bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intermittent maser flare around the high-mass young stellar object G353.273+0.641
Authors: Motogi Kazuhito , Sorai Kazuo , Fujisawa Kenta , Sugiyama Koichiro , Honma Mareki 
Published: July 2012

AbstractThe water maser site associated with G353.273+0.641 is classified as a dominant blueshifted H2O maser, which shows an extremely wide velocity range (± 100 km s−1) with almost all flux concentrated in the highly blueshifted emission. The previous study has proposed that this peculiar H2O maser site is excited by a pole-on jet from high mass protostellar object. We report on the monitoring of 22-GHz H2O maser emission from G353.273+0.641 with the VLBI Exploration of Radio Astrometry (VERA) and the Tomakamai 11-m radio telescope. Our VLBI imaging has shown that all maser features are distributed within a very small area of 200 × 200 au2, in spite of the wide velocity range (> 100 km s−1). The light curve obtained by weekly single-dish monitoring shows notably intermittent variation. We have detected three maser flares during three years. Frequent VLBI monitoring has revealed that these flare activities have been accompanied by a significant change of the maser alignments. We have also detected synchronized linear acceleration (−5 km s−1yr−1) of two isolated velocity components, suggesting a lower-limit momentum rate of 10−3 M⊙ km s−1yr−1 for the maser acceleration. All our results support the previously proposed pole-on jet scenario, and finally, a radio jet itself has been detected in our follow-up ATCA observation. If highly intermittent maser flares directly reflect episodic jet-launchings, G353.273+0.641 and similar dominant blueshifted water maser sources can be suitable targets for a time-resolved study of high mass protostellar jet.
VERA Observations of the H2O Maser Burst in Orion KL
Authors: Hirota Tomoya , Tsuboi Masato , Fujisawa Kenta , Honma Mareki , Kawaguchi Noriyuki , Kim Mi Kyoung , Kobayashi Hideyuki , Imai Hiroshi , Omodaka Toshihiro , Shibata Katsunori M. , Shimoikura Tomomi , Yonekura Yoshinori 
Published: July 2012

AbstractIn 2011 February, a burst of the 22 GHz H2O maser in Orion KL was reported. In order to identify the bursting maser features, we have been carrying out observations of the 22 GHz H2O maser in Orion KL with VERA, a Japanese VLBI network dedicated for astrometry. The bursting maser turns out to consist of two spatially different features at 7.58 and 6.95 km s−1. We determine their absolute positions and find that they are coincident with the shocked molecular gas called the Orion Compact Ridge. We tentatively detect the absolute proper motions of the bursting features toward the southwest direction, perpendicular to the elongation of the maser features. It is most likely that the outflow from the radio source I or another young stellar object interacting with Compact Ridge is a possible origin of the H2O maser burst. We will also carry out observations with ALMA in the cycle 0 period to monitor the submillimeter H2O maser lines in the Orion Compact Ridge region. These follow-up observations will provide novel information on the physical and chemical properties of the mastering region.
On the Methanol masers in G9.62+0.20E: Preliminary colliding-wind binary (CWB) calculations
Authors: van den Heever S. P. , van der Walt D. J. , Pittard J. M. , Hoare M. G. 
Published: July 2012

AbstractA comparison between the observed periodic flaring of methanol maser sources in the star forming region G9.62+0.20E and the continuum emission from parts of a background HII region is made. Using a colliding wind binary (CWB) model preliminary calculations show that the CWB model results fit the maser light curves very well.
Methanol masers and millimetre lines: a common origin in protostellar envelopes
Authors: Torstensson Karl J. E. , van Langevelde Huib Jan , van der Tak Floris F. S. , Vlemmings Wouter H. T. , Kristensen Lars E. , Bourke Stephen , Bartkiewicz Anna 
Published: July 2012

