High-Precision Optical
 Interferometry of Faint and
    Low-Contrast Targets
Requires Coherent Integration

        Anders...
Outline

    Optical Interferometry
●



    The problem of short exposures
●



    How to coherently integrate
●



    ...
Optical Interferometry

    Resolution limit of telescopes
●



    Size of stars
●



    Separate telescopes
●



    Fo...
The SNR problem

    Atmosphere
●



    Fringe motion
●



    Short exposures
●



    Few photons
●



    Average many...
Incoherent Averaging

    V 2 averaging
●



        Just amplitude
    –
        squared, forget
        phase.
    Tripl...
Coherent integration

    Imagine a world in which we can make
●


    long integrations.
Incoherent vs. Coherent

    Improves SNR on both amplitude and
●


    phase   i nc




                                 ...
How to coherently integrate

    Estimate phase for
●


    each exposure and
    shift.
    Multi-wavelength
●


    meas...
How to coherently integrate

    Two ways:
●



        Fast real-time control loop.
    –

             Better when read ...
HR 5544 V=4.5 star

    2x (red end) to 10x (blue end) better
●




                                
The meaning of the phase

    Several components.
●



    Fit a model including atm and source.
●
Binary star measurement

    More phases, and better SNR.   Tauri
●
Binary star measurement

    10x better dM than Armstrong (2006)
●
Stellar Diameters

    Measured as location of null in visibility
●


    versus wavelength.   Ophichus
Stellar Diameters
Imaging

    No special software needed:
●



        Complex visibilities. Can use standard AIPS
    –
        package.
 ...
Conclusions

    Coherent integration works
●



    Demonstrated with NPOI data
●



    Improves SNR
●



    Better ste...
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High-Precision Optical Interferometry of Faint and Low-Contrast Targets Requires Coherent Integration

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High-Precision Optical Interferometry of Faint and Low-Contrast Targets Requires Coherent Integration

  1. 1. High-Precision Optical Interferometry of Faint and Low-Contrast Targets Requires Coherent Integration Anders M. Jorgensen 1 , David Mozurkewich 2 , Henrique Schmitt 3,4 1Electrical Engineering, New Mexico Tech 2Seabrook Engineering, MD 3Naval Research Laboratory, DC 4Interferometrics, inc., MD
  2. 2. Outline Optical Interferometry ● The problem of short exposures ● How to coherently integrate ● Some coherent integration results ● Diameter of a star – Binary star measurements – Imaging of a binary star – Conclusion ●
  3. 3. Optical Interferometry Resolution limit of telescopes ● Size of stars ● Separate telescopes ● Fourier transform ● ●
  4. 4. The SNR problem Atmosphere ● Fringe motion ● Short exposures ● Few photons ● Average many exposures ● But how? –
  5. 5. Incoherent Averaging V 2 averaging ● Just amplitude – squared, forget phase. Triple phase ● Three telescopes, –  one phase. Throwing away ● phase information
  6. 6. Coherent integration Imagine a world in which we can make ● long integrations.
  7. 7. Incoherent vs. Coherent Improves SNR on both amplitude and ● phase i nc inco oh er here en Co he t Co nt r en he t r en t Co ba her se en lin t e
  8. 8. How to coherently integrate Estimate phase for ● each exposure and shift. Multi-wavelength ● measurements. Enough photons in Wavelength ● band even if not in channel.
  9. 9. How to coherently integrate Two ways: ● Fast real-time control loop. – Better when read noise high: Infrared, VLTI. ● Combine in software after the fact. – Better when atmosphere is fast: Visible, NPOI. ●
  10. 10. HR 5544 V=4.5 star 2x (red end) to 10x (blue end) better ● 
  11. 11. The meaning of the phase Several components. ● Fit a model including atm and source. ●
  12. 12. Binary star measurement More phases, and better SNR. Tauri ●
  13. 13. Binary star measurement 10x better dM than Armstrong (2006) ●
  14. 14. Stellar Diameters Measured as location of null in visibility ● versus wavelength. Ophichus
  15. 15. Stellar Diameters
  16. 16. Imaging No special software needed: ● Complex visibilities. Can use standard AIPS – package. Tauri Gaussian noise. –
  17. 17. Conclusions Coherent integration works ● Demonstrated with NPOI data ● Improves SNR ● Better stellar diameters ● Better binary parameters ● Imaging in the usual way ●

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