scholarly journals VLBI Astrometry

1994 ◽  
Vol 158 ◽  
pp. 437-444
Author(s):  
J. E. Reynolds
Keyword(s):  
Reference Frame ◽  
High Precision ◽  
Reference Frames ◽  
Reasonable Number ◽  
Optical Reference ◽  
The Status ◽  
Substantial Progress ◽  
Global Reference Frame ◽  
Made In

VLBI is at present the most accurate technique for measuring radiosource positions and the only method capable of high precision for a reasonable number of sources. The applications of VLBI astrometry in stellar, Galactic and extra-Galactic regimes are reviewed. In particular, substantial progress has been made in the last few years towards a global reference frame of extragalactic radiosource positions. The status of this frame, and of the link to the optical reference frames is also described.

THE STATUS OF TWO-NEUTRINO AND NEUTRINOLESS DOUBLE BETA DECAY SEARCHES

1993 ◽  
Vol 02 (03) ◽  
pp. 507-546 ◽  
Author(s):  
M.K. MOE
Keyword(s):  
Beta Decay ◽  
Neutrinoless Double Beta Decay ◽  
Double Beta Decay ◽  
Experimental Activity ◽  
The Past ◽  
The Status ◽  
Substantial Progress ◽  
Direct Counting ◽  
Made In

Substantial progress has been made in double beta decay experiments in the past few years, including the beginning of sensitive new searches for neutrinoless double beta decay, and several additional positive detections of the two-neutrino mode by geochemical, radiochemical, and direct-counting techniques. This review discusses the recent experimental activity.

scholarly journals Interrelation of Present Optical and Radio Reference Frames

1984 ◽  
Vol 110 ◽  
pp. 357-360
Author(s):  
Chr. de Vegt
Keyword(s):  
Reference Frame ◽  
Northern Hemisphere ◽  
Reference Frames ◽  
Systematic Errors ◽  
Future Developments ◽  
Optical Reference

Comparison of optical and radio positions in the northern hemisphere yields local systematic differences up to 0″.2, mainly due to combined systematic errors of current optical reference frame and contributing main catalogues. Interrelations of radio/optical frame and future developments are discussed.

scholarly journals The Possibility to Link Radio and Optical Reference Frames With Artificial Satellites

1990 ◽  
Vol 141 ◽  
pp. 194-194
Author(s):  
Tong Fu
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Artificial Satellites ◽  
Radio Sources ◽  
Bl Lac Objects ◽  
Extragalactic Radio Sources ◽  
Bl Lac ◽  
Optical Reference ◽  
Radio Stars ◽  
Fundamental Reference

Based on extragalactic radio sources, a new high precision extragalactic radio reference frame can be established from radio interferometric measurements. To link the optical fundamental reference frame presently represented by the FK4/5 to the extragalactic radio frame, the optical counterparts of extragalactic radio sources (quasars, BL Lac objects etc.) and radio stars are the most important classes of objects. Besides these two classes of objects, are there any other objects which can be used to link the optical and radio frames? A posible answer is that artificial satellites could be a candidate class of objects contributing to this subject.

scholarly journals High-Precision Timing of Millisecond Pulsars and Precision Astrometry

1995 ◽  
Vol 166 ◽  
pp. 163-171 ◽  
Author(s):  
V. M. Kaspi
Keyword(s):  
Solar System ◽  
High Precision ◽  
Reference Frames ◽  
Millisecond Pulsar ◽  
Millisecond Pulsars ◽  
Pulsar Timing ◽  
Solar System Objects ◽  
Optical Reference ◽  
Precision Astrometry

We present the technique of long-term, high-precision timing of millisecond pulsars as applied to precision astrometry. We provide a tutorial on pulsars and pulsar timing, as well as up-to-date results of long-term timing observations of two millisecond pulsars, PSRs B1855+09 and B1937+21. We consider the feasibility of tying the extragalactic and optical reference frames to that defined by solar system objects, and we conclude that precision astrometry from millisecond pulsar timing has a bright future.

scholarly journals Fundamental radio reference frame from VLA observations of minor planets

1988 ◽  
Vol 128 ◽  
pp. 97-97 ◽  
Author(s):  
G. H. Kaplan ◽  
K. J. Johnston ◽  
P. K. Seidelmann ◽  
C. M. Wade ◽  
T. S. Carroll
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Thermal Emission ◽  
Optical Observations ◽  
Minor Planets ◽  
Very Large Array ◽  
Test Particles ◽  
Optical Reference ◽  
Microwave Regime

The weak thermal emission from the largest minor planets can be detected in the microwave regime by the Very Large Array (VLA). Signal-to-noise ratios are sufficiently high to permit precise measurement of the positions of these objects at all points in their orbits with respect to background extragalactic sources. We are in the process of obtaining observations of astrometric accuracy for minor planets 1 Ceres, 2 Pallas, 4 Vesta, and 10 Hygeia.Minor planets have historically served as “test particles” in the solar system, and optical observations of these objects have been valuable in the determination of fundamental astronomical constants. In particular, optical observations of minor planets have played an important role in the establishment of the fundamental optical reference frame by permitting the determination of the orientation of the Earth's orbit relative to the stars defining the frame.Similarly, radio observations of these bodies can play a corresponding role in the establishment of a fundamental radio reference frame. Our observations will provide a direct link between the dynamical and radio reference frames, and provide important information on the relationship between the radio and optical reference frames.

scholarly journals Towards the Definition of a Unified Celestial Optical/Radio Reference Frame

1988 ◽  
Vol 129 ◽  
pp. 317-318
Author(s):  
K. J. Johnston ◽  
J. Russell ◽  
Ch. de Vegt ◽  
J. Hughes ◽  
D. Jauncey ◽  
...  
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Radio Observations ◽  
Minimum Density ◽  
Optical Reference ◽  
Definition Of ◽  
Celestial Reference Frame

An almost inertial celestial reference frame based upon extragalactic sources is in the process of being established. This reference frame is to be global with a minimum density of one source/100 square degrees. The source positions will be based upon radio observations and will allow optical reference frames to be related to this frame at the 0.03 arc second level.

