scholarly journals On the Feasibility of a Star Coordinate Determination in the Radio Astrometry Reference System

1986 ◽  
Vol 109 ◽  
pp. 765-771
Author(s):  
V.S. Gubanov
Keyword(s):  
Reference Frame ◽  
Mutual Orientation ◽  
Radio Sources ◽  
Extragalactic Source ◽  
Vlbi Observations ◽  
Artificial Earth ◽  
Sufficient Magnitude ◽  
The Stability ◽  
The Relationship ◽  
Star Field

At present it is evident that the stability of a celestial coordinates system with an accuracy of at least per century, with respect to an internal frame can be derived only from VLBI observations of compact extragalactic radio sources. At the same time it is expected that the need for improved stars' coordinates will be strongly felt at least up to the end of this century, because stars are important and more convenient observational objects then very weak extragalactic sources or artificial Earth satellites (AES). One therefore wonders if one can use the high precision and stability of the radio astrometric reference frame to stabilize and improve the reference frame given by star catalogues. The problem of the relationship between these systems has so far been investigated in the form of determining the parameters of their mutual orientation, and/or studying systematic errors of star catalogues (Gubanov, 1978; Gubanov and Kumkova, 1978, 1981). This problem has been attacked by direct photography of several optically identified radio sources or VLBI observations of few radio stars. The present paper shows the feasibility of determining the place of any star of sufficient magnitude with reference to the radio astrometric frame, as given by extragalactic source positions (Gubanov, 1983). This is done by introducing an AES, equipped with radio signal for VLBI observations and a corner reflector for laser ranging, which can be observed by radio methods as well as optically (Gubanov, 1976). This satellite should also be bright enough in the reflected sun's light to be observed in the star field with a precision photoelectric satellite camera.

scholarly journals Secular Motions of Extragalactic Radio-Sources and the Stability of the Radio Reference Frame

1995 ◽  
Vol 166 ◽  
pp. 283-283 ◽  
Author(s):  
T.M. Eubanks ◽  
D.N. Matsakis ◽  
F.J. Josties ◽  
B.A. Archinal ◽  
K.A. Kingham ◽  
...  
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Current Source ◽  
Radio Sources ◽  
Data Set ◽  
Extragalactic Radio Sources ◽  
Secular Changes ◽  
Vlbi Data ◽  
The Stability ◽  
Mass Concentrations

The best current approximation to an inertial reference frame is provided by Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources with red shifts (z) up to 3.8. The stability of the resulting reference frame directly depends on the amount of any secular changes in the observed source positions.Two types of potentially observable secular motions should be present in extragalactic source positions. Gravitational accelerations of the solar system will cause secular motions through aberration, amounting to, e.g., about 4 microarcsec (μas) year–1 due to the mass of the galaxy. Extragalactic mass concentrations will cause gravitational deflections in the apparent positions of more distant radio sources, and these will change with time as the mass concentrations evolve. This effect could easily cause secular motions of order 1 μas year–1 in some, or even most, radio sources with z ≥ 1.The present astrometric VLBI data set contains about one million observations over a 15 year period, with current source proper motion formal errors being as small as 2.5 μas year–1. Proper motion estimates from these data reveal many sources with statistically significant proper motion estimates of order 30 μas year–1, about an order of magnitude larger than expected. Work continues to determine if the observed motions are due to systematic errors or reflect true secular changes in source positions. The results from a continued proper motion analysis of the complete astrometric VLBI data set will be presented.

scholarly journals Astrometry and Geodesy from VLBI

1993 ◽  
Vol 156 ◽  
pp. 159-171
Author(s):  
C. Ma ◽  
J. L. Russell
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Radio Sources ◽  
Dual Frequency ◽  
Terrestrial Reference Frames ◽  
Vlbi Observations ◽  
Using Data ◽  
Celestial Reference Frame ◽  
Right Ascension ◽  
Better Than

Dual frequency Mark III VLBI observations acquired since 1979 by several geodetic and astrometric observing programs have been used to establish precise celestial and terrestrial reference frames. The program to establish a uniformly distributed celestial reference frame of ∼400 compact radio sources with optical counterparts was begun in 1987. Some 700 sources have been considered as part of this effort and a preliminary list of ∼400 has been observed. At present, 308 sources have formal 1σ errors less than 1 mas in right ascension and 308 have similar precision in declination. The astrometric results include some data acquired for geodetic purposes. The geodetic results using data to September, 1992 include the positions of 105 sites with formal 1σ horizontal errors generally less than 1 cm at 1992.6 and the velocities of 64 sites with formal 1σ horizontal errors generally better than 2 mm/yr.

