Stellar interferometry with a K-band integrated optics beam combiner instrument at the CHARA Array - I. First on-sky fringes for CHARIOT
We present the instrument description and the first on-sky observations for the new CHara ARray Integrated Optics Testbench (CHARIOT) at the CHARA Array. CHARIOT is a 2-telescope proof-of-concept instrument that utilises a fibre-connectorised beam combiner fabricated by ultrafast laser-inscription in Infrasil quartz glass, which presents low-OH contamination and high transparency over the whole K-band. With its fibre-connected architecture, CHARIOT is designed as a plug-and-play testbed instrument to test and validate fibred astrophotonic components on-sky. At this point, CHARIOT is able to measure raw fringe squared visibilities with a sub-1% precision for stars with K-mag<2. Under poor to moderate seeing conditions, the current limiting magnitude for fringe detection is K-mag = 5.212 (HD210824). These results demonstrate that CHARIOT's performance is already comparable to the former JouFLU instrument. With additional improvements, the limiting magnitude could be extended and the precision for fainter stars improved. The successful on-sky demonstration paves the way for a new high precision K-band beam combiner instrument at the CHARA array.