Reference frames in astrometry

1988 ◽  
Vol 128 ◽  
pp. 25-32 ◽  
Author(s):  
Chr. de Vegt ◽  
K. J. Johnston
Keyword(s):  
Reference Frame ◽  
Present Status ◽  
Reference Frames ◽  
Order Of Magnitude ◽  
Optical Wavelengths ◽  
Near Future ◽  
Magnitude Increase ◽  
Fundamental Reference ◽  
Made In

Present and near future advances in astrometry at radio and optical wavelengths will allow at least an order of magnitude increase in the precision with which fundamental reference frames are defined compared with those available ten years ago. A brief review is given of the present status of fundamental celestial reference frames with a view towards defining the problems encountered in establishing a fundamental reference frame and methods of linking these reference frames. An estimate is made of the progress to be made in reference frames over the next ten years.

High-precision GNSS-positioning in GSK-2011 reference frame

2019 ◽  
Vol 944 (2) ◽  
pp. 2-14 ◽  
Author(s):  
N.A. Bovshin
Keyword(s):  
Reference Frame ◽  
High Precision ◽  
Reference Frames ◽  
Geodetic Network ◽  
Terrestrial Reference Frame ◽  
Reference Station ◽  
Gnss Positioning ◽  
Processing Procedure ◽  
Gnss Observations ◽  
Correct Processing

The paper deals with a high-precision geodetic network densification by means of GNSS based geodetic solutions, in the view of the fact that the initial data are represented in different reference frames. Indeed, reference station positions are represented in GSK-2011 terrestrial reference frame whereas GNSS satellites` ephemeris are represented in other reference frames, such as ITRFs, WGS84, etc. Two methods are considered in the paper to provide GNSS observations with a correct processing procedure

scholarly journals Dense optical reference frames: UCAC and URAT

2007 ◽  
Vol 3 (S248) ◽  
pp. 310-315
Author(s):  
N. Zacharias
Keyword(s):  
Reference Frame ◽  
Focal Plane ◽  
Reference Frames ◽  
Field Of View ◽  
Radio Sources ◽  
Proper Motions ◽  
Naval Observatory ◽  
Optical Reference ◽  
Celestial Reference Frame ◽  
The U.S

AbstractA series of ground-based, dedicated astrometric, observational programs have been performed or are in preparation which provide a dense and accurate optical reference frame. Integral to all these programs are new observations to link the Hipparcos Celestial Reference Frame (HCRF) to the International Celestial Reference Frame (ICRF), based on compact, extragalactic radio sources.The U.S. Naval Observatory CCD Astrograph Catalog (UCAC) 3rd release is in preparation. A pixel re-reduction is in progress to improve astrometric and photometric accuracy as well as completeness of this all-sky reference catalog to 16th magnitude. Optical counterparts of ICRF radio sources have been observed with 0.9-meter telescopes contemporaneously. Scanning of over 5000 early-epoch astrograph plates on StarScan has been completed. These data will improve the proper motions of stars in the 10 to 14 mag range for the UCAC3 release.A 111 million-pixel CCD was successfully fabricated in 2006 and test observations at the USNO astrograph are underway. Four of such detectors will be used for the USNO Robotic Astrometric Telescope (URAT) focal plane assembly. Phase I of URAT will use the astrograph to reach 18th magnitude, while the new 0.85-meter telescope with a 4.5 deg diameter field of view will reach 21st magnitude. The URAT primary mirror has been fabricated.

scholarly journals Comparison of the Optical and Radio Reference Frames

1986 ◽  
Vol 7 ◽  
pp. 103-108 ◽  
Author(s):  
K. J. Johnston ◽  
Chr. de Vegt
Keyword(s):  
Radio Emission ◽  
Reference Frame ◽  
Radio Telescope ◽  
Reference Frames ◽  
Radio Sources ◽  
Large Array ◽  
Very Large Array ◽  
Extragalactic Radio Sources ◽  
Optical Reference ◽  
Lack Of Knowledge

The Very Large Array (VLA) has made possible the measurement of the precise positions of the radio emission associated with stars. This allows the direct comparison of the optical reference frame (FK4) with the radio reference frame which is defined by the quasi-absolute positions of extragalactic radio sources. This comparison is limited by the small number of bright stars that display detectable radio emission and the lack of knowledge of the precise coincidence of the radio emission with the optical photocenter of the star. Since the VLA is the most sensitive astrometrically capable radio telescope, positions of the largest number of stars north of declination -20 degrees can be measured. The accuracy of the positions on the extragalactic reference frame should approach a milliarcsecond.

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