Maser Features Research Articles

VLBI observations of the H2O gigamaser in TXS 2226-184

Context.Outside the Milky Way the most luminous H2O masers at 22 GHz, called megamasers because of their extreme luminosity with respect to the Galactic and extragalactic H2O masers associated with star formation, are mainly detected in active galactic nuclei. In the case of the H2O maser detected in the nuclear region of the galaxy TXS 2226-184, the term gigamaser was used for the first time. However, the origin of this very luminous H2O maser emission has never been investigated in detail.Aims.We study the nature of the 22 GHz H2O gigamaser in TXS 2226-184 by measuring its absolute position for the first time at milliarcsecond resolution, by comparing the morphology and characteristics of the maser emission on very long baseline interferometry (VLBI) scales after about 20 years, and by trying to detect its polarized emission.Methods.We observed the 22 GHz H2O maser emission toward TXS 2226-184 three times: the very first time with the NRAO Very Long Baseline Array (VLBA, epoch 2017.45) and the next two times with the European VLBI Network (EVN, epochs 2017.83 and 2018.44). The first two epochs (2017.45 and 2017.83) were observed in phase-reference mode, while the last epoch (2018.44) was observed in full-polarization mode, but not in phase-reference mode to increase the on-source integration time. We also retrieved and analyzed the VLBA archival data at 22 GHz of TXS 2226-184 observed in epoch 1998.40.Results.We detected six H2O maser features in epoch 2017.45 (VLBA), one in epoch 2017.83 (EVN), and two in epoch 2018.44 (EVN). All but one are red-shifted with respect to the systemic velocity of TXS 2226-184; we detected only one blue-shifted maser feature and it is the weakest one. All the H2O maser features but the blue-shifted one are composed of two components with very different linewidths. For the first time we were able to measure the absolute position of the H2O maser features with errors below 1 milliarcsec. No linear and circular polarization was detected.Conclusions.We were able to associate the H2O maser features in TXS 2226-184 with the most luminous radio continuum clump reported in the literature. The comparison between epochs 1998.40 and 2017.45 reveals a difference in the morphology and velocity of the maser features that can be justified accounting for maser variability.

The First VERA Astrometry Catalog

AbstractWe present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric-annual-parallax and proper-motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported, while the rest of the 78 sources are referred to in previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry is revisited and compared with that from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould’s Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameters of $R_{0}=7.92\pm 0.16_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$kpc and $\Omega _{\odot }=30.17\pm 0.27_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$km$\:$s$^{-1}\:$kpc$^{-1}$, where $R_{0}$ and $\Omega _{\odot }$ are the distance from the Sun to the Galactic center and the Sun’s angular velocity of the Galactic circular rotation, respectively.

The Megamaser Cosmology Project. XI. A Geometric Distance to CGCG 074-064

Abstract As part of the survey component of the Megamaser Cosmology Project, we have discovered a disk megamaser system in the galaxy CGCG 074-064. Using the Green Bank Telescope and the Very Large Array, we have obtained spectral monitoring observations of this maser system at a monthly cadence over the course of two years. We find that the systemic maser features display line-of-sight accelerations of ∼4.4 km s−1 yr−1 that are nearly constant with velocity, while the high-velocity maser features show accelerations that are consistent with zero. We have also used the High-Sensitivity Array to make a high-sensitivity very long baseline interferometric map of the maser system in CGCG 074-064, which reveals that the masers reside in a thin, edge-on disk with a diameter of ∼1.5 mas (0.6 pc). Fitting a three-dimensional warped disk model to the data, we measure a black hole mass of and a geometric distance to the system of Mpc. Assuming a cosmic microwave background-frame recession velocity of 7308 ± 150 km s−1, we constrain the Hubble constant to (stat.) ± 1.4 (sys.) km s−1 Mpc−1.

36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?

