bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linear polarization of hydroxyl masers in circumstellar envelope outer regions
Authors: Wolak P. , Szymczak M. , Gérard E. 
Published: July 2012

AbstractA recent polarimetric survey of OH masers in a large sample of AGB and post-AGB stars revealed widespread occurrence of polarized features. We made a statistical analysis of the polarization properties of this large data set. We discuss the alignment of polarization position angles between the extreme blue- and red-shifted parts of the 1612 MHz spectrum. The average polarization angle of OH masers from the opposite sides of the envelope agrees within 20° for 80% of the sources in the sample. For two objects monitored over ~6 years the polarization position angle at 1612 MHz is constant within measurement uncertainties: this suggests a stable and a very regular structure of the circumstellar magnetic fields. Alternatively, this could indicate a galactic origin of the field which may be amplified by the stellar wind in the outermost parts of the envelopes.
The variability of cosmic methanol masers in massive star-forming regions
Authors: Maswanganye Jabulani P. , Gaylard Michael J. 
Published: July 2012

AbstractThe methanol masers associated with G35.20-1.74 were monitored at 12178 MHz for four years and 6668 MHz for five years using the 26m Hartebeesthoek telescope. This source showed irregular variability and a single large flare event during the monitoring window.
Masers in star forming regions
Authors: Bartkiewicz Anna , van Langevelde Huib Jan 
Published: July 2012

AbstractMaser emission plays an important role as a tool in star formation studies. It is widely used for deriving kinematics, as well as the physical conditions of different structures, hidden in the dense environment very close to the young stars, for example associated with the onset of jets and outflows. We will summarize here the recent observational and theoretical progress on this topic since the last maser symposium: the IAU Symposium 242 in Alice Springs.
A Highly-collimated Water Maser Bipolar Outflow in the Cepheus A HW3d Massive Protostellar Object
Authors: Chibueze James O. , Imai Hiroshi , Tafoya Daniel , Omodaka Toshihiro , Kameya Osamu , Hirota Tomoya , Chong Sze-Ning , Torrelles José M. 
Published: July 2012

AbstractWe report the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the HW3d object within the Cepheus A star-forming region. We measured proper motions of 30 water maser features, tracing a compact bipolar outflow. This outflow is highly collimated, extending through ~400 mas (290 AU), and having a typical proper motion velocity of ~6 mas yr−1 (~21 km s−1). The dynamical timescale of the outflow was estimated to be ~100 years, showing that the outflow is tracing a very early star-formation phase. Our results provide strong support that the HW3d object harbors an internal massive protostar, as previous observations suggested. In addition, we have analyzed Very Large Array (VLA) archive 1.3 cm continuum data of the 1995 and 2006 epochs obtained towards Cepheus A. These results indicate possible different protostars around HW3d and/or strong variability in its radio continuum emission.
High-mass Star Formation in the Regions IRAS 19217+1651 and 23151+5912
Authors: Migenes V. , Rodríguez I. T. , Trinidad M. A. 
Published: July 2012

AbstractWe present and discuss VLA-EVLA high-sensitivity and spatial resolution observations of Water Vapor MASERs and continuum emission towards two sources that have been proposed in the literature to be high-mass star forming regions: IRAS 19217+1651 and 23151+5912. Our results indicate the presence of disks which can confirm that these regions are high-mass star forming regions.
325 GHz Water Masers in Orion Source I
Authors: Niederhofer Florian , Humphreys Elizabeth , Goddi Ciriaco , Greenhill Lincoln J. 
Published: July 2012

AbstractRadio Source I in the Orion BN/KL region provides the closest example of high mass star formation. It powers a rich ensemble of SiO and H2O masers, and is one of only three star-forming regions known to display SiO maser emission. Previous monitoring of different SiO masers with the VLBA and VLA has enabled the resolution of a compact disk and a protostellar wind at radii <100 AU from Source I, which collimates into a bipolar outflow at radii of 100-1000 AU (see contribution by Greenhill et al., this volume). Source I may provide the best case of disk-mediated accretion and outflow recollimation in massive star formation. Here, we report preliminary results of sub-arcsecond resolution 325 GHz H2O maser observations made with the SMA. We find that 325 GHz H2O masers trace a more collimated portion of the Source I outflow than masers at 22 GHz, but occur at similar radii suggesting similar excitation conditions. A velocity gradient perpendicular to the outflow axis, indicating rotation, supports magneto-centrifugal driving of the flow.
Molecular outflows toward methanol masers: detection techniques and their properties.
Authors: de Villiers Helena M. , Thompson M. A. , Chrysostomou A. , van der Walt D. J. 
Published: July 2012

