A comparison of on-sky NIR Point Spread Functions (PSFs) on the WIRC instrument on the 200" Hale telescope at Palomar Observatory.
On the left are defocused observations performed with WIRC on-sky, showing significant variations due to phase variations from seeing effects, and due to time variable optical aberrations from the telescope during the night.
The middle panel shows focused observations from WIRC, which also are significantly affected from seeing variations, but also have much lower observing efficiency (in terms of photon collecting time vs. down time) than the defocused observations.
The right panel shows diffused PSFs, demonstrating a homogenized PSF that is optically spread out over many pixels, minimizing seeing effects, flat fielding and guiding errors, and increasing observing efficiency. The PSF is stable throughout the observations.
This is video is the work of Dr. Ming Zhao and is used here with permission to supplement the discussion in Stefansson et al. 2017 (in prep; we will update with an arxiv link here once published), regarding the use of a near infrared diffuser on-sky with the WIRC instrument on the 200" telescope at Palomar Observatory.
