We consider the propagation of spectral-line radiation in a correlated turbulent atmosphere. The ensembles of turbulent velocities u(r,t) and optical depths, τν, are assumed to be Gaussian. We investigate the explicit analytical solution of the stochastic radiative transfer equation for the intensity Iν of radiation. The scattering term is not taken into account. It is shown that, in addition to the usual Doppler broadening of the spectral line, correlated turbulent motions of atoms and molecules give rise to considerable changes in the shape of a spectral line. We find that the mean intensity I(0)ν (Iν=I(0)ν+I′ν, I′ν = 0) obeys the usual radiative transfer equation with renormalized extinction factor αeffν if the correlation length R0 of the turbulence is small as compared to a photon free path. A simple analytical expression for αeffν is given. This expression integrally depends on the two-point correlation function of the turbulent velocity field.

This discussion of recent maser surveys in the southern sky will allow us to see the context of the new methanol multibeam survey, which is currently in progress and described elsewhere at this symposium. My emphasis will be on masers that arise in star-forming regions in the disc of our Galaxy. I discuss outcomes from existing surveys, and comparison of different maser species, with special attention to the recognition of blue-shifted outflows.

We present VLBA observation towards the nucleus of a nearby radio galaxy NGC 1052. In NGC 1052, two-sided jet structure and a dense plasma circumnuclear torus with a radius of 0.7 pc have been found around the central mass. It emits a H2O megamaser, which is redshifted with respect to the systemic velocity of the galaxy (1491 kms−1) with a large velocity width of 100 kms−1 (FWHM). The maser gas is found at the inner jet components of both the approaching and receding jets. The maser gas is positionally coincident with a plasma torus. The maser gas in NGC 1052 could be explained as a circumnuclear torus or disk, as found for the nucleus of NGC 4258.

We present an atlas of extragalactic water vapor masers. As of 2007, one hundred galaxies have been detected as sources of water vapor maser emission, two thirds of them discovered since 2003. Extragalactic water masers fall in at least three categories: those associated with nuclear jets or winds, those in starbursts or star-forming regions, and those in AGN accretion disks. While all maser systems offer the possibility of unique investigations into their physical environments, it is the disk masers that have been most aggressively sought because of their potential for use as precision distance indicators. Type 2 Seyfert and LINER galaxies are hosts to such disk masers. Insingle-dish spectra, disk masers are often revealed by the presence of high-velocity emission features (defined roughly by having anomalous velocities in excess of 200 km s−1). About one third of the extragalactic water masers detected to date show evidence of disk origin. Only a few galaxies are currently identified as jet-type or star-forming type. The remaining systems show only a few narrow doppler components, usually near the systemic velocity, and are difficult to categorize. These unclassified systems are detected toward AGNs and are also possibly associated with disks or winds near the nucleus. Detection rates in large maser surveys are typically 5% or less, but the observing efficiency and sensitivity of the Green Bank Telescope (GBT) allow for short integration times (typically 10 minutes to detect a narrow 30 mJy line) so many galaxies can be searched. Recently, GBT surveys targeting type 2 Seyfert galaxies identified by the SDSS have been the most productive, identifying 17 systems in surveys observed during 2006.

OH (1720 MHz) masers serve as indicators of SNR – molecular cloud interaction sites. These masers are collisionally excited in warm (50–100 K) shocked gas with densities of order 105cm−3 when the OH column density is in the range 1016−1017cm−2. Here I present excitation calculations which show that when the OH column density exceeds 1017cm−2 at similar densities and temperatures, the inversion of the 1720 MHz line switches off and instead the 6049 MHz transition in the first excited rotational state of OH becomes inverted. This line may serve as a complementary signal of warm, shocked gas when the OH column density is large.

We are carrying out a program to observe the 6.7 GHz methanol maser emission in high-mass star-forming regions using large FOV (~2'), astrometric, VLBI data. Here we report on the first results of the inner few arc seconds in Cepheus A East. We find a maser filament extending over ~1.7” (1200 AU), straddling the waist of Cep A HW2. The region in which the CH3OH masers are found contains several YSO's and it is not clear whether the CH3OH masers are associated with several different objects or rather the larger scale surrounding environment.

Until recently, high spatial resolution full Stokes maser polarimetry was the sole domain of northern interferometers and a wealth of sources in the far south remained unexplored due to a lack of suitable instrumentation having both high spatial and high velocity resolution. The Australia Telescope Long Baseline Array (LBA) has now switched to disk-based software correlation, permitting full Stokes observing in spectral line mode with velocity channels which are sufficiently narrow to sample usefully the polarization structure. To illustrate the utility of this valuable addition to radio astronomy, we present preliminary results of the first such polarimetric observation, the subject of which are the OH masers in the star-forming region G340.054–0.244.

