Search

The Methanol Multibeam survey has produced the largest and most complete census of methanol and excited-state hydroxyl masers in the Galaxy to date. Observing the entire Galactic plane visible from the Southern hemisphere for 6668-MHz methanol and 6030/6035-MHz hydroxyl masers, to an rms sensitivity of 0.015 Jy km s-1, the survey has detected a total of 972 methanol maser sources, implying a total Galactic population of ~1290 sources with flux densities above the survey 3σ peak flux density limit of 0.51 Jy. We present here the statistical properties of the methanol detections of the survey, including distributions in flux density, variability and range of source velocities. The data suggest that the weaker masers exhibit greater variability. We also present an analysis of the Galactic distribution of 6668-MHz methanol masers. For the Galactic distribution, we present kinematic distance resolutions to an additional 202 sources to those published previously, and collate these with previous allocations, as well as exploring a recent Bayesian distance approach based on maser parallaxes to separately determine distances. We examine Galactic structure and determine the luminosity function of the Galactic population of methanol masers. We find that more luminous masers have an evenly distributed wide range of velocity widths compared with less luminous masers being dominated by narrow velocity ranges, with the implication that this may be tied to the evolution of the host protostar(s). We also see an indication that brighter sources are seen towards the arm origins. [ABSTRACT FROM AUTHOR]

We report on observations of the hydroxyl radical (OH) within The HI, OH, Recombination line survey (THOR) pilot region. The region is bounded approximately between Galactic coordinates l = 29.°2 to 31.°5 and b = -1. ° 0 to +1.°0 and includes the high-mass star-forming region W43. We identify 103 maser sites, including 72 with 1612 MHz masers, 42 showing masers in either of the main-line transitions at 1665 and 1667MHzand four showing 1720MHz masers. Most maser sites with either main-line or 1720 MHz emission are associated with star formation, whereas most of the 1612 MHz masers are associated with evolved stars. We find that nearly all of the main-line maser sites are co-spatial with an infrared source, detected by GLIMPSE. We alsofind diffuse OH emission, as well as OH in absorption towards selected unresolved or partially resolved sites. Extended OH absorption is found towards the wellknown star-forming complex W43 Main. [ABSTRACT FROM AUTHOR]

We present a model in which the 22 GHz H2O masers observed in star-forming regions occur behind shocks propagating in dense regions (preshock density n0 ~ 106-108 cm-3). We focus on high-velocity (υs ≳ 30 km s-1) dissociative J shocks in which the heat of H2 re-formation maintains a large column of ~300-400 K gas; at these temperatures the chemistry drives a considerable fraction of the oxygen not in CO to form H2O. The H2O column densities, the hydrogen densities, and thewarm temperatures produced by these shocks are sufficiently high to enable powerful maser action. The observed brightness temperatures (generally ~ 1011-1014 K) are the result of coherent velocity regions that have dimensions in the shock plane that are 10-100 times the shock thickness of ~1013 cm. The masers are therefore beamed toward the observer, who typically views the shock "edge-on," or perpendicular to the shock velocity; the brightest masers are then observed with the lowest line-of-sight velocities with respect to the ambient gas. We present numerical and analytic studies of the dependence of the maser inversion, the resultant brightness temperature, the maser spot size and shape, the isotropic luminosity, and the maser region magnetic field on the shock parameters and the coherence path length; the overall result is that in galactic H2O 22 GHz masers, these observed parameters can be produced in J shocks with n0 ~ 106-108 cm-3 and υs ~ 30-200 km s-1. A number of key observables such as maser shape, brightness temperature, and global isotropic luminosity depend only on the particle flux into the shock, j = n0υs , rather than on n0 and vs separately. [ABSTRACT FROM AUTHOR]

