> Is there any extinction file for APO to calibrate spectroscopy data? No, not that I know of. Somebody should really take the time to do this though. Unless I am mistaken, it just takes a few standard star observations in photometric conditions (with a wide slit). > If not, is it ok to use the for KPNO available in Iraf libraries? Yes. I have found that using the KPNO extinction is better than not applying an extinction correction at all. Gordon APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 85 in the apo35-dis archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-dis/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-dis@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO