Megan M. Kiminki

(formerly Megan M. Bagley)

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


Here's a quick reference on using IRAF's apall task. These notes assume that you have some familiarity with IRAF and the process of reducing spectra.

Apall has many parameters. For maximum interactivity the first time through, set all the yes/no questions on the first page to yes. Other parameters you may want to set, either before running or during an interactive run, 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 in apextract.) 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.