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 Realization of an Inertial Reference Frame From Mark III VLBI

1990 ◽  
Vol 141 ◽  
pp. 271-280 ◽  
Author(s):  
C. Ma
Keyword(s):  
Reference Frame ◽  
Standard Errors ◽  
Radio Sources ◽  
Inertial Reference Frame ◽  
Dual Frequency ◽  
Extragalactic Radio Sources ◽  
Vlbi Observations

Over 350 000 dual frequency Mark III VLBI observations from several geodetic and astrometric observing programs have been used to realize an inertial reference frame through the positions of 325 compact extragalactic radio sources uniformly distributed over the sky with standard errors typically under 1 milliarcsecond (mas). Internal and external tests indicate that the reference frame defined by the relative positions of these radio sources should be accurate and stable at the 1-2 mas level. Because the conventional precession and nutation models are adjusted in the estimation of the source positions, the positions and relative angles are not degraded over the interval of observations or at epochs away from the reference epoch.

scholarly journals VLBI Positions of Eight Stellar Systems

1988 ◽  
Vol 129 ◽  
pp. 327-328
Author(s):  
A. E. Niell ◽  
J.-F. Lestrade ◽  
R. A. Preston ◽  
R. L. Mutel ◽  
R. B. Phillips
Keyword(s):  
Reference Frame ◽  
Stellar Systems ◽  
Radio Sources ◽  
Jet Propulsion ◽  
Extragalactic Radio Sources ◽  
Vlbi Observations ◽  
Jet Propulsion Laboratory

Radio positions of eight stellar systems have been derived with accuracies of 3 to 300 milliarcseconds from MkIII VLBI observations conducted with multi-station arrays. The best accuracy was obtained during a relatively strong outburst of the RS CVn system HR 5110. The epoch J2000.0 positions are obtained in the Jet Propulsion Laboratory VLBI reference frame of extragalactic radio sources.

scholarly journals Accurate Positions of 120 Radio Sources with Declinations Above −45°

1984 ◽  
Vol 110 ◽  
pp. 363-364
Author(s):  
A. E. Niell ◽  
J. L. Fanselow ◽  
O. J. Sovers ◽  
J. B. Thomas ◽  
K. M. Liewer ◽  
...  
Keyword(s):  
Reference Frame ◽  
Radio Sources ◽  
Deep Space ◽  
Entry Angle ◽  
Positional Accuracy ◽  
Deep Space Network ◽  
Space Network ◽  
Vlbi Observations

Development of a catalogue of approximately 100 radio sources having positional accuracy of ~0.005 arcseconds is one goal of the DSN radio reference frame program. This objective is set by the navigation requirements of the Galileo Project for reconstruction of the probe entry angle into the atmosphere of Jupiter. These radio positions are determined by VLBI observations using the antennas of the NASA Deep Space Network on two intercontinental baselines – California-Spain and California-Australia. Since 1978, measurements have been made simultaneously at 2.3 and 8.4 Ghz. Sixteen to twenty-four hours of data on each of the two baselines are usually obtained within a few days of each other, and since mid-1982 these pairs of observations have been made at approximately six week intervals.

scholarly journals VLBI observations of weak extragalactic radio sources for the alignment of the future Gaia frame with the ICRF

2007 ◽  
Vol 3 (S248) ◽  
pp. 324-325
Author(s):  
G. Bourda ◽  
P. Charlot ◽  
R. Porcas ◽  
S. Garrington
Keyword(s):  
Radio Emission ◽  
Reference Frame ◽  
Radio Sources ◽  
High Quality ◽  
Preliminary Results ◽  
Vlbi Observations ◽  
Extended Radio ◽  
Optical Wavelengths ◽  
Space Astrometry ◽  
Celestial Reference Frame

AbstractThe space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between the optical and radio positions, it will be important to align the Gaia frame and the International Celestial Reference Frame (ICRF) with the highest accuracy. Currently, it is found that only 10% of the ICRF sources are suitable to establish this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional high-quality radio sources for aligning the two frames. The sample consists of about 450 sources, typically 20 times weaker than the current ICRF sources, which have been selected by cross-correlating optical and radio catalogues. This paper presents the observing strategy and includes preliminary results of observation of 224 of these sources with the European VLBI Network in June 2007.

