/ftp/cats/I/325



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I/325               Radio-optical reference frame link     (Zacharias+ 2013)
The following files can be converted to FITS (extension .fit or fit.gz)
	icrf-u2.dat icrf-u4.dat
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Query from: http://vizier.cds.unistra.fr/viz-bin/VizieR?-source=I/325
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drwxr-xr-x 317 cats archive 8192 Feb 28 11:16 [Up] drwxr-xr-x 4 cats archive 4096 Jan 13 2023 [TAR file] -rw-r--r-- 1 cats archive 469 Dec 19 2022 .message -r--r--r-- 1 cats archive 10671 Jan 25 2016 ReadMe -rw-r--r-- 1 cats archive 1039 Feb 15 2016 +footg5.gif -rw-r--r-- 1 cats archive 6466 Feb 15 2016 +footg8.gif -r--r--r-- 1 cats archive 111118 Dec 10 2013 icrf-u2.dat [txt] [txt.gz] [fits] [fits.gz] [html] -rw-r--r-- 1 cats archive 10174 Feb 15 2016 icrf-u2.sim -r--r--r-- 1 cats archive 113732 Dec 10 2013 icrf-u4.dat [txt] [txt.gz] [fits] [fits.gz] [html] -rw-r--r-- 1 cats archive 10473 Feb 15 2016 icrf-u4.sim -rw-r--r-- 1 cats archive 30720 Feb 15 2016 ori.tar -r--r--r-- 1 cats archive 526500 Dec 8 2013 z3.pdf
Beginning of ReadMe : I/325 Radio-optical reference frame link (Zacharias+ 2013) ================================================================================ Radio-optical reference frame link using the USNO astrograph and deep CCD imaging (optical position results) Zacharias M.I., Zacharias N. <U.S. Naval Observatory, Washington DC (2013)> =2013yCat.1325....0Z =2014AJ....147...95Z ================================================================================ ADC_Keywords: Fundamental catalog ; Positional data ; VLBI Keywords: astrometry ; reference systems ; QSO Abstract: Between 1997 and 2004 several observing runs were conducted mainly with the CTIO 0.9m to image ICRF counterparts (mostly QSOs) in order to determine accurate optical positions. Contemporary to these deep CCD images the same fields were observed with the USNO astrograph in the same bandpass. These provide accurate positions on the Hipparcos/Tycho-2 system for stars in the 10 to 16 magnitude range used as reference stars for the deep CCD imaging data. Here we present final optical position results of 413 sources based on astrograph data reductions using UCAC2 and UCAC4 type reference stars. These optical positions are compared to radio VLBI positions. The current optical system is not perfectly aligned to the ICRF radio system with rigid body rotation angles of 3 to 5 mas (3sigma) found between them for all 3 axes. Furthermore, statistically, the optical-radio position differences are found to exceed the total, combined, known errors in the observations. Systematic errors in the optical reference stars as well as physical offsets between the centers of optical and radio emissions are both identified as likely causes. A detrimental, astrophysical, random noise (DARN) component is postulated to be on about the 10mas level. If confirmed by future observations, this could severely limit the Gaia to ICRF reference frame alignment accuracy to an error of about 0.5mas per coordinate axis with the current number of sources envisioned to provide the link. A list of 36 ICRF sources without the detection of an optical counterpart to a limiting magnitude of about R=22 is provided as well. Description: The following tables provide the observed, optical positions of 413 ICRF sources on the Hipparcos Catalogue Reference System (HCRS), as well as position differences to the ICRF radio positions and auxiliary data. Details of the project are described in the Astronomical Journal paper with the same title. Most targets were observed with the Cerro Tololo 0.9m telescope, some with the Kitt Peak 2.1 m telescope. All targets are between about -86 and +32 degree declination spanning all 24 hours in RA. The link to the primary optical coordinate system is provided by USNO astrograph observations performed within weeks of the deep CCD imaging. Primary reference stars are drawn from the Tycho-2 Catalogue, excluding stars fainter than about V = 11. The astrograph data provides secondary reference stars in the 10 to 16 mag range used to reduce the deep CCD exposures. For both the deep and the astrograph data the same bandpass (579 to 643 nm) was used with custom filters. Excluding outliers the RMS radio-optical position differences are about 25 mas per coordinate. Thus these data constitute the most precise of its kind so far. The astrograph data were reduced with 2 different procedures, following the pixel reduction schemes of the UCAC2 and UCAC4 type reductions, respectively. The main differences are: - UCAC2-type reductions utilize Gauss function image profile fits, followed by empirical corrections of x,y data due to pixel phase errors, while UCAC4-type reductions use modified Lorentz profiles for stellar image fits, matching the observed PSF very well. - UCAC2-type reductions use linear corrections as a function of various parameters to mitigate systematic position errors caused by the poor charge-transfer efficiency of the astrograph CCD, while UCAC4-type reductions utilize bin-by-bin empirical corrections. The UCAC2-type reductions show slightly smaller scatter in the optical to radio position differences, while the UCAC4-type data lines up with the radio coordinate system axes better.