please can someone help me to understand how IRAF calculate errors of my extracted spectrum.
After I finish with spectra extraction in IRAF at the end I will get wavelength and flux calibrated spectra. This spectra is fits file where I have 4 extensions. When I am checking header of my fits wile name of these extensions are:
BANDID1 - spectrum - background fit, weights none, cleaned (if I understand this is my final spectrum of the object)
BANDID2 - raw - background fit, weights none, clean no (I think this is original spectra before reduction)
BANDID3 - background - background fit (background
BANDID4 - sigma - background fit, weights variance, clean yes (I think this is my error)
Can someone explain to me how IRAF calculate BANDID4 and please correct me if my understanding of these BANDID 1, 2, 3, and 4 is wrong I will appreciate this
Thanks in advance