AbstractClass II methanol masers are thought to trace the brief phase in the evolution of a massive YSO, where outflows are expected to occur. Molecular line maps of the CO isotopes of a subset of 6.7 GHz sources from the MMB catalogue were observed with the JCMT telescope. Utilising optically thick 12CO, a search was done to detect broadened line wings (initially only on the source G20.08-0.13). The physical parameters of these detected lobes were then calculated.
Masers in evolved star winds
Authors: Richards Anita M. S. 
Published: July 2012

AbstractThis review summarises current observations of masers around evolved stars and models for their location and behaviour, followed by some of the many highlights from the past 5 years. Some of these have been the fruition of long-term monitoring, a vital aspect of study of stars which are both periodically variable and prone to rapid outbursts or transition to a new evolutionary stage. Interferometric imaging of masers provide the highest-resolution probes of the stellar wind, but their exponential amplification and variability means that multiple observations are needed to investigate questions such as what drives the wind from the stellar surface; why does it accelerate slowly over many tens of stellar radii; what causes maser variability. VLBI parallaxes have improved our understanding of individual objects and of Galactic populations. Masers from wide range of binary and post-AGB objects are accessible to sensitive modern instruments, including energetic symbiotic systems. Masers have been detected up to THz frequencies withHerscheland ALMA's ability to resolve a wide range of maser and thermal lines will provide accurate constraints on physical conditions including during dust formation.
Maser emission during post-AGB evolution
Authors: Desmurs J.-F. 
Published: July 2012

AbstractThis contribution reviews recent observational results concerning astronomical masers toward post-AGB objects with a special attention to water fountain sources and the prototypical source OH 231.8+4.2. These sources represent a short transition phase in the evolution between circumstellar envelopes around asymptotic giant branch stars and planetary nebulae. The main masing species are considered and key results are summarized.
Water Fountains in Pre-Planetary Nebulae: The Case of IRAS16342–3814
Authors: Claussen Mark , Sahai Raghvendra , Morris Mark , Rogers Hannah 
Published: July 2012

AbstractWe present a brief review of Very Long Baseline Array (VLBA) observations of water masers in the so-called water fountain pre-planetary nebulae, and report on new VLBA and Very Large Array (VLA) data for the water masers in the prototypical water fountain source IRAS16342–3814, taken approximately monthly in 2008–2009. A new and very strong water maser is found at an LSR velocity of −3 km s−1, which is offset from the central (likely stellar) velocity. The new VLBA observations still show a similar general structure as was observed in 2002, but there are details which are difficult to explain.
Preliminary results on SiO v=3 J=1−0 maser emission from AGB stars
Authors: Desmurs J.-F. , Bujarrabal V. , Lindqvist M. , Alcolea J. , Soria-Ruiz R. , Bergman P. 
Published: July 2012

AbstractWe present the results of SiO maser observations at 43 GHz toward two AGB stars using the VLBA. Our preliminary results on the relative positions of the different J=1–0 SiO masers (v=1,2 and 3) indicate that the current ideas on SiO maser pumping could be wrong at some fundamental level. A deep revision of the SiO pumping models could be necessary.
1612 MHz OH maser monitoring with the Nançay Radio Telescope
Authors: Engels D. , Gérard E. , Hallet N. 
Published: July 2012

Abstract20 OH/IR stars are monitored in the 1612 MHz OH maser line with the Nançay Radio Telescope. The program started in 2008 with monthly observations of the full sample and will last at least until end of 2012. The aim is the determination of the linear diameter of the circumstellar shell using the phase lag between the light curves of the varying OH maser lines. To use them for distance determinations, angular diameters are obtained by interferometric measurements while the stars pass the maximum of their OH maser flux density variations. The periods of the OH/IR stars monitored are between 425 and >2000 days.
SiO Maser Surveys of Nearby Miras and their Kinematics in the Galaxy
Authors: Deguchi Shuji 
Published: July 2012

