Tiny Tim for Spitzer

Version 2.0

June 2006

Developed by John Krist

for the Spitzer Science Center

Get help from : help@spitzer.caltech.edu

Tiny Tim is a program for computing point spread function (PSF) models. It was originally designed for simulating Hubble Space Telescope (HST) PSFs and has been in wide use by the HST community since it was introduced in 1991. At the request of (and under contract to) the Spitzer Science Center, a new version was developed in early 2000 specifically for Spitzer. Only Tiny Tim/Spitzer is described here; the HST version, which is a completely separate program, can be obtained from http://www.stsci.edu/software.

Tiny Tim/Spitzer is written in standard C and is distributed as source code. It has been successfully compiled on a variety of systems, including UNIX, Microsoft Windows, and Linux. It s not fancy - there are no widget interfaces or fancy graphics. It simply asks a few basic questions and then goes off and computes the PSF model.

Tiny Tim/Spitzer is not an optical ray-tracing program, like Code V or Zemax. Those programs are used to design optical systems and determine their performance. Tiny Tim is hard-coded to easily model PSFs for specific optical systems, using parameters (aberrations, vignetting properties, etc.) derived from ray tracing software and measurements of on-orbit data. Information from other sources, like spectral sensitivities and detector characteristics, may also be included.

Questions and comments should be directed to help@spitzer.caltech.edu.

Uses of Model PSFs

Model PSFs have been used for a wide variety of applications:

Proposal planning: predict limiting sensitivities and resolution
Photometry: PSF profile fitting by the shifting and scaling of models; testing completeness by generating synthetic images
Algorithm testing: photometric, deconvolution, and dithering algorithm testing
PSF subtraction
Data modeling: convolution of model data with model PSFs to simulate observed images

PSFs from the HST version of Tiny Tim have been used for all of the above. It has been especially useful for algorithm testing, since the PSFs are noiseless and can be generated at subsampled resolutions.

Installation, Compilation, and Documentation

The Tiny Tim/Spitzer manual is available here. The source code for Tiny Tim is provided in a gzip-compressed tar file. This file should be downloaded in binary mode and then unpacked on your machine, like so:

gunzip stinytimv2.0.tar.gz
tar xvf stinytimv2.0.tar

The tarball will be unpacked in a directory called stinytim. Information on how to compile the code is available in the documentation.

Instrument Notes

Extensive instrument notes are available in the documentation. Additional notes are provided here.

IRS: For the spectroscopic modules, the calculated PSF is that seen by the slit. The models do not include any optics beyond the focal plane

Acknowledging Tiny Tim/Spitzer

If you use Tiny Tim/Spitzer in a publication, please include the following acknowledgment:

"This research made use of Tiny Tim/Spitzer, developed by John Krist for the Spitzer Science Center. The Center is managed by the California Institute of Technology under a contract with NASA"

Updated 7 Aug 2006