Discovery of large-scale methanol and hydroxyl maser filaments in W3(OH)

Images of the 6.7-GHz methanol maser emission from W3(OH) made at 50- and 100-mas angular resolution with the Multi-Element Radio-Linked Interferometer Network (MERLIN) are presented. The masers lie across the western face of the ultracompact H  ii region in extended filaments which may trace large-scale shocks. There is a complex interrelation between the 6.7-GHz methanol masers and hydroxyl (OH) masers at 1.7 and 4.7 GHz. Together the two species trace an extended filamentary structure that stretches at least 3100 au across the face of the ultracompact H  ii region. The dominant 6.7-GHz methanol emission coincides with the radio continuum peak and is populated by masers with broad spectral lines. The 6.7-GHz methanol emission is elongated at position angle 50° with a strong velocity gradient, and bears many similarities to the methanol maser disc structure reported in NGC 7538. It is surrounded by arcs of ground state OH masers at 1.7 GHz and highly excited OH masers at 13.44 GHz, some of which have the brightest methanol masers at their focus. We suggest that this region hosts the excitation centre for the ultracompact H  ii region.     

OH maser outburst in the W3 nebula

We report the results of three-year long observations of OH masers at 1665 MHz in the W3(OH) source carried out with the 32-m antenna of Svetloe Radio Astronomical Observatory.We found that the strongest activity during the period from December 2011 through March 2012 was exhibited by the region at radial velocity ?46.2km s^?1. The region showed no activity in the ensuing time. The most striking outburst was the event that occurred on January 23, 2013 at UT 03:27. At that time the flux of the region increased by a factor of seven in 90 s, and then decreased down to the initial level. Such a time scale yields the upper estimate of 0.18 AU (2.7 × 10¹² cm) for the linear size of the maser dot. In 2013–2014 intensity variations were found the ?47.6 and ?45.1km s^?1 components with time scales on the order of 10 hours and anticorrelated behavior of the left- and right-hand polarization fluxes. This is the first time that such phenomena have been found in the behavior of OH maser emission, and they cannot be explained by any existing models of maser variability.     

Strong magnetic field in W75N OH maser flare

A flare of OH maser emission was discovered in W75N in 2000. Its location was determined with the Very Long Baseline Array (VLBA) to be within 110 au from one of the ultracompact H  ii regions, Very Large Array 2 (VLA2). The flare consisted of several maser spots. Four of the spots were found to form Zeeman pairs, all of them with a magnetic field strength of about 40 mG. This is the highest ever magnetic field strength found in OH masers, an order of magnitude higher than in typical OH masers. Three possible sources for the enhanced magnetic field are discussed: (i) the magnetic field of the exciting star dragged out by the stellar wind; (ii) the general interstellar field in the gas compressed by the magnetohydrodynamic shock; and (iii) the magnetic field of planets which orbit the exciting star and produce maser emission in gaseous envelopes.     

Full polarization structure of the OH main-line maser envelopes of W Hydrae

Simultaneous MERLIN observations of the OH 1665- and 1667-MHz maser lines in the circumstellar envelope of the semiregular star W Hya have been taken in all Stokes parameters. The 1665-MHz emission comes from two elongated clusters located 80 au from the star. The 1667-MHz emission arises in an incomplete shell of radius 130 au, with the blueshifted features located in the northern part of the envelope and the redshifted components clustered south of the centre. The circularly polarized maser components exhibit spatial separation along the north–south direction. The linearly polarized components were found from the near side of the envelope. Their polarization position angles indicate that the projected axis of the magnetic field at PA ≃ −20° is consistent with spatial segregation of circular polarization. The intensity of the magnetic field, estimated from a tentative measurement of Zeeman splitting, is about 0.6 mG at the location of the 1667-MHz emission, with the field pointing away from the observer. A small change of position angles of linear polarization observed in both maser lines is interpreted as a weak Faraday effect in the maser regions with an electron density of about 2 cm⁻³. The overall polarization structure of the envelope suggests an ellipsoidal or weak bipolar geometry. In such a configuration, the circumstellar magnetic field may exert a non-negligible influence on mass loss. The velocity field in the circumstellar envelope recovered from observations of SiO, H₂O, OH and CO lines at five radial distances reveals a logarithmic velocity gradient of 0.25 and 0.21 in the 1665- and 1667-MHz maser regions respectively. The acceleration within tens of stellar radii cannot be explained by the classical model of radiation pressure on dust.     

The brightest OH maser in the sky: A flare of emission in W75 N

A flare of maser radio emission in the 1665-MHz OH line with a flux density of about 1000 Jy was discovered in the star-forming region W75 N in 2003. At the time of its observations, it was the strongest OH maser in the entire history of research since the discovery of cosmic OH masers in 1965. The linear polarization of the flare emission reached 100%. A weaker flare with a flux density of 145 Jy was observed in this source in 2000–2001; this was probably a precursor of the intense flare. The intensity of two other spectral features decreased when the flare emerged. This change in the intensity of the emission from maser condensations (a brightening of some of them and a weakening of others) can be explained by the passage of a magnetohydrodynamic shock through regions of enhanced gas concentration.     

Model of OH maser in the circumstellar envelop of Mira stars

In this paper, we calculate the mass and velocity distribution of the envelope of Mira stars, for an axisymmetric distribution of the envelope mass. We also calculate the inversion regions of the four 18 cm lines of OH. We assume that the radiation pressure comes from the central star and the thermal emission of the dust itself. We consider pumping mechanisms due to emission from the central star, collision, emission from the dust itself and cosmic microwave background. The model reproduces some of the general features seen in the real sources.     