AbstractTo understand the origin of the CH3OH maser emission, we map the distribution and excitation of the thermal CH3OH emission in a sample of 14 relatively nearby (<6 kpc) high-mass star forming regions that are identified through 6.7 GHz maser emission. The images are velocity-resolved and allow us to study the kinematics of the regions. Further, rotation diagrams are created to derive rotation temperatures and column densities of the large scale molecular gas. The effects of optical depth and subthermal excitation are studied with population diagrams. For eight of the sources in our sample the thermal CH3OH emission is compact and confined to a region <0.4 pc and with a central peak close (<0.03 pc) to the position of the CH3OH maser emission. Four sources have more extended thermal CH3OH emission without a clear peak, and for the remaining two sources, the emission is too weak to map. The compact sources have linear velocity gradients along the semi-major axis of the emission of 0.3 – 13 kms−1 pc−1. The rotation diagram analysis shows that in general the highest rotation temperature is found close to the maser position. The confined and centrally peaked CH3OH emission in the compact sources indicates a single source for the CH3OH gas and the velocity fields show signs of outflow in all but one of the sources. The high detection rate of the torsionally excited vt = 1 line and signs of high-K lines at the maser position indicate radiative pumping, though the general lack of measurable beam dilution effects may mean that the masing gas is not sampled well and originates in a very small region.
The infrared environment of methanol maser rings at high spatial resolution
Authors: De Buizer James M. , Bartkiewicz Anna , Szymczak Marian 
Published: July 2012

AbstractThe recent discovery of methanol maser emission coming from ring-like distributions has led to the plausible hypothesis that they may be tracing circumstellar disks around forming high mass stars. In this article we discuss the distribution of circumstellar material around such young and massive accreting (proto)stars, and what infrared emission geometries would be expected for different disk/outflow orientations. For four targets we then compare the expected infrared geometries (as inferred from the properties of the maser rings) with actual high spatial resolution near-infrared and mid-infrared images. We find that the observed infrared emission geometries are not consistent with the masers residing in circumstellar disks.
Masers as evolutionary tracers of high-mass star formation
Authors: Breen Shari L. , Ellingsen Simon P. 
Published: July 2012

AbstractDetermining an evolutionary clock for high-mass star formation is an important step towards realising a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. We have carried out detailed studies of a large number of sources suspected of undergoing high-mass star formation and have found that common maser transitions offer the best opportunity to determine an evolutionary scheme for these objects. We have investigated the relative evolutionary phases of massive star formation associated with the presence or absence of combinations of water, methanol and main-line hydroxyl masers. The locations of the different maser species have been compared with the positions of 1.2 mm dust clumps, radio continuum, GLIMPSE point sources and Extended Green Objects. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species in high-mass star formation regions. We present our proposed sequence for the presence of the common maser species associated with young high-mass stars and highlight recent advances. We discuss future investigations that will be made in this area by comparing data from the Methanol Multibeam (MMB) Survey with chemical clocks from the Millimetre Astronomy Legacy Team 90 GHz (MALT90) Survey.
Class I methanol masers in low-mass star formation regions
Authors: Kalenskii S. V. , Slysh V. I. , Johansson L. E. B. , Bergman P. , Kurtz S. , Hofner P. , Walmsley C. M. 
Published: July 2012

AbstractFour Class I maser sources were detected at 44, 84, and 95 GHz toward chemically rich outflows in the regions of low-mass star formation NGC 1333I4A, NGC 1333I2A, HH25, and L1157. One more maser was found at 36 GHz toward a similar outflow, NGC 2023. Flux densities of the newly detected masers are no more than 18 Jy, being much lower than those of strong masers in regions of high-mass star formation. The brightness temperatures of the strongest peaks in NGC 1333I4A, HH25, and L1157 at 44 GHz are higher than 2000 K, whereas that of the peak in NGC 1333I2A is only 176 K. However, a rotational diagram analysis showed that the latter source is also a maser. The main properties of the newly detected masers are similar to those of Class I methanol masers in regions of massive star formation. The former masers are likely to be an extension of the latter maser population toward low luminosities of both the masers and the corresponding YSOs.
10 years of 12.2 GHz methanol maser VLBI observations towards NGC 7538 IRS1 N: proper motions and maser saturation
Authors: Pestalozzi Michele , Jerkstrand Anders , Conway John 
Published: July 2012

