bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical analysis of the physical properties of the 6.7 GHz methanol maser features based on VLBI data
Authors: Sarniak R. , Szymczak M. , Bartkiewicz A. 
Published: July 2018

AbstractMethanol masers observed at high angular resolution are useful tool to investigate the processes of high-mass star formation. Here, we present the results of statistical analysis of the 6.7 GHz methanol maser structures in 60 sources observed with the EVN. The parameters of the maser clouds and exciting stars were derived. There is evidence that the emission structures composed of larger number of maser clouds are formed in the vicinity of more luminous exciting stars.
Missing flux in VLBI observations of SiO maser at 7 mm in IRC+10011
Authors: Desmurs J.-F. , Alcolea J. , Bujarrabal V. , Colomer F. , Soria-Ruiz R. 
Published: July 2018

AbstractVLBI observations of SiO masers recover at most 40-50% of the total flux obtained by single dish observations at any spectral channel. Some previous studies seems to indicate that, at least, part of the lost flux is divided up into many weak components rather than in a large resolved emission area. Taking benefit of the high sensitivity and resolution of the HSA, we investigate the problem of the missing flux in VLBI observations of SiO maser emission at 7 mm in the AGB stars and obtain a high dynamic range map of IRC+10011. We conclude that the missing flux is mostly contained in many very weak maser components.
Masers as probes of the gas dynamics close to forming high-mass stars
Authors: Moscadelli Luca , Sanna Alberto , Goddi Ciriaco 
Published: July 2018

AbstractImaging the inner few 1000 AU around massive forming stars, at typical distances of several kpc, requires angular resolutions of better than 0″.1. Very Long Baseline Interferometry (VLBI) observations of interstellar molecular masers probe scales as small as a few AU, whereas (new-generation) centimeter and millimeter interferometers allow us to map scales of the order of a few 100 AU. Combining these informations all together, it presently provides the most powerful technique to trace the complex gas motions in the proto-stellar environment. In this work, we review a few compelling examples of this technique and summarize our findings.
Extragalactic class I methanol maser: A new probe for starbursts and feedback of galaxies
Authors: Chen Xi , Ellingsen Simon P. 
Published: July 2018

AbstractWe report progress on research relating to 36.2 GHz extragalactic class I methanol masers, including a review of published work and new observations at high angular resolution. These observations reveal that extragalactic class I masers are excited in shocked gas and maybe associated with starbursts, galactic-scale outflows from active galactic nuclei (AGNs) feedback, or the inner-end region of the galactic bar. The current observational results suggests that extragalactic class I methanol masers provide a new probe for starbursts and feedback in active galaxies.
How maser observations unravel the gas motions in the Galactic Center
Authors: Immer K. , Reid M. , Brunthaler A. , Menten K. , Zhang Q. , Lu X. , Mills E. A. C. , Ginsburg A. , Henshaw J. , Longmore S. , Kruijssen D. , Pillai T. 
Published: July 2018

AbstractThe Central Molecular Zone (CMZ), the inner 450 pc of our Galaxy, is an exceptional region where the volume and column densities, gas temperatures, velocity dispersions, etc. are much higher than in the Galactic plane. It has been suggested that the formation of stars and clusters in this area is related to the orbital dynamics of the gas. The complex kinematic structure of the molecular gas was revealed by spectral line observations. However, these results are limited to the line-of-sight-velocities. To fully understand the motions of the gas within the CMZ, we have to know its location in 6D space (3D location + 3D motion). Recent orbital models have tried to explain the inflow of gas towards and its kinematics within this region. With parallax and proper motion measurements of masers in the CMZ we can discriminate among these models and constrain how our Galactic Center is fed with gas.
A study on evolved stars by simultaneous observations of H2O and SiO masers using KVN
Authors: Cho Se-Hyung , Yun Youngjoo , Kim Jaeheon , Yoon Dong-Hwan , Kim Dong-Jin , Choi Yoon Kyung , Dodson Richard , Rioja María , Imai Hiroshi 
Published: July 2018