We have conducted phase-reference VLBI observations of H2O and CH3OH masers toward two high-mass star forming regions, Sh 2-255 IR and AFGL 5142. In Sh 2-255 infrared water masers are aligned along a direction close to the orientation of a large scale H2 jet, tracing possibly shocked material in a precessing jet, or, alternatively, the disk-wind emerging from the disk atmosphere. In AFGL 5142 water masers trace expansion at the base of a protostellar jet, whilst methanol masers are more probably tracing infalling than outflowing gas. Our results suggest that water and methanol masers trace different kinematic structures in the circumstellar gas.

We present recent results from our project of concurrent radio and infrared interferometry of oxygen-rich Mira stars. Our pilot study on the Mira variable S Ori included coordinated VLBA mapping of the v=1, J=1-0 43.1 GHz and v=2, J=1-0 42.8 GHz SiO maser radiation at one epoch and concurrent near-infrared K-band interferometry to constrain the stellar photospheric diameter. We recently obtained new maps of these SiO maser transitions toward S Ori at three additional epochs with the VLBA and concurrent mid-infrared interferometric data with VLTI/MIDI. The MIDI data are analyzed using recent self-excited dynamic model atmospheres including molecular shells close to continuum-forming layers, which we complement by a radiative transfer model of the dust shell. The modelling of our MIDI data results in phase-dependent continuum photospheric angular diameters. The dust shell can best be modelled with Al2O3 grains alone. We find that the mean SiO maser ring radii lie between about 1.9 and 2.4 stellar continuum radii. The maser spots mark the region of the molecular atmospheric layers shortly outward of the steepest decrease of the mid-infrared model intensity profile. Our results suggest that the SiO maser shells are co-located with the Al2O3 dust shell near minimum visual phase. Their velocity structure indicates a radial gas expansion. Preliminary results from a study of the Mira star GX Mon suggest a similar picture.

Stars at the top of the asymptotic giant branch (AGB) can exhibit maser emission from molecules like SiO, H2O and OH. These masers appear in general stratified in the envelope, with the SiO masers close to the central star and the OH masers farther out in the envelope. As the star evolves to the planetary nebula (PN) phase, mass-loss stops and ionization of the envelope begins, making the masers disappear progressively. The OH masers in PNe can be present in the envelope for periods of ~1000 years but the H2O masers can survive only hundreds of years. Then, H2O maser emission is not expected in PNe and its detection suggests that these objects are in a very particular moment of its evolution in the transition from AGB to PNe. We discuss the unambiguous detection of H2O maser emission in two planetary nebulae: K 3-35 and IRAS 17347-3139. The water-vapor masers in these PNe are tracing disk-like structures around the core and in the case of K3-35 the masers were also found at the tip of its bipolar lobes. Kinematic modeling of the H2O masers in both PNe suggest the existence of a rotating and expanding disk. Both PNe exhibit a bipolar morphology and in the particular case of K 3-35 the OH masers are highly polarized close to the core in a disk-like structure. All these observational results are consistent with the models where rotation and magnetic fields have been proposed to explain the asymmetries observed in planetary nebulae.

The nuclei of ULIRGs harbor massive young stars, an accreting central black hole, or both. Results are presented for molecular gas that is exposed to X-rays (1–100 keV, XDRs) and far-ultraviolet radiation (6–13.6 eV, PDRs). Attention is paid to species like HCO+, HCN, HNC, OH, H2O and CO. Line ratios of HCN/HCO+ and HNC/HCN discriminate between PDRs and XDRs. Very high J (>10) CO lines, observable with HIFI/Herschel, discriminate very well between XDRs and PDRs. In XDRs, it is easy to produce large abundances of warm (T > 100 k) H2O and OH. In PDRs, only OH is produced similarly well.

We study the maser emission arising from a thin, planar, gaseous ring in Keplerian rotation around a central mass when it is observed edge-on. Assuming that the absorption coefficient within the amplifying ring is a decreasing function of distance from the central mass (i.e., κ = κ0r−q), we calculated position-velocity (PV) diagrams for the most intense maser features using different values of the exponent q. We found that, depending on the value of q, these diagrams can be qualitatively different.

