The NOVA Fringe Tracker: A second generation cophasing facility for up tósix telescopes at the VLTI
conference paper
The NOVA Fringe Tracker (NFT) is a proposed solution tóthe call by ESO for a second generation fringe tracking facility. This instrument at the VLTI will enable the cophasing of up tó6 telescopes simultaneously. Using broad band optics with detection from 1.2 tó2.4 microns, a unique configuration is employed that eliminates so-called "photometric crosstalk." This refers tóimbalance in the beam combiner which results in fluctuations of the incoming wavefronts and the proportion of power accepted by a spatial filter masquerading as a visibility, a common problem afflicting previous interferometric instruments and fringe trackers. Alsóproposed for use in "science instruments" (for the measurement of visibility), the "Polarization-Based Collimated Beam Combiner," with its achievement of photometric symmetry in hardware, is particularly suited for combined use of the smaller AT (1.8 meter) telescopes with the UT (8 meter) telescopes involving a 20:1 intensity ratióof the interfering beams, and alsófor fringe tracking using highly resolved sources having a very small visibility. Recent enhancements tóthe proposed fringe tracker include selectable modes which detect only a single quadrature phase, both quadrature phases, or an uneven combination of the two. Optimization of partial spatial filtering using pinholes has been performed using a wavefront simulator and simulated tracking loop. Aiming for an instrument achieving the best limiting sensitivity, analysis and simulations predict that reliable cophasing will be obtained using the 1.8 meter AT telescopes tracking on an unresolved reference star with a K magnitude of 10. © 2012 SPIE.
Topics
Astronomical interferometryBeam combinerFringe trackingNear infraredPhase referencingVisibility estimationVLTIAstronomical interferometryBeam combinerFringe trackingNear InfraredPhase-referencingVisibility estimationVLTIInterferometryOptical telescopesPhotometrySensitivity analysisVisibilityWavefrontsTelescopes
TNO Identifier
470055
ISSN
0277786X
ISBN
9780819491466
Article nr.
84451L
Source title
Optical and Infrared Interferometry III, 1-6 July 2012, Amsterdam, Netherlands