Masers as probes of the gas dynamics close to forming high-mass stars

2017 ◽  
Vol 13 (S336) ◽  
pp. 201-206 ◽  
Author(s):  
Luca Moscadelli ◽  
Alberto Sanna ◽  
Ciriaco Goddi
Keyword(s):  
Gas Dynamics ◽  
Very Long Baseline Interferometry ◽  
High Mass ◽  
Powerful Technique ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Massive Forming ◽  
Typical Distances ◽  
New Generation ◽  
Better Than

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.

scholarly journals The Gould's Belt Distances Survey

2012 ◽  
Vol 8 (S289) ◽  
pp. 36-43 ◽  
Author(s):  
Laurent Loinard
Keyword(s):  
Star Formation ◽  
Very Long Baseline Interferometry ◽  
Young Stars ◽  
Solar Neighborhood ◽  
Radio Sources ◽  
Proper Motions ◽  
Long Baseline ◽  
Trigonometric Parallax ◽  
Vlbi Observations ◽  
Better Than

AbstractVery Long Baseline Interferometry (VLBI) observations can provide the positions of compact radio sources with an accuracy of order 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and proper motions of any object within 500 pc of the Sun to better than a few percent. Because they are magnetically active, young stars are often associated with compact radio emission detectable using VLBI techniques. Here we show how VLBI observations have already constrained the distance to the most often studied nearby regions of star formation (Taurus, Ophiuchus, Orion, etc.) and have started to provide information about their internal structure and kinematics. We will then briefly describe a large project, the ‘Gould's Belt Distances Survey,’ which has been designed to provide a detailed view of star formation in the solar neighborhood using VLBI observations.

scholarly journals Analysis of the Residuals between Theoretical Nutations and VLBI Observations

2002 ◽  
Vol 12 ◽  
pp. 124-125 ◽  
Author(s):  
V. Dehant ◽  
M. Feissel ◽  
O. de Viron ◽  
M. Yseboodt ◽  
Ch. Bizouard
Keyword(s):  
Very Long Baseline Interferometry ◽  
Short Description ◽  
Time Intervals ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Vlbi Data ◽  
Theoretical Developments

The recent theoretical developments have provided accurate series of nutations, which are close to the Very Long Baseline Interferometry (VLBI) data. At the milliarcsecond (mas) level, three series are available: MHB2000 (Mathews et al. 2000), FG2000 (Getino and Ferrándiz 2000), and SF2000 (Shirai and Fukushima 2000a,b) (see Dehant 2000, and in this volume, for more information and for a short description of these models).In the first part of our work we have compared these models with the (VLBI) observations (Ma et al. 2000) by computing rms of the residuals for several time intervals of measurements. We have concluded that these series have comparable precision.

scholarly journals VLBI observations of the G25.65+1.05 water maser superburst

2019 ◽  
Vol 491 (3) ◽  
pp. 4069-4075 ◽  
Author(s):  
R A Burns ◽  
G Orosz ◽  
O Bayandina ◽  
G Surcis ◽  
M Olech ◽  
...  
Keyword(s):  
Path Length ◽  
Massive Star ◽  
Very Long Baseline Interferometry ◽  
Complex Structure ◽  
Rapid Onset ◽  
Line Of Sight ◽  
Star Forming ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Water Maser

ABSTRACT This paper reports observations of a 22 GHz water maser ‘superburst’ in the G25.65+1.05 massive star-forming region, conducted in response to an alert from the Maser Monitoring Organisation (M2O). Very long baseline interferometry (VLBI) observations using the European VLBI Network (EVN) recorded a maser flux density of 1.2 × 104 Jy. The superburst was investipgated in the spectral, structural, and temporal domains and its cause was determined to be an increase in maser path length generated by the superposition of multiple maser emitting regions aligning in the line of sight to the observer. This conclusion was based on the location of the bursting maser in the context of the star-forming region, its complex structure, and its rapid onset and decay.

scholarly journals The Milliarcsecond Structure of Active Galactic Nuclei Observed with VLBI

1989 ◽  
Vol 134 ◽  
pp. 525-528
Author(s):  
T. J. Pearson ◽  
A. C. S. Readhead
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Relativistic Motion ◽  
Powerful Radio ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Central Engine

Very Long Baseline Interferometry at radio wavelengths is the only technique available for imaging the central few parsecs of powerful radio galaxies and quasars. VLBI observations have shown that in many nuclei radio-emitting material is collimated into a jet on a scale less than a parsec and ejected at relativistic velocities. The interpretation of the observations is complicated by the relativistic motion, however: the images are dominated by those parts of the source that are moving almost directly towards the observer, and thus amplified by relativistic aberration. Nonetheless, the VLBI images are vital for understanding the nature of the central engine, the cause of the collimation, and the physics of the jets.

Corrections to the Luni-Solar Precession From Radio Positions of Extragalactic Objects

1990 ◽  
Vol 141 ◽  
pp. 285-292
Author(s):  
H. G. Walter
Keyword(s):  
Pilot Study ◽  
Fixed Points ◽  
Reference Frame ◽  
Apparent Motion ◽  
Very Long Baseline Interferometry ◽  
Confidence Limits ◽  
Independent Observation ◽  
Long Baseline ◽  
Better Than

In an attempt of a realization of the radio reference frame a compilation catalogue of positions is derived from independent observation catalogues of extragalactic objects the coordinates of which had been determined by means of Very Long Baseline Interferometry. The compilation catalogue comprises 209 objects which are divided into a core consisting of 50 objects having mean positional accuracies of 0.5 milliseconds of arc (mas) and an extension with positional accuracies better than 2 mas. Comparison of this catalogue with an independent compilation catalogue led to confidence limits at the 1 mas level. - The compilation catalogue is supposed to represent a static reference frame of fixed extragalactic points. As the epochs of the contributing observations span nearly 10 years it was tried to interpret the apparent motion of the fixed points recognizable in the observation catalogues as an effect of luni-solar precession. The pilot study points at a reduction of the conventional value of about 2 mas per year.

