mk2dspec: Make/add artificial 2D spectra using 1D spectra templates

Package: artdata

Usage

mk2dspec input

Parameters

input
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.

Description

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.
scale
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.

Examples

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]

See also

mk1dspec, mknoise, mkheader