Methanol (CH3OH) is one of the most abundant interstellar molecules, offering a vast number of transitions to be studied, including many maser lines. However, while the strongest Galactic CH3OH lines, the so-called class II masers, show no indications for the presence of superluminous counterparts in external galaxies, the less luminous Galactic class I sources appear to be different. Here we report class I 36 GHz (λ ≈ 0.8 cm) CH3OH 4−1 → 30 E line emission from the nearby galaxies Maffei 2 (D ≈ 6 Mpc) and IC 342 (D ≈ 3.5 Mpc), measured with the 100 m telescope at Effelsberg at three different epochs within a time span of about five weeks. The 36 GHz methanol line of Maffei 2 is the second most luminous among the sources detected with certainty outside the Local Group of galaxies. This is not matched by the moderate infrared luminosity of Maffei 2. Higher-resolution data are required to check whether this is related to its prominent bar and associated shocks. Upper limits for M 82, NGC 4388, NGC 5728 and Arp 220 are also presented. The previously reported detection of 36 GHz maser emission in Arp 220 is not confirmed. Nondetections are reported from the related class I 44 GHz (λ ≈ 0.7 cm) methanol transition towards Maffei 2 and IC 342, indicating that this line is not stronger than its 36 GHz counterpart. In contrast to the previously detected 36 GHz CH3OH emission in NGC 253 and NGC 4945, our 36 GHz profiles towards Maffei 2 and IC 342 are similar to those of previously detected nonmasing lines from other molecular species. However, by analogy to our Galactic center region, it may well be possible that the 36 GHz methanol lines in Maffei 2 and IC 342 are composed of a large number of faint and narrow maser features that remain spatially unresolved. In view of this, a search for a weak broad 36 GHz line component would also be desirable in NGC 253 and NGC 4945.

Classifying Maser features with Fortran and shell script for proper motion study of Water masers in W49N

The 22-GHz Water masers in the W49N star-forming region are one of the richest and most luminous sources in our Galaxy, at the distance of 11.11 kpc. Very Long Baseline Interferometric (VLBI) observations allow us to study both physics of these masers and the star formation process. However, observational results often show numerous (up to several thousand) maser spots, making manual data analysis time-consuming. Therefore, we have developed a new software with simple computer codes to classify maser features in this source observed with KaVA by Asanok et al. (in preparation). Fortran computer language and bash shell script are developed and tested by applying to 3 epochs of data sets. The peak flux and relative position of maser spots are measured using AIPS software. The analysis procedures are as follows: (1) the data are extracted to the package in table format (peak flux and x-y relative positions), (2) maser spots are counted under specified rules, (3) the maser feature is calculated by using flux-weighted mean method, and (4) the output results are compared with those obtained from the conventional method. Preliminary results show that these newly developed codes are able to automatically identify up to 30% of those maser features found by the conventional method in a consistent manner. Therefore, further improvement and development are needed for future application.

Overall variation of the H2O masers around W Hydrae in 28 years

Abstract In this paper, we present the distribution of H$_2$O masers associated with the semi-regular variable star W Hydrae (W Hya). We have collected the radio interferometric data of the maser distribution taken with the Very Large Array (VLA), the Kashima–Nobeyama InterFErometer (KNIFE), the Multi-Element Radio Link Network (MERLIN), the VLBI Exploration of Radio Astrometry (VERA), and the combined array of the Korean VLBI Network (KVN) and VERA (KaVA) in order to trace the maser distribution variation in two decades. Even though differences in the sensitivities and angular resolutions of the interferometric observations should be taken into account, we attempt to find possible correlation of the maser distribution with the stellar light curve. Our failure in the measurement of the annual parallax of the masers with VERA is likely caused by the properties of the maser features, which have been spatially resolved by the synthesized beam and survived for only half a year or less. No dependence of the maser spot flux density on its size is found in the KNIFE data, suggesting that maser spot size is determined by the physical boundary, as is expected for a clump affected by outward propagation of a stellar pulsation shock wave, rather than the (spherical) geometry of maser beaming in the maser gas clump.

14 years of 6.7 GHz periodic methanol maser observations towards G188.95+0.89

AbstractWe report the results of 14 years of monitoring of G188.95+0.89 periodic 6.7 GHz methanol masers using the Hartebeesthoek 26-m radio telescope. G188.95+0.89 (S252, AFGL5180) is a radio-quiet methanol maser site that is often interpreted as precursors of ultra-compact HII regions or massive protostar sites. At least five bright spectral components were identified. The maser feature at 11.36 km s-1 was found to experience an exponential decay during the monitoring period. The millimetre continuum reveals two cores associated with the source.

