The LBT interferometric camera LINC

C. Straubmeier1, A. Eckart1, T. Bertram1, T. Herbst2

1I. Physikalisches Institut, University of Cologne, Germany

2MPI for Astronomy, Heidelberg, Germany

AUTHORS

E-mail contact: cstraubm@ph1.uni-koeln.de, eckart@ph1.uni-koeln.de

http://www.ph1.uni-koeln.de/workgroups/astro_instrumentation/linc/
http://www.mpia-hd.mpg.de//Public/index_en.html
some applications for the GC are discussed in: A&A 374, 95 (2001)

A collaboration of the University of Cologne, the MPI für Astronomie in Heidelberg and the Osservatorio Astrofisico di Arcetri is developing the Large Binocular Telescope Interferometric Camera (LINC), an imaging camera system working from 0.6 to 2.4 m. Compared to other optical interferometers the LBT will offer superior conditions for high resolution imaging in the near-infrared, as the two 8.4 m mirrors share a common mount and will deliver a so far unprecedented combination of angular resolution, field of view and collecting area. The contribution of the University of Cologne to LINC will be the closed-cycle 77 K camera dewar and an imaging fringe-tracker operating at JHK bands. The fringe-tracker system will be located at the combined focus of the telescope close to the science detector and will monitor the phase difference of the two incoming wavefronts. The closed-loop correction of the phase offset is an important step for the interferometric performance of the telescope as it ensures a time-stable interferometric image quality by eliminating the highly time-variable pistonic wavefront shifts due to changing air-masses above the two mirrors. In this poster we present the current status of our imaging fringe-tracker, which mainly consists of a near-infrared detector array mounted on a remotely controlled three dimensional linear-stage, both operating at cryogenic temperatures. While the pointing of the telescope can still be exclusively defined by the needs of the science detector, this concept maximizes the sky coverage of the science camera by enabling the fringe-tracker to lock on any suitable 'guide-star' located within the optically useable and for wavefront correction physically meaningful field of view. Furthermore we present the results of numerical simulations showing the influence of atmospheric piston and telescope flexure on the point-spread function of a guide star as measured by the fringe-tracker. The Galactic center will be one of the prime targets of LINC.