# HOW-TO Use TinyTim¶

The TinyTim package (http://www.stsci.edu/hst/observatory/focus/TinyTim) is used to create PSF images for the instruments of the Hubble Space Telescope. In Astro-WISE only the ACS instrument for the WFC detectors for Hubble is supported, and hence the use of TinyTim is limited to that configuration.

TinyTim images are used in particular when running surface photometry tools such as Galfit.

When running TinyTim several choices must be made:

The meaning of the configurable parameters and their defaults:

• Av=None or embv=None Interstellar extinction of x magnitudes is applied to the object spectrum, specified in the form of E(B-V) or visual extinction (Av). Do not specify both.
• angle=None, see also major=None, minor=None Convolve the PSF with a elliptical Gaussian kernel approximating x milliarcseconds RMS of jitter along its major axis, y mas jitter along the minor axis, with the major axis rotated by z degrees from the +X image axis. All three parameters must be specified if any of them is.
• chip=1 For which of the WFC ccds should tinytim make a PSF model chip 1 or 2.
• coeff=2000.0 Depending on the value of spectrum, if spectrum=2 (blackbody) this is the Temperature in Kelvin of the black body, if spectrum=3 (Power law) this is the powerlaw coefficient.
• diameter=3.0 Diameter of PSF in arcsec (maximum=25.7arcsec). Recommended size=3.0arcsec.
• ebmv=None or Av=None Interstellar extinction of x magnitudes is applied to the object spectrum, specified in the form of E(B-V) or visual extinction (Av). Do not specify both.
• filename=psf_image: DO NOT CHANGE this default
• filter=F555W: name of filter to model.
• instrument=15: DO NOT CHANGE this default
• jitter=None Convolve the PSF with a symmetrical Gaussian kernel approximating x milliarcseconds RMS of jitter.
• major=None, see also minor=None, angle=None Convolve the PSF with a elliptical Gaussian kernel approximating x milliarcseconds RMS of jitter along its major axis, y mas jitter along the minor axis, with the major axis rotated by z degrees from the +X image axis. All three parameters must be specified if any of them is.
• minor=None, see also major=None, angle=None Convolve the PSF with a elliptical Gaussian kernel approximating x milliarcseconds RMS of jitter along its major axis, y mas jitter along the minor axis, with the major axis rotated by z degrees from the +X image axis. All three parameters must be specified if any of them is.
• paramfile=tiny.conf. DO NOT CHANGE this default.
• spectrum=2. The only SUPPORTED VALUES here are 2 and 3 from the following list:
1. Select a spectrum from list
1. Blackbody
1. Power law : F(nu) = nu$$^i$$
1. Power law : F(lambda) = lambda$$^i$$
1. Read user-provided spectrum from ASCII table
• wmag=None Increase or decrease by a factor of x the default number of wavelengths used in computing a polychromatic PSF (ie. wmag=0.5 would use only half the default number of wavelengths, while wmag=2 would double the number, more finely sampling the response curve). Increasing wmag provides a somewhat smoother PSF at radii beyond about 3”. A minimum of one wavelength will be used.
• x=-1 Enter position x on detector in INTEGER pixels (X range = 0-4095)
• y=-1 Enter position y on detector in INTEGER pixels (Y range = 0-2047)

An object model was made to store these choices and run TinyTim.

## Running TinyTim¶

There is a DBRecipe to make TinyTim. The only arguments it takes is a dictionary specifying the process parameters and a switch to commit the result to the database and dataserver:

awe> task = TinyTimTask(pars={'TinyTimImage.tinytimconf.x': 200,
'TinyTimImage.tinytimconf.y': 250}, commit=1)


The configurable parameters can be shown as conventional, using the “Pars” class:

awe> p = Pars(TinyTimImage)
awe> p.show()
etc.