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I/251      VLBI International Celestial Reference Frame (ICRF)     (Ma+, 1997)

Definition and Realization of the International Celestial Reference System by VLBI Astrometry of Extragalactic Objects Ma C., Feissel M. <IERS Tech. Note 23 (1997)> Realization of the International Celestial Reference Frame from VLBI Astrometry Ma C. <Bull. American Astron. Soc., 191, #16.13 (1997)> =1997AAS...191.1613M The international celestial reference frame as realized by very long baseline interferometry. Ma C., Arias E.F., Eubanks T.M., Fey A.L., Gontier A.-M., Jacobs C.S., Sovers O.J., Archinal B.A., Charlot P. <Astron. J. 116, 516 (1998)> =1998AJ....116..516M
ADC_Keywords: Fundamental catalog ; Positional data; VLBI Keywords: astrometry - catalogs - quasars: general - radio continuum - reference systems - techniques: interferometric Description: The International Celestial Reference Frame (ICRF), is intended for adoption be the International Astronomical Union (IAU) as the conventional celestial system, under the name International Celestial Reference System (ICRS). (See http://maia.usno.navy.mil/iauc19/iaures.html#B5). A Working Group on Reference Frames (WGRF), with the participation of International Earth Rotation Service (IERS), was appointed by the IAU to accomplish the task of constructing the ICRF. The WGRF set up a list of 608 extragalactic radio sources uniformly distributed on the sky and evaluated their J2000.0 Very Long Baseline Interferometry (VLBI) coordinates in the ICRS by applying a no rotation constraint with respect to an earlier realization of the IERS Celestial reference system, RSC(IERS) 95 C 02 . The first realization of the ICRF has J2000.0 coordinates of 608 objects and is named RSC(WGRF)95 R 01. Radio sources in RSC(WGRF)95 R 01 are divided into three categories (see file "guide.txt"): defining, candidate and other sources. In order to provide radio source coordinates to link to the Hipparcos stellar reference frame to the ICRS, the WGRF issued a shorter version of the ICRF, RSC(WGRF) 95 R 02. It is a subset of RSC(WGRF) 95 R 01 that contains J2000.0 coordinates of 253 radio sources covering the declination range -81 degrees to +85 degrees. The 212 defining sources of RSC(WGRF)95 R 01 included 17 Hipparcos link objects. An additional 41 other radio sources had to be added RSC(WGRF) 95 R 02 for the link. The median positional accuracy of RSC(WGRF) 95 R 02 is 0.4 mas. The other 357 sources of RSC(WGRF) 95 R 01 have coordinates with lower precision (median= 0.8 mas) but they are still consistent with the ICRS. The direction of the axes of the ICRF are consistent with those of the FK5 system within the uncertainties of the latter. On the basis of Fricke's (1982A&A...107L..13F) and Schwan (1988) considerations, the uncertainty of the pole position relative to the mean pole at J2000.0 is ±50 mas. Studies by Morrison et al. (1990A&A...240..173M) and Lindegren et al. (1995A&A...304...44L) have shown that the FK5 origin of right ascensions has an uncertainty of the order of ±100 mas. The accuracy of the tie of the Hipparcos stellar frame to ICRS is ±0.6 mas at the Hipparcos mean epoch of observation (1991.25) and ±0.25 mas/year for the time evolution. The tie between the dynamical planetary frame and ICRS is known within ±3 mas (Folkner et al. 1994A&A...287..279F). Abstract of the 1998AJ....116..516M paper: A quasi-inertial reference frame is defined based on the radio positions of 212 extragalactic sources distributed over the entire sky. The positional accuracy of these