Seeing trends from deployable Shack-Hartmann wavefront sensors, MMT Observatory, Arizona, USA

J. Duane Gibson; G. Grant Williams; Thomas Trebisky

doi:10.1117/12.924897

17 September 2012 Seeing trends from deployable Shack-Hartmann wavefront sensors, MMT Observatory, Arizona, USA

J. Duane Gibson, G. Grant Williams, Thomas Trebisky

Proceedings Volume 8444, Ground-based and Airborne Telescopes IV; 844432 (2012) https://doi.org/10.1117/12.924897
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

Deployable Shack-Hartmann wavefront sensors (WFS) for the f/5 and f/9 secondary configurations have been used at the 6.5-meter MMT Observatory (MMTO) since 2003. Probe mirrors for these WFS's are moved into the optical path of the telescope between scientific observations multiple times each night. Results from the wavefront measurements are then used to bend the primary mirror (M1) and to reposition the secondary mirror (M2) to correct for wavefront errors. In addition to measuring the optical wavefront error, the Shack-Hartmann data are used to determine the delivered seeing using the measured spot sizes. This study attempts to analyze the more than 75,000 WFS measurements and associated seeing values obtained at the MMTO since 2003. The overall WFS data reduction and analysis procedure is discussed. This data analysis includes: 1) finding the spots in each image, 2) centroiding the spots, 3) measuring a point-spread function, 4) determining an average spot width and a derived seeing value, and 5) computing the best-fit Zernike polynomial coefficients. Wavefront slopes are calculated from spot displacements and wavefront aberrations are fit with a 19-term Zernike polynomial. As part of this study, the WFS-derived seeing values are correlated with other observing parameters, such as mirror-air temperature contrasts. Finally, seasonal climate and local weather (e.g., prevailing wind direction) effects on astronomical seeing are evaluated.

Citation Download Citation

J. Duane Gibson, G. Grant Williams, and Thomas Trebisky "Seeing trends from deployable Shack-Hartmann wavefront sensors, MMT Observatory, Arizona, USA", Proc. SPIE 8444, Ground-based and Airborne Telescopes IV, 844432 (17 September 2012); https://doi.org/10.1117/12.924897

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