The construction of the Large Quasar Astrometric
Catalogue (LQAC)
Barache, C.1, Bouquillon, S.1, Souchay, J.1, Andrei, A. H.2, Taris, F.1, Gontier, A.‐M.1, Lambert, S.B.1, Arias, E. F.3 and Le Poncin‐Lafitte, C.1
1 Observatoire de Paris, SYRTE, France, 2 Observatorio Nacional and Observatorio do Valongo, MCT/UFRJ, Rio de Janeiro, Brasil, 3 Bureau International des Poids et Mesures, Svrte, France

We gather the 12 largest quasar catalogues (4 from radio interferometry programs, 8 from optical survey) and we carry out systematic cross‐identifications of the objects to obtain their best position estimates, and to provide physical information at both optical and radio wavelengths. This
catalogue compilation designated the LQAC (Large Quasar Astrometric Catalogue), gives equatorial coordinates of 113666 quasars with magnitudes at
9 bandwidths, 5 radio fluxes, redshift and absolute magnitude (when the information is available). We made use of VO tools like Aladin for preliminary
studies. For cross idenfication, data processing and validation, we made use of two different software packages with the same parameters and strategy: VO Topcat with Stilts and homemade Fortran programs. .

Scientific and technical objectives for LQAC

VO Tools used for LQAC Construction

The main scientific objective was to build an astrometric and multi-wavelength- catalogue gathering
all known QSO’s named Large Quasar Astrometric Catalogue (LQAC). This catalogue was also
useful to help for the construction of the optical catalogue reference frame (LQRF- A.Andrei et al.,2009 ), to complete optical data for radio sources from the International Celestial Reference Frame(ICRF2-.Gontier et al, 2009) and for the preparation of an input QSO catalogue for GAIA
mission.The creation of this catalogue was also interesting for studies like the link between QSO’s
radio position and optical positions, the analysis of QSO neighbourhood, their distribution in space
and their color magnitude diagrams.

The Virtual Observatory Tools used to construct the LQAC were Aladin freewarefrom CDS (http://aladin.u-strasbg.fr/aladin) to visualize the catalogues origin. We
used VizieR tools from CDS (http://vizier.u-strasbg.fr/viz-bin/VizieR) to get thediﬀerents catalogue files. At last we used Topcat and Stilts(http://www.starlinl.ac.uk/stiltsandhttp:/www.star.bris.ac.uk/mbt/topcat) to makecross matching and to construct the LQAC Data Base. The LQAC is now accessibleon the CDS web with the reference J/A+A/494/799 in VizieR web service.

The main technical objective was to compile the largest QSO catalogues following the astrometricprecision of each catalogue in decreasing order. For each QSO, its original catalogue was kept and aspecific processing was done to detect the right or wrong double identifications. To our compiled setof catalogues we added only QSO from Veron and Veron (2006) catalogue which were notidentified. We added also magnitude from large star survey catalogues (2mas, GSC2.3, B1.0) tocomplete magnitude information whenever it was necessary. To control our procedures we worked
with two diﬀerents softwares (home Fortran programs and virtual observatory tools) and two
diﬀerents teams working on the same original catalogues taken one by one and with the samecompilation strategy

The LQAC vizualised by Aladin and Topcat VO tools

LQAC Catalog
The final catalogue LQAC was constructed with the compilation of 12 large QSO catalogues (opticaland radio) and includes 113666 quasars, 5 radio fluxes (1.4Ghz, 2.3Ghz, 5.0Ghz, 8.4Ghz, 24Ghz), 7
photometric magnitude visible (u, b, v, g, r, i, z), 2 infrared magnitude (j, k) and the redshift value.
The accuracy of the QSO sources was at the level of the milliarcsecond for sources from ICRF andnot worse than 2 arc seconds for sources from Hewitt and Burbidge catalogue and Veron and Veron
catalogue. The name of the catalogues and their contents are presented in Tables 1 and 2.
After the construction of this catalogue, we have written an article on it in Astronomy andAstrophysics which has been published this year (Souchay, et al. 2009, A&A 494, 799-815).

The LQAC xml file visualised
by Vizier CDS Web service

References
Souchay, et al.2009, A&A 494, 799‐815
Veron‐Cetty,M.‐P.,&Veron,P.2006,A&A,455,773
Lambert, S. B.; Gontier, A.‐M. 2009, A&A 493,317‐323
A. H. Andrei et al. A&A 2009 in press

Our complete LQAC xml
file visualised with Topcat
using table data viewConclusion
We are now preparing a new version of LQAC (LQAC2.0) to improve the catalogue.
We will resolve the wrong double qso (300 pair of QSO’s are in LQAC, their double
status being doubtful). We will add some picture associated to each QSO and we will
improve the homogeneity of magnitudes..We will also add a criterion of source
geometry (for instance near star form than galaxy form). The VO tools used for theLQAC were useful to get and to study catalogues (Aladin,VizieR), to make crossmatching of sources (Topcat) and to manage, distribute the LQAC file catalogue easily(Topcat). However, these tools are a little limited for instance to get the data from verylarge catalogues, to make some complex cross-matching. Moreover we have founddiﬃculties to get the magnitude system photometric used in the magnitude of sources inVO tables.

LQAC url at CDS : http://vizier.u‐strasbg.fr/viz‐bin/VizieR?‐source=J/A%2bA/494/799/refs