We report the first detection of a methanol maser in the A transition at 23.4 GHz, discovered during the HO southern Galactic Plane Survey (HOPS) with the 22-m Mopra Radio Telescope. In the region covered by HOPS, the 23.4-GHz maser was found at only one location, G0.16, which was also a prominent source of maser emission in the E series near 25 GHz. The Australia Telescope Compact Array (ATCA) was used to follow up these detections at high angular resolution and prove the maser nature of the observed emission. The analysis shows that the new methanol maser at 23.4 GHz is a class I maser, which has properties similar to the 9.9- and 25-GHz masers (i.e. traces strong shocks with higher than average temperature and density). All class I masers were found to originate at the same spatial location (within the measurement uncertainty of 0.5 arcsec) in the vicinity of the dominant infrared source, but at a clearly distinct position from nearby OH, HO and class II methanol masers at 6.7 GHz. All maser species are distributed approximately on a line, but it is not clear at present whether this has any physical significance. We also detected a weak (1.3 mJy) continuum source at 25 GHz near the OH maser (at the most northern site, associated with a class II methanol maser and an HO maser renowned for its extremely wide spread of velocity components). The continuum source has not been reported at lower frequencies and is therefore a candidate hypercompact H region. We also used the ATCA to find the strongest and only the fifth known 9.9-GHz maser towards G0.16 and another 23.4-GHz maser towards G0.06 not seen in HOPS. [ABSTRACT FROM AUTHOR]

We present the second portion of an unbiased survey of the Galactic plane for 6668-MHz methanol masers. This section of the survey spans the longitude range 6° to 20°. We report the detection of 119 maser sources, of which 42 are new discoveries. The masers are tightly constrained to the Galactic plane, with only four outside a latitude range of . This longitude region includes the brightest known 6668-MHz methanol maser, 9.621+0.196, as well as the two brightest newly discovered sources in the southern survey as a whole. We list all the sources associated with the 3-kpc arms within longitude and consider further candidates beyond 15° longitude. We identify three new sources associated with the Galactic bar and comment on the density of masers in relation to the bar orientation. [ABSTRACT FROM AUTHOR]

We present a new version of the movie of the SiO masers around the Mira variable TX Cam. It consists of 73 frames (60 observed epochs) with data covering almost two complete stellar cycles between 1997 May 24 and 2000 May 21. Observations were carried out using the Very Long Baseline Array in biweekly and later at monthly intervals. The purpose of this paper is to discuss the global properties of the emission in the extended atmosphere of the star as well as the kinematics of individual components. The existence of shock waves and their contribution to the morphology and the kinematics of the gas is also examined and compared with theoretical models. Contrary to the dominant expansion observed in the first cycle, both expansion and contraction are observed in the second cycle. The maser variability is correlated with the pulsation of the star but not with the optical intensity. Most of the individual components identified follow the behaviour of the ring, but there are exceptions with more complex three-dimensional trajectories. [ABSTRACT FROM AUTHOR]

We present the light curves of the 6.7 and 12.2 GHz methanol masers in the star-forming region G9.62+0.20E for a time-span of more than 2600 d. The earlier reported period of 244 d is confirmed. The results of monitoring the 107 GHz methanol maser for two flares are also presented. The results show that flaring occurs in all three masing transitions. It is shown that the average flare profiles of the three masing transitions are similar. The 12.2 GHz masers are the most variable of the three masers with the largest relative amplitude having a value of 2.4. The flux densities for the different masing transitions are found to return to the same level during the low phase of the masers, suggesting that the source of the periodic flaring is situated outside the masing region, and that the physical conditions in the masing region are relatively stable. On the basis of the shape of the light curve we excluded stellar pulsations as the underlying mechanism for the periodicity. It is argued that a colliding wind binary can account for the observed periodicity and provide a mechanism to qualitatively explain periodicity in the seed photon flux and/or the pumping radiation field. It is also argued that the dust cooling time is too short to explain the decay time of about 100 d of the maser flare. A further analysis has shown that for the intervals from days 48 to 66 and from days 67 to 135 the decay of the maser light curve can be interpreted as due to the recombination of a thermal hydrogen plasma with densities of approximately and , respectively. [ABSTRACT FROM AUTHOR]

