The calibration hardware system of the Large Synoptic Survey Telescope (LSST) is designed to measure two quantities: a telescope’s instrumental response and atmospheric transmission, both as a function of wavelength. First of all, a “collimated beam projector” is designed to measure the instrumental response function by projecting monochromatic light through a mask and a collimating optic onto the telescope. During the measurement, the light level is monitored with a NIST-traceable photodiode. This method does not suffer from stray light effects or the reflections (known as ghosting) present when using a flat-field screen illumination, which has a systematic source of uncertainty from uncontrolled reflections. It allows for an independent measurement of the throughput of the telescope’s optical train as well as each filter’s transmission as a function of position on the primary mirror. Second, CALSPEC stars can be used as calibrated light sources to illuminate the atmosphere and measure its transmission. To measure the atmosphere’s transfer function, we use the telescope’s imager with a Ronchi grating in place of a filter to configure it as a low resolution slitless spectrograph. In this paper, we describe this calibration strategy, focusing on results from a prototype system at the Cerro Tololo Inter-American Observatory (CTIO) 0.9 meter telescope. We compare the instrumental throughput measurements to nominal values measured using a laboratory spectrophotometer, and we describe measurements of the atmosphere made via CALSPEC standard stars during the same run.
|Original language||English (US)|
|Title of host publication||Observatory Operations|
|Subtitle of host publication||Strategies, Processes, and Systems VII|
|Editors||Robert L. Seaman, Alison B. Peck, Chris R. Benn|
|State||Published - 2018|
|Event||Observatory Operations: Strategies, Processes, and Systems VII 2018 - Austin, United States|
Duration: Jun 11 2018 → Jun 15 2018
|Name||Proceedings of SPIE - The International Society for Optical Engineering|
|Conference||Observatory Operations: Strategies, Processes, and Systems VII 2018|
|Period||6/11/18 → 6/15/18|
Bibliographical noteFunding Information:
MC was supported by the David and Ellen Lee Postdoctoral Fellowship at the California Institute of Technology. CWS is grateful to the DOE Office of Science for their support under award DE-SC0007881. NM is supported by National Science Foundation Graduate Research Fellowship Program, under NSF grant number DGE 1745303. NM thanks the LSSTC Data Science Fellowship Program, his time as a Fellow has benefited this work.
© 2018 SPIE
- Photometric calibration