An Experimental Investigation on Thermal Conductivity and Viscosity of Graphene doped CNTs /TiO2 Nanofluid

2020 ◽  
Vol 17 (3) ◽  
Author(s):  
A.M. Zetty Akhtar ◽  
M.M. Rahman ◽  
K. Kadirgama ◽  
M.A. Maleque
Keyword(s):  
Thermal Conductivity ◽  
Zeta Potential ◽  
Base Fluid ◽  
Minimum Quantity Lubrication ◽  
Cutting Fluid ◽  
Cutting Zone ◽  
Observation Method ◽  
The Stability ◽  
The Relationship ◽  
Zeta Potential Analysis

This paper presents the findings of the stability, thermal conductivity and viscosity of CNTs (doped with 10 wt% graphene)- TiO2 hybrid nanofluids under various concentrations. While the usage of cutting fluid in machining operation is necessary for removing the heat generated at the cutting zone, the excessive use of it could lead to environmental and health issue to the operators. Therefore, the minimum quantity lubrication (MQL) to replace the conventional flooding was introduced. The MQL method minimises the usage of cutting fluid as a step to achieve a cleaner environment and sustainable machining. However, the low thermal conductivity of the base fluid in the MQL system caused the insufficient removal of heat generated in the cutting zone. Addition of nanoparticles to the base fluid was then introduced to enhance the performance of cutting fluids. The ethylene glycol used as the base fluid, titanium dioxide (TiO2) and carbon nanotubes (CNTs) nanoparticle mixed to produce nanofluids with concentrations of 0.02 to 0.1 wt.% with an interval of 0.02 wt%. The mixing ratio of TiO2: CNTs was 90:10 and ratio of SDBS (surfactant): CNTs was 10:1. The stability of nanofluid checked using observation method and zeta potential analysis. The thermal conductivity and viscosity of suspension were measured at a temperature range between 30˚C to 70˚C (with increment of 10˚C) to determine the relationship between concentration and temperature on nanofluid’s thermal physical properties. Based on the results obtained, zeta potential value for nanofluid range from -50 to -70 mV indicates a good stability of the suspension. Thermal conductivity of nanofluid increases as an increase of temperature and enhancement ratio is within the range of 1.51 to 4.53 compared to the base fluid. Meanwhile, the viscosity of nanofluid shows decrements with an increase of the temperature remarks significant advantage in pumping power. The developed nanofluid in this study found to be stable with enhanced thermal conductivity and decrease in viscosity, which at once make it possible to be use as nanolubricant in machining operation.

Relationship between Faithfulness and Preference of Stars in a Planetarium

2019 ◽  
Vol 2 (1) ◽  
pp. 10402-1-10402-11
Author(s):  
Midori Tanaka ◽  
Takahiko Horiuchi ◽  
Ken’ichi Otani
Keyword(s):  
Light Source ◽  
Preference Rating ◽  
Experimental Procedure ◽  
Male And Female ◽  
Astronomical Observations ◽  
Low Luminance ◽  
Projection Pattern ◽  
The Relationship ◽  
Star Field

Abstract A planetarium imitates a starry sky with physical and technical limitations using a dome, projector, and light source. It is widely used for entertainment, and astronomy and physics educations. In our previous study, we investigated the evaluation for faithful reproduction of a star field in a planetarium by performing psychometric experiments with 20 observers for plural projection patterns with different reproduction factors (color, luminance, and size of projected stars). In this study, we investigate the relationship between faithfulness and preference of a star field in a planetarium through a psychometric experiment with 47 observers. The experimental procedure followed the previous study. The rating of faithfulness improved for the projection pattern with a smaller star size. For the preference evaluation, the projection pattern with low luminance significantly lowered the preference rating. The results of the experiment indicate that the preferable star reproduction was different between male and female observers, whereas the faithful star reproduction was not significantly different in the evaluations between male and female observers. The male observers sought a faithful star reproduction as the preferred reproduction. In contrast, the female observers did not feel the faithful star reproduction preferable, and evaluated the more brilliant star reproduction as the preferred reproduction. These results were not dependent on the experience in astronomical observations.

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