sources is better than about 1mas in both coordinates. The radio positions are based upon a general solution for all applicable dual-frequency 2.3 and 8.4GHz Mark III very long baseline interferometry data available through the middle of 1995, consisting of 1.6 million pairs of group delay and phase delay rate observations. Positions and details are also given for an additional 396 objects that either need further observation or are currently unsuitable for the definition of a high-accuracy reference frame. The final orientation of the frame axes has been obtained by a rotation of the positions into the system of the International Celestial Reference System and is consistent with the FK5 J2000.0 optical system, within the limits of the link accuracy. The resulting International Celestial Reference Frame has been adopted by the International Astronomical Union as the fundamental celestial reference frame, replacing the FK5 optical frame as of 1998 January 1. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file guide.txt 82 380 Detailed description of the RSC(WGRF)95 R 01 rsc95def.dat 144 212 ICRF RSC(WGRF)95 R 01 defining sources (Table 3 of 1998AJ....116..516M paper) rsc95can.dat 144 294 ICRF RSC(WGRF)95 R 01 candidate sources (Table 4 of 1998AJ....116..516M paper) rsc95oth.dat 144 102 ICRF RSC(WGRF)95 R 01 other sources (Table 5 of 1998AJ....116..516M paper) rsc95r01.dat 144 608 ICRF RSC(WGRF)95 R 01 all sources rsc95r02.dat 91 253 ICRF RSC(WGRF)95 R 02 subset
See also: I/218 : New Reference Frame defined by Extragalactic Radio Source (IAU WG, 1995) I/239 : The Hipparcos and Tycho Catalogues (ESA 1997) http://hpiers.obspm.fr/webiers/results/icrf/README.html : ICRF Home Page http://aa.usno.navy.mil/AA/data/docs/ICRS_links.html : ICRS at USNO http://hpiers.obspm.fr/webiers/results/icrf/Updating.html : Updating Table 1: Summary of catalog differences (from 1998AJ....116..516M) -------------------------------------------------------------------------------- Rotation angles RMS residuals Internal trends Catalog pair A1 A2 A3 ki2 RAcosDE DE Arc Length Dmax Dmax/sigma (mas) (mas) mas/100deg -------------------------------------------------------------------------------- WGRF vs. IERS95 0.1 -0.4 0.0 2.92 0.23 0.39 0.55 0.32 14 WGRF vs. RORF -0.2 -0.5 0.0 2.77 0.10 0.38 0.42 0.32 15 IERS95 vs. IERS94 0.0 0.0 0.0 2.85 0.30 0.31 0.52 0.29 12 WGRF vs. GSFC -0.1 -0.1 -0.0 1.68 0.09 0.29 0.39 0.15 7 WGRF vs. JPL 0.1 -0.3 -0.2 2.84 0.26 0.44 0.51 0.66 15 GSFC vs. JPL 0.2 -0.3 0.2 3.42 0.30 0.36 0.58 0.38 14 WGRF vs. WGRFna 0.2 0.0 0.0 0.18 0.05 0.06 0.12 0.07 2 WGRF vs. WGRFel 0.0 0.0 0.0 0.04 0.01 0.02 0.04 0.02 2 WGRF vs. WGRFng 0.0 -0.1 0.0 0.99 0.03 0.12 0.22 0.19 8 Table 2: Alignment of the ICRF axes with the ICRS (from 1998AJ....116..516M) ---------------------------------------------------- Parameter Value ---------------------------------------------------- A1 (mas) -0.006±0.018 A2 (mas) 0.007±0.018 A3 (mas) 0.005±0.021 DDE (mas/100°) 0.0 DDE (mas/100°) 0.2 BDE (mas/100°) -0.28 ±0.02 wrmsRAcosDE (mas) 0.14 wrmsDE (mas) 0.20 Byte-by-byte Description of file: rsc95can.dat, rsc95def.dat, rsc95oth.dat Byte-by-byte Description of file: rsc95r01.dat
Bytes Format Units Label Explanations