AbstractI review recent developments of SiO maser observations of miras, and discuss their kinematics in the Galaxy. They are deeply related to problems in other fields, such as the noncircular motion of Galactic spiral arms, streaming motions of stars in the solar neighborhood, and the interface between the interstellar and circumstellar medium revealed by Far-IR imaging of some miras, as well as the bar structure of the Galaxy. Recent automated surveys of variable stars in optical bands have increased the number of red variables enormously. Most of these stars were not observed in the radio before because of their blue colors. We have obtained radial velocities of these long-period variables with SiO masers. The longitude-velocity diagrams have revealed interesting deviations of stellar motions from the circular motion of the Galaxy, some of which show spatial motion similar to that of the Hercules group of stars. Important developments of SiO maser observations have been made for symbiotic stars, one of which showed a nova eruption with concurrent γ ray emission in 2010 (V407 Cyg). SiO masers have been monitored for this star after the nova eruption. I summarize the SiO maser observations of individual stars also.
Identification of Class I Methanol Masers with Objects of Near and Mid-Infrared Bands and the Third Version of the Class I Methanol Maser (MMI) Catalog
Authors: Bayandina Olga , Val'tts Irina , Larionov Grigorii 
Published: July 2012

AbstractAn identification has been conducted of class I methanol masers with 1) short-wave infrared objects EGO (extended green objects) - tracer bipolar outflow of matter in young stellar objects, and 2) isolated pre-protostellar gas-dust cores of the interstellar medium which are observed in absorption in the mid-infrared in the Galactic plane. It is shown that more than 50% of class I methanol masers are identified with bipolar outflows, considering the EGO as bipolar outflows (as compared with the result of 22% in the first version of the MMI catalog that contains no information about EGO). 99 from 139 class I methanol masers (71%) are identified with SDC. Thus, it seems possible that the MMI can be formed in isolated self-gravitating condensations, which are the silhouette of dark clouds - IRDC and SDC.
25 GHz methanol masers in regions of massive star formation
Authors: Britton Tui R. , Voronkov Maxim A. 
Published: July 2012

AbstractThe bright 25 GHz series of methanol masers is formed in highly energetic regions of massive star formation and provides a natural signpost of shocked gas surrounding newly forming stars. A systematic survey for the 25 GHz masers has only recently been carried out. We present the preliminary results from the interferometric follow up of 51 masers at 25 GHz in the southern sky.
44-GHz class I methanol maser survey towards 6.7-GHz class II methanol masers
Authors: Byun Do-Young , Kim Kee-Tae , Bae Jae-Han 
Published: July 2012

AbstractThe Class II 6.7-GHz methanol maser is a tracer of high mass young stellar objects. We present results of a 44-GHz class I methanol maser and 22-GHz water maser survey using the KVN (Korean VLBI Network) 21-m single dish radio telescopes towards 284 6.7-GHz maser sites. Class I methanol maser and water maser emission is detected towards 116 (41%) and 136 (48%) sources, respectively. About 50 sources have a peak flux density higher than 10 Jy at 44-GHz. They are candidates for VLBI studies using the KVN.
The VLBI mapping survey of the 6.7 GHz methanol masers with the JVN/EAVN
Authors: Fujisawa K. , Hachisuka K. , Sugiyama K. , Doi A. , Honma M. , Yonekura Y. , Hirota T. , Sawada-Satoh S. , Murata Y. , Motogi K. , Ogawa H. , Chen X. , Kim K.-T. , Shen Z.-Q. 
Published: July 2012

AbstractWe present VLBI maps of the 6.7 GHz methanol maser emission in 32 sources obtained using the Japanese VLBI Network (JVN) and the East-Asian VLBI Network (EAVN). All of the observed sources provide new VLBI maps, and the spatial morphologies have been classified into five categories similar to the results obtained from European VLBI Network observations (Bartkiewicz et al. 2009). The 32 methanol sources are being monitored to measure the relative proper motions of the methanol maser spots.
New OH Observations toward Northern Class I Methanol Masers
Authors: Val'tts I. E. , Litovchenko I. D. , Bayandina O. S. , Alakoz A. V. , Larionov G. M. , Mukha D. V. , Nabatov A. S. , Konovalenko A. A. , Zakharenko V. V. , Alekseev E. V. , Nikolaenko V. S. , Kulishenko V. F. , Odincov S. A. 
Published: July 2012