AbstractThe Korean VLBI Network (KVN) is a unique millimeter VLBI system which is consisted of three 21 m telescopes with relatively short baselines. We present the preliminary results of simultaneous monitoring observations of the 22.2 GHz H2O and 43.1/42.8/86.2/129.3 GHz SiO masers based on the KVN Key Science Project (KSP). We obtained the astrometrically registered maps of the H2O and SiO masers toward nine evolved stars using the source frequency phase referencing method (SFPR). The SFPR maps of the H2O and SiO masers enabled us to investigate the spatial structure and kinematics from the SiO to H2O maser regions including the development of an outward motion from the ring-like or elliptical structures of SiO masers to the asymmetric structures of the 22.2 GHz H2O maser features. In particular, the 86.2/129.3 GHz SiO (v=1, J=2–1 and J=3–2) masers were clearly imaged toward several objects for the first time. The SiO v=1, J=3–2 maser shows different distributions compared to those of the SiO v=1, 2, J=1–0 and v=1, J=2–1 masers implying a different physical condition.
Maser Emission in G 339.884−1.259
Authors: Krishnan V. , Moscadelli L. , Ellingsen S. P. , Bignall H. E. , Breen S. L. , Dodson R. , Hyland L. J. , Phillips C. J. , Reynolds C. , Stevens J. 
Published: July 2018

AbstractWe present multi–epoch VLBI observations of the methanol and water masers in the high–mass star formation region G 339.884−1.259, made using the Australian Long Baseline Array (LBA). Our sub–milliarcsecond precision measurements trace the proper motions of individual maser features in the plane of the sky. When combined with the direct line–of–sight radial velocity (vlsr), these measure the 3 D gas kinematics of the associated high–mass star formation region, allowing us to probe the dynamical processes to within 1000 AU of the core.
Maser, infrared and optical emission for late-type stars in the Galactic plane
Authors: Quiroga-Nuñez L. H. , van Langevelde H. J. , Sjouwerman L. O. , Pihlström Y. M. , Reid M. J. , Brown A. G. A. , Green J. A. 
Published: July 2018

AbstractRadio astrometric campaigns using VLBI have provided distances and proper motions for masers associated with young massive stars (BeSSeL survey). The ongoing BAaDE project plans to obtain astrometric information of SiO maser stars located in the inner Galaxy. These stars are associated with evolved, mass-losing stars. By overlapping optical (Gaia), infrared (2MASS, MSX and WISE) and radio (BAaDE) sources, we expect to obtain important clues on the intrinsic properties and population distribution of late-type stars. Moreover, a comparison of the Galactic parameters obtained with Gaia and VLBI can be done using radio observations on different targets: young massive stars (BeSSeL) and evolved stars (BAaDE).
On the origin of methanol maser variability: Clues from long-term monitoring
Authors: Szymczak M. , Olech M. , Sarniak R. , Wolak P. , Bartkiewicz A. 
Published: July 2018

AbstractHigh-mass young stellar objects (HMYSO) displaying methanol maser flux variability probably trace a variety of phenomena such as accretion events, magnetospheric activity, stellar flares and stellar wind interactions in binary systems. A long-term monitoring of the 6.7 GHz methanol line in a large sample of HMYSOs has been undertaken to characterize the variability patterns and examine their origins. The majority of the masers show significant variability on time-scales between a week and a few years. High amplitude short flares of individual features occurred in several HMYSOs. The maser features with low luminosity tend to be more variable than those with high luminosity. The variability of the maser features increases when the bolometric luminosity the powering star decreases. Statistical analysis of basic properties of exciting objects and the variability measures supports an idea that burst activity of methanol masers is driven mainly by changes in the infrared pumping rate.
The Structure of the Radio Recombination Line Maser Emission in the Envelope of MWC349A
Authors: Moran James M. , Zhang Qizhou , Emery Deanna L. 
Published: July 2018

AbstractThe Submillimeter Array (SMA) has been used to image the emission from radio recombination lines of hydrogen at subarcsecond angular resolution from the young high-mass star MWC349A in the H26α, H30α, and H31α transitions at 353, 232, and 211 GHz, respectively. Emission was seen over a range of 80 km s−1 in velocity and 50 mas (corresponding to 60 AU for a distance of 1200 pc). The emission at each frequency has two distinct components, one from gas in a nearly edge-on annular disk structure in Keplerian motion, and another from gas lifted off the disk at distances of up to about 25 AU from the star. The slopes of the position-velocity (PV) curves for the disk emission show a monotonic progression of the emission radius with frequency with relative radii of 0.85 ± 0.04, 1, and 1.02 ± 0.01 for the H26α, H30α, and H31α transitions, respectively. This trend is consistent with theoretical excitation models of maser emission from a region where the density decreases with radius and the lower transitions are preferentially excited at higher densities. The mass is difficult to estimate from the PV diagrams because the wind components dominate the emission at the disk edges. The mass estimate is constrained to be only in the range of 10–30 solar masses. The distribution of the wind emission among the transitions is surprisingly different, which reflects its sensitivity to excitation conditions. The wind probably extracts significant angular momentum from the system.
Registration of H2O and SiO masers in the Calabash Nebula, to confirm the Planetary Nebula paradigm
Authors: Dodson R. , Rioja M. , Bujarrabal V. , Kim J. , Cho S. H. , Choi Y. K. , Youngjoo Y. 
Published: July 2018