2- 5 A4 --- --- [ICRF] 7- 22 A16 --- ICRF *ICRF designation 26- 33 A8 --- IERS *IERS designation 35 A1 --- c *[DCO] Defining / Candidate / Other category of source 36 I1 --- X ? X band structure index 38 I1 --- S ? S band structure index 40 A1 --- Hip *[* ] Link to Hipparcos reference frame 43- 44 I2 h RAh Right Ascension (J2000) hours 46- 47 I2 min RAm Right Ascension (J2000) minutes 49- 57 F9.6 s RAs Right Ascension (J2000) seconds 60 A1 --- DE- Declination (J2000) sign 61- 62 I2 deg DEd Declination (J2000) degrees 64- 65 I2 arcmin DEm Declination (J2000) arcminutes 67- 74 F8.5 arcsec DEs Declination (J2000) arcseconds 78- 85 F8.6 s e_RAs Uncertainty in Right Ascension 88- 94 F7.5 arcsec e_DEs Uncertainty in Declination 96-101 F6.3 --- Corr [-1,1]? RA/Dec correlation 103-111 F9.1 d Ep Mean date of observation (JD) 113-121 F9.1 d O1 First date of observation (JD) 123-131 F9.1 d Ol Last Julian date of observation (JD) 134-137 I4 --- Nsess Number of observing sessions 139-144 I6 --- Ndel Number of delay, delay rate obs. pairs
Note on ICRF: ICRF Designations, constructed from J2000.0 coordinates with the format ICRF JHHMMSS.s+DDMMSS or ICRF JHHMMSS.s-DDMMSS They follow the recommendations of the IAU Task Group on Designations. Note on IERS: IERS Designations, previously constructed from B1950 coordinates. The complete format, including acronym and epoch in addition to the coordinates, is IERS BHHMM+DDd or IERS BHHMM-DDd Note on c: Category of source, present in file rsc95r01.dat only: D = defining source (all sources of files rsc95def.dat) C = candidate source (all sources of files rsc95can.dat) O = other source (all sources of files rsc95oth.dat) Note on Hip: * = the source serves to link the Hipparcos stellar reference frame to the ICRS
Byte-by-byte Description of file: rsc95r02.dat
Bytes Format Units Label Explanations
2- 5 A4 --- --- [ICRF] 7- 22 A16 --- ICRF *ICRF designation 26- 33 A8 --- IERS *IERS designation 36- 37 A2 --- status *[DL ] Status of source 40- 41 I2 h RAh Right Ascension (J2000) hours 43- 44 I2 min RAm Right Ascension (J2000) minutes 46- 54 F9.6 s RAs Right Ascension (J2000) seconds 57 A1 --- DE- Declination (J2000) sign 58- 59 I2 deg DEd Declination (J2000) degrees 61- 62 I2 arcmin DEm Declination (J2000) arcminutes 64- 71 F8.5 arcsec DEs Declination (J2000) arcseconds 75- 82 F8.6 s e_RAs Uncertainty in Right Ascension 85- 91 F7.5 arcsec e_DEs Uncertainty in Declination
Note on ICRF: ICRF Designations, constructed from J2000.0 coordinates with the format ICRF JHHMMSS.s+DDMMSS or ICRF JHHMMSS.s-DDMMSS They follow the recommendations of the IAU Task Group on Designations. Note on IERS: IERS Designations, previously constructed from B1950 coordinates. The complete format, including acronym and epoch in addition to the coordinates, is IERS BHHMM+DDd or IERS BHHMM-DDd Note on status: D = Defining source not contributing to the link L = Source included in the frame only because they serve the Hipparcos link DL= Defining source which are also Hipparcos link object
History: * 17-Jul-1998 (Julie Anne Watko, James E. Gass [SSDOO/ADC]): The RSC(WGRF) 95 R 01 files were provided by the author. ADC has added the table of RSC(WGRF) 95 R 02 as found on the IERS Web site as a convenience to users. * 04-Dec-1998 (Francois Ochsenbein, Patricia Bauer [CDS]): Added in this ReadMe extracts from the 1998AJ....116..516M paper. References: Folkner W.M, et al.,1994, A&A, 287, 279 =1994A&A...287..279F Fricke, W. 1982, A&A, 107, L13 =1982A&A...107L..13F Kovalevsky J. et al., 1997, A&A, 323, 620 =1997A&A...323..620K Lindegren L., et al., 1995, A&A, 304, 44 =1995A&A...304...44L Ma C. and Feissel M., eds. June 1997. IERS Technical Note 23 (Paris: Observatoire de Paris). Morrison L.U, et al., 1990, A&A, 240, 173 =1990A&A...240..173M
(End) Julie Anne Watko, James E. Gass [SSDOO/ADC] 17-Jul-1998
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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