scholarly journals First Hints of Pressure Waves in a Helical Extragalactic Jet: S5 0836+710

2014 ◽  
Vol 1 (1) ◽  
pp. 265-268
Author(s):  
Manel Perucho
Keyword(s):  
Very Long Baseline Interferometry ◽  
Physical Structure ◽  
Pressure Waves ◽  
Ridge Line ◽  
The Core ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Open Questions ◽  
Propagation Axis ◽  
Extragalactic Jets

One of the open questions in extragalactic jet Astrophysics is related to the nature of the observed radio jet, namely whether it traces a pattern or the flow structure itself. In this paper I summarize the evidence collected for the presence of waves in extragalactic jets. The evidence points towards the peak of emission in helical jets corresponding to pressure-maxima of a wave that is generated within the core region and propagates downstream. Making use of a number of very long baseline interferometry (VLBI) observations of the radio jet in the quasar S5 0836+710 at dierent frequencies and epochs, Perucho et al. (2012a) were able to observe wave-like behavior within the observed radio-jet. The ridge-line of the emission in the jet coincides within the errors at all frequencies. Moreover, small differences between epochs at 15 GHz reveal wave-like motion of the ridge-line transversal to the jet propagation axis. The authors conclude that the helicity is a real, physical structure. I report here on those results and discuss them in the light of new results recently announced by other authors that confirm the presence of waves in the close-by object BL Lac (Cohen et al., in preparation).

scholarly journals Receiving And Data Acquisition Systems Of Rt-32 For Vlbi Observations / Rt-32 Uztveršanas Un Datu Reģistrācijas Sistēmas Vlbi Novērojumiem

2012 ◽  
Vol 49 (6-II) ◽  
pp. 30-42
Author(s):  
Vl. Bezrukovs ◽  
I. Shmeld ◽  
M. Nechaeva ◽  
J. Trokss ◽  
D. Bezrukovs ◽  
...  
Keyword(s):  
Data Acquisition ◽  
Radio Astronomy ◽  
Very Long Baseline Interferometry ◽  
Low Frequency ◽  
Current Status ◽  
Data Acquisition Systems ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Parabolic Antenna ◽  
Vlbi Data

Abstract Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methanol maser single dish observations. The apparatus system of RT-32 is equipped with two independent VLBI data acquisition systems: TN-16, and DBBC in combination with MK5b. Both systems are employed in interferometric observations depending on the purpose of experiment and the enabled radiotelescopes. The current status of RT-32, the availability of its receiving and data acquisition units for VLBI observations and the previous VLBI sessions are discussed.

scholarly journals Models for Source Structure Corrections

2000 ◽  
Vol 180 ◽  
pp. 29-39
Author(s):  
P. Charlot
Keyword(s):  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Radio Sources ◽  
Time Varying ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Spatially Extended ◽  
Astrometric Data ◽  
Celestial Reference Frame ◽  
Source Structure

AbstractAt the milliarcsecond scale, most of the extragalactic radio sources exhibit spatially-extended intrinsic structures which are variable in both time and frequency. Such radio structures set limits on the accuracy of source positions determined with the Very Long Baseline Interferometry (VLBI) technique unless their effects in the astrometric data can be accounted for. We review the modeling scheme for calculating source structure corrections and discuss the magnitude and impact of these effects for the sources that are part of the International Celestial Reference Frame (ICRF). Results obtained by applying source structure corrections to actual VLBI observations on the time-varying source 4C39.25 (0923 + 392) are also presented.

scholarly journals Very Long Baseline Interferometry Observations Using the Tracking and Data Relay Satellite as an Orbiting Radio Telescope

1988 ◽  
Vol 129 ◽  
pp. 457-458 ◽  
Author(s):  
R. P. Linfield ◽  
G. S. Levy ◽  
J. S. Ulvestad ◽  
C. D. Edwards ◽  
J. F. Jordan ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Very Long Baseline Interferometry ◽  
Geostationary Orbit ◽  
Brightness Temperatures ◽  
Long Baseline ◽  
Vlbi Observations

An antenna in geostationary orbit was used for VLBI observations at 2.3 GHz, in combination with ground antennas in Australia and Japan. 23 of the 25 observed sources were detected on orbiter-ground baselines, with baseline lengths as large as 2.15 earth diameters. Brightness temperatures between 1012 K and 4 × 1012 K were measured for 10 sources.

scholarly journals Recent developments in supernova research with VLBI

2013 ◽  
Vol 9 (S296) ◽  
pp. 53-57 ◽  
Author(s):  
Norbert Bartel ◽  
Michael F. Bietenholz
Keyword(s):  
Very Long Baseline Interferometry ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Expansion Velocity ◽  
Radial Density ◽  
Density Profiles ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Recent Developments ◽  
Circumstellar Medium

AbstractVery long baseline interferometry (VLBI) observations during the last 30 years have resolved many supernovae and provided detailed measurements of the expansion velocity and deceleration. Such measurements are useful for estimating the radial density profiles of both the ejecta and the circumstellar medium left over from the progenitor. VLBI measurements are also the most direct way of confirming the relativistic expansion velocities thought to occur in supernovae associated with gamma-ray bursts. Well-resolved images of a few supernovae have been obtained, and the interaction of the ejecta as it expands into the circumstellar medium could be monitored in detail. We discuss recent results, for SN 1979C, SN 1986J, and SN 1993J, and note that updated movies of the latter two of the supernovae from soon after the explosion to the present are available from the first author's personal website.

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