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.

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 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.

Maser Emission in G 339.884−1.259

2017 ◽  
Vol 13 (S336) ◽  
pp. 334-335
Author(s):  
V. Krishnan ◽  
L. Moscadelli ◽  
S. P. Ellingsen ◽  
H. E. Bignall ◽  
S. L. Breen ◽  
...  
Keyword(s):  
Star Formation ◽  
High Mass ◽  
Mass Star ◽  
Proper Motions ◽  
Star Formation Region ◽  
Formation Region ◽  
Gas Kinematics ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Water Masers

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.

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.

Very long baseline interferometry polarization studies of quasars and active galactic nuclei

1986 ◽  
Vol 64 (4) ◽  
pp. 434-439 ◽  
Author(s):  
J. F. C. Wardle ◽  
D. H. Roberts
Keyword(s):  
Active Galactic Nuclei ◽  
Linear Polarization ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
First Results ◽  
Polarization Studies ◽  
Theoretical Issues

We present some first results of a program to map the distribution of linear polarization in compact radio sources with milliarcsecond resolution. We show first-epoch maps of 3C345 and 0735 + 178 and first- and second-epoch maps of OJ287. In general, the polarization is mainly associated with optically thin (jet) components. In the case of OJ287, polarization maps made 1 year apart are strikingly different. We also discuss some of the theoretical issues raised by these observations.

scholarly journals The Astrometric Possibilities of Very-Long-Baseline Interferometry

1986 ◽  
Vol 109 ◽  
pp. 143-155
Author(s):  
D. S. Robertson
Keyword(s):  
Plane Wave ◽  
Arrival Time ◽  
Very Long Baseline Interferometry ◽  
Radio Sources ◽  
Arrival Times ◽  
Long Baseline ◽  
The Difference ◽  
Different Sources

In the application of Very-Long-Baseline Interferometry (VLBI) to astrometric problems the fundamental observable is the difference in the arrival times of a wavefront at two widely separated receiving stations. Since the radio sources being observed are sufficiently distant that the arriving wavefront can be considered to be a plane wave, the differential arrival time is a measure of the component of the baseline in the direction of the source. Equivalently, if the baseline is known, the differential arrival time is sufficient to determine a circle on the sky containing the source. It is easy to show that a minimum of ten observations distributed among three different sources is sufficient to determine all of the source coordinates and the baseline coordinates simultaneously (Robertson, 1975).

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 Use of the Long Baseline Array in Australia for Precise Geodesy and Absolute Astrometry

2009 ◽  
Vol 26 (1) ◽  
pp. 75-84 ◽  
Author(s):  
Leonid Petrov ◽  
Chris Phillips ◽  
Alessandra Bertarini ◽  
Adam Deller ◽  
Sergei Pogrebenko ◽  
...  
Keyword(s):  
Data Analysis ◽  
Heterogeneous Network ◽  
Radio Sources ◽  
Radio Telescopes ◽  
Geodetic Vlbi ◽  
Novel Technique ◽  
Long Baseline ◽  
Better Than

AbstractWe report the results of a successful 12-hour 22-GHz VLBI experiment using a heterogeneous network that includes radio telescopes of the Long Baseline Array (LBA) in Australia and several VLBI stations that regularly observe in geodetic VLBI campaigns. We have determined positions of three VLBI stations, atca-104, ceduna and mopra, with an accuracy of 4–30 mm using a novel technique of data analysis. These stations have never before participated in geodetic experiments. We observed 105 radio sources, and amongst them 5 objects which have not previously been observed with VLBI. We have determined positions of these new sources with the accuracy of 2–5 mas. We make the conclusion that the LBA network is capable of conducting absolute astrometry VLBI surveys with an accuracy better than 5 mas.

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