Water masers in Compton-thick AGN

Aims. Investigations of H2O maser galaxies at X-ray energies reveal that most active galactic nuclei (AGN) associated with water masers are characterized by high levels of absorption. With the aim of finding new maser sources for possible interferometric follow-ups, we have searched for water maser emission in a well-defined sample of heavily absorbed AGN (NH > 1023 cm−2), including Compton-thick (CT) sources. Methods. Previous surveys already searched for 22 GHz water maser emission in all the galaxies in this sample. With the goal of providing a detection or a stringent upper limit on the H2O luminosity, we reobserved some of the non-detected sources with the Green Bank Telescope. A new luminous H2O maser (LH2O ∼ 200 L⊙) was detected in the mid-IR-bright Seyfert 2 galaxy IRAS 15480−0344 and then followed-up with the Very Long Baseline Array. In order to shed light on the origin of the maser (jet, outflow, or disk), we recently observed the radio continuum emission in IRAS 15480-0344 with the European VLBI network (EVN) at 1.7 and 5.0 GHz. Results. With the newly discovered megamaser in IRAS 15480−0344 revealing a narrow (∼0.6 km s−1) and a broad (∼90 km s−1) component, the maser detection rate of the CT AGN sample is 50% (18/36), which is one of the highest ever found in maser surveys. The EVN maps show two bright sources (labeled SW and NE) in the nuclear region of IRAS 15480−0344, which we interpret as jet knots tracing regions where the radio plasma impacts dense molecular clouds. The narrow maser feature is approximately at the center of the imaginary line connecting the two continuum sources, likely pinpointing the core, and might be associated with the accretion disk or a nuclear outflow. The location of the broad maser feature, instead, coincides with source NE, suggesting that the maser emission might be produced by a jet-cloud interaction, as it was proposed for NGC 1068 and Mrk 348.

OH maser emission in the THOR survey of the northern Milky Way

Context. OH masers trace diverse physical processes, from the expanding envelopes around evolved stars to star-forming regions or supernovae remnants. Providing a survey of the ground-state OH maser transitions in the northern hemisphere inner Milky Way facilitates the study of a broad range of scientific topics. Aims. We want to identify the ground-state OH masers at ∼18 cm wavelength in the area covered by The HI/OH/Recombination line survey of the Milky Way (THOR). We will present a catalogue of all OH maser features and their possible associated environments. Methods. The THOR survey covers longitude and latitude ranges of 14.°3 < l < 66.°8 and b < ± 1.°25. All OH ground state lines 2Π3/2 (J = 3/2) at 1612 (F = 1−2), 1665 (F = 1−1), 1667 (F = 2−2) and 1720 MHz (F = 2−1) have been observed, employing the Very Large Array (VLA) in its C configuration. The spatial resolution of the data varies between 12.5″ and 19″, the spectral resolution is 1.5 km s−1, and the rms sensitivity of the data is ∼10 mJy beam−1 per channel. Results. We identify 1585 individual maser spots (corresponding to single spectral features) distributed over 807 maser sites (regions of size ∼103 − 104 AU). Based on different criteria from spectral profiles to literature comparison, we try to associate the maser sites with astrophysical source types. Approximately 51% of the sites exhibit the double-horned 1612 MHz spectra typically emitted from the expanding shells of evolved stars. The separations of the two main velocity features of the expanding shells typically vary between 22 and 38 km s−1. In addition to this, at least 20% of the maser sites are associated with star-forming regions. While the largest fraction of 1720 MHz maser spots (21 out of 53) is associated with supernova remnants, a significant fraction of the 1720 MHz maser spots (17) are also associated with star-forming regions. We present comparisons to the thermal 13CO(1–0) emission as well as to other surveys of class II CH3OH and H2O maser emission. The catalogue attempts to present associations to astrophysical sources where available, and the full catalogue is available in electronic form. Conclusions. This OH maser catalogue presents a unique resource of stellar and interstellar masers in the northern hemisphere. It provides the basis for a diverse range of follow-up studies from envelopes around evolved stars to star-forming regions and Supernova remnants.

