W49 A is a star-forming region (SFR) found in the constellation of Aquila. It contains 3 active regions: W49 North (W49 N), W49 South West (W49 SW) and W49 South (W49 S). We present preliminary results from two epochs (e-)MERLIN observations of all ground-state OH masers towards the star-forming region (SFR) complex W49 A. The first epoch of observations was done in full-polarization mode with MERLIN in 2005 while the second epoch was obtained only in dual circular polarization during the test observations of the upgraded e-MERLIN in 2013. The overall maser spatial distributions in both epochs are in good agreement. We found several new high velocity maser features up to +34 km s−1 and −28 km s−1. The magnetic field strengths are between 1.1 to 10.8 mG. All three sources show evidence of magnetic field reversal.

In 2014 we conducted a survey for 6.7 GHz methanol masers with the Arecibo Telescope toward far infrared sources selected from the Hi-GAL catalog of massive cores. We found a number of sources with weak 6.7 GHz methanol masers, possibly indicating regions in early stages of star formation. Here we describe the results of follow-up observations that were conducted with the Very Large Array in New Mexico to characterize this new population of “weak” 6.7 GHz methanol masers.

We summarize a long-term monitoring of 11 periodic 6.7 GHz methanol masers and a search for new periodic sources. Observations were carried out with the Torun 32 m telescope. Periods of observed sources range from 29 to 658 days and the data consist of more than 10 observed cycles for most of the masers. Inspection of archival data resulted in identification of 3 new periodic sources while 2 new periodic objects were found in observations started in 2014.

We present radio continuum and water maser observations toward the high-mass star-forming region IRAS 23151+5912 from the VLA and VLBA archive, respectively. We detected a continuum source, which seems to be a hypercompact HII region. In addition, a water maser group about 4″ south from the continuum source was detected. We present preliminary results of the analysis of three observations epochs of the water masers, which are tracing an arc-like structure. However, its kinematics is quite complex, since while one section of the structure seems to be moving away from one center, another section seems to be approaching.

We present the initial results from a class I 44-GHz methanol maser follow-up survey, observed with the MOPRA telescope, towards 272 sources from the Methanol Multi-beam survey (MMB). Over half (∼60%) of the 6.7 GHz class II MMB maser sources are associated with a class I 44-GHz methanol maser at a greater than 5σ detection level. We find that class II MMB masers sources with an associated class I methanol maser have stronger peak fluxes compared to regions without an associated class I maser. Furthermore, as part of the MOPRA follow-up observations we simultaneously observed SiO emission which is a known tracer of shocks and outflows in massive star forming regions. The presence of SiO emission, and potentially outflows, is found to be strongly associated with the detection of class I maser emission in these regions.

A strong outburst of 6.7 GHz methanol maser occurred in the high-mass young stellar object (HMYSO) G24.33+0.14 between November 2010 and January 2013. The target was observed with the Torun 32 m radio telescope as a part of a long-term monitoring programme. Almost all twelve spectral features from 108 to 120 km s−1 varied synchronously with time delays between the flux minima of about two weeks. This may indicate that the variability is driven by global changes in the pump rate. The flare peaks of the two features with the highest relative amplitude of 40-60 are delayed by about 2.5 months while their profiles undergo essential transformation with a velocity drift of 0.23 km s−1yr−1. This may suggest that the variability is caused by a rapid increase of the pump rate and excitation of a large portion of the HMYSO environment by an accretion event.

Methanol masers observed at high angular resolution are useful tool to investigate the processes of high-mass star formation. Here, we present the results of statistical analysis of the 6.7 GHz methanol maser structures in 60 sources observed with the EVN. The parameters of the maser clouds and exciting stars were derived. There is evidence that the emission structures composed of larger number of maser clouds are formed in the vicinity of more luminous exciting stars.

Methanol masers at 6.7 GHz are the brightest of class II methanol masers and have been found exclusively towards massive star forming regions. These masers can thus be used as a unique tool to probe the early phases of massive star formation. We present here the SED studies of 284 methanol masers chosen from the MMB catalogue, which falls in the Hi-GAL range (|l| ≤ 60°, |b| ≤ 1°). The masers are studied using the ATLASGAL, MIPSGAL and Hi-GAL data at wavelengths ranging from 24−870 micrometers. A single grey body component fit was used to model the cold dust emission whereas the emission from the warm dust is modelled by a black body. The clump properties such as isothermal mass, FIR luminosity and MIR luminosity were obtained using the best fit parameters of the SED fits. We discuss the physical properties of the sources and explore the evolutionary stages of the sources having 6.7 GHz maser emission in the timeline of high mass star formation.