AbstractWe present the outcomes of the consistent analysis of 6 epochs of VLBA 12.2 GHz data obtained between 1995 and 2005 towards the known high-mass star formation reigon NGC7538 IRS1 N. Our analysis concentrates on the study of the main spectral/spatial feature, which is 20 VLBA synthesized beams in size with a distinct velocity gradient. We looked for proper motion signals relative to the central peak which, in an edge-on disc framework, is expected to be stationary. We also study the peak flux and the spatial brightness profile of the main maser feature searching for maser variability. Our results are twofold: we detect a clear proper motion signal of three spatial features (0.21, 0.1, 0.65 mas yr−1) and conclude that these can be made consistent with previous modelling of a Keplerian disc seen edge-on around a high-mass protostar. We further detect a consistent decrease of the peak flux over the time-span 1995-2005 (~ 5.4 Jy yr−1), confirmed when taking into account earlier data (1986, 1987) as well as by the 6.7 GHz maser emission. Also, the width of the spatial brightness profile of the main feature seems to decrease between 1995 and 2005 by some 50%. We consider these observables as clear signs of partial maser saturation.
Internal Proper Motion of 6.7 GHz Methanol Masers in Ultra Compact HII Region S269
Authors: Sawada-Satoh S. , Fujisawa K. , Sugiyama K. , Wajima K. , Honma M. 
Published: July 2012

AbstractWe present the internal proper motion of 6.7-GHz methanol masers in S269, an Ultra Compact HII region. The maser distribution in S269 consists of several maser groups, and the spatial structure of the main groups A and B are consistent with the past VLBI image. The remarkable result of comparing the two VLBI maps is that 6.7-GHz methanol maser distribution and velocity range within each group have been kept for eight years. Angular separation between the two groups A and B increases by 3.6 mas, which corresponds to a velocity of 11.5 km s−1.
The radial velocity acceleration of the 6.7 GHz methanol maser in Mon R2 IRS3
Authors: Sugiyama K. , Fujisawa K. , Shino N. , Doi A. 
Published: July 2012

AbstractWe present the radial velocity acceleration of the 6.7 GHz methanol maser in a high-mass star-forming region Monoceros R2 (Mon R2). The methanol maser is associated with an infrared source IRS3. The methanol maser of Mon R2 shows at least three spectral features having radial velocities (Vlsr) of 10.8, 12.7, and 13.2 km s−1. The radial velocity of a feature at Vlsr = 12.7 km s−1 has changed during ten years from Aug. 1999 to Oct. 2009, corresponding to an acceleration of 0.08 km s−1 yr−1. We observed the 6.7 GHz methanol masers of Mon R2 in Oct. 2008 using the Japanese VLBI Network (JVN). Compared with the previous VLBI image obtained in Nov. 1998 using the European VLBI Network (EVN), the maser feature at Vlsr = 12.7 km s−1 showed relative proper motions of ~2.5 mas yr−1 (about 10 km s−1 at 0.83 kpc) toward the intensity peak of IRS3. The radial velocity acceleration could be caused by an inflow from a disk or envelope around a high-mass young stellar object (YSO) at IRS3.
The final 112-frame movie of the 43 GHz SiO masers around the Mira Variable TX Cam
Authors: Gonidakis Ioannis , Diamond Philip J. , Kemball Athol J. 
Published: July 2012

AbstractThe proximity of the SiO masers to the star, makes them a powerful tool for studying the properties of the extended stellar atmosphere. This project is a long monitoring campaign of the 43 GHz SiO masers (v=1 J=1→0) around the Mira Variable TX Cam. The target source was observed with the Very Long Baseline Array (VLBA) from the 24th of May 1997 to the 25th of January 2002 in bi-weekly or monthly intervals, covering 3.06 stellar cycles. The time-span and frequency of observations helped us examine the long and short-term properties of the emission and study the dynamics of the gas, the existence of shock waves and their contribution to the morphology and kinematics. Maps from each epoch were concatenated into a 112-frame movie showing the evolution of the emission around TX Cam.
OH mainline maser polarisation properties of post-AGB stars
Authors: Chapman Jessica M. , Gonidakis Ioannis , Deacon Rachel M. , Green Anne 
Published: July 2012

AbstractThe Parkes 64-m telescope was used to study the OH mainline polarisation properties at 1665 and 1667 MHz for a sample of 36 evolved stars, identified by their far-infrared and OH 1612 MHz maser properties as likely post-AGB stars.
The Hamburg Database of Circumstellar OH Masers
Authors: Engels Dieter 
Published: July 2012

