlated variations occurred in the masers in six of the ten sources that provided useful data.

A program monitoring the variability of a sample of 56 6.7 GHz methanol masers was started in December 1998. The sources are observed on a weekly basis. We present preliminary results of the monitoring program.

A sample of 174 methanol sources has been observed with the 32 m Toruń radio telescope at four or five epochs separated by 3-7 months. Observations of the 6.7 GHz maser line revealed that about 80% of sources are variable. 20% of sources showed strong variations of the integrated flux density usually on time-scales of 5-12 months. These variations were associated with strong changes in the relative intensities of maser features. Methanol emission from five sources disappeared. The time-scales of variability were longer than 12 months for only 23% of variable sources. It is suggested that the variability of methanol emission is related to the dynamics of the maser regions.

We review the state of the Onsala blind survey of the galactic plane, searching for new 6.7 GHz methanol masers. We also describe preliminary results of millimeter follow-up observations of the new detections and high resolution observations using the EVN. We conclude that blind surveys are important to complement targeted searches done until now and give the possibility to detect new classes of objects.

A blind survey for 6.7GHz methanol maser emission has been made with the 32 m Toruń radio telescope. The survey consists of 4,800 spectra on an equilateral triangular grid pattern with each grid point separated by 4.4 covering a field of ∼21 deg2 at galactic longitudes 20° to 40° and galactic latitudes ±0°52. The average sensitivity was 1.6 Jy and the spectral resolution was 0.04kms−1. A total of 99 sources were detected, 28 of which were not found during previous searches of IRAS-selected ultracompact HII regions. The peak flux density of new detections is usually lower than 30 Jy. About half of the methanol masers have no IRAS counterparts within a radius of 2. The nature of these sources is unclear.

We summarise our recent VLBI observations of a large sample of methanol maser sources associated with high-mass star-forming regions.

The Australia Telescope Compact Array (ATCA) has been used to make the first full polarization observations of 6.7 GHz methanol masers. Linear polarization was detected towards all four sources observed, at levels between a few and 10%, while none of the sources show circular polarization stronger than approximately 1.5%. Linear polarization appears to be more common in the 6.7 GHz methanol maser transition than it is for the 12.2 GHz transition, consistent with the hypothesis that the 6.7 GHz masers are more saturated.

Sensitive radio continuum observations of G305.20+0.21 are performed to look for evidence of an ultracompact HII region. None is found at either 8.64 or 4.8GHz above a 5σ detection limit of about 0.25mJy in both cases. Since G305.20+0.21 is such a bright infrared source, there is a large discrepancy between the expected radio flux and the observed upper limits. This is interpreted as evidence that G305.20+0.21 is a massive protostar traced by a methanol maser site.

We present results of 6.7 GHz methanol maser observations using the European VLBI Network (EVN) toward the G34.3+0.2 complex, which contains a prototypical cometary HII region and a dust enshrouded, probably emerging massive star, G34.24+0.13. We have investigated the methanol maser distribution in both objects and compared it with the OH and water masers in the main HII region. The masers in G34.24+0.13 lie on top of the 1.3 mm continuum emission showing that methanol masers are present, even at this early evolutionary stage.

We report results of EVN interferometric study of two star-forming regions L1206 and GL2789 in the brightest methanol maser line at 6.7 GHz. Using measured absolute positions both methanol masers were identified with protostars which are sources of bipolar outflows. Both masers consist of several maser spots, with some of them being aligned in a linear structure with velocity gradient probably delineating edge-on circumstellar disks. We estimated the radii of such disks to be 140 AU and 280 AU (or 700 AU for the whole structure treated as a disk) for L1206 and GL2789 respectively. The brightness temperatures of the most intense features in L1206 and GL2789 are at least 1.1 × 1010 K and 1.4 × 109K respectively.

In the star forming region W48 the spectrum of methanol lines is studied. It is found that the intensity of the 20 − 3−1E (12.2 GHz) line anti-correlates with the intensity of the 51-60A+ (6.7 GHz). All other class II methanol lines in the spectrum of W48 (21 − 30A+ (157 GHz), 31 − 40A+ (107 GHz) (possibly) and J0 - J−1E (157 GHz)) demonstrate the same behaviour as 20 − 3−1E (12.2 GHz) line. This fact contradicts to the current models of the class II methanol maser emission. The effect is confirmed in the sample of 67 sources. For the explanation of this fact some possibilities are considered.