Access to Astronomical Catalogues

← Click to display the menu
J/AJ/127/3609       VLBI observations of southern ICRF sources   (Ojha+, 2004)

VLBI observations of southern hemisphere ICRF sources. I. Ojha R., Fey A.L., Johnston K.J., Jauncey D.L., Reynolds J.E., Tzioumis A.K., Quick J.F.H., Nicolson G.D., Ellingsen S.P., Dodson R.G., Mcculloch P.M. <Astron. J., 127, 3609-3621 (2004)> =2004AJ....127.3609O
ADC_Keywords: Radio sources ; QSOs ; Morphology ; Redshifts Keywords: astrometry - galaxies: active - quasars: general - radio continuum: galaxies - reference systems - surveys Abstract: We present 8.4GHz very long baseline interferometry (VLBI) observations of 69 southern hemisphere extragalactic sources in the International Celestial Reference Frame. These are the first in a series of observations intended to image all such sources at milliarcsecond resolution in order to determine their continued suitability for reference-frame use based on intrinsic structure. We use the resultant images to calculate a core fraction, that is, the ratio of core flux density to total flux density, for all observed sources. The resulting distribution, with a mean value of 0.83, suggests that most sources are relatively compact. However, just over half the observed sources show significant extended emission in the form of multiple compact components. These sources are probably poorly suited for high-accuracy reference-frame use unless intrinsic structure and potential variability can be taken into account. Our observations represent the first large, comprehensive VLBI imaging survey in the southern hemisphere, significantly extending the existing limited VLBI surveys and, along with some well-known objects, containing many sources that have never been imaged at milliarcsecond resolution. The overlap with Very Long Baseline Array images of sources between 0° and -35° declination helps determine the limits to imaging with the southern hemisphere-accessible telescopes. Description: The observations reported in this paper were made using the five telescopes that make up the Australian Long Baseline Array (LBA),5 as well as telescopes in South Africa and Hawaii. Because of limited mutual visibility between the last two sites, each observing epoch is split into two sessions, one involving observation with the LBA and South Africa and the other involving observation with the LBA and Hawaii. The data from the two epochs are calibrated separately and then combined in order to image with the best possible u-v plane coverage. Images from two epochs are presented here. The first epoch consisted of a 24hr session with the LBA and Kokee on 2002 July 16, followed by a 48hr session with the LBA and Hartebeesthoek from 2002 July 18 through July 20. The second epoch consisted of a 24hr session with the LBA and Hartebeesthoek on 2002 November 14, followed by a 48hr session with the LBA and Kokee on 2002 November 15 and 16. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file objects.dat 37 69 Objects position (from Simbad) table2.dat 51 74 Parameters of Naturally Weighted Images table3.dat 23 69 Physical Characteristics of Sources table4.dat 43 121 Gaussian Models
Byte-by-byte Description of file: objects.dat
Bytes Format Units Label Explanations
1- 3 A3 --- --- [PKS] 5- 12 A8 --- PKS PKS source name (based on B1950 position) 18- 19 I2 h RAh Simbad right ascension (J2000) 21- 22 I2 min RAm Simbad right ascension (J2000) 24- 27 F4.1 s RAs ? Simbad right ascension (J2000) 29 A1 --- DE- Simbad declination sign (J2000) 30- 31 I2 deg DEd Simbad declination (J2000) 33- 34 I2 arcmin DEm Simbad declination (J2000) 36- 37 I2 arcsec DEs ? Simbad declination (J2000)
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 8 A8 --- PKS PKS source name 10 A1 --- Obs [de] Epoch of observation (1) 12- 14 F3.1 mas aaxis Restoring beam FWHM of the major axis 16- 18 F3.1 mas baxis Restoring beam FWHM of the minor axis 20- 22 I3 deg PA [-90/90] Restoring beam position angle (2) 24- 27 F4.2 Jy Sp8.4GHz Peak flux at 8.4GHz in units of Jy/beam 29- 32 F4.1 mJy RMS Root-mean-square of final hybrid image residuals in units of mJy/beam 34- 51 A18 mJy Level Contour levels in units of mJy/beam (3)
Note (1): Epoch as follows: d = Epoch 2002 July 16-20 e = Epoch 2002 Nov. 14-16 Note (2): Measured north through east. Note (3): Contours levels are represented by the geometric series 1,...,2n, e.g. for n=5 the contour levels would be ±1,2,4,8,16,32
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 8 A8 --- PKS PKS source name 10 A1 --- ID [QGLA] Optical identification (1) 12 A1 --- l_z Limit flag on z 13- 17 F5.3 --- z ? Redshift 19- 23 F5.2 mag Vmag ? Visual magnitude
Note (1): Optical identification ad follows: Q = QSO G = galaxy L = BL Lacertae A = Other
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 8 A8 --- PKS PKS source name 10 A1 --- Obs [bc] Epoch of observation (1) 12 I1 --- Comp [1/3] Component number 14- 18 F5.3 Jy S8.4GHz Flux density at 8.4GHz 20- 24 F5.1 mas Sep Component separation from arbitrary origin 26- 29 I4 deg PA1 [-180/180]? Position angle between component and origin (2) 31- 34 F4.2 mas aaxis FWHM of the major axis 36- 39 F4.2 --- b/a Major to minor axis ratio 41- 43 I3 deg PA2 [-90/90]? Major axis position angle (2)
Note (1): Epoch as follows: b = Epoch 2002 July 16-20 c = Epoch 2002 Nov. 14-16 Note (2): Measured north through east.
History: From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 13-Jan-2007
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

catalogue service

© UDS/CNRS

Contact