First observations with an H-band integrated optics beam combiner at the VLTI

Abstract

This paper reports results obtained with the Very Large Telescope Interferometer Commissioning Instrument (VLTI-VINCI) where the fiber interferometric coupler MONA was temporarily replaced by an integrated optics beam combiner (IONIC). The two-beam combiner operating in the H atmospheric band was tested at Paranal during two weeks in July 2002. Fringes were recorded on several stars with the siderostats and the Unit Telescopes (UT). We demonstrate that integrated optics allows beam combination with a high interferometric efficiency, stability and spatial filtering. The instrumental visibility of VLTI+IONIC is better than 85%, which is just 5% under the visibility of the IONIC device alone. During this run, the flux injection in the IONIC combiner was not optimized since we used the K-band MONA optics. However, we obtain fringes with the 35 cm siderostats on a star of magnitude mH = 2.47 (k2 Scl). It allows us to extrapolate a magnitude around mH ∼6 with 8 m telescopes without adaptive optics and in the same poor injection conditions.