AbstractA new version of the Hamburg Database of Circumstellar OH Masers at 1612, 1665, and 1667 MHz was released in 2012 January. The database now lists 13170 OH maser observations of stars in the Milky Way. They belong to 6318 different objects and 2324 of them were detected in at least one of the transitions. The database contains flux densities and velocities of the two strongest maser peaks, the expansion velocity of the shell and the radial velocity of the star. Compared to the first version presented in 2007 at the IAU Symposium 242 in Alice Springs new observations published 2008–2011 are included. Interferometric observations and monitoring programs of the maser emission were also added. Access to the database is possible over the Web (www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual objects and lists of objects. A general object search is possible in selected regions of the sky and by defining ranges of flux densities and/or velocities.
Imaging the water masers toward the H2O-PN IRAS 18061–2505
Authors: Gómez Yolanda , Tafoya Daniel , Suárez Olga , Gómez Jose F. , Miranda Luis F. , Anglada Guillem , Torrelles Jóse M. , Vázquez Roberto 
Published: July 2012

AbstractIt has been suggested that the presence of disks or tori around the central stars of pre Planetary Nebulae and Planetary Nebulae is related to the collimation of the jet that are frequently observed in these sources. These disks or tori can be traced by the maser emission of some molecules such as water. In this work we present Very Large Array (VLA) observations of the water maser emission at 22 GHz toward the PN IRAS 18061–2505, for which the masers appear located on one side of the central star. For comparison with the observations, we present a simple kinematical model of a disk rotating and expanding around the central star. The model matches qualitatively the observations. However, since the masers appear only on one side of the disk, these results are not conclusive.
TWINKLING STARS The disappearing SiO masers of W Aql
Authors: Ramstedt Sofia , Vlemmings Wouter , Mohamed Shazrene , Choi Yoon Kyung , Olofsson Hans 
Published: July 2012

AbstractW Aql is a binary S-type AGB star showing SiO maser emission. The dust distribution around the star is asymmetric, possibly indicating gravitational interaction between the binary pair. There are indications that the gas distribution also exhibits asymmetries. To investigate the source of the circumstellar structures, we applied for and were rewarded VLBI time to map the distribution of the SiO masers around this source and to constrain the presence and distribution of a possible magnetic field. Using VERA observations we also aim at measuring an accurate parallax to determine the binary separation, however, from showing peak emission of 21 Jy in June 2010, the SiO(1-0) v=1 line at 43 GHz has now disappeared. We find no correlation with the stellar pulsational period.
Water maser follow-up of the Methanol Multi-Beam Survey.
Authors: Titmarsh Anita , Ellingsen Simon , Breen Shari , Caswell James , Voronkov Maxim 
Published: July 2012

AbstractThe Australia Telescope Compact Array has been used to observe all the 603 6.7 GHz methanol masers detected in the Methanol Multi-Beam survey between l = 310° - 20°. To date we have measured positions with arcsecond accuracy for all the observations in the l = 6° - 20°.
SHOOTING STARS Masers from red giants
Authors: Ramstedt Sofia , Vlemmings Wouter , Humphreys Elizabeth , Alves Felipe 
Published: July 2012

AbstractSiO maser emission probes the region close to the stellar surface where the wind is formed and is observed to better constrain the physical conditions in this region. We have started a long-term project where high-excitation 28SiO maser lines (i.e., J=5-4, v=1 and 2) are observed in a large sample of southern AGB stars. The primary goals are to put constraints on the physical conditions in the extended atmospheres, and to achieve a better understanding of the maser excitation process. Since the maser emission is strong and often highly linearly polarized, the detected sources could also complement the polarization calibrator catalogue for ALMA. Preliminary results show a high detection rate and that in approximately 20% of the sources, the v=2 transition emits stronger than the v=1 transition. We interpret this as possibly indicative of a hot dust shell very close to the stars.
Mrk 1419 - a new distance determination
Authors: Impellizzeri C. M. Violette , Braatz James A. , Kuo Cheng-Yu , Reid Mark J. , Lo K. Y. , Henkel Christian , Condon James J. 
Published: July 2012

