- Form:SKYLINE s1 [s2] [s3] ... [s15] [INT]
-
- s1
- is the buffer number of the sky spectrum.
- s2 ... s15
- are buffer numbers whose wavelength
scales are to be re-calibrated using the night sky spectrum s1.
- INT
- requests interactive deletion of lines
from the list of identified night sky lines.
SKYLINE searches the night sky spectrum in buffer 's1' for known night sky
emission lines. All spectra must be linear wavelength calibrated. If it
finds at least two lines in the spectrum it will use them to compute a
corrected zero-point for the wavelength scale (the dispersion term is not
changed). This new zero-point is then applied to all of the other spectra
supplied on the command line. All of the spectra should be on the same
linear wavelength scale (using the ALIGN command) to begin with.
If the keyword INT is used then you will be given the option to delete
lines from the list of night sky lines found in spectrum 's1'.
Example:
- MASH 1 8 SP=30,40 BK=10,20 BK=50,60 SKY=2
-
- COPW 1 20
- ! Copy wavelength parameters
- COPW 2 20
-
- ALIGN 1 DSP=7.0
- ! Xform to linear wavelength
- ALIGN 2 DSP=7.0
-
- SKYLINE 2 1 INT
- ! Correct zero-point
MASH is used to operate on image 8, producing a sky-subtracted program
spectrum in buffer 1 and the sky spectrum in buffer 2. Wavelength
parameters are copied from a previously calibrated comparison spectrum (in
buffer 20). The two spectra are transformed to a linear wavelength scale
using ALIGN. Then the zero-point of the wavelength scale is corrected using
SKYLINE. This procedure can remove instrumental flexure if your spectra
contain usable night-sky lines.