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The Taiwanese-American Occultation Survey (TAOS I)

The Taiwanese-American Occultation Survey (TAOS I). Matthew Lehner ASIAA. Why attempt an occultation survey?. Direct searches well-suited to objects larger than R ~30 km Much of the mass may be in smaller objects Models predict a major change in size distribution for smaller objects

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The Taiwanese-American Occultation Survey (TAOS I)

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  1. The Taiwanese-American Occultation Survey (TAOS I) Matthew Lehner ASIAA

  2. Why attempt an occultation survey? • Direct searches well-suited to objects larger than R ~30 km • Much of the mass may be in smaller objects • Models predict a major change in size distribution for smaller objects • Occultations of bright stars can reveal smaller and/or more distant objects! • No orbital information! • Can measure inclination distribution if enough events.

  3. Occultation Events Fresnel Scale: F = 2 km at 50 AU Minimum event width: Objects in relative motion, v ~ 25 km/sec Event timescale ~200ms! 10 km

  4. Spectral Instruments SI-800 thinned, backside illuminated, 2048×2052 CCD cameras: Readout time of 2.5 seconds, want 5 Hz sampling

  5. “Zipper Mode” • “rowblocks” of 76 rows • Sky background 27 times as bright • Streaks from bright stars • Readout every star in image at 5 Hz 512×76 rowblock

  6. Occultation by (286) Iclea2006 February 6

  7. TAOS: four small robotic telescopes • 50 cm aperture • F/2.0 • 3 square degree field • 2K square CCD • Robotic operation • Synchronized imaging

  8. The telescopes operate at the Lu-Lin Observatory in Central Taiwan

  9. TAOS Results from 2009

  10. Wang et al. (2009)

  11. Data Volume • 810.1 hours of three telescope data in 2009 analysis • 2590.4 hours now collected • 711.1 hours of four telescope data • Sensitivity goes as the power of number of telescopes • Improved selection criteria • Expect significant improvement in sensitivity for next analysis run 2009 analysis

  12. Frame Transfer Camera • Full frame readout • 2×2 binning • 10 Hz • No zipper mode • No streaks • No excess sky • Only ¼ FOV • 1k×1k imaging area • 2 to 3 times as many stars • Limiting magnitude R=14 rather than 11.5 400 600 220 α~0.3 α~0.4

  13. The Trans-neptunian Automated Occultation Survey (TAOS II) Matthew Lehner ASIAA

  14. A factor of 100 • 7 times more of observing time • 250 observable nights/yr • 1-5 times higher event rate (model dep.) • 20 Hz sampling, higher S/N • smaller objects • 10 times more stars monitored • Rlimit= 17.5 with 1/2 FOV • 40 times higher SNR needed • Larger aperture • Better seeing & sampling • No zipper mode!

  15. Telescope #1 Primary Telescope #3

  16. Camera • High speed readout with ultra low noise • High duty cycle Monolithic CMOS • new technology • Back-illuminated • 200 KHz readout • 2e- read noise • sub-aperture readout mode • large format now available 2.5k × 2.5k 16 µm pixels 80% coverage 154 mm

  17. San Pedro Màrtir

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