Ghez Research Group
NIRC2 Narrow Camera Distortion Solution
(Yelda et al. 2010)
All files are zipped FITS files of size 1024 x 1024 pixels, with each
pixel specifying the required shift (in pixels) to undistort an image.
Please forward any questions or comments to: syelda [at] astro [dot] ucla [dot] edu
Description of Distortion Solution
Details on the creation, testing, and application of the NIRC2 narrow camera distortion
solution can be found in Yelda et al. (2010).
Here we highlight some of the details.
The optical distortion of the camera was characterized and solved for using, for the
very first time, on-sky measurements of a globular cluster. This is in contrast
to earlier efforts, which used pin-hole masks.
(Left) Optical distortion in the NIRC2 camera obtained from positional
measurements of stars in the globular cluster M92.
Arrows indicate the difference between measurements made with
NIRC2 (arrow tail) and ACS/WFC (arrow head), which
has a well characterized distortion solution to the ~0.5 mas
level (Anderson et al. 2006, Anderson et al. 2007).
(Right) Post-fit residuals after applying a 3rd-order bivariate
smoothing spline to the distortion map. Typical residuals are on the
order of 0.1 pix (~1 mas).
Positional errors of Galactic center stars using the new distortion solution
versus the preship solution (left) and versus P. B. Cameron's solution
(right). The new solution is a factor of ~3-4
improved in both X (red crosses) and Y (blue plus signs)
over the pre-ship solution and in Y over the PBC solution.
How to Use this Solution with Drizzle:
Python code to undistort individual frames using the IRAF package
drizzle: nirc2dewarp.py (Last updated: 2010 Nov. 20)
We thank Shelley Wright for her help with this code.
Also see notes on this at: AstroBetter
How to rotate images to get North up:Position Angle