Transcript Long-Slit Spectroscopy

Long-Slit Spectra
Reduction with
IRAF
Arp 63
Fig.2: Galaxy spectrum
Fig.1: Galaxy + slit
l
Fig.3: Star spectrum
Bias subtraction
noao.imred.ccdred
• zerocombine
• ccdproc / imarith
Frame - <bias>
Fig.4: Bias image
imstat
#
IMAGE
Zero
NPIX
1036324
MEAN
197.6
MIDPT
197.7
STDDEV
0.7823
MIN
193.7
MAX
201.5
Flat-field correction
noao.imred.ccdred
• flatcombine
• ccdproc / imarith
Frame - <bias>
----------------<flat> - <bias>
Fig.5: Flat image
imstat
#
IMAGE
Flat
NPIX
1036324
MEAN
10913.
MIDPT
12410.
STDDEV
5605.
MIN
912.1
MAX
19706.
Flat-field normalization
noao.twodspec.longslit
• response
Fig.6: Flat-field fitting along dispersion
Fig.7: Normalized flat
imstat
#
IMAGE
nFlat
NPIX
1036324
MEAN
1.
MIDPT
0.996
STDDEV
0.03019
MIN
0.1302
MAX
1.135
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.10: Cosmic-rays mask
Fig.9: Spectrum with cosmic-rays
Fig.11: Cleaned image
Wavelength calibration
noao.twodspec.longslit
•
•
•
•
Fig.12: Helium-Argon lamp spectrum
identify
reidentify
fitcoords
transform
Fig.13: Spectral lines identification
Fig.15: Bidimensional fit
li = 4458.3 Å
dl = 2.6 Å/px
Fig.14: Fit residuals
Checking calibration
Fig.16: Before calibration
Fig.17: After calibration
Fig.18: Night-sky [OI] lines
Flux calibration
Feige 56
noao.twodspec.apextract
• apall
noao.onedspec
• standard
• sensfunc
noao.twodspec.longslit
Fig.19: Standard star spectrum
• calibrate
Fig.20: Star profile across dispersion
Fig.21: Tracing along dispersion
Fig.22: Extracted 1-D spectrum
Fig.23: Star fluxes measurement
counts
Fig.24: Calibration curve (upper)
erg cm-2 sec-1 Å-1
Fig.25/26: Before and after flux calibration
Frame
------------calib. func.
Fig.27: Calibrated spectrum (red)
Night-sky subtraction
noao.twodspec.longslit
• background
Fig.28: Fit of the sky across dispersion
Fig.29: Spectrum after sky subtraction