AbstractWe report on the astrometric registration of VLBI images of the SiO and H2O masers in OH 231.8+4.2, the iconic Proto-Planetary Nebula also known as the Calabash nebula, using the KVN and Source/Frequency Phase Referencing. This, for the first time, robustly confirms the alignment of the SiO masers, close to the AGB star, which drives the bi-lobe structure with the water masers in the out-flow.
Masers and ALMA
Authors: Peck Alison B. , Impellizzeri C. M. Violette 
Published: July 2018

AbstractMasers have been well-known phenomena for decades, but water masers at 183, 321, 325 and 658 GHz have only been detected since the 1990s. Early detections came from single-dish telescopes with follow-up observations from the PdBI and the Submillimeter Array. Detecting them at these short wavelengths has been very difficult due to water in our atmosphere, meaning that even in very good weather, one can only detect very bright masers, such as those in stellar atmospheres. In the last 7 years, a new window on submillimeter water masers, both Galactic and now extragalactic, has opened. Located at high altitude, above a large fraction of the Earth’s atmosphere, ALMA sits on the edge of the driest desert on the planet, meaning that the air that does remain above the telescope is frequently extremely low in water vapor content. Combine this with sensitive, stable receivers covering a number of masing transitions from 183-658 GHz and you have an excellent machine for detecting and characterizing submillimeter water masers. In addition, other molecules also exhibit maser emission in the ALMA observing bands, such as SiO and HCN.
Class II 6.7 GHz Methanol Maser Association with Young Massive Cores Revealed by ALMA
Authors: Chibueze James O. , Csengeri Timea , Tatematsu Ken’ichi , Hasegawa Tetsuo , Iguchi Satoru , Alhassan Jibrin A. , Higuchi Aya E. , Bontemps Sylvain , Menten Karl M. 
Published: July 2018

AbstractThe association of 6.7 GHz class II methanol (CH3OH) masers with ATLASGAL/ ALMA 0.9 mm massive dense cores is presented in this work from a statistical viewpoint. 42 of the 112 cores (37.5%) detected with the Atacama Compact Array (ACA) excite 6.7 GHz CH3OH masers. ACA cores have offsets 0\rlap.″17 to 4\rlap.″79 from the methanol multibeam survey (MMB), with a median of 2.″19. Approximately 90% of the MMB-associated cores are of masses > 40 M⊙. Because all the cores show evidence of outflow activity, and only a fraction of the cores excited CH3OH masers, we suggest that outflows precede the emergence of maser emission. This first ALMA survey of massive dense cores combined with the MMB survey along with other maser specie surveys is a promising tool to trace the evolutionary sequence of high-mass stars.
Constraining Theories of SiO Maser Polarization: Analysis of a π/2 EVPA Change
Authors: Tobin T. L. , Kemball A. J. , Gray M. D. 
Published: July 2018

AbstractThe full theory of polarized SiO maser emission from the near-circumstellar environment of Asymptotic Giant Branch stars has been the subject of debate, with theories ranging from classical Zeeman origins to predominantly non-Zeeman anisotropic excitation or propagation effects. Features with an internal electric vector position angle (EVPA) rotation of ∼π/2 offer unique constraints on theoretical models. In this work, results are presented for one such feature that persisted across five epochs of SiO ν = 1, J = 1 − 0 VLBA observations of TX Cam. We examine the fit to the predicted dependence of linear polarization and EVPA on angle (θ) between the line of sight and the magnetic field against theoretical models. We also present results on the dependence of mc on θ and their theoretical implications. Finally, we discuss potential causes of the observed differences, and continuing work.
Interferometric and single-dish observations of 44, 84 and 95 GHz Class I methanol masers
Authors: Rodríguez-Garza Carolina B. , Kurtz Stanley E. , Gómez-Ruiz Arturo I. , Hofner Peter , Araya Esteban D. , Kalenskii Sergei V. 
Published: July 2018