Flaring water masers associated with W49N

Aims.We present our monitoring observations and analysis of water masers associated with W49N taken in 2017 and 2018. A significant flare occurred during these observations.Methods.We used ground-based radio telescopes in Simeiz (RT-22), Torun (RT-32), Medicina (RT-32), Effelsberg (RT-100) with broadband spectrometers. Observational data were collected and processed automatically.Results.We report a powerful flare of thev= +6 km s−1water maser feature; it increased in over ten months toS1.3 cm= 84 kJy in 2017 December, then decayed to the pre-flare quiescent value ofS1.3 cm= 8.7 kJy in 2018 August. We infer that this flaring feature is unsaturated based on the relationship between line width and flux density.

RadioAstron reveals super-compact structures in the bursting H2O maser source G25.65+1.05

Water masers are well-known to be variable on a variety of time scales, but only three Galactic H2O masers are known to flare to the level of 105–106 Jy (TB∼1017 K): Orion KL, W49N, and the recently discovered G25.65+1.05. Recently detected flaring activity of H2O maser in the massive star-forming region G25.65+1.05 gave us a unique opportunity to study the fine structure of H2O maser emission in the bursting state with extremely high space VLBI angular resolution. Observation of the source was carried out with ∼9 Earth diameter space-ground baseline within the framework of the RadioAstron project. H2O maser emission from two spectral features, including the bursting one, was detected in the experiment. Only ∼1% of the bursting H2O maser emission was detected on the space-ground baselines: it indicates the presence of a very compact spatial structure with a size of ∼25 μas, which corresponds to 0.05 AU or ∼5 solar diameters at the distance to the source of 2.08 kpc, and the brightness temperature of ∼3 × 1016 K. Analysis of the flux density as a function of the baseline length for the bursting H2O maser feature in the source shows that most of the emission comes from an extended “halo” structure, while the core of emission is very compact and has an extreme brightness temperature. These results are in agreement with the model of interacting maser clouds considered as the likely explanation of the nature of the burst in the source. Under the assumption of such a model, the beam size of maser emission is reduced while the brightness temperatures similar to the highest observed values are produced.

EVN observations of 6.7 GHz methanol maser polarization in massive star-forming regions

Context. Magnetohydrodynamical simulations show that the magnetic field can drive molecular outflows during the formation of massive protostars. The best probe to observationally measure both the morphology and the strength of this magnetic field at scales of 10–100 au is maser polarization. Aims. We measure the direction of magnetic fields at milliarcsecond resolution around a sample of massive star-forming regions to determine whether there is a relation between the orientation of the magnetic field and of the outflows. In addition, by estimating the magnetic field strength via the Zeeman splitting measurements, the role of magnetic field in the dynamics of the massive star-forming region is investigated. Methods. We selected a flux-limited sample of 31 massive star-forming regions to perform a statistical analysis of the magnetic field properties with respect to the molecular outflows characteristics. We report the linearly and circularly polarized emission of 6.7 GHz CH3OH masers towards seven massive star-forming regions of the total sample with the European VLBI Network. The sources are: G23.44−0.18, G25.83−0.18, G25.71−0.04, G28.31−0.39, G28.83−0.25, G29.96−0.02, and G43.80−0.13. Results. We identified a total of 219 CH3OH maser features, 47 and 2 of which showed linearly and circularly polarized emission, respectively. We measured well-ordered linear polarization vectors around all the massive young stellar objects and Zeeman splitting towards G25.71−0.04 and G28.83−0.25. Thanks to recent theoretical results, we were able to provide lower limits to the magnetic field strength from our Zeeman splitting measurements. Conclusions. We further confirm (based on ∼80% of the total flux-limited sample) that the magnetic field on scales of 10–100 au is preferentially oriented along the outflow axes. The estimated magnetic field strength of |B||| > 61 mG and >21 mG towards G25.71−0.04 and G28.83−0.25, respectively, indicates that it dominates the dynamics of the gas in both regions.

