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Best Practices for JWST Transit Planning: Insights from the Kepler Mission

This presentation by Jessie Christiansen at the JWST Transit Planning Meeting outlines best practices for photometer development and transit observation based on Kepler's experience. Key points include achieving precise pointing with minimal jitter, effective calibration techniques, and managing thermal factors through detailed ancillary data collection. It emphasizes the importance of early and frequent testing, suggests not to overlook saturation opportunities, and highlights potential pitfalls in processing, including the challenges posed by accumulated high-energy particle hits.

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Best Practices for JWST Transit Planning: Insights from the Kepler Mission

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Presentation Transcript

  1. Kepler – Best Performance and Best Practices JWST Transit Planning Meeting March 11, 2014 Jessie Christiansen jessie.christiansen@caltech.edu

  2. How to build an exquisite photometer

  3. Pointing • Pre-launch requirement of 3mas (~1 millipixel) pointing jitter in 15 mins • Measured month to month drift 10-15 millipixels • Largely eliminated the requirement for absolute flatfielding (large scale flat a geometric model derived from optics) • Tweaks/sudden impulses are substantially more difficult to cotrend/detrend after the fact (we modified the ADCS to eliminate the drift) • This will be more of an issue with K2

  4. Focus • We’re building an $8b thermometer • Ideally, separate temperature change timescales from scientific timescales • As much thermal ancillary data as possible (reaction wheel heaters! etc) • Tailor photometry method to capture flux – either large apertures or PRF-fitting • L2/sun shade = excellent Too quantized

  5. Calibration • Test early, test often • Don’t scrimp on calibration pixels - Undershoot was 10x worse when found, but was found early enough in testing that some patches were able to be made - Moire pattern (resonance in the LDE amplifier circuit), not so much

  6. Reaction wheels • Better pointing jitter achieved with higher RPM (Kepler was more stable with three wheels at high RPM than four wheels at low RPM) • Zero crossings degraded pointing and flux time series – if timing is negotiable, try to keep them away from transits

  7. Saturation • Don’t be afraid of saturation! • (If you have a handle on your non-linearity and you have the ability to capture the spilled charge). • Theta Cyg (4.5th mag), • CH Cyg (8th mag) • Bright TESS and K2 targets should be on the table

  8. Gotchas • Provide multiple levels of processing/calibration • Time system – Kepler AND EPOXI both had trouble • Accumulation of high-energy particle hits on the detectors (SPSDs, CMEs…) • Try not to use variable stars as guide stars • Don’t forget about Jupiter! (And solar system objects in general…)

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