Near-infrared astrometry and photometry of Southern ICRF quasars

Free access article

Issue		A&A Volume 437, Number 3, July III 2005


Page(s)		1135 - 1146
Section		Celestial mechanics and astrometry
DOI		http://dx.doi.org/10.1051/0004-6361:20042426

A&A 437, 1135-1146 (2005)
DOI: 10.1051/0004-6361:20042426

Near-infrared astrometry and photometry of Southern ICRF quasars

J. I. B. Camargo, G. Daigne, C. Ducourant and P. Charlot

Observatoire Aquitain des Sciences de l'Univers, CNRS-UMR 5804, BP 89, 33270 Floirac, France
e-mail: camargo@obs.u-bordeaux1.fr

(Received 23 November 2004 / Accepted 10 March 2005)

Abstract
We present high quality astrometry, along with J, H, and $K_{\rm s}$ photometry, for 30 southern ICRF quasars observed with the ESO NTT/SOFI at La Silla. Our main purpose is to document the optical counterpart of ICRF quasars, by reporting their position in a stellar reference frame and their near-infrared photometry. Our investigation lies within the scope of extending the (radio) extragalactic reference frame into the optical range. An internal precision generally better than 10 mas was obtained in positioning the near-infrared counterpart of these quasars within their stellar surroundings. The actual astrometric accuracy is estimated from the departure between the observed and the radio (VLBI) positions of quasars, and is about 35 mas, mainly due to the statistical uncertainties of the stellar reference catalogue (UCAC2). The positional accuracy was improved to 25 mas for a subset of 14 quasars observed with extended fields of view, as obtained from mosaics of overlapping images. The 3-band photometry was achieved with a precision most often better than 0.04 mag, based on calibration with the 2MASS magnitudes. A spectral index $\alpha$ ( $F_{\nu}\propto\nu^{\alpha}$ ) was derived from the observed quasar fluxes in the near-infrared. With a mean value $\langle\alpha\rangle=-1$ , this spectral index does not show any significant correlation with the radio spectral index.

Key words: astrometry -- infrared: general -- methods: numerical -- reference systems

SIMBAD Objects
Tables at the CDS

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.