The assignment: Lab 3: Stellar Spectral extraction and reduction
You should follow Josh Walawender's IRAF tutorial up through the line identification section, at which point you should check out the helpful tips on apall and identify page.
When you have applied your wavelength solution, you should have an image similar to mine:
Specifically, you should have wavelength instead of pixel number on the x axis.
After you've completed that step, you just need to identify your stellar type. In order to do this, you need to correct for the chip sensitivity, which involves dividing by some sort of spectral flat. For long-slit spectroscopy, this is best done using a standard star (which corrects for atmospheric extinction in addition to chip sensitivity) or line ratios (which also corrects for interstellar extinction), but for this lab it will not be necessary.
In the lab, you are asked to interpolate over Balmer lines in Vega's spectrum. This essentially means fitting a continuum to Vega. This can be done easily in splot. You need to use t to fit a continuum (then press f because you want a fit), then use i to save your continuum fit as another image. You should be familiar with fitting routines from earlier work (see, e.g., my helpful tips on apall above. You should also know how to use imarith to divide spectra. If not, ask!
This website is a nice reference when identifying stellar type, but be careful: don't take these spectra as being correct without doing a sanity check, e.g. "is this F star hotter or colder than the sun? should it be?" You should also use tables 11.2, 11.4, and 11.5 from your textbook to independently determine spectral type.
An atlas of stellar spectra
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Page written by Adam Ginsburg