VLBI observation of masers is a powerful mean to understand the early evolutionary phase of massive star formation. A few different scenarios of outflow evolution in the massive protostars have been proposed, and cannot be readily examined because the precise timing of appropriate maser phenomena is difficult. In particular, it has been a matter of debate whether a well-collimated or a less-collimated outflow comes first in the very early phase of the massive protostellar evolution. Long-term, multi-epoch VLBI monitoring is probably the most important method to trace the outflow evolution. Such a monitoring of a massive star-forming region W75N(B) has been very successful. Since the first detection of the expanding water maser shell associated with the star-forming region VLA 2 of W75N(B) in 1999, the observations in 2005 and 2007 displayed that the expanding water maser shell has been evolved to well-collimated from a less collimated morphology. Observations in 2012 also confirmed such a transition. It would be a major breakthrough in our knowledge of the formation and evolution of the first stages of massive protostars. We performed multi-epoch VLBI observations in mid-2014. On the contrary to its expansion for 13 years, the maser shell at VLA 2 observed in 2014 is comparable to the size observed in 2012. The quenching of the maser shell size indicates that the previously expanding outflow has been decelerated plausibly due to the interaction with surrounding interstellar medium.

Since the discovery of periodic variability of Class II methanol masers associated with high-mass star formation, several possible driving mechanisms have been proposed to explain this phenomenon. Here the colliding wind binary (CWB) hypothesis is proposed to describe the periodic variability. It is shown that the recombination of a partially ionized gas describes the flare profiles remarkably well. In addition, the quiescent state flux density is also described remarkably well by the time-dependent change of the electron density. This suggests that the periodicity is caused by the time-dependent change in the radio free-free emission from the background HII regions against which the maser is projected.

We present the results from the Australian Long Baseline Array (LBA) observations of the ground- and excited-state OH masers at high resolutions towards the massive star-forming region G351.417+0.645 in 2012. We obtain the most accurate spatial gradient of magnetic fields at ground state transitions and verify the reliability of magnetic field strengths measured from previous lower resolution observations. In comparison with previous LBA observations in 2001 at 6.0 GHz, we identified several matched Zeeman pairs. We found that the OH maser features have no significant change of magnetic field strengths and directions with small internal proper motions, implying quite stable physical conditions. Additionally, we found that 1665- and 6035-MHz OH maser features reveal the same trend of reversal of magnetic fields. Moreover, we also analyzed the physical conditions at different locations from the coincidence of different OH maser transitions based on current OH maser models.

We present a case study of a single high-mass protostar associated with an infrared quiet massive clump selected from the ATLASGAL survey. The thermal dust emission reveals a single collapsing object associated with a prominent molecular outflow. We detect bright emission from a torsionally excited state transition of CH3OH offset from the protostar that is well explained by shocks at the transition from the infalling envelope onto an accretion disk.

We present multi–epoch VLBI observations of the methanol and water masers in the high–mass star formation region G 339.884−1.259, made using the Australian Long Baseline Array (LBA). Our sub–milliarcsecond precision measurements trace the proper motions of individual maser features in the plane of the sky. When combined with the direct line–of–sight radial velocity (vlsr), these measure the 3 D gas kinematics of the associated high–mass star formation region, allowing us to probe the dynamical processes to within 1000 AU of the core.

From 2014 to 2015, we conducted a total of 469 days observation of the 6.7 GHz methanol maser in a star forming region G33.641-0.228, known to be a bursting maser source. As a result, eleven bursts were detected. On MJD 57364, the flux density grew by more than six times w.r.t the day before. Moreover, during the largest burst, the flux density repeatedly increased and decreased rapidly with time-scale as short as 0.24 day. Since these characteristics of the burst are similar to the solar burst, we speculate that the burst of the 6.7 GHz methanol maser in G33.641-0.228 might occur with a similar mechanism of the solar burst.

The brightness of maser features are fascinating and give valuable insight for circumstellar physics of oxygen-rich, intermediate-mass stars, in particular the final evolution of circumstellar envelopes (CSEs). The variety of accompanying masers such as SiO, H2O, and OH in the CSEs may provide unique probes into different stages of rapid CSE evolution. However, with only sparse monitoring of these masers one can sometimes find it difficult to accurately interpret their spatio-kinematics, origins and excitation mechanisms. Examples can be seen in the variety of proposed models for water masers associated with “water fountains” and for silicon-monoxide masers. In order to better understand these issues, one needs to consider continuous monitoring of the individual maser gas clumps over a few stellar cycles or episodic ejection events. Here I present our previous long-term monitoring observations, especially for the water fountain source W43A. Our current efforts involve programs of intensive monitoring observations of circumstellar maser sources over decadal time periods. These programs with the East Asia VLBI Network observe H2O and SiO maser lines simultaneously mapped at high cadence (2–8 weeks) with VLBI observations.