AbstractMaser emission of OH(1720) is formed, according to modern concepts, under the influence of collisional pumping. Class I methanol masers (MMI) are also formed by a collisional mechanism of the inversion of the molecular levels. It is not excluded in this case that physical conditions in the condensations of the interstellar medium where masers are formed may be similar for MMI and OH(1720) masers, and they can associate with each other. To establish a possible association between these two kinds of masers, and obtain reliable statistical estimates, a survey of class I methanol masers at a frequency of 1720 MHz has been carried out.
22 GHz Water Maser Survey of the Xinjiang Astronomical Observatory
Authors: Zhou Jian-jun , Esimbek Jarken , Wu Gang 
Published: July 2012

AbstractWater masers are good tracers of high-mass star-forming regions. Water maser VLBI observations provide a good probe for studying high-mass star formation and galactic structure. We plan to make a blind survey toward the northern Galactic plane in future years using the 25 m radio telescope of the Xinjiang Astronomical Observatory. We will select some water maser sources discovered in the survey and perform high resolution observations to study the gas kinematics close to high-mass protostars.
Masers in Starburst Galaxies
Authors: Darling Jeremy 
Published: July 2012

AbstractMasers in starburst galaxies are outstanding probes of a range of phenomena related to galaxy and black hole evolution, star formation, and magnetic fields. Here I briefly discuss five related topics: (1) Galactic analog water masers in nearby galaxies; (2) multiwavelength solutions to the OH megamaser puzzle in major galaxy mergers; (3) formaldehyde anti-inversion in starburst galaxies; (4) OH spoofing in HI surveys; and (5) new discovery space in radio line surveys. New insights into the physical conditions responsible for OH megamasers, including indications of a critical molecular gas density obtained from the formaldehyde “densitometer,” will be applicable to future surveys, particularly surveys for redshifted hydrogen where OH lines arising in major galaxy mergers can “contaminate” the disk population identified by the HI 21 cm line. Blind radio spectral line surveys also offer the opportunity for unexpected discoveries of new nonthermal radio lines.
Searching for new OH megamasers out to redshifts z>1
Authors: Willett Kyle W. 
Published: July 2012

AbstractWe have carried out a search for 18-cm OH megamaser (OHM) emission with the Green Bank Telescope. The targeted galaxies comprise a sample of 121 ULIRGs at 0.09<z<1.5, making this is the first large, systematic search for OHMs at z>0.25. Nine new detections of OHMs are reported, all at redshifts z<0.25. For the remainder of the galaxies, observations constrain the upper limit on OH emission; this rules out OHMs of moderate brightness (LOH>103 L⊙) for 26% of the sample, and extremely bright OHM emission (LOH>104 L⊙) for 73% of the sample. Losses from RFI result in the OHM detection fraction being significantly lower than expected for galaxies with LIR>1012 L⊙. The new OHM detections are used to calculate an updated OH luminosity function, with Φ∝ LOH−0.66; this slope is in agreement with previous results. Non-detections of OHMs in the COSMOS field constrain the predicted sky density of OHMs; the results are consistent with a galaxy merger rate evolving as (1+z)m, where m≤6.
Expectations of maser studies with FAST
Authors: Zhang Jiang Shui , Li Di , Wang Jun Zhi 
Published: July 2012

AbstractThe Five-hundred-meter Aperture Spherical radio Telescope (FAST) is being built by the Chinese and will be the largest single dish radio telescope in the world. FAST, with much increase in sensitivity, will give astronomers good opportunities to answer many fundamental questions in astronomy. Here we give a brief introduction of FAST and its enormous potential for studying Galactic and extragalactic masers.
The origin of Keplerian megamaser disks
Authors: Wardle Mark , Yusef-Zadeh Farhad 
Published: July 2012

AbstractSeveral examples of thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and black hole mass and that such disks are naturally formed as molecular clouds pass through the galactic nucleus and temporarily engulf the central supermassive black hole. For initial cloud column densities below about 1023.5 cm−2 the disk is non-self gravitating, but for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic centre.
Methanol Maser Parallaxes and Proper Motions
Authors: Xu Y. , Reid M. J. , Moscadelli L. , Menten K. M. , Zheng X. W. , Brunthaler A. , Zhang B. , Rygl K. L. J. , Li J. J. , Sanna A. 
Published: July 2012

