Increasing the reliability of ISOCAM cross-identifications by use of a probability pattern^*

¹ Observatoire Astronomique de Strasbourg, 11 rue de l'Université, 67000 Strasbourg, France
² ISO Data Centre, Science Operations and Data Systems Division, European Space Agency, Villafranca del Castillo, PO Box 50727, 28080 Madrid, Spain e-mail: sott@iso.vilspa.esa.es
³ CEA/DSM/DAPNIA Saclay, Service d'Astroph., L'Orme de Merisiers, Bat. 709, 91191 Gif-sur-Yvette, France e-mail: rgastaud@cea.fr

Corresponding author: S. Derriere, derriere@astro.u-strasbg.fr

Received: 16 May 2002
Accepted: 13 March 2003

Abstract

The built-in play at the wheels of the ISOCAM instrument affects the accuracy of the astrometry of sources from the ISOCAM Parallel Catalogue. We present the results of different methods for cross-identifying ISOCAM sources with reference catalogues in the optical (USNO-A2.0) and in the near infrared (2MASS). For a sample of 7197 ISOCAM sources, the fraction having a real counterpart in the USNO and 2MASS catalogues was estimated to be 95% and 91% respectively. Using a nearest neighbor method for cross-identification, only 74% of the possible associations with USNO (79% with 2MASS) are retrieved. With the use of a so-called probability pattern to perform the associations, these values increase to 77% for USNO and 83% for 2MASS. In addition, the overall reliability of associations increases from 77 to 87% with USNO, and from 81 to 90% with 2MASS.