De-biasing interferometric visibilities in VLTI-AMBER data of low SNR observations ^*

¹ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy e-mail: licausi@oa-roma.inaf.it
² Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
³ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Laboratoire d'Astrophysique Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France

Received: 11 April 2007
Accepted: 26 November 2007

Abstract

Aims. We have found that the interferometric visibilities of VLTI-AMBER observations, extracted via the standard reduction package, are significantly biased when faint targets are concerned. The visibility biases derive from a time variable fringing effect (correlated noise) appearing on the detector.

Methods. We have developed a method to correct this bias that consists in a subtraction of the extra power caused by such correlated noise, so that the real power spectrum at the spatial frequencies of the fringing artifact can be restored.

Results. This pre-processing procedure is implemented in a software program called AMDC, available to the community, which is to be run before the standard reduction package. Results obtained on simulated and real observations are presented and discussed.