AbstractWe present observations of massive star-forming regions selected from the IRAS Point Source Catalog. The observations were made with the Very Large Array and the Large Millimeter Telescope to search for Class I methanol masers. We made interferometric observations of 125 massive star-forming regions in the 44 GHz methanol maser transition; 53 of the 125 fields showed emission. The data allow us to demonstrate associations, at arcsecond precision, of the Class I maser emission with outflows, HII regions and shocks traced by 4.5 μm emission. We made single-dish observations toward 38 of the 53 regions with 44 GHz masers detected to search for the methanol transitions at 84.5, 95.1, 96.7, 107.0, and 108.8 GHz. We find detection rates of 74, 55, 100, 3, and 45%, respectively. We used a wide-band receiver which revealed many other spectral lines that are common in star-forming regions.
The innermost regions of massive protostars traced by masers, high-resolution radio continuum, and near-infrared imaging
Authors: Massi Fabrizio , Moscadelli Luca , Arcidiacono Carmelo , Bacciotti Francesca 
Published: July 2018

AbstractWhether high-mass stars (M > 7M⊙) emerge from a scaled-up version of the low-mass star formation scenario, i. e. through disk-mediated accretion, is still debated. We present the first results of an observational programme aimed to map the innermost regions of high-mass stellar objects by combining together high-spatial resolution maser and radio continuum observations, and near-infrared imaging.
X-Ray Characteristics of Water Megamaser Galaxies
Authors: Leiter K. , Kadler M. , Wilms J. , Braatz J. , Grossberger C. , Krauß F. , Kreikenbohm A. , Langejahn M. , Litzinger E. , Markowitz A. , Müller C. 
Published: July 2018

AbstractWe have compiled the X-ray characteristic properties for a unique and homogeneous sample of Type 2 AGN with water megamaser activity observed by XMM-Newton and for a control sample of non-maser galaxies, both analyzed in a uniform way. A comparison of the luminosity distributions confirms previous results (from smaller and/or less systematic studies) that water maser galaxies appear more luminous than non-maser sources. In addition, the maser phenomenon is associated with more complex X-ray spectra, higher column densities and higher equivalent widths of the Fe Kα line. Both a sufficiently luminous X-ray source and a high absorbing column density in the line of sight favor the appearance of the water megamaser phenomenon in AGN.
Measuring Magnetic Fields from Water Masers Associated with a Synchrotron Protostellar Jet
Authors: Goddi Ciriaco , Surcis Gabriele 
Published: July 2018

AbstractThe Turner-Welch Object in the W3(OH) high-mass star forming complex drives a synchrotron jet, which is quite exceptional for a high-mass protostar, and is associated with a strongly polarized water maser source, W3(H2O), making it an optimal target to investigate the role of magnetic fields on the innermost scales of protostellar disk-jet systems. We report here full polarimetric VLBA observations of water masers. The linearly polarized emission from water masers provides clues on the orientation of the local magnetic field, while the measurement of the Zeeman splitting from circular polarization provides its strength. By combining the information on the measured orientation and strength of the magnetic field with the knowledge of the maser velocities, we infer that the magnetic field evolves from having a dominant component parallel to the outflow velocity in the pre-shock gas (with field strengths of the order of a few tens of mG), to being mainly dominated by the perpendicular component (of order of a few hundred of mG) in the post-shock gas where the water masers are excited. The general implication is that in the undisturbed (i.e. not-shocked) circumstellar gas, the flow velocities would follow closely the magnetic field lines, while in the shocked gas the magnetic field would be re-configured to be parallel to the shock front as a consequence of gas compression.
OH masers as probes: How does the variability fade away during the AGB - post-AGB transition?
Authors: Engels D. , Etoka S. , West M. , Gérard E. 
Published: July 2018

AbstractWe are currently performing a monitoring program of the 1612 MHz OH maser emission of several dozen Galactic disk OH/IR stars with the Nancay Radio Telescope (NRT). They are complemented by several OH/IR stars toward the Galactic center, which were monitored with the Hartebeesthoek radio telescope. We use the maser variations to probe the underlying stellar variability. As early monitoring programs already have shown, some stars are large amplitude variables with periods up to 7 years, others show small or even no amplitude variations. This dichotomy in the variability behaviour is assumed to mark the border between the AGB and the post-AGB stages. With the current program, we wish to find objects in transition and to describe their variability properties. We consider the fading out of pulsations with steadily declining amplitudes as a viable process. Promising candidates in the disk are the small-amplitude variables OH 138.0+7.2 and OH 51.8−0.2. ’Non-variable’ OH/IR stars in the Galactic center region may be as frequent as in the disk.
Serotonin concentration enhancers at clinically relevant doses reduce [11C]AZ10419369 binding to the 5-HT1B receptors in the nonhuman primate brain
Authors: Yang Kai-Chun , Takano Akihiro , Halldin Christer , Farde Lars , Finnema Sjoerd J. 
Published: July 2018