In this paper, we re-analyse the amplification process of broad-band continuum radiation by astronomical masers in the one-dimensional case. The basic equations appropriate for the scalar maser and the random nature of the maser radiation field are derived from basic physical principles. Comparison with the standard radiation transfer equation allows us to examine the underlying assumptions involved in the current theory of astronomical masers. Simulations are carried out to follow the amplification of different realizations of the broad-band background radiation by the maser. The observable quantities such as intensity and spectral line profile are obtained by averaging over an ensemble of the emerging radiation corresponding to the amplified background radiation field. Our simulations show that the fluctuations of the radiation field inside the astronomical maser deviate significantly from Gaussian statistics even when the maser is only partially saturated. Coupling between different frequency modes and the population pulsing are shown to have increasing importance in the transport of maser radiation as the maser approaches saturation. Our results suggest that the standard formulation of radiation transfer provides a satisfactory description of the intensity and the line narrowing effect in the unsaturated and partially saturated masers within the framework of the one-dimensional model. However, the application of the same formulation to the strong saturation regime should be considered with caution. [ABSTRACT FROM AUTHOR]

Results of interferometric observations of the class I methanol masers OMC-2 and NGC 2264 in the 70-61 A+ and 80-71 A+ lines at 44 and 95 GHz, respectively, are presented. The maser spots are distributed along the arcs bent toward infrared sources, which are young stellar objects. The distributions of the maser spots at 44 and 95 GHz are virtually identical, and the fluxes from the brightest spots are similar. The measured sizes of the maser spots at 44 GHz are, on average, about 50 AU. The brightness temperature of the strongest components at 44 GHz is 1.7 × 107 K and 3.9 × 107 K for OMC-2 and NGC 2264, respectively. A simple model for the excitation of Class I methanol masers is proposed; it yields an estimate of the limiting brightness temperature of the emission. The model is based solely on the properties of the methanol molecule without invoking the physical parameters of the medium. Using it, we showed that the emission opening angles for NGC 2264 and OMC-2 do not exceed 3° and 4.5°, respectively. The depth of the masing region is about 1000 AU. The emission directivity is naturally realized in the model of of maser consisting of a thermalized core and a thin inverted envelope, probably, with an enhanced methanol abundance. The maser emission has the greatest intensity in the direction tangential to the envelope. The size of the masing envelope estimated from the measured depth and spot extens is ∼2 × 104 AU, or 0.15 pc. This size is close to the sizes of the dense molecular cores surrounding the young stellar objects IRS 4 in OMC-2 and IRS 1 in NGC 2264. [ABSTRACT FROM AUTHOR]

A new OH maser was detected in January 2008 toward the infrared source IRAS 05338-0624 in the dark cloud L1641N. The observations were carried out on the Nan cay Radio Telescope (France) in the 1667 and 1665 MHz OH lines. In the spectra of both lines, thermal OH emission from the surrounding molecular cloud is present at radial velocities VLSR = 6–9 km/s. In addition, a narrow maser feature is present in both lines at VLSR = 2 km/s in the profiles obtained on January 7, 2008; the peak flux densities at 1667 and 1665 MHz are 1.5 and 0.4 Jy, respectively. No OH maser emission was detected in February–July 2008. Then, a maser feature was again observed in the 1665 MHz line on August 20, 2008, at the same velocity as in January, VLSR = 2 km/s, with a peak flux density of 0.4 Jy. No 1667 MHz counterpart was observed with an upper limit of ∼0.1 Jy. Emission in both OH lines was again absent on September 18. The source was also observed in the H2O line at λ = 1.35 cm on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) on February 7 and 13, 2008. In both cases, a maser feature was detected at VLSR = 9 km/s, with peak flux densities of 35 and 15 Jy, respectively. After the its apparent absence in April, H2O maser emission reappeared on May 14, 2008, at VLSR = 7 km/s with a flux density of about 15 Jy. The history of previous observations of the object in the OH and H2O lines is traced. The maser displays strong and rapid flux variability in the lines of both molecules, as is typical of young low-luminosity stellar objects at early stages of their evolution. [ABSTRACT FROM AUTHOR]

The University of Tasmania Mt Pleasant 26-m and Ceduna 30-m radio telescopes have been used to search for 6.7-GHz class II methanol masers towards 200 GLIMPSE ( The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) sources. The target regions were selected on the basis of their mid-infrared colours as being likely to be young high-mass star formation regions and are either bright at 8.0 μm, or have extreme [3.6]–[4.5] colour. Methanol masers were detected towards 38 sites, nine of these being new detections. The prediction was that approximately 20 new 6.7-GHz methanol masers would be detected within 3.5 arcmin of the target GLIMPSE sources, but this is the case for only six of the new detections. A number of possible reasons for the discrepancy between the predicted and actual number of new detections have been investigated. It was not possible to draw any firm conclusions as to the cause, but it may be because many of the target sources are at an evolutionary phase prior to that associated with 6.7-GHz methanol masers. Through comparison of the spectra collected as part of this search with those in the literature, the average lifetime of individual 6.7-GHz methanol maser spectral features is estimated to be around 150 yr, much longer than is observed for 22-GHz water masers. [ABSTRACT FROM AUTHOR]

