mk2dspec -- Make/add 2D spectra using 1D spectra templates
- Spectra to create or modify.
- output = ""
- Output spectra when modifying input spectra. If no output spectra are given then existing spectra in the input list are modified directly. If an output list is given then it must match in number the input list.
- models = ""
- List of model parameter files. If the list of model files is shorter than the list of input images then the last model file is reused. The model parameter files contain lines giving one dimensional spectrum template name, intensity scale, type of cross dispersion profile, profile width in the center line, change of width per line, profile position in the center line, and change of position per line (see the DESCRIPTION section).
- comments = yes
- Include comments recording task parameters in the image header?
WHEN CREATING NEW SPECTRA
- title = ""
- Image title to be given to the spectra. Maximum of 79 characters.
- ncols = 100, nlines = 512
- Number of columns and lines.
- header = "artdata$stdheader.dat"
- Image or header keyword data file. If an image is given then the image header is copied. If a file is given then the FITS format cards are copied. This only applies to new images. The data file consists of lines in FITS format with leading whitespace ignored. A FITS card must begin with an uppercase/numeric keyword. Lines not beginning with a FITS keyword such as comments or lower case are ignored. The user keyword output of imheader is an acceptible data file. See mkheader for further information.
This task creates or modifies two dimensional spectra by taking one dimensional spectra, convolving them with a spatial profile across the dispersion, and adding them into two dimensional images. The one dimensional spectra may be real data or artificial data created with the task mk1dspec . No noise is included but may be added with the task mknoise . The spatial profile is fully subsampled and may vary in width and position along the dispersion axis. The spatial axis is along the first dimension and the dispersion is along the second dimension.
For new images a set of header keywords may be added by specifying an image or data file with the header parameter (see also mkheader ). If a data file is specified lines beginning with FITS keywords are entered in the image header. Leading whitespace is ignored and any lines beginning with words having lowercase and nonvalid FITS keyword characters are ignored. In addition, comments may be added to the image header recording the model file name and the contents of the model file.
The spatial profile models are specified in one or more model parameter files. These files contain lines giving a one dimensional spectrum template name, intensity scale, type of cross dispersion profile, profile width in the center line, change of width per line, profile position in the center line, and change of position per line. More specifically:
- <template name>
- The one dimensional spectrum template is any one dimensional IRAF image. If the spectrum template length is less than the two dimensional spectrum, the profile extends only over that number of lines and, if it is longer, then only the first part of the spectrum is used.
- The template spectrum is scaled by this parameter to define the total flux for the two dimensional profile.
- <profile type>
- The spatial profiles are identified by two keywords, "gaussian"
or "slit". The profiles are defined by the following formulae,
gaussian: I(x) = exp (-ln(2) * (2*(x-xc)/fwhm)**2) slit: I(x) = exp (-ln(2) * (2*(x-xc)/fwhm)**10)
where x is the column coordinate, xc is the profile center, and fwhm is the full width at half maximum. The "gaussian" profile is the usual gaussian specified in terms of a FWHM. The "slit" profile is one which is relatively flat and then rapidly drops to zero. The profile is normalized to unit integral so that the total flux across the profile is given by the scaled 1D spectrum flux.
- fwhm, dfwhm
- The full width at half maximum and derivative with line number. The fwhm is
defined for the middle of the image. The FWHM as a function
of line, l, is,
fwhm + (l - nlines/2) * dfwhm
- center, dcenter
- The profile center and derivative with line number. The center is
defined for the middle of the image. The center as a function
of line, l, is,
center + (l - nlines/2) * dcenter
The provision for having the spectra tilted relative to the columns is useful for understanding undersampling effects. However, note that the spectral lines are not perpendicular to the dispersion but are always aligned with the image lines.
1. Create an artificial multifiber spectrum:
cl> type multifiber.dat arc 4 gauss 3 0 20 .01 spec1 .5 gauss 3 0 30 .01 spec2 .4 gauss 3 0 40 .01 spec3 .9 gauss 3 0 50 .01 spec4 .2 gauss 3 0 60 .01 spec5 .6 gauss 3 0 70 .01 spec6 1 gauss 3 0 80 .01 spec7 1 gauss 3 0 90 .01 cl> mk1dspec arc cont=0 peak=500 nl=30 cl> mk1dspec spec1 nlines=99 seed=1 cl> mk1dspec spec2 nlines=80 seed=2 cl> mk1dspec spec3 nlines=45 seed=3 cl> mk1dspec spec4 nlines=95 seed=4 cl> mk1dspec spec5 nlines=66 seed=5 cl> mk1dspec spec6 nlines=90 seed=6 cl> mk1dspec spec7 nlines=85 seed=7 cl> mk2dspec multifiber model=multifiber.dat
In this example artificial one dimensional spectra are generated with mk1dspec .
2. Create an artificial multislit spectrum:
cl> type multislit.dat arc 10 slit 18 0 120 .01 sky 2.5 slit 18 0 140 .01 sky 2.5 slit 18 0 160 .01 sky 2.5 slit 18 0 180 .01 sky 2.5 slit 18 0 200 .01 sky 2.5 slit 18 0 220 .01 spec1 .05 gauss 3 0 140 .01 spec2 .2 gauss 4 0 161 .01 spec3 .1 gauss 3 0 179 .01 spec4 .1 gauss 3 0 200 .01 spec5 .15 gauss 4 0 220 .01 cl> mk1dspec sky peak=1 nl=100 cl> mk2dspec multislit model=multislit.dat nc=400
Note how two spectra are overlaid to provide a sky spectrum with a narrower object spectrum.
3. Create an artificial long slit spectrum:
cl> type longslit.dat sky 22 slit 160 0 220 .01 spec5 .05 gauss 3 0 140 .01 spec1 .05 gauss 3 0 190 .01 spec4 .5 gauss 3 0 220 .01 spec2 2 gauss 40 0 220 .01 spec5 .1 gauss 3 0 240 .01 spec1 .02 gauss 3 0 290 .01 cl> mk2dspec longslit model=longslit.dat nc=400
Note how objects are overlaid on a long slit sky spectrum. The width of the spec2 spectrum is wider simulating a galaxy spectrum.
4. To include noise use the task mknoise :
cl> mk2dspec longslit model=longslit.dat nc=400 cl> mknoise longslit rdnoise=10 gain=2 poisson+ ncos=100
5. Use a real long slit spectrum and add an object with an artificial spectrum:
cl> mk1dspec artspec1d nlines=50 cl> mk2dspec ls005 out=ls005new model=STDIN artspec1d 1 gauss 5 0 125 0 [EOF]