Principal Term of Nutation from the Combination of VLBI Observations and Optical Astrometry

1997 ◽  
pp. 481-486 ◽  
Author(s):  
C. Bizouard ◽  
N. Capitaine ◽  
C. Ron ◽  
J. Vondrák
Keyword(s):  
Principal Term ◽  
Vlbi Observations

scholarly journals Note on the Determination of the Neaely Diurnal Free Nutation (Core Nutation) and the Principal Term of Nutation Based on the Astrometric Data

1991 ◽  
Vol 127 ◽  
pp. 385-391
Author(s):  
Ya.S. Yatskiv ◽  
L.D. Kovbasyuk
Keyword(s):  
Accurate Determination ◽  
Principal Term ◽  
Direct Observations ◽  
Vlbi Observations ◽  
Core Boundary ◽  
Insufficient Time ◽  
Astrometric Data ◽  
Free Nutation ◽  
Precession Constant

Due to the highly accurate determination of the corrections to the nutation terms (the IAU-1980 nutation theory) by VLBI observations, the proposal for adoption of the new nutation theory or standard model of nutation is being discussed. At this point there are two unsolved problems:(a)VLBI observations can’t provide reliable estimates of the principal nutation term. The reason is that the correlation between this term and the precession constant is high due to the insufficient time span of these observations (about 10 years).(b)period of free core nutation (FCN) which depends on the ellipticity of the mantle-core boundary has not been, so far, reliably determined from direct observations.In the present paper, we would like to draw attention to the results of the analysis of astrometric latitude and time observations which could be useful for resolving these problems.

scholarly journals Principal Term of Nutation from the Combination of VLBI Observations and Optical Astrometry

1997 ◽  
Vol 165 ◽  
pp. 481-486 ◽  
Author(s):  
C. Bizouard ◽  
N. Capitaine ◽  
C. Ron ◽  
J. Vondrák
Keyword(s):  
Reference Frame ◽  
Principal Term ◽  
Vlbi Observations ◽  
Celestial Pole ◽  
Previous Solution

AbstractThe celestial pole offsets (CPO) in provisional HIPPARCOS reference frame determined from the optical astrometry observations since 1899.7 until 1992.0 (Vondrák et al., 1996) and CPO determined from VLBI observations since 1980.0 until 1996.0 (Ma et al., 1996) are combined to get amplitudes of the long periodic nutation terms 18.6 and 9.3 years, respectively. The amplitudes are compared with previous solution based only on VLBI observations (Souchay et al., 1995).

A large rotating structure around AB Doradus A at VLBI scale

2019 ◽  
Vol 15 (S354) ◽  
pp. 189-194
Author(s):  
J. B. Climent ◽  
J. C. Guirado ◽  
R. Azulay ◽  
J. M. Marcaide
Keyword(s):  
Magnetic Reconnection ◽  
Main Sequence ◽  
Complex Structure ◽  
Main Sequence Star ◽  
Polar Cap ◽  
Vlbi Observations ◽  
Rotating Structure ◽  
Source Structure ◽  
Expected Position

AbstractWe report the results of three VLBI observations of the pre-main-sequence star AB Doradus A at 8.4 GHz. With almost three years between consecutive observations, we found a complex structure at the expected position of this star for all epochs. Maps at epochs 2007 and 2010 show a double core-halo morphology while the 2013 map reveals three emission peaks with separations between 5 and 18 stellar radii. Furthermore, all maps show a clear variation of the source structure within the observing time. We consider a number of hypothesis in order to explain such observations, mainly: magnetic reconnection in loops on the polar cap, a more general loop scenario and a close companion to AB Dor A.

Finding AGN with wide-eld VLBI observations

2011 ◽  
Author(s):  
Enno Middelberg ◽  
Adam Deller ◽  
John Morgan ◽  
Helge Rottmann ◽  
Walter Alef ◽  
...  
Keyword(s):  
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 3D magnetized jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

2021 ◽  
Vol 502 (2) ◽  
pp. 1843-1855
Author(s):  
Antonios Nathanail ◽  
Ramandeep Gill ◽  
Oliver Porth ◽  
Christian M Fromm ◽  
Luciano Rezzolla
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Opening Angle ◽  
Hollow Core ◽  
Binary Neutron Star ◽  
Vlbi Observations ◽  
Superluminal Motion ◽  
General Relativistic ◽  
Star Binary ◽  
Magnetohydrodynamic Simulations

ABSTRACT We perform 3D general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of θcore ≈ 4°, an opening angle of θjet ≳ 10°, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta _{\rm obs}= 35.7^{\circ \, \, +1.8}_{\phantom{\circ \, \, }-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.

scholarly journals VLBI Observations of the Radio Jet in 3C 273

1988 ◽  
Vol 129 ◽  
pp. 27-28
Author(s):  
S. C. Unwin ◽  
R. J. Davis
Keyword(s):  
Dynamic Range ◽  
Large Range ◽  
High Dynamic Range ◽  
No Emission ◽  
The Core ◽  
Vlbi Observations ◽  
High Dynamic ◽  
Quasar 3C 273

We present a new high dynamic range map of the quasar 3C 273, made from observations with a VLBI network of 12 telescopes. This new map at 18 cm wavelength has one of the highest dynamic ranges yet achieved with VLBI, and it shows the ‘jet’ extending to at least 180 milliarcsec, or 330 pc from the nucleus of the quasar. Strong limits can be placed on the brightness of any ‘counter-jet’ on kiloparsec-scales, as no emission is visible on the opposite side of the ‘core’. Combining with other VLBI, VLA and MERLIN maps shows that the jet is visible and continuous over a very large range of scales, from 1 pc to 40 kpc.

scholarly journals VLBI Pulsar Astrometry

2001 ◽  
Vol 205 ◽  
pp. 404-407
Author(s):  
R.M. Campbell
Keyword(s):  
Proper Motion ◽  
Vlbi Observations ◽  
Recent Developments

I briefly review the means by which VLBI observations can determine the position, proper motion, and parallax of a pulsar, consider a subset of the applications of such results, and highlight recent developments in pulsar gating at JIVE.

scholarly journals Serendipitous VLBI Observations of Intraday Variability in the BL Lac Objects 1334–127, 2131–021, and 2155–152

1998 ◽  
Vol 164 ◽  
pp. 273-274
Author(s):  
P. Yu. Kochanev ◽  
D. C. Gabuzda
Keyword(s):  
Rapid Variability ◽  
Bl Lac Objects ◽  
Polarization Structure ◽  
Vlbi Observations ◽  
Bl Lac ◽  
Vlbi Data ◽  
Intraday Variability

AbstractGlobal λ = 6 cm VLBI polarization observations of intraday variability in the three BLLacertae objects 1334–127, 2131–021, and 2155–152 are analyzed. Integrated VLA measurements during the VLBI observations show that although there were no substantial total intensity variations, the polarizations for these three sources varied significantly during the VLBI experiment. The VLBI data were divided into 2-3 hour segments in order to search for corresponding rapid variability in the VLBI polarization structure. Our analysis shows that the VLA polarization variability in 2155–152 and 2131–021 is present in the VLBI data (i.e., it occurred on mas scales), but this is not the case for 1334–127.

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