Constraining Theories of Polarized SiO Maser Transport: Multi-epoch Analysis of a π/2 Electric Vector Rotation Feature

Abstract The detailed polarization mechanisms of SiO masers originating from the near-circumstellar environment of asymptotic giant branch stars are not yet definitively known. Prevailing theories are broadly classified as either Zeeman or non-Zeeman in origin, the latter including effects such as anisotropic pumping or anisotropic resonant scattering. The predicted behavior of the linear and circular polarization fractions and the electric vector position angle (EVPA) vary by theory. In particular, individual maser features that exhibit a rotation in linear polarization of ∼π/2 as a function of frequency over their extent can be utilized as a test of several maser polarization transport theories. In this paper, we analyze one SiO (ν = 1, J = 1 − 0) maser feature toward the Mira variable, TX Cam, that exhibits this internal polarization rotation and persists across five epochs (spanning ∼3 months). We compare our results to the predictions by several maser polarization theories and find that the linear polarization across the feature is consistent with a geometric effect for a saturated maser originating when the angle between the projected magnetic field and the line of sight (θ) crosses the Van Vleck angle θ F ∼ 55°. However, the EVPA exhibits a smooth rotation across the spatial extent of the feature rather than the expected abrupt π/2 flip. We discuss possible explanations for this discrepancy and alternative theories. Circular polarization across the feature is also analyzed, and it is most accurately described by Zeeman effects giving rise to a circular polarization fraction of the form .

Simultaneous VLBI Astrometry of H2O and SiO Masers toward the Semiregular Variable R Crateris

Abstract We obtained, for the first time, astrometrically registered maps of the 22.2 GHz H2O and 42.8, 43.1, and 86.2 GHz SiO maser emission toward the semiregular b-type variable (SRb) R Crateris, at three epochs (2015 May 21, and 2016 January 7 and 26) using the Korean Very-long-baseline Interferometry Network. The SiO masers show a ring-like spatial structure, while the H2O maser shows a very asymmetric one-side outflow structure, which is located at the southern part of the ring-like SiO maser feature. We also found that the 86.2 GHz SiO maser spots are distributed in an inner region, compared to those of the 43.1 GHz SiO maser, which is different from all previously known distributions of the 86.2 GHz SiO masers in variable stars. The different distribution of the 86.2 GHz SiO maser seems to be related to the complex dynamics caused by the overtone pulsation mode of the SRb R Crateris. Furthermore, we estimated the position of the central star based on the ring fitting of the SiO masers, which is essential for interpreting the morphology and kinematics of a circumstellar envelope. The estimated stellar coordinate corresponds well to the position measured by Gaia.

Evolution of the H2O and OH Maser Emission in W75 N

The results of a study of H2O and OH maser emission in the complex region of active star formation W75 N are presented. Observations were obtained using the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) and the Nan3ay radio telescope (France). Flaring H2O maser features may be identified with maser spots associated with the sources VLA 1 and VLA 2. Themain H2O flares occurred in VLA 1. The flare emission was associated with either maser clusters having closely spaced radial velocities and sizes up to ~2 AU or individual features. The maser emission is generated in a medium where turbulence on various scales is present. Analysis of the line shapes during flare maxima does not indicate the presence of the simplest structures—homogeneous maser condensations. Strong variability of the OH maser emission was observed. Zeeman splitting of the 1665-MHz line was detected for several features of the same cluster at a radial velocity of +5.5 km/s. The mean line-of-sight magnetic field in this cluster is ~0.5 mG, directed away from the observer. Flares of the OH masers may be due to gas compression at a shock or MHD wave front.

The Maser Emitting Structure and Time Variability of the SIS Lines J = 14 - 13 and 15 - 14 in IRC+10216.

We present new high angular resolution interferometer observations of the υ = 0 J = 14 - 13 and 15 - 14 SiS lines towards IRC+10216, carried out with CARMA and ALMA. The maps, with angular resolutions of reveal (1) an extended, roughly uniform, and weak emission with a size of (2) a component elongated approximately along the East-West direction peaking at at both sides of the central star, and (3) two blue- and red-shifted compact components peaking around to the NW of the star. We have modeled the emission with a 3D radiation transfer code finding that the observations cannot be explained only by thermal emission. Several maser clumps and one arc-shaped maser feature arranged from 5 to 20R⋆ from the central star, in addition to a thin shell-like maser structure at ≃ 13R⋆ are required to explain the observations. This maser emitting set of structures accounts for 75% of the total emission while the other 25% is produced by thermally excited molecules. About 60% of the maser emission comes from the extended emission and the rest from the set of clumps and the arc. The analysis of a time monitoring of these and other SiS and 29SiS lines carried out with the IRAM 30 m telescope from 2015 to present suggests that the intensity of some spectral components of the maser emission strongly depends on the stellar pulsation while other components show a mild variability. This monitoring evidences a significant phase lag of ≃ 0.2 between the maser and NIR light-curves.