AbstractDue to their compactness, persistence and slow motion, Class II CH3OH masers are excellent targets for parallax and proper motion measurements for massive star-forming regions in the Galactic Disk. These measurements can be used to improve our understanding of the spiral structure and dynamics of the Milky Way. At the same time, Class II CH3OH masers can also be used to study gas kinematics close to the exciting star, tracing rotation, infall and/or outflow motions.
VLBI multi-epoch water maser observations toward massive protostars
Authors: Torrelles José M. , Gómez José F. , Patel Nimesh A. , Curiel Salvador , Anglada Guillem , Estalella Robert 
Published: July 2012

AbstractVLBI multi-epoch water maser observations are a powerful tool to study the gas very close to the central engine responsible for the phenomena associated with the early evolution of massive protostars. In this paper we present a summary of the main observational results obtained toward the massive star-forming regions of Cepheus A and W75N. These observations revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g., non-collimated “short-lived” pulsed ejections in different massive protostars), and provided new insights in the study of the dynamic scenario of the formation of high-mass stars (e.g., simultaneous presence of a jet and wide-angle outflow in the massive object Cep A HW2, similar to what is observed in low-mass protostars). In addition, with these observations it has been possible to identify new, previously unseen centers of high-mass star formation through outflow activity.
Astrometry of Galactic Star-Forming Regions ON1 and ON2N with VERA
Authors: Nagayama Takumi ,   VERA project members
Published: July 2012

AbstractWe conducted the astrometry of H2O masers in the Galactic star-forming regions ON1 and ON2N with the VLBI Exploration of Radio Astrometry (VERA). The measured distances to ON1 and ON2N are 2.47±0.11 kpc and 3.83±0.13 kpc, respectively. In the case that ON1 and ON2N are on a perfect circular rotation, we estimate the angular rotation velocity of the Galactic rotation at the Sun (the ratio of the Galactic constants) to be 28 ± 2 km s−1 kpc−1 using the measured distances and three-dimensional velocity components of ON1 and ON2N. This value is larger than the IAU recommended value of 25.9 km s−1 kpc−1, but consistent with other results recently obtained with the VLBI technique.
VLBI maser kinematics in high-mass SFRs: G23.01–0.41
Authors: Sanna Alberto , Moscadelli Luca , Cesaroni Riccardo , Goddi Ciriaco 
Published: July 2012

AbstractVery Long Baseline Interferometry studies of different maser species observed at multiple epochs allow complementary measurements of the 3-dimensional velocity field of gas close (≲ 103 AU) to massive young stellar objects. Here, we review our recent results toward the high-mass star-forming region G23.01–0.41, where all the strongest molecular maser transitions known to date cluster within 2000 AU from the center of an hot molecular core and are associated with a so called extended green object. The overall maser kinematics reveals a common outflowing motion from a central object; the details of the spatial distribution and velocity field of each maser species hint at the presence of different dynamical structures: a collimated jet, a wide-angle wind, and a flattened rotating core. We further compare the simultaneous presence of maser emission from different molecular species with a recent evolutionary sequence for masers associated with massive young stellar objects.
Astrometry of water masers in post-AGB stars
Authors: Imai Hiroshi ,   VERA collaboration
Published: July 2012

AbstractMeasurements of trigonometric parallaxes and secular motions of evolved stars, especially post-AGB stars including central objects of planetary nebulae and water fountain sources as well as peculiar or unclassified stars, provide unambiguous source distance scales and information on their orbits in the Milky Way Galaxy. True source luminosities and kinematical properties should lead us to elucidate the true characteristics and evolutional tracks of these stars. Here we present the recent results of astrometry towards H2O maser sources with the VLBI Exploration of Radio Astormetry (VERA). The target sources include a planetary nebula (K3–35), a pre-PN (IRAS 19312+1950), a water fountain (IRAS 18286−0959) and a K-type star (IRAS 22480+6002). We have demonstrated that parental stars of the former three sources should be intermediate-mass stars from their luminosities and orbits in the Milky Way. It is suggested that IRAS 22480+6002 should be a K-type supergiant previously suggested rather than an RV Tau variable star.