This paper focuses on highlights of the symposium and attempts to synthesize recent results in terms of key advances and unsolved problems related to maser research.

The Japanese VLBI network (JVN) has begun observations of 6.7-GHz methanol masers associated with massive star-forming regions. The JVN is a newly-established VLBI array with baselines ranging from 50 to 2560 km spread across the Japanese islands. Three observing bands of 6.7, 8.4, and 22 GHz are now available. The array consists of ten antennas: VERA Mizusawa 20 m, VERA Ishigaki 20 m, VERA Iriki 20 m, Usuda 64 m, Yamaguchi 32 m, Tomakomai 11 m, Tsukuba 32 m, Kashima 34 m, VERA Ogasawara 20 m, and Gifu 11 m, the first five of which have 6.7-GHz receiving systems. In summer 2005, we obtained the first fringes at 6.7 GHz, and VLBI images of 12 methanol maser sites including seven that had not previously been imaged with VLBI at this band. In 2006 summer, we obtained phase-reference observations toward several methanol maser sites.

Highly collimated jets found in AGB and post-AGB stars are expected to play an important role for shaping planetary nebulae. Recent VLBI observations of H2o maser sources have revealed that some of the spatio-kinematical structures of H2o maser sources exhibit stellar jets with extremely spatially and kinematically high collimation. Such stellar H2o maser jets, so-called “water fountains”, have been identified in about 10 sources to date. Here we review recent VLBI observations and relevant observational results of the water fountain sources. They have revealed a typical dynamical age and the detailed kinematical structures of the water fountains, the possibility of the existence of “equatorial flows”, and the evolutionary status of the host stars. The location and kinematics of one of the water fountain sources in the Galaxy is also revealed and shown here.

The Arecibo Methanol Maser Galactic Plane Survey (AMGPS) is a blind survey for 6.7 GHz methanol masers in a section of the Galactic plane visible from the Arecibo radio telescope. The survey for these signposts of massive star formation is complete at a flux density level of 0.27 Jy making it the most sensitive blind survey for methanol masers carried out to date, and resulted in the detection of 86 methanol masers, 48 of which are new discoveries. The properties of methanol masers discovered in the survey are consistent with their being associated with early phases of massive star formation. The data also show the tangent point of the Carina-Sagittarius spiral arm to be around a Galactic longitude of 49.6°.

Galactic nuclei are well known sources of OH and H2O maser emission. It appears that intense star formation in ultra-luminous infrared galaxies drives most OH sources. In contrast, nuclear activity appears to drive most H2O sources. When H2O emission originates in accretion disk structures, constrained geometry and dynamics enable robust interpretation of spectroscopic and imaging data. The principal science includes study of AGN geometry at parsec and sub-parsec radii and measurement of geometric distances in the Hubble Flow. New high accuracy estimates of the “Hubble constant, H○” obtained from maser distances may enable new substantively improved constraints on fundamental cosmological parameters (e.g., dark energy).

Using the Submillimeter Array (SMA) we have imaged for the first time the 321.226 GHz, 1029 − 936 ortho-H2O maser emission. This is also the first detection of this line in the Cepheus A high-mass star-forming region. The 22.235 GHz, 616 – 523 water masers were also observed with the Very Large Array 43 days following the SMA observations. Three of the nine detected submillimeter maser spots are associated with the centimeter masers spatially as well as kinematically, while there are 36 22 GHz maser spots without corresponding submillimeter masers. In the HW2 source, both the 321 GHz and 22 GHz masers occur within the region of ~1″ which includes the disk-jet system, but the position angles of the roughly linear structures traced by the masers indicate that the 321 GHz masers are along the jet while the 22 GHz masers are perpendicular to it. We interpret the submillimeter masers in Cepheus A to be tracing significantly hotter regions (600~2000 K) than the centimeter masers.

Observations of 10 transitions of HCO+, CO and CS isotopomers were taken with the IRAM 30 m telescope for a sample of 28 methanol maser sources detected in the Torun unbiased survey of the galactic plane. About 64% of the sources show line wings in one or more transitions, indicating the presence of molecular outflows. Two sources show evidence for infall motion. Comparison of the widths of line wings and methanol maser emission suggests that the 6.7 GHz maser line traces the environment of massive young stellar objects of various kinematic regimes. Calculations based on the CO and HCO+ lines and the CS line intensity ratios refine the physical parameters. Specifically, a gas density of <107 cm−3 is sufficient for strong maser emission and a high methanol fractional abundance (>5×10−7) is required.