The Extraordinary Outburst in the Massive Protostellar System NGC 6334I-MM1: Emergence of Strong 6.7 GHz Methanol Masers

Abstract We report the first sub-arcsecond VLA imaging of 6 GHz continuum, methanol maser, and excited-state hydroxyl maser emission toward the massive protostellar cluster NGC 6334I following the recent 2015 outburst in (sub)millimeter continuum toward MM1, the strongest (sub)millimeter source in the protocluster. In addition to detections toward the previously known 6.7 GHz Class II methanol maser sites in the hot core MM2 and the UCHII region MM3 (NGC 6334F), we find new maser features toward several components of MM1, along with weaker features ∼1″ north, west, and southwest of MM1, and toward the nonthermal radio continuum source CM2. None of these areas have heretofore exhibited Class II methanol maser emission in three decades of observations. The strongest MM1 masers trace a dust cavity, while no masers are seen toward the strongest dust sources MM1A, 1B, and 1D. The locations of the masers are consistent with a combination of increased radiative pumping due to elevated dust grain temperature following the outburst, the presence of infrared photon propagation cavities, and the presence of high methanol column densities as indicated by ALMA images of thermal transitions. The nonthermal radio emission source CM2 (2″ north of MM1) also exhibits new maser emission from the excited 6.035 and 6.030 GHz OH lines. Using the Zeeman effect, we measure a line-of-sight magnetic field of +0.5 to +3.7 mG toward CM2. In agreement with previous studies, we also detect numerous methanol and excited OH maser spots toward the UCHII region MM3, with predominantly negative line-of-sight magnetic field strengths of −2 to −5 mG and an intriguing south–north field reversal.

Monitoring observations of 6.7 GHz methanol masers

We report results of 6.7 GHz methanol maser monitoring of 139 star-forming sites with the Torun 32 m radio telescope from June 2009 to February 2013. The targets were observed at least once a month, with higher cadences of 2-4 measurements per week for circumpolar objects. Nearly 80 percent of the sources display variability greater than 10 per cent on a time-scale between a week and a few years but about three quarters of the sample have only 1-3 spectral features which vary significantly. Irregular intensity fluctuation is the dominant type of variability and only nine objects show evidence for cyclic variations with periods of 120 to 416 d. Synchronised and anti-correlated variations of maser features are detected in four sources with a disc-like morphology. Rapid and high amplitude bursts of individual features are seen on 3-5 occasions in five sources. Long (>50 d to 20 months) lasting bursts are observed mostly for individual or groups of features in 19 sources and only one source experienced a remarkable global flare. A few flaring features display a strong anti-correlation between intensity and line-width that is expected for unsaturated amplification. There is a weak anti-correlation between the maser feature luminosity and variability measure, i.e. maser features with low luminosity tend to be more variable than those with high luminosity. The analysis of the spectral energy distribution and continuum radio emission reveals that the variability of the maser features increases when the bolometric luminosity and Lyman flux of the exciting object decreases. Our results support the concept of a major role for infrared pumping photons in triggering outburst activity of maser emission.

LBA high resolution observations of ground- and excited-state OH masers towards G351.417+0.645

AbstractWe 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.

Dynamics of jet/outflow driven by high-mass young stellar object revealed by KaVA 22 GHz water maser observations

AbstractWe have started survey observations of the 22 GHz water maser sources associated with high-mass young stellar objects (HM-YSOs) as a part of the KaVA (KVN and VERA Array) large program (LP). The aim of our LP is to understand dynamical evolution of jets/outflows from HM-YSOs by analyzing 3D velocity structures of water maser features. In the first year (2016-2017), an imaging survey toward 25 HM-YSOs has been conducted and the 22 GHz water masers are detected toward 21 sources. Spatial distributions of maser features for individual sources are mapped. To complement physical properties in the vicinity of HM-YSOs, we have carried out ALMA cycle 3 observations of thermal molecular lines and continuum emissions toward 11 selected samples. Summary of the KaVA first year observations and the initial results from the ALMA toward one of our targets, G25.82-0.17, are reported.