AbstractWater vapor megamasers from the center of active galaxies provide a powerful tool to trace accretion disks at sub-parsec resolution and, through an entirely geometrical method, measure direct distances to galaxies up to 200 Mpc. The Megamaser Cosmology Project (MCP) is formed by a team of astronomers with the aim of identifying new maser systems, and mapping their emission at high angular resolution to determine their distance. Two types of observations are necessary to measure a distance: single-dish monitoring to measure the acceleration of gas in the disk, and sensitive VLBI imaging to measure the angular size of the disk, measure the rotation curve, and model radial displacement of the maser feature. The ultimate goal of the MCP is to make a precise measurement of H0 by measuring such distances to at least 10 maser galaxies in the Hubble flow. We present here the preliminary results from a new maser system, Mrk 1419. Through a model of the rotation from the systemic masers assuming a narrow ring, and combining these results with the acceleration measurement from the Green Bank Telescope, we determine a distance to Mrk 1419 of 81 ± 10 Mpc. Given that the disk shows a significant warp that may not be entirely traced by our current observations, more sensitive observations and more sophisticated disk modeling will be essential to improve our distance estimation to this galaxy.
Optical Properties of the Host Galaxies of Extragalactic Nuclear H2O Masers
Authors: Zaw Ingyin , Zhu Guangtun , Blanton Michael , Greenhill Lincoln J. 
Published: July 2012

AbstractAlthough most nuclear 22GHz (λ=1.35 cm) H2O masers are in Seyfert 2 and LINER galaxies, only a small fraction of such galaxies host water masers. We systematically study the optical properties of the galaxies with and without nuclear H2O maser emission to better understand the relationship between H2O maser emission and properties of the central supermassive black hole and improve the detection rates in future surveys. To this end, we cross-matched the galaxies from H2O maser surveys, both detections and non-detections, with the Sloan Digital Sky Survey (SDSS) low-redshift galaxy sample. We find that maser detection rates are higher at higher optical luminosity (MB), larger velocity dispersion (σ), and higher ion [O III] λ5007 luminosity, with [O III] λ5007 being the dominant factor, and that the isotropic maser luminosity is correlated with these variables. These correlations are natural if maser emission depends on the host SMBH mass and AGN activity. We also find that the detection rate is higher for galaxies with higher extinction. These results indicate that, by pre-selecting galaxies with high extinction-corrected [O III] λ5007 flux, future maser surveys can increase detections efficiencies by a factor of ~3 to ~5.
Long term Arecibo monitoring of the water megamaser in MG J0414+0534
Authors: Castangia Paola , Impellizzeri C. M. Violette , McKean John P. , Henkel Christian , Brunthaler Andreas , Roy Alan L. , Wucknitz Olaf 
Published: July 2012

AbstractWe monitored the 22 GHz maser line in the lensed quasar MG J0414+0534 at z = 2.64 with the 300-m Arecibo telescope for almost two years to detect possible additional maser components and to measure a potential velocity drift of the lines. The main maser line profile is complex and can be resolved into a number of broad features with line widths of 30-160 km s−1. A new maser component was tentatively detected in October 2008 at a velocity of +470 km s−1. After correcting for the estimated lens magnification, we find that the H2O isotropic luminosity of the maser in MG J0414+0534 is ~26,000 solar luminosities, making this source the most luminous ever discovered. Both the main line peak and continuum flux densities are surprisingly stable throughout the period of the observations. An upper limit on the velocity drift of the main peak of the line has been estimated from our observations and is of the order of 2 km s−1 per year. We discuss the results of the monitoring in terms of the possible nature of the maser emission, associated with an accretion disk or a radio jet. This is the first time that such a study is performed in a water maser source at high redshift, potentially allowing us to study the parsec-scale environment around a powerful radio source at cosmological distances.
Maser astrometry with VERA and Galactic structure
Authors: Honma Mareki , Nagayama Takumi , Hirota Tomoya , Matsumoto Naoko , Sakai Nobuyuki , Kawaguchi Noriyuki ,   VERA project members
Published: July 2012

AbstractSince 2007 VERA (VLBI Exploration of Radio Astrometry) has been producing astrometric results (distances and/or proper motions) for Galactic maser sources. Nearly 30 parallaxes have been obtained for star-forming regions and late-type stars. By using VERA's astrometric results for star-forming regions, combined with those obtained with VLBA and EVN, fundamental Galactic parameters and Galactic structure may be derived. Our results show that R0 = 8.4 ± 0.4 kpc and Ω⊙ ≡ Ω0 + V⊙/R0=30.7±0.8 km s−1 kpc−1, and also show that the rotation curve of the Galaxy is nearly flat. The determinations of Galactic parameters and structures demonstrate that the maser astrometry can not only contribute significantly to research of individual maser sources, but also to studies of the structure of the Galaxy.