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Optimizing Secondary Support and Focal Plane Flare Management in Alt-Az Mount Observations

This document discusses the creation and management of focal plane flares in secondary support setups. It addresses the impact of field rotation in Alt-Az mounts and how counter-rotating instruments can mitigate flare effects. We present methods for masking flares in post-processing to minimize noise, achieving effective image integration across varying exposure times. Additionally, we explore the compromise of spider scale factors in maintaining coronagraph performance while discussing the implications on observation quality and throughput.

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Optimizing Secondary Support and Focal Plane Flare Management in Alt-Az Mount Observations

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  1. Secondary Support Issues • Secondary supports create focal plane flares • Field rotates in Alt-Az mount • Counter-rotating instrument spreads flares in focal plane. • Masking flares in software can reduce impact to 1/n for n independent (no flare overlap) exposures.

  2. Secondary Flares – Single ExposureNo Noise First Focus Second Focus

  3. Secondary Flares – Single Exposure1 Minute Integration, mK= 6 Second Focus – No Sky First Focus - Sky

  4. Secondary Flares – Long exposure 2 Hour exposures across zenith: sky/star split 50:50 Images sky subtracted K Star at dec – 10° Star at dec – 30° First Focus

  5. Secondary Flares – Long exposure K Star at dec – 10° Star at dec – 30° Second Focus

  6. Secondary Flares - Conclusions • Spider Scale Factor of 30 makes NICI observations relatively independent of star’s position and time of observation. • Scale factor of 30 is compromise between tolerancing, throughput, coronagraph performance and manufacturability. • Since spiders occupy about 0.25% of the Gemini Pupil area, spider mask loss is about 6-7%

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