6 July 2018 Aligning the ZTF science focal plane using stellar images
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Abstract
The Zwicky Transient Facility (ZTF) is a next-generation, optical, synoptic survey that leverages the success of the Palomar Transient Factory (PTF). ZTF has a large science focal plane (SFP) that needs to be aligned such that all portions of the CCDs are simultaneously placed in focus to optimize the survey’s efficiency. The SFP consists of 16 large, wafer-scale science CCDs, which are mosaicked to achieve 47 deg2 field of view. The SFP is aligned by repositioning each CCD based on the measured height map, which is a map of the camera’s z position at which each portion of the CCD is in focus. This height map is measured using on-sky stellar images in order to recreate the optical path that will be used throughout the survey. We present our technique for placing the SFP in focus, which includes two different methods to measure the height map of the SFP. The first method measures the height at which a star is in focus by fitting a parabola to each star’s photometric width as the star is moved in and out of focus. The second method measures the height by decomposing a defocused star into its image moments. We will discuss the strengths and limitations of each method and their outputs. By repositioning the CCDs, we were able to reduce the standard deviation of the height map from 33 to 14microns, which improved the survey’s speed by ∼ 81%.
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Gina E. Duggan, Gina E. Duggan, Richard Dekany, Richard Dekany, Jennifer Milburn, Jennifer Milburn, } "Aligning the ZTF science focal plane using stellar images", Proc. SPIE 10702, Ground-based and Airborne Instrumentation for Astronomy VII, 107024K (6 July 2018); doi: 10.1117/12.2309994; https://doi.org/10.1117/12.2309994
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