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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
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