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Dark Energy and Large Synoptic Survey Telescope

Harvard University Department of Physics Laboratory for Particle Physics and Cosmology. Dark Energy and Large Synoptic Survey Telescope. Precision Calibration Apparatus: Calibrating the Throughput and Response of Astronomical Instrumentation. Peter Doherty

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Dark Energy and Large Synoptic Survey Telescope

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  1. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Dark EnergyandLarge Synoptic Survey Telescope Precision Calibration Apparatus: Calibrating the Throughput and Response of Astronomical Instrumentation Peter Doherty Harvard University Laboratory for Particle Physics and Cosmology Department of Energy Site Visit August 21, 2009

  2. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Precision Calibration: Introduction Measurement of a source is a sum of integrals: We improve upon traditional celestial calibration sources by: • Measuring a source with a known spectrum, namely, a narrowband tunable laser • Compare the system response (telescope throughput) to a known detector (NIST-calibrated photodiode) • In a related (but separate) effort, continuously monitoring the atmosphere during acquisition of astronomical data DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty 2

  3. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Precision Calibration: Current and Future • Current and Future Efforts: • Calibrating the Telescope and Detector: • Pan-STARRS Calibration Screen • LSST Calibration Screen • Portable Calibration System • Monitoring Atmospheric Throughput: • Real time water vapor monitor system (Leibler) • Tunable-Lidar monitoring of atmospheric extinction (with UNM/GTRI) DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  4. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Precision Calibration: Calibration Procedure Wavelength Calibration Procedure • Illuminate full telescope aperture with monochromatic light • Take a calibration “flat” while monitoring input light with calibrated photodiode • Normalize flat to flux seen by photodiode • Move to the next wavelength and repeat, until entire visible spectrum is spanned • Construct wavelength-dependent response for each pixel in the telescope’s CCD camera • End result: Measurement of relative system throughput, including telescope mirrors, corrector optics, filters, and detector DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty 4

  5. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Pan-STARRS Calibration Screen: Overview Accomplished: Installation of the world’s most advanced telescope instrument calibration system in the Pan-STARRS dome at Haleakala Hawaii Features: Rear projection screen mounted inside telescope dome Multiple fixed and tunable light sources: Quartz tungsten halogen white light NIST SIRCUS Laser (680 to 1100 nm) Supercontinuumlaser and monochromator (450 to 1100 nm) NIST calibrated photodiode for flux calibration Digital Micro-mirror Device for image projection Integrated into telescope control system DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  6. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Pan-STARRS Calibration Screen: Diagram DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  7. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Pan-STARRS Calibration Screen: Assembly DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  8. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Pan-STARRS Calibration Screen: Photograph DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty 8

