Megan M. Kiminki

(formerly Megan M. Bagley)

Graduate Student

Department of Astronomy / Steward Observatory
University of Arizona
A picture of teddy-bear cholla. Cactus in bloom in northwest Tucson. Hubble Space Telescope image of the HH 666 protostellar jet. Observing at the Magellan Telescopes. The Magellan telescopes in Chile. Saguaro in Sabino Canyon.

Aperture Extraction in IRAF: Apall for Beginners


[I wrote this many years ago when I was first learning how to reduce slit spectroscopy in IRAF.]


Apall has a zillion parameters. I tend to set all the yes/no options on the first page to yes the first time I find apertures for a data set. Other parameters you may want to set, depending on your data (either before running or while running interactively) are:

After you hit enter for a few questions, apall enters interactive mode. You will see a cut across your 2D spectrum, with apertures automatically identified. (If things look really weird, you might have the dispersion axis set incorrectly.) Useful commands at this stage include:

Next, apall traces the aperture and asks you to confirm the fit. Ideally, there is a lovely curve that is relatively easy to fit. Delete any outlying points with "d", then hit "f" to see the new fit. If the trace is so ugly that no pattern is visible, try fitting a horizonal line. When satisfied, hit "q" to exit the trace.