How Accurate are SuperCOSMOS Positions?

AbstractOptical positions from the SuperCOSMOS Sky Survey have been compared in detail with accurate radio positions that define the second realisation of the International Celestial Reference Frame (ICRF2). The comparison was limited to the IIIaJ plates from the UK/AAO and Oschin (Palomar) Schmidt telescopes. A total of 1 373 ICRF2 sources was used, with the sample restricted to stellar objects brighter than BJ = 20 and Galactic latitudes |b| > 10°. Position differences showed an rms scatter of $0.16\text{ arcsec}$ in right ascension and declination. While overall systematic offsets were < $0.1\text{ arcsec}$ in each hemisphere, both the systematics and scatter were greater in the north.

A Low frequency Southern Sky Survey Using the Mauritius Radio Telescope

10.1017/s0074180900168494 ◽

2002 ◽

Vol 199 ◽

pp. 25-31

Author(s):

N. Udaya Shankar

Keyword(s):

Radio Telescope ◽

Low Frequency ◽

Fourier Synthesis ◽

North East ◽

The North ◽

Sky Survey ◽

Correlation Receiver ◽

Complex Correlation ◽

Right Ascension ◽

East West

The Mauritius Radio Telescope (MRT) is a Fourier synthesis instrument which has been built to fill the gap in the availability of deep sky surveys at low radio frequencies in the southern hemisphere. It is situated in the north-east of Mauritius at a southern latitude of 20°.14 and an eastern longitude of 57°.73. The aim of the survey with the MRT is to contribute to the database of southern sky sources in the declination range −70° ≤ δ ≤ −10°, covering the entire 24 hours of right ascension, with a resolution of 4' × 4'.6sec(δ + 20.14°) and a point source sensitivity of 200 mJy (3σ level) at 151.5 MHz.MRT is a T-shaped non-coplanar array consisting of a 2048 m long East-West arm and a 880 m long South arm. In the East-West arm 1024 fixed helices are arranged in 32 groups and in the South arm 16 trolleys, with four helices on each, which move on a rail are used. A 512 channel, 2-bit 3-level complex correlation receiver is used to measure the visibility function. At least 60 days of observing are required for obtaining the visibilities up to the 880 m spacing. The calibrated visibilities are transformed taking care of the non-coplanarity of the array to produce an image of the area of the sky under observation.This paper will describe the telescope, the observations carried out so far, a few interesting aspects of imaging with this non-coplanar array and present results of a low resolution survey (13' × 18') covering roughly 12 hours of right ascension, and also present an image with a resolution of 4' × 4'.6sec(δ + 20.14°) made using the telescope.

Stability of the Extragalactic Reference Frame Realized by VLBI

International Astronomical Union Colloquium ◽

10.1017/s0252921100063685 ◽

1991 ◽

Vol 127 ◽

pp. 135-144 ◽

Cited By ~ 1

Author(s):

C. Ma ◽

D.B. Shaffer

Keyword(s):

Reference Frame ◽

Radio Sources ◽

Dual Frequency ◽

Real Motion ◽

Rates Of Change ◽

Upper Limits ◽

Crustal Dynamics ◽

Vlbi Data ◽

AbstractThe 318 compact extragalactic radio sources with positions derived from dual frequency Mark III VLBI data acquired by the geodetic and astrometric programs of NASA, NOAA, NRL and USNO form a celestial reference frame with stability in orientation and relative position at the 1 mas level. This paper examines the reference frame realized using 461,000 observations from 1021 observing sessions between 1979 August and 1990 August in the NASA Crustal Dynamics Project VLBI data base. Catalogs of positions estimated from subsets of data (annual, seasonal, network) show differences in orientation typically less than 1 mas provided precession and nutation are adjusted using a reference day. For 17 sources with >5 year time span and >200 one-day position estimates, the rates of change of right ascension and declination are generally less than 5 mas/century, giving upper limits on real motion.

Astrometry and Geodesy from VLBI

10.1017/s0074180900173140 ◽

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 ◽

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.

Relationship between the JPL radio celestial reference frame and a preliminary FK5 frame

10.1017/s007418090011928x ◽

1988 ◽

Vol 128 ◽

pp. 67-70

Author(s):

Jean-François Lestrade ◽

Yves Requième ◽

Michel Rapaport ◽

Robert A. Preston

Keyword(s):

Reference Frame ◽

Very Long Baseline Interferometry ◽

Long Baseline ◽

The Mean ◽

Mean Differences ◽

Right Ascension ◽

Radio Stars

Very Long Baseline Interferometry (VLBI) and optical positions of 8 radio stars are compared in the J2000.0 system. The mean differences in right ascension and declination found are +0.02″ ± 0.04″ and −0.02″ ± 0.07″, respectively. These differences show that the JPL radio celestial reference frame is aligned on a preliminary FK5 frame to at least this level.

Realization of a multifrequency celestial reference frame through a combination of normal equation systems

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936083 ◽

2019 ◽

Vol 630 ◽

pp. A101 ◽

Cited By ~ 1

Author(s):

M. Karbon ◽

A. Nothnagel

Keyword(s):

Radio Source ◽

Reference Frame ◽

Reference Frames ◽

Very Long Baseline Interferometry ◽

Normal Equation ◽

Long Baseline ◽

Combination Approach ◽

Right Ascension ◽

24 Ghz

Context. We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of very long baseline interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources. Aims. We produce a multifrequency catalog of radio source positions with full variance–covariance information across all radio source positions of all input catalogs. Methods. We combined three catalogs, one observed at 8 GHz (X band), one at 24 GHz (K band) and one at 32 GHz (Ka band). Rather than only using the radio source positions, we developed a new, rigorous combination approach by carrying over the full covariance information through the process of adding normal equation systems. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined catalog. Results. The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8 GHz, 824 sources also observed at 24 GHz, and 674 at 32 GHz. The frame is aligned with ICRF3 within ±3 μas and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.