  9. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Pan-STARRS Calibration Screen: Installed DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  10. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Pan-STARRS Calibration Screen: Future Plans System Enhancements 2009/2010: Installation of Ekspla Tunable laser for wavelength coverage from 350 nm to 1100 nm with a single source Improved Photodiode measurement and control system for more precise flux measurements Closing the loop with the CCD/DMD image flattener Further integration of instrument into telescope system software Incorporating calibration data into the Pan-STARRS Image Processing Pipeline DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  11. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology LSST Calibration Screen: Overview Similar in concept to Pan-STARRS calibration screen, but much different in scale: Similarities: Ekspla (or similar) tunable laser source with wavelength coverage from 350 nm to 1100 nm NIST calibrated photodiode(s) for flux measurements Differences: Cannot use single DMD projector: not enough focal length, and a large central obscuration Much larger! Pan-STARRS = 1.8 meters, LSST = 8.5 meters Multiple small projectors? DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  12. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology LSST Calibration Screen: LSST vs. Pan-STARRS Comparison of Pan-STARRS Mirror Size to LSST Mirror Size DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  13. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology LSST Calibration Screen: Filling the Aperture Filling the LSST Aperture with “Small” Projectors 12 Projectors - 1.7m Diameter 48 Projectors - 0.85m Diameter DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  14. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology LSST Calibration Screen: Small Projector Concept: A fiber fed parabolic reflector Lens Diffuser Optical Fiber Parabolic Mirror Diffuse emitter and parabolic collimator. Light from a fiber is collimated and illuminates a diffuser. The size of the diffuse emitter determines the range of angles into which light is emitted. Uniform surface brightness on the emitter ensures uniform intensity into all angles. LPPC is currently constructing a prototype in our optics lab DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  15. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology LSST Calibration Screen: “Leaky” Fiber Panel Concept: A flat screen built of glowing optical fiber Mirror Optical Fiber Diffuser Collimator Would a spiral work better? A prototype screen assembled in LPPC Lab DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  16. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Portable Calibration System: Overview A transportable light source and photon flux measurement system for calibrating throughput of astronomical telescopes and instrumentation Makes use of existing observatory dome screen Flexible I/O and triggering modes to support a wide variety of operating modes allowing integration with diverse telescope systems In 2009/2010 LPPC will design and construct the Integrating Photodiode Amplifier. Other parts are COTS. DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  17. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Atmospheric Water Vapor: Overview • Variation in aerosols and water vapor are the main sources of temporal variation in atmospheric transmission, and the airmass dependence of extinction varies with wavelength. • To investigate these two effects (aerosols and water vapor) we are engaged in two lines of research: • Monitoring water vapor in the atmosphere via differential imaging • Measuring atmospheric aerosol content via lidar backscatter • We are engaged in experiments of both types. DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  18. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Calibration: Undergraduate Projects • Atmospheric Water Vapor via Differential Imaging • Concept: Monitor bright stars simultaneously in two pass-bands: • 940nm (on absorption line) and 880nm (off absorption line). • Monitor cloud density and correlate with simultaneous • imaging through the CTIO 4m Blanco telescope • Distribution of water vapor and its variability spatially and • temporally as well as airmass dependence. • Two undergraduates travelled to CTIO in Chile with Dr. Stubbs in • early July and are working to reduce their data and determine • the results. DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  19. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Monitoring Atmospheric Extinction UNM/GTRI Astronomical Lidar for Extinction (ALE) • “Light from distant galaxies travels towards Earth-based telescopes for millions of years, and in the last millisecond of its trip about 20 percent of that valuable light, which carries information about the very structure of the universe, is lost as it traverses our atmosphere. For centuries, astronomers have looked through the atmosphere with their telescopes, but have seldom looked at the atmosphere in an effort to precisely correct for this lost light.” • John McGraw, Professor of Physics and Astronomy, University of New Mexico ALE has been developed by the University of New Mexico and the Georgia Institute of Technology Research Institute Measures backscatter from the stratosphere to monitor minute-to-minute changes in extinction due to aerosols Current system uses a fixed, 537 nm source Harvard/LPPC will collaborate with ALE creators in testing the system using a tunable laser source with wavelength coverage from 410 to >1100 nm DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

  20. Harvard University Department of Physics Laboratory for Particle Physics and Cosmology Precision Calibration Apparatus: Credits Harvard University/LPPC: Christopher Stubbs, Professor of Physics and Astronomy Peter Doherty, Senior Instrumentation Engineer Steve Sansone, Scientific Instrument Builder Gautham Narayan, Graduate Student Claire Cramer, Post-Doctoral Research Scientist Camille Leibler, Undergraduate Student Kenneth Gottlieb, Undergraduate Student National Institute of Standards and Technology Keith Lykke, Physicist, Laser Applications Group Steven Brown, Physicist, Laser Applications Group John Woodward, Physicist, Laser Applications Group Allan Smith, Physicist, Laser Applications Group University of Hawaii, Institute for Astronomy John Tonry, Astronomer  Jeffrey Morgan, Pan-STARRS Sr. Telescope Supervising Engineer  Robert Calder, PS1 Operations Manager  Large Synoptic Survey Telescope Kirk Gilmore, LSST Camera System Scientist, SLAC David L. Burke, Kavli Institute for Particle Astrophysics and Cosmology, SLAC Laser Applications Group DOE Site Visit 8/21/2009 - Dark Energy and LSST– Precision Calibration Apparatus-Doherty

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