Outstanding problems concerning mass-loss from evolved stars include initial wind acceleration and what determines the clumping scale. Reconstructing physical conditions from maser data has been highly uncertain due to the exponential amplification. ALMA and e-MERLIN now provide image cubes for five H2O maser transitions around VY CMa, at spatial resolutions comparable to the size of individual clouds or better, covering excitation states from 204 to 2360 K. We use the model of Gray et al. 2016, to constrain variations of number density and temperature on scales of a few au, an order of magnitude finer than is possible with thermal lines, comparable to individual cloud sizes or locally almost homogeneous regions. We compare results with the models of Decin et al. 2006 and Matsuura et al. 2014 for the circumstellar envelope of VY CMa; in later work this will be extended to other maser sources.

We briefly introduce the VLBI maser astrometric analysis of IRAS 18043–2116 and IRAS 18113–2503, two remarkable and unusual water fountains with spectacular bipolar bow shocks in their high-speed collimated jet-driven outflows. The 22 GHz H2O maser structures and velocities clearly show that the jets are formed in very short-lived, episodic outbursts, which may indicate episodic accretion in an underlying binary system.

Post-Asymptotic giant branch (post-ABG) sources with high-velocity spectral features of H2O maser emission detected toward their circumstellar envelopes (CSEs) are known as Water Fountain (WF) nebulae. These are low- or intermediate-mass Galactic stellar sources that are undergoing the late stages of an intense mass-loss process. The velocity and the spatial distribution of the H2O maser spectral features can provide information about the kinematics of the molecular gas component of their CSEs. Hence, observational studies toward WF nebulae could help to better understand the formation of the asymmetric structures (hundred to thousand AUs) commonly seen toward Planetary nebulae (PNe). Here we present preliminary results of observations done toward the WF IRAS 15445-5449 using the Australia Telescope Compact Array (ATCA) and the Very Large Telescope (SINFONI/VLT). Assuming that the pumping of the H2O maser transitions is a consequence of shocks between different velocity winds, the spatial distribution of the emission shed light on the scales of the regions affected by the propagation of the shock-fronts.

The Korean VLBI Network (KVN) is a unique millimeter VLBI system which is consisted of three 21 m telescopes with relatively short baselines. We present the preliminary results of simultaneous monitoring observations of the 22.2 GHz H2O and 43.1/42.8/86.2/129.3 GHz SiO masers based on the KVN Key Science Project (KSP). We obtained the astrometrically registered maps of the H2O and SiO masers toward nine evolved stars using the source frequency phase referencing method (SFPR). The SFPR maps of the H2O and SiO masers enabled us to investigate the spatial structure and kinematics from the SiO to H2O maser regions including the development of an outward motion from the ring-like or elliptical structures of SiO masers to the asymmetric structures of the 22.2 GHz H2O maser features. In particular, the 86.2/129.3 GHz SiO (v=1, J=2–1 and J=3–2) masers were clearly imaged toward several objects for the first time. The SiO v=1, J=3–2 maser shows different distributions compared to those of the SiO v=1, 2, J=1–0 and v=1, J=2–1 masers implying a different physical condition.

Studies of Galactic LPVs based on astrometric VLBI are presented. We use a VLBI array, “VERA”, to measure parallaxes and calibrate the K-band period luminosity relation (PLR) of the Galactic Miras. Since the PLR offers a distance indicator, its calibration is crucial to reveal their spatial distribution. Parallaxes of dozens of LPVs are presented. For the longer period stars, the mass-loss is high and the stars are obscured and recognized as OH/IR stars. We estimated mid-infrared absolute magnitudes of dozens of OH/IR stars and found that they show a loose concentration around −14 mag at λ of 11.6 μm, indicating an existence of PLR for OH/IR stars. Astrometry of OH/IR stars will also help us to study non-steady spiral arms as proposed from the latest simulation study of the galactic dynamics. We will start astrometric VLBI observation of two OH/IR stars NSV25875 and OH127.8+0.0 at 43 GHz with VERA.