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

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 com- biner (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 in- tegrated 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 (κ 2 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.

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