SearchCal: a Virtual Observatory tool for searching calibrators in optical long-baseline interferometry

II. The faint-object case

¹ Laboratoire Fizeau, UNS/OCA/CNRS UMR6525, Parc Valrose, 06108 Nice Cedex 2, France
e-mail: Daniel.Bonneau@oca.eu
² UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France

Received: 1 June 2010
Accepted: 19 August 2011

Abstract

Context. In long-baseline interferometry, images or astrophysical parameters are obtained from the raw fringe contrast after a careful calibration process. We have already developed the software (SearchCal) to select suitable bright calibration stars (V ≤ 10; K ≤ 5.0) for obtaining the ultimate precision of current interferometric instruments like the VLTI. With the expected gain in sensitivity of AMBER and PRIMA on the VLTI, the need for fainter calibrators should now be adressed.

Aims. We present a new version of SearchCal dedicated to the creation of an evolving catalog of stars suitable as calibrators with K magnitude  >5 around the scientific target.

Methods. Star catalogs available at the CDS are searched via web requests and provide the useful astrometric and photometric informations for selecting calibrators. The missing photometries are computed with an accuracy of about 0.1 mag. The stellar angular diameter is estimated with a precision of about 10% through newly determined surface-brightness versus color-index relations based on the I, J, H and K magnitudes. For each star the squared visibility is computed taking into account the central wavelength and the maximum baseline of the predicted observations.

Results. The version of SearchCal for faint objects that allows to find calibrators for interferometric observations up to K  ~  15 is available as a web service at the address: http://www.jmmc.fr/searchcal