Multi-Element Radio-Linked Interferometer Network polarization measurements of the OH 18-cm masers in ON1 are presented. OH maser emission is detected in all four ground state lines. The bulk of the masers lie in an elongated distribution covering 2 arcsec at position angle 130°, near the southern edge of the ultracompact H ii region. The maser distribution is orthogonal to the bipolar outflow seen in HCO+ at position angle (PA) 44°. An isolated group of 1720-MHz masers is also seen 6 arcsec to the east. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large-scale order, with field values ranging from −0.4 to −4.6 mG. [ABSTRACT FROM AUTHOR]

Multi Element Radio Linked Interferometer Network (MERLIN) measurements of 1.6-GHz hydroxyl (OH) masers associated with Orion-Becklin–Neugebauer/Kleinmann–Low (Orion-BN/KL) are presented, and the data are compared with data on other masers, molecular lines, compact radio continuum sources and infrared sources in the region. OH masers are detected over an area of 30 arcsec in diameter, with the majority lying along an approximately E–W structure that extends for ∼18 arcsec, encompassing the infrared sources IRc2, IRc6 and IRc7. Radial velocities range from −13 to +42 km s−1. The system of OH masers shows a velocity gradient together with non-circular motions. The kinematics are modelled in terms of an expanding and rotating disc or torus. The rotation axis is found to be in the same direction as the molecular outflow. There is an inner cavity of radius ∼1300 au with no OH masers. The inner cavity, like the H2O ‘shell’ masers and SiO masers, is centred on radio source I. Some of the OH masers occur in velocity-coherent strings or arcs that are longer than 5 arcsec (2250 au). One such feature, Stream A, is a linear structure at position angle ∼45°, lying between IRc2 and BN. We suggest that these masers trace shock fronts, and have appeared, like a vapour trail, 200 yr after the passage of the runaway star BN. The radio proper motions of BN, source I and source n project back to a region near the base of Stream A that is largely devoid of OH masers. The 1612-MHz masers are kinematically distinct from the other OH masers. They are also more widely distributed and appear to be associated with the outflow as traced by H2O masers and by the 2.12-μm emission from shocked H2. The magnetic field traced by the OH masers ranges from 1.8 to 16.3 mG, with a possible reversal. No OH masers were found associated with even the most prominent proplyds within 10 arcsec of Ori C. [ABSTRACT FROM AUTHOR]

We propose a novel method enabling to create a high-contrast dark resonance in the 87Rb vapor D2-line. The method is based on an optical pumping of atoms into the working states by a two-frequency, linearly-polarized laser radiation propagating perpendicularly to the probe field. This new scheme is compared to the traditional scheme involving the σ+-polarized probe beam only, and significant improvement of the dark resonance parameters is found. Qualitative considerations are confirmed by numerical calculations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

New observations yielding precise position measurements of masers in NGC 3576, NGC 3603 and RCW 79 have been made with the Australia Telescope Compact Array. Two water masers and one OH maser are new discoveries, and the remaining 15 measurements refine positions of previously known masers of OH, methanol and water. The total of 18 maser detections are confined to nine distinct locations, all containing water. Three locations host all three species; two have water with methanol and one has water with OH. The specific combination of masers at any one site is believed to provide clues to the evolutionary stage of the very young massive star responsible for exciting the masers; the various combinations of masers are considered in this context. [ABSTRACT FROM AUTHOR]

Holographic measurements of deformations in a large antenna reflector are described. The deformations were brought about by changing elevation angle and gravitational loading. A phase-switching arrangement was used, which allowed a single, already installed and operating receiver to be shared by both the main antenna signal and a reference signal. Natural H2O masers in our galaxy were used as signal sources, and a reference antenna was attached rigidly to the antenna under test so as to move with it. Observing techniques are described that accommodate changes in source elevation angles and antenna feed position while acquiring a data set. [ABSTRACT FROM AUTHOR]

