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Download The Role of Interferometers in Future Space Astrophysics Missions Ron Allen Space Telescope Science Institute Synthesis Imaging Scientist Space Interferometry

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  • The Role of Interferometers in Future Space Astrophysics MissionsRon AllenSpace Telescope Science Institute

    Synthesis Imaging ScientistSpace Interferometry MissionAstrophysics 2020:Large Space Missions Beyond the Next Decade

    Ron Allen STScI

  • Why interferometersISome recognized advantages:Precision astrometry (SIM):precision Baseline length x Collector diameterUltra-high resolution imaging of bright targets:Only way to get the required resolution.Allows decoupling of the resolution and S/NSimple, bright targets using a few baselines (VLBI, SIM) and limited observing time.More complex targets using many baselines (VLA, SI) and/or lots of observing time.

    Ron Allen STScI

  • Why interferometers IISome less-well-recognized advantages to interferometric/synthetic imaging with constellations of collectors:Superior control of the PSF;Suppression of scattered light halo around the PSF; and,Opportunities to increase mission robustness.

    Ron Allen STScI

  • Superior control of the PSF PSF is defined in a computer only at the moment when the image is calculated:Can make use of various redundancies (e.g. closure phase) in the data coming from the constellations interferometers.Allows resolution to be improved, even incrementally.Offers opportunity for improvements in image quality with better computer algorithms.Computer power required is modest.Your laptop may be enough

    Ron Allen STScI

  • Suppressing the PSF Halo Residual polishing errors on filled aperture surfaces result in a halo of scattered light around bright stars. This halo: increases the inner working angle for coronagraphy, and;reduces the dynamic range for photometry in the immediate vicinity of bright stars.

    Ron Allen STScI

  • Example from HST/ACS J. Krist 2004, SPIE 5487, 1284

    Ron Allen STScI

  • Ron Allen STScI

  • Array PSFs can look awful Machalek, Waghorn, & Allen in prep.

    Ron Allen STScI

  • But still be clean underneath

    Ron Allen STScI

  • Why does this happen ?This is a different kind of improvement, and not simply a result of using a computer to image.It happens as long as the dominant sources of error in fringe amplitude and phase at different U,V sample points are independent of each other.Its as if the equivalent aperture had a purely random polishing error at every scale size included in the image.This will be the case for many sources of instability in each interferometer (e.g. delay line jitter, etc.).It is not true for station-keeping errors, but these are expected to be relatively slow and may be eliminated by using closure phase imaging.

    Ron Allen STScI

  • Comparison with HST/ACS

    Ron Allen STScI

  • SIM photon and phase noise

    Ron Allen STScI

  • Mission robustness Reduce cost and single points of failureMost elements can be identicalLoss of elements not crippling for sciencePermit upgrades to array over timeArray can continue to operateUpgrades incremental with improved elementsHitch-hike on freight missionsSmall elements can be stowawaysCarried on supply missions to lunar base

    Ron Allen STScI

  • Summary The physics of image formation and restoration using interferometers is well understood and applicable to UV/OIR space interferometers. The required computing power is modest.Constellations of collectors as imagers decouple resolution from sensitivity, permit better PSF control, and offer new flexibility in mission design, construction, and repair.Some of the outstanding technical challenges presently include space demonstrations of feasibility, station-keeping, beam combination, and wide-field imaging.

    Ron Allen STScI

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