NAME

simprism -- Simulate FOC objective prism spectra and images.

USAGE

simprism spectrum output obsmode

DESCRIPTION

The simprism task will simulate an FOC objective prism spectrum by applying a dispersion function to an input spectrum and converting the result to counts as a function of pixel. You can specify the desired observation mode, i.e., the filter set and prism to use, as well as simulation parameters such as wavelength range, exposure time and offset from the undispersed position. The dispersed spectrum can be convolved with a user specified PSF. The result is a two-dimensional image, simulating an FOC prism image.

The main routine runs as a script. Tasks in the images and fourier packages are used, so those packages must be loaded before using this task.

PARAMETERS

spectrum = "crcalspec$hz4_001.tab" [string]

File name of the spectrum to be simulated. The program expects an STSDAS table with column names "WAVELENGTH" and "FLUX". Currently the wavelength must be in Angstroms; the flux can be in any of the following units:

        FNU             erg s^-1 cm^-2 Hz^-1
        FLAM            erg s^-1 cm^-2 A^-1
        PHOTONU         photons s^-1 cm^-2 Hz^-1
        PHOTLAM         photons s^-1 cm^-2 A^-1
        COUNTS          photons s^-1 cm^-2 dlambda^-1
        ABMAG           -2.5 log_10 (FNU) - 48.60
        STMAG           -2.5 log_10 (FLAM) - 21.10
        VEGAMAG         -2.5 log_10 (F/F_vega)
	OBMAG           -2.5 log_10 (COUNTS)
        JY              10^26 erg s^-1 cm^-2 Hz^-1 (ABMAG=8.9)
        MJY             10^23 erg s^-1 cm^-2 Hz^-1 (ABMAG=16.4)

output = "" [string]

The name of the output image.

obsmode = "foc,f/96,f140m,prism1" [string]

Full specification of the observing mode of the instrument. This parameter should contain "foc" if an FOC observation is being simulated, and the relay should be "f/96" or "f/48". Filters can be listed as well as the prism. For both relays, prism1 is far UV, and prism2 is near UV. Keywords in the list can be separated by either commas or spaces.

If you specify an invalid obsmode, an error message will be displayed that indicates at what point in the instrument graph table the problem occurred. If problems occur, you can use the task grafpath in the STSDAS synphot package to find a valid obsmode.

(psffile = "") [string]

The name of a 2-D image containing a PSF. If the name is not null, the dispersed spectrum is convolved with the PSF to produce the output image.

(npix= 256) [int, min=1, max=INDEF]

Width of image to create. Normally simprism creates a 2-D image of size npix1 by npix2.

If npix1 = 1, psffile = "", and angle = 0., the output image will be 1-D with length npix2. It would be more user-friendly if you could use npix1 to specify the length, with npix2 = 1, but this is NOT possible because simprism is a cl script that uses a 2-D temporary image with the dispersion in the Y direction.

(npix= 1024) [int, min=1, max=INDEF]

Height of image to create.

(wstart = 1100.) [real]

Starting wavelength in Angstroms of simulated spectrum. The parameter can have values between 1100 Angstroms and 7000 Angstroms.

(wstop = 7000.) [real]

Ending wavelength in Angstroms of simulated spectrum. Valid range is 1100 to 7000 Angstroms.

(dw = 10.) [real]

Wavelength spacing used to create a temporary 1-D dispersed spectrum which is resampled onto pixels for the output.

(texp = 900.) [real]

Exposure time in seconds. The spectrum is calculated in counts/second and multiplied by the exposure time.

(yzero = 100.) [real]

Y pixel coordinate of undispersed image. This is where the object would have been if the prism were not in place. This value can be negative, i.e. off the image.

(angle = 8.5) [real]

The angle in degrees from vertical, measured clockwise, at which to place the spectrum in the image prior to convolution.

(graphtab = "crcomp$hstgraph_*") [string]

Name of the graph table to use.

(comptab = "crcomp$hstcomp_*") [string]

Name of the components table to use.

(verbose = yes) [boolean]

List the steps being performed?

(dispfiles = "") [pset]

Pset for the name of the dispersion file to use when dispersing the reference spectrum. The dispersion file is an ASCII file containing wavelength (in Angstroms) as its first column and pixel offset as its second column. The pixel offset is from the undispersed position yzero, and it is measured positive toward decreasing image line numbers. By default the relay and prism names are obtained from the obsmode, and the correct dispersion file is automatically selected. If you have created your own dispersion file, however, you would specify its value in the dispfiles pset.

(area = 45238.93416) [real]

The area in square centimeters of the telescope aperture. The default value is for the HST.

EXAMPLES

1. Simulate a prism spectrum of the star "hz4" using a reference spectrum located in "crcalspec", creating the output spectrum "hz4.hhh". It will use the f/96 relay of the FOC with the f140m filter and the far-UV prism. The spectrum will be convolved with "f96_f140m_psf.hhh" as a PSF.

fo> simprism crcalspec$hz4_001.tab hz4.hhh "foc,f/96,f140m,prism1"
                 psf=f96_f140m_psf.hhh

BUGS

REFERENCES

This task was written by David Bazell.

SEE ALSO

objcalib

Type "help focprism opt=sys" for a higher-level description of the focprism package.