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Detector Mosaic Design Considerations for a Wide FOV Drift-Scan Survey Telescope

Detector Mosaic Design Considerations for a Wide FOV Drift-Scan Survey Telescope. John T. McGraw Mark R. Ackermann Peter C. Zimmer University of New Mexico and Lt. Eric Golden AFRL. The Near Earth Space Surveillance Initiative (NESSI).

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Detector Mosaic Design Considerations for a Wide FOV Drift-Scan Survey Telescope

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  1. Detector Mosaic Design Considerations for a Wide FOV Drift-Scan Survey Telescope John T. McGraw Mark R. Ackermann Peter C. Zimmer University of New Mexico and Lt. Eric Golden AFRL

  2. The Near Earth Space Surveillance Initiative (NESSI) NESSI is a collaboration between the University of New Mexico (CTI) and McDonald Observatory of The University of Texas at Austin (HET). The project is funded by AFRL.

  3. UNM/USAFA Cooperative Research • Design and implementation • Data reduction and analysis • Follow-up observations RR Lyrae Star W UMa Eclipsing Variable

  4. The CCD/Transit Instrument (CTI) • 1.8-m, f/2.2 parabolic primary • Paul-Baker optical system • 3.96-m focal length • 52 arcsec/mm field scale • Existing thermally-compensating structure

  5. The Paul-Baker Optical System Very wide FOV Excellent images Compact design Proposed for LSST

  6. Time-Delay and Integrate (TDI) Readout Mode Advantages: Stable telescope does not move Constant gravity load Instrumental signature averaged over rows • “Features:” • Meridian TDI adds to the PSF • Differential track rate

  7. HET and CTI FOV E W CTI and HET Survey Geometry

  8. Elements of an astronomical survey • Discover new objects and phenomena • Synoptically monitor objects • Motion • Variability • Provide a statistically significant, unbiased sample of objects • Discover targets of opportunity • Enable follow up observations

  9. The CCD/Transit Instrument (CTI II) • Meridian-pointing 1.8-m telescope • Images formed on multiple CCDs operated in TDI mode • no moving parts • multiple optical/IR colors each night • Fully automated operation • Photometric imaging over 1 - 2° FOV • surveys ~120°2 each night • V22.5 nightly detection limit

  10. Science Drivers Supernova detection AGN Reverberation IR Astrometry

  11. Optical and Near IR Astrometry • Single-image astrometry includes stars 90° apart – parallaxes • Goal: 3 mas rms per night stellar centroids • HET spectra – spectral type and radial velocity

  12. SN Ia: The universe is expanding. • Doppler shift measurements give higher recession velocities for more distant galaxies. • The rubber band experiment.

  13. The universe is expanding – Hubble’s Law.Hubble’s Constant is the slope of this line.The slope determines the “age” of the universe.

  14. We see the remnant of the Big Bang that initiated the universe in the cosmic microwave background.

  15. One way of visualizing an open, flat or closed universe.

  16. The fate of the universe is determined by what’s in it.

  17. Type Ia supernovae are “standard candles.”

  18. Type Ia supernovae can measure cosmological distances.

  19. Supernovae at large distance map the former conditions of the universe.

  20. The history of cosmic expansion provided by SNe Ia.

  21. Interpreting cosmological parameter space can be tricky.

  22. The annotated version of the previous figure.

  23. Active Galactic Nuclei • Discovery of Quasars • Quasar Lensing • AGN Reverberation

  24. Active Galactic Nuclei • The Nature of Quasars

  25. Active Galactic Nuclei • The “Standard Model” • Accretion disc scale ~ 1 pc

  26. Active Galactic Nuclei • AGN phenomenon is ubiquitous • Milky Way? • All galaxies? • Evolution?

  27. Active Galactic Nuclei • Mapping: Model, Orientation, Time History • Light travel timescale ~ 3 years • Dynamical timescale ~ r/V ~ 10 – 100 years

  28. The Obscure Universe • The outsider’s view of gravitational lensing:

  29. The Obscure Universe • Geometry of Different Optical paths • Source geometry • Lens geometry • Source dust chemistry • Well-sampled light curves • Optical path length measurement • Effects of microlensing • Dust in lenses

  30. The Obscure Universe • Luminosity variability • Days to years • Intrinsic variability • Optical path length • Microlensing • Colley et al. 2002

  31. Active Galactic Nuclei • AGN Reverberation • Mapping the scale, structure, and time-dependent structure changes in the environs of massive black holes • Testing the standard model of AGNs • Examples: N1275, N7742

  32. Active Galactic Nuclei • Quasars • 1° wide strip, α = 8 hours (NGC)  120°² • 25 quasars/°² to B = 21  3000 quasars • Conservatism: 2° FOV, tilt to cover 10°, B fainter than 22 at S/N = 10, 2df data  all quasars • Galaxies (same geometry, B = 19.7) •  18000 galaxies • SNe (same geometry, B = 21 point source) •  100 ~ SNe/year

  33. PSF Analysis: Motion-induced components Model input: 0.85 arcsec FWHM Moffatt function

  34. Small Pixels Ameliorate Motion-Induced Blur • Deconvolution kernel is fully deterministic • Blur caused by: • Discrete shifting of pixels • Curved celestial trajectories – α and δ • Differential track rate – all TDI operations

  35. Design Criteria • Fully sample the PSF at the R bandpass • Include near-IR bandpasses • V, R and I optical bandpasses • Multiple devices for greater dynamic range • Configure optics/focal plane to take advantage of modal 0.85 arcsec seeing at McDonald Observatory • Observe Galactic north pole (δ=28°) • Strip must intersect HET field of regard

  36. Analysis of Three Optical Designs • Paul-Baker • And variants involving refractive correctors • Prime focus • Variants include differing numbers of refractive corrector elements • Gregorian • And variants • Astronomical Lidar for Extinction • Photometric engineering data

  37. The CCD/Transit Instrument (CTI II)Strawman Focal Plane Mosaic • Focal Plane Mosaic Strawman Alternatives (EEV CCDs)

  38. The CCD/Transit Instrument (CTI II)Performance • CTI S/N (Strawman Mosaic)

  39. The CCD/Transit Instrument (CTI II)Performance • S/N at the Detection Limit

  40. Current Survey ComparisonsVital Statistics • CTI II Bottom Line: • Visible to mid-IR photometry in a single survey • Comparable resolution and depth to other surveys • Significantly greater repeat observations for variability/astrometry • Smaller total area, but widely distributed in galactic latitude and longitude due to nature of transit instrument survey • Significant increase in dynamic range • Spectroscopic follow-up to same limiting magnitude with HET

  41. The CCD/Transit Instrument (CTI II)Summary • CTI II is being designed and built • Frontline Research – Science Drivers • Technology transfer to other sky survey telescopes • The “niche” • Photometric and astrometric precision • Repeated observations with one sidereal day cadence • Spectroscopic observations, including real-time targets • Issues: • Final optical design – f/5.5 • Detector mosaic • Detector size, pixel size, need for deconvolution • Curved channel, OTA devices • Bandpasses – optical and IR

  42. The CCD/Transit Instrument (CTI)A Sample Sweep West North South East

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