We observed the 43 GHz v = 1, 2, and 3 and 86 GHz v = 1 SiO maser transitions quasi-simultaneously for a Mira-variable-dominated sample of over 80 sources from the Bulge Asymmetries and Dynamical Evolution (BAaDE) project, using ATCA, and statistically compared the relative line strengths. On average, the 43 GHz v = 1 line is brighter than the 86 GHz v = 1 line by a factor of . As a result, an 86 GHz v = 1 observed sample can be observed to 85.9% of the distance of a 43 GHz v = 1 observed sample using the same sensitivity. We discuss what impact this may have on the BAaDE Galactic plane survey using the VLA and ALMA. Despite fewer v = 3 detections, specific trends are discerned or strengthened when the 43 GHz v = 3 line is detected. In particular the 43 and 86 GHz v = 1 lines are on average equal for sources with no detectable 43 GHz v = 3 emission, but the 43 GHz v = 1 line strength is on average about twice as bright as the 86 GHz v = 1 line for sources with detectable 43 GHz v = 3 emission. Some weak correlations are found between line strengths and Midcourse Space Experiment flux densities and colors, which are tightened when considering only sources with detectable 43 GHz v = 3 emission. We discuss these trends in the context of a radiative pumping model to highlight how the 43 GHz v = 3 line, when coupled with the v = 1 and v = 2 lines, can further our understanding of variable conditions like density in the circumstellar envelopes. [ABSTRACT FROM AUTHOR]

We performed a systematic 6.7 GHz Class II methanol maser survey using the Shanghai Tianma Radio Telescope toward targets selected from the all-sky Wide-Field Infrared Survey Explorer (WISE) point catalog. In this paper, we report the results from the survey of those at high Galactic latitudes, i.e., 2°. Of 1473 selected WISE point sources at high latitude, 17 point positions that were actually associated with 12 sources were detected with maser emission, reflecting the rarity (1%–2%) of methanol masers in the region away from the Galactic plane. Out of the 12 sources, 3 are detected for the first time. The spectral energy distribution at infrared bands shows that these new detected masers occur in the massive star-forming regions. Compared to previous detections, the methanol maser changes significantly in both spectral profiles and flux densities. The infrared WISE images show that almost all of these masers are located in the positions of the bright WISE point sources. Compared to the methanol masers at the Galactic plane, these high-latitude methanol masers provide good tracers for investigating the physics and kinematics around massive young stellar objects, because they are believed to be less affected by the surrounding cluster environment. [ABSTRACT FROM AUTHOR]

We conducted Very Large Array C-configuration observations to measure positions and luminosities of Galactic Class II 6.7 GHz methanol masers and their associated ultra-compact H ii regions. The spectral resolution was 3.90625 kHz and the continuum sensitivity reached 45 μJy beam−1. We mapped 372 methanol masers with peak flux densities of more than 2 Jy selected from the literature. Absolute positions have nominal uncertainties of 0.″3. In this first paper on the data analysis, we present three catalogs; the first gives information on the strongest feature of 367 methanol maser sources, and the second provides information on all detected maser spots. The third catalog presents derived data of the 127 radio continuum counterparts associated with maser sources. Our detection rate of radio continuum counterparts toward methanol masers is approximately one-third. Our catalogs list properties including distance, flux density, luminosity, and the distribution in the Galactic plane. We found no significant relationship between luminosities of masers and their associated radio continuum counterparts, however, the detection rate of radio continuum emission toward maser sources increases statistically with the maser luminosities. [ABSTRACT FROM AUTHOR]

This article presents information about contribution made by masers in the field of applied physics in last 50 years. The maser and its younger optical cousin, the laser, remain prototypical examples of the powerful technologies inspired by quantum mechanics and 20th-century physics. Today, masers are extending the reach of quantum mechanics to revolutionary new methods of computation and communication and are probing theories that seek to unify quantum mechanics with general relativity, the other major part of 20th-century physics. Through stimulated emission, the population inversion amplifies electromagnetic fields that are resonant with the transition frequeny between the two quantum states.