OH 4765-MHz maser flares in Mon R2

We perform two-dimensional numerical calculations of the tidal interaction between the companion star and the disc around the primary in a cataclysmic variable system with parameters appropriate for the eclipsing dwarf nova binary IP Peg. We show that a spiral shock pattern is indeed obtained. We find, however, that it is impossible to reproduce the two-armed spiral that has been recently observed in IP Peg for realistic discs.     

The association of OH and methanol masers in W3(OH)

We present single-baseline Multi-Element Radio-Linked Interferometer Network (MERLIN) measurements of excited OH 6.0-GHz masers and methanol 6.7-GHz masers for the source W3(OH). These allow us to compare the positions of individual maser spots of these two species to ∼15 mas accuracy for the first time, and to compare these with previously published positions of ground-state OH masers near 1.7 GHz and excited-state OH masers near 4.7 GHz. There is a strong association between OH 6035-MHz and 1665-MHz masers. OH and methanol have very similar distributions, but associations of individual masers are relatively rare: most methanol 6.7-GHz masers are within 100 mas of OH 6.0-GHz masers, but only four methanol masers are within 15 mas of an OH 6.0-GHz maser. There are no correspondences of either species with excited OH 4.7-GHz masers. Zeeman splitting of the 6.0-GHz OH lines indicates an ordered magnetic field ranging from 3.2 to 14.4 mG. The magnetic fields estimated from co-propagating masers such as 6035 and 1665 MHz are generally in good agreement with each other.     

Recombination lines,lit by OH maser spectra,from radio opaque compact regions (II)

Stimulated by powerful OH maser radiation, recombination lines dispersion parameters are theoretically studied. For nonresonant perturbation factor, as it is appeared to be, suitable recombination lines response is achieved only with fine effect of interference of photons, bound into finite maser linewidth.The supposed parameters of lines as well as their number are found as functions of quantum numbers, radiation temperatures of maser sources. Compact regions plasma influence on these recombination lines is taken in considerations. Results of the calculations, mostly based on Paper I (this issue) are tabulated.For optically thick media, as compact zones ofHii are at 18 cm, investigation of intrinsic regions of so-called star-cocoons by maser-stimulated lines would be a method to search after time variable details of molecular sources by themselves both with morphological peculiarities of compact zones.     

An ISO survey of possible water and hydroxyl IRASER transitions towards the star-forming regions W49, W3(OH) and Sgr B2M

We report ISO LWS observations towards the star-forming regions W49N, W3(OH) and Sgr B2M in LWS04 mode (high-resolution Fabry–Perot scans). Possible far-infrared laser emission was detected in a water line at 133.55 μm towards W49N, but the spectral resolution was inadequate to establish firmly the nature of the emission. An additional water line was marginally detected in absorption at the 3 σ level, also towards W49N, at 169.74 μm. No OH lines were detected towards Sgr B2M or W3(OH) at either 134.83 or 135.95 μm, either in emission or in absorption.     

A search for massive young stellar objects with 98 CH_3OH maser sources

Using the 13.7m telescope of the Purple Mountain Observatory (PMO),a survey of the J = 1 - 0 lines of CO and its isotopes was carried out on 98 methanol maser sources in January 2008.Eighty-five sources have infrared counterparts within one arcmin.In the survey,except for 43 sources showing complex or multiple-peak profiles,almost all the 13CO line profiles of the other 55 sources have large line widths of 4.5km s-1 on average and are usually asymmetric.Fifty corresponding Infrared Astronomical Satellite (I...     

Very Large Array observations of broad 6-cm excited-state OH lines in W49A

Using the Very Large Array (VLA), we observed all three of the 6-cm lines of the  ²Π_1/2, J = 1/2  state of OH with sub-arcsecond resolution (∼0.4 arcsec) in W49A. While the spatial distribution and the range in velocities of the 6-cm lines are similar to those of the ground-state (18-cm) OH lines, a large fraction of the total emission in all three 6-cm lines has large linewidths (∼5–10 km s⁻¹) and is spatially extended, very unlike typical ground-state OH masers, which typically are point-like at VLA resolutions and have linewidths ≤1 km s⁻¹. We find brightness temperatures of 5900, 4700 and ≥730 K for the 4660, 4750 and 4765-MHz lines, respectively. We conclude that these are indeed maser lines. However, the gains are ∼0.3, again very unlike the 18-cm lines, which have gains  ≥10⁴  . We compare the excited-state OH emission with that from other molecules observed with comparable angular resolution to estimate physical conditions in the regions emitting the peculiar, low-gain maser lines. We also comment on the relationship with the 18-cm masers.     

Observations of OH 4765-MHz maser emission from star-forming regions

We report observations of the 4765-MHz maser transition of OH (²Π_1/2, J=1/2, F=1→0) towards 57 star-forming regions, taken with the 32-m Toruń telescope. Nine maser sources were detected, of which two had not been reported previously. The newly discovered sources in W75N and Cep A and four previously known sources were monitored over periods ranging from a few weeks to six months. Significant variations of the maser intensity occurred on time-scales of one week to two months. The relationships between the flux density and the linewidth for the new sources, established during the rise and fall phases of bursts that lasted 6–8 weeks, are consistent with a model of saturated masers.