Advances in the reconstruction of LBT LINC-NIRVANA images

¹ INAF – Osservatorio Astrofisico di Arcetri, Lgo. E. Fermi 5, 50125 Firenze, Italy e-mail: bertero@disi.unige.it
² DISI, Università di Genova, Via Dodecaneso 35, 16146 Genova, Italy
³ INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy

Received: 1 March 2007
Accepted: 15 May 2007

Abstract

Context.LINC-NIRVANA, the Fizeau interferometer of the Large Binocular Telescope (LBT), will require routine use of image reconstruction methods for data reduction. To this purpose our group has already developed the software package AIRY (Astronomical Image Restoration in interferometrY).

Aims.Observations of a target, with different orientations of the baseline of LINC-NIRVANA, will provide images with different orientations with respect to the CCD camera. This rotation effect was not taken into account in our previous work. Therefore in this paper we propose a method able to compensate for the rotation of the field of view. Moreover we investigate acceleration techniques for reducing the computational burden of multiple image deconvolution.

Methods.The basic method is a suitable modification of the Richardson-Lucy algorithm, also implementing an approach we proposed for reducing boundary effects. Acceleration techniques, proposed by Biggs & Andrews, are extended and applied to this new algorithm. Finally a method for estimating the unknown point spread function (PSF) by extracting and extrapolating the image of a reference star is developed and implemented.

Results.The method introduced for compensating object rotation and reducing boundary effects, as well as its accelerated versions, are tested on simulated LINC-NIRVANA images, using the VLT image of the Crab Nebula as test object. The results are very promising. Moreover the method for PSFs extraction is tested on simulated images, derived from the LBT image of the galaxy NGC 6946 and obtained by convolving this image with PSFs computed by means of the numerical code LOST (Layer Oriented Simulation Tool).