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Published March 2019 | public
Journal Article

Exposure-time Correction for the ZTF Camera


A correction factor is derived to account for nonuniformities in the exposure time as seen by different positions on the focal plane of the ZTF camera. These nonuniformities arise from a combination of the shutter opening and closing motion; the geometrical setup of the telescope; and the presence of obstructions in the beam beyond the pupil plane. The correction to the exposure time is measured by comparing a set of dome-flat images taken with multiple shutter opening/closing motions to those obtained with a normal exposure of the same total duration. The correction to the exposure time is small, of the order of 30 ms averaged over the entire field of view with peaks of ~60 ms at the east and west edges of the camera. The effect is thus of the order of 0.1% on average for the nominal ZTF survey exposures of 30 s. Comparing the results obtained from three sets of dedicated observations acquired in 2017 December, we assess the stability of the correction factor to be better than 7% both in time and with respect to variations of the experimental conditions.

Additional Information

© 2019. The Astronomical Society of the Pacific. Received 2018 November 16; accepted 2018 November 26; published 2019 January 29. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. Major funding has been provided by the U.S National Science Foundation under grant No. AST-1440341 and by the ZTF partner institutions: the California Institute of Technology, the Oskar Klein Centre, the Weizmann Institute of Science, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron, the University of Wisconsin-Milwaukee, and the TANGO Program of the University System of Taiwan.

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