CCD astrometry of faint compact extragalactic radio sources. III.

Abstract

Abstract. Optical positions relative to the Hipparcos Catalogue (ESA 1997) have been obtained for the optical counterparts of 38 faint (B ∼ 20−24) southern compact extragalactic radio sources (CERS). Many of these sources are not detectable -or their coordinates not adequately measurable -by means of direct photography with a widefield telescope, so the positions were determined using a multi-step procedure involving CCD and photographic observations. This method responds both to the requirement of attaining small positional errors, and the need to refer the positions to a standard astrometric system. Estimated precisions as good as 50 mas were achieved. For 16 of the above objects we are proposing a completely new optical identification or providing a revised finder. A comparison of our optical positions with available VLBI radio positions is presented. The residuals obtained are in most cases consistent with the precision of our optical data, and provide an evaluation of these CERS as radio/optical frame link sources (or their identification as astrophysically interesting astrometric outliers). Twenty nine of the CERS observed are either defining or candidate fiducial objects of the present International Celestial Reference System (ICRS, Ma et al. 1998), so the optical data we have obtained for them is potentially useful to help mantain and possibly improve the current link of the Hipparcos reference frame to the ICRS.

An unbiased sample of bright southern compact steep spectrum and gigahertz peaked spectrum sources

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European Southern Observatory Very Large Telescope Optical Spectroscopy of Bl Lacertae Objects. Iii. An Extension of the Sample

“…PKS 1145−676 This radio source was classified as a quasar due to its point-like appearance by White et al (1987). The flat radio spectrum and optical variability (Beasley et al 1997;Costa 2002) prompted a blazar classification. We detect several emission lines ([OII] λ3727, Hβ λ4861, [OIII] λλ4959,5007, Hα λ6563, [NII] λ6585) at z = 0.210.…”