Astrometric Reduction of Cassini ISS Images of Enceladus in 2015 Based on Gaia DR1

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317005555 ◽

2017 ◽

Vol 12 (S330) ◽

pp. 411-412

Author(s):

Q. F. Zhang ◽

V. Lainey ◽

A. Vienne ◽

N. J. Cooper ◽

Q. Y. Peng ◽

...

Keyword(s):

Standard Deviation ◽

Reference Frame ◽

Gaia Dr1 ◽

Astrometric Observation ◽

AbstractThe Gaia DR1 catalogue stars are taken as reference ones to reduce the Cassini ISS images of Enceladus in 2015, and a total of 494 Cassini-centered astrometric observation are obtained in right ascension(α) and declination (δ) in the international Celestial Reference Frame(ICRF). Compared with JPL ephemerides SAT367, we derive that their mean residuals are a few tens meters in α*cos(δ) and a few kilometers in δ, and their standard deviation is not over 2 kilometers. Compared with the results from UCAC4 catalogue stars, The Gaia DR1 has the equivalent precision of reduction.

The Effect of Companions on the SIM Reference Frame

International Astronomical Union Colloquium ◽

10.1017/s0252921100000531 ◽

2000 ◽

Vol 180 ◽

pp. 386-391

Author(s):

Christopher S. Jacobs ◽

Slava G. Turyshev

Keyword(s):

Reference Frame ◽

Proper Motion ◽

Field Of View ◽

Optical Interferometer ◽

Galactic Astronomy ◽

Right Ascension ◽

Precision Astrometry ◽

Accuracy And Stability ◽

Space Interferometry

AbstractThe Space Interferometry Mission (SIM) is a 10-m Michelson space-based optical interferometer designed for precision astrometry (4μas, 3μas/yr) with better accuracy hoped for over a narrow field of view. It is intended to search for planets and investigate a number of problems in Galactic and extra-galactic astronomy.The accuracy and stability of SIM’s celestial reference frame is subject to degradation over the 5-year mission from the reflex motion induced by massive companions of the objects used to construct the celestial reference frame. We present the results of simulations which show the sensitivity of reference frame accuracy to companions as a function of mass and period. We assume that pre-launch ground surveys will eliminate all objects with RMS radial velocity > 10 m/s. We further assume that the standard astrometric parameters of position, parallax, and proper motion plus acceleration terms in right ascension and declination will be allowed to absorb reflex motion.

The Naval Observatory “Short” Plate Being Taken As Part Of The Palomar Sky Survey II

10.1017/s0074180900139798 ◽

1988 ◽

Vol 133 ◽

pp. 337-339

Author(s):

David G. Monet

Keyword(s):

Reference Frame ◽

Short Exposure ◽

Naval Observatory ◽

Sky Survey ◽

The Us ◽

Short Plate ◽

The US Naval Observatory has commissioned a short exposure plate for each field in the Palomar Sky Survey II. These plates should provide the necessary intermediate reference frame for the determination of right ascension and declination for faint objects on the “deep” plates using catalog coordinates for bright stars measured on the “short” plate.

The VLBI celestial reference frame of the NASA Crustal Dynamics Project

10.1017/s0074180900119308 ◽

1988 ◽

Vol 128 ◽

pp. 73-81 ◽

Cited By ~ 2

Author(s):

C. Ma

Keyword(s):

Reference Frame ◽

Weighted Average ◽

Radio Sources ◽

Extragalactic Radio Sources ◽

Statistical Errors ◽

Crustal Dynamics ◽

Vlbi Data ◽

Right Ascension ◽

Average Position

A celestial reference frame can be defined by precise positions of extragalactic radio sources using Mark III VLBI data available to the NASA Crustal Dynamics Project for geodynamic research. Seven years of such data have been analyzed to generate a catalogue of 101 sources with formal statistical errors between 0.01 and 0.77 ms in right ascension and between 0.2 and 9.3 mas in declination. In order to achieve such precision it is necessary to adjust the standard IAU nutation model. The rotations and scatter of the positions from year to year are generally less than 1 mas. A comparison of this catalogue with a completely independent catalogue derived from Mark II data shows a weighted average position difference, after a rotation, of 1.9 mas.

The Celestial Reference Frame Defined by VLBI

10.1017/s0074180900134862 ◽

1988 ◽

Vol 129 ◽

pp. 325-326

Author(s):

C. Ma ◽

D. B. Shaffer

Keyword(s):

Reference Frame ◽

Radio Sources ◽

Arc Length ◽

Dual Frequency ◽

Extragalactic Radio Sources ◽

Statistical Errors ◽

Fundamental Quantity ◽

Crustal Dynamics ◽

VLBI currently produces the most accurate positions of celestial objects. From 1979 to 1987, 114 extragalactic radio sources have been observed with dual-frequency Mark III VLBI as part of the NASA Crustal Dynamics Project and the NGS POLARIS/IRIS program. The formal statistical errors of conventional celestial coordinates are as small as 0.3 milliarcseconds. The fundamental quantity measured by VLBI is the arc length between radio sources. Thus, we suggest that VLBI be used to establish a coordinate reference frame based solely on radio positions, and that this system not necessarily be coupled to right ascension and declination.