Long-Slit SpectraReduction with

IRAF

λ

Fig.1: Galaxy + slit Fig.2: Galaxy spectrum

Fig.3: Star spectrum

Arp 63

Bias subtraction

noao.imred.ccdred

• zerocombine• ccdproc / imarith

imstat# IMAGE NPIX MEAN MIDPT STDDEV MIN MAX Zero 1036324 197.6 197.7 0.7823 193.7 201.5

Frame - <bias>Fig.4: Bias image

Flat-field correction

noao.imred.ccdred

• flatcombine• ccdproc / imarith

imstat# IMAGE NPIX MEAN MIDPT STDDEV MIN MAX Flat 1036324 10913. 12410. 5605. 912.1 19706.

Frame - <bias>----------------- <flat> - <bias>

Fig.5: Flat image

noao.twodspec.longslit• response

imstat# IMAGE NPIX MEAN MIDPT STDDEV MIN MAX nFlat 1036324 1. 0.996 0.03019 0.1302 1.135

Fig.6: Flat-field fitting along dispersion

Fig.7: Normalized flat

Flat-field normalization

Cosmic-rays removal

noao.imred.ccdred

• cosmicrays

crutils

• cosmicrays• crmedian

Fig.8: Spectrum after bias and flat correction

L.A. Cosmics (Van Dokkum, 2001)

Fig.9: Spectrum with cosmic-rays

Fig.10: Cosmic -rays mask

Fig.11: Cleaned image

Wavelength calibration

noao.twodspec.longslit

• identify• reidentify• fitcoords• transform

Fig.12: Helium-Argon lamp spectrum

λi = 4458.3 Å

δλ = 2.6 Å/px

Fig.13: Spectral lines identification

Fig.14: Fit residuals

Fig.15: Bidimensional fit

Checking calibration

Fig.16: Before calibration Fig.17: After calibration

Fig.18: Night- sky [OI] lines

Flux calibrationnoao.twodspec.apextract

• apall

noao.onedspec

• standard• sensfunc

noao.twodspec.longslit

• calibrate

Feige 56

Fig.19: Standard star spectrum

Fig.20: Star profile across dispersion Fig.21: Tracing along dispersion

Fig.22: Extracted 1-D spectrum

counts

erg cm-2 sec-1 Å-1

Fig.23: Star fluxes measurement

Fig.24: Calibration curve (upper)

Frame ------------- calib. func.

Fig.25/26: Before and after flux calibration

Fig.27: Calibrated spectrum (red)

Night-sky subtractionnoao.twodspec.longslit

• background

Fig.29: Spectrum after sky subtraction

Fig.28: Fit of the sky across dispersion