AbstractThe serotonin (5-HT) system plays an important role in the pathophysiology and treatment of several major psychiatric disorders. Currently, no suitable positron emission tomography (PET) imaging paradigm is available to assess 5-HT release in the living human brain. [11C]AZ10419369 binds to 5-HT1B receptors and is one of the most 5-HT-sensitive radioligands available. This study applied 5-HT concentration enhancers which can be safely studied in humans, and examined their effect on [11C]AZ10419369 binding at clinically relevant doses, including amphetamine (1 mg/kg), 3,4-methylenedioxymethamphetamine (MDMA; 1 mg/kg) or 5-hydroxy-L-tryptophan (5-HTP; 5 mg/kg). Twenty-six PET measurements (14 for amphetamine, 6 for MDMA and 6 for 5-HTP) using a bolus and constant infusion protocol were performed in four cynomolgus monkeys before or after drug administration. Binding potential (BPND) values were determined with the equilibrium method (integral interval: 63–123 min) using cerebellum as the reference region. BPND values were significantly decreased in several examined brain regions after administration of amphetamine (range: 19–31%), MDMA (16–25%) or 5-HTP (13–31%). Reductions in [11C]AZ10419369 binding were greater in striatum than cortical regions after administration of 5-HTP, while no prominent regional differences were found for amphetamine and MDMA. In conclusion, [11C]AZ10419369 binding is sensitive to changes in 5-HT concentration induced by amphetamine, MDMA or 5-HTP. The robust changes in BPND, following pretreatment drugs administered at clinically relevant doses, indicate that the applied PET imaging paradigms hold promise to be successfully used in future human studies.
Suppression of AURKA alleviates p27 inhibition on Bax cleavage and induces more intensive apoptosis in gastric cancer
Authors: Hou Daisen , Che Zhihui , Chen Ping , Zhang Wenli , Chu Yiwei , Yang Dongqin , Liu Jie 
Published: July 2018

AbstractBax is a key molecule in mitochondria-apoptosis pathway, however it is not always an efficient apoptosis inducer in chemotherapeutic agents-treated cancer cells. Here, we found that specific inhibition of AURKA by MLN8237-induced calpain-mediated Bax cleavage at N-terminal 33th asparagine (c-Bax) to promote apoptosis. The c-Bax, as Bax, could also efficiently located to mitochondria but c-Bax is a stronger apoptosis inducer than Bax. Morever, c-Bax-induced apoptosis could not be blocked by the canonical Bax inhibitor, Bcl-2. Further study found p27 was degraded and subsequently Bax was transformed to c-Bax through calpain. Also, p27 efficiently inhibited Bax cleavage and p27 knockdown sensitized apoptosis through Bax cleavage when cancer cells were treated with MLN8237. It is also demonstrated that the anti-apoptotic role of p27 lies its cytoplasmic localization. Finally, we found that the positive correlation between AURKA and p27 in advanced gastric cancer patients. In conclusion, we found that MNL8237 suppressed cell growth by regulating calpain-dependent Bax cleavage and p27 dysregulation in gastric cancer cells.
Microscopic mechanism of biphasic interface relaxation in lithium iron phosphate after delithiation
Authors: Kobayashi Shunsuke , Kuwabara Akihide , Fisher Craig A. J. , Ukyo Yoshio , Ikuhara Yuichi 
Published: July 2018

AbstractCharge/discharge of lithium-ion battery cathode material LiFePO4 is mediated by the structure and properties of the interface between delithiated and lithiated phases. Direct observations of the interface in a partially delithiated single crystal as a function of time using scanning transmission electron microscopy and electron energy-loss spectroscopy help clarify these complex phenomena. At the nano-scale, the interface comprises a thin multiphase layer whose composition varies monotonically between those of the two end-member phases. After partial delithiation, the interface does not remain static, but changes gradually in terms of orientation, morphology and position, as Li ions from the crystal bulk diffuse back into the delithiated regions. First-principles calculations of a monoclinic crystal of composition Li2/3FePO4 suggest that the interface exhibits higher electronic conductivity than either of the end-member phases. These observations highlight the importance of the interface in enabling LiFePO4 particles to retain structural integrity during high-rate charging and discharging.