GENERIC - A GSMT spectrograph. The user is required to specific wavelength region and resolution and very little else and an unspecific instrument is "created" by means of an IRAF script.
MOMFOS - The PF, optical, fiber-fed spectrograph. Tables are set up which describe the properties of the telescope and this instrument in some detail.
IFU Spec (??) -
HiR Spec (??) -
cl>
>cd spectimedb
>cd GSMT
>ls
> GENERIC/ MOMFOS/
>cd GENERIC
>ls
HgCdTe
extinct_nearir generic_VIS
irsky1_5
bg
generic gsmt_cass
emissivity generic_IR_Cass
irsky
<make working directory and go to it>
>cd <working directory>
>copy spectimedb$GSMT/GENERIC/* .
There are several levels at which the user may use an ITC. We will illustrate with a few example at different levels of complexity starting with the simplest:.
* Maximum spectral resolution
* Maximum slit width (arcsec)
* Spectral resolution
* center wavelength
* slit width (arcsec)
* sampling of monochromatic slit image (pixels)
Setup then "designs" a spectrograph with reasonable collimator, camera, and grating specs.
The throughput of the spectrograph is the product of the throughput of the telescope, spectrograph and detector. At the moment, the files create a combination as follows (the defining file is in parenthese):
telescope (GSMT_spectrograph) : 1.0
spectrograph (specpars PSET): 1.0
HgCdTe detector (HgCdTe): 0.52 - 0.65 as a linear function of wavelength
between 0.8 and 2.6 microns (fairly realistic).
Once setup has been run one simply runs sptime. Default parameters are used for the other parameters of the spectrograph. sptime does not prompt for parameters. Type: lpar sptime to see the parameters you may set.
>sptime sn=20 - gives text output with exposure time required to reach specified S/N ratio. Note there is a parameter which sets the maximum integration time (default 3600 sec). If the requested S/N ratio is not achieve in less than the max, the number of multiple integrations required will also becomputed.
>sptime sn=50 refflux=23 - computes time to reach S/N of 50 for an object of magnitude 23 (whose flux at the reference wavelength corresponds to a body of magnitude 23).
>epar spectime - one can adjust the parameters freely. For example, one will frequently want to change the following parameters:
output - select different output graphs to be displayed (ALL gets everything). extinction - insert the name of different atmospheric extinction tables spectrum - insert the name of an (ascii) table containing the target object spectrum (the default is a blackbody spectrum and the user specifies the magnitude at the central wavelength. Read the example: spectrum_example for format. [This file is not very interesting at the moment. Would Joan or Arjun be interested in providing a useful example? The format is described in the sptime documentation.]
[discuss handling
sky conditions
spectral resolutions]
>lpar specpars (Type: lpar sptime | page
to page through the long list).
or
>epar specpars
The specpars contains most of the spectrograph-defining parameters.
Note, however, that the observing wavelength, diffraction order and slit
width are set in sptime, not in specpars. Also, the blaze wavelength and
the observing wavelength have been set equal because I am assuming that
we are not interested in grating blaze funtion effects in this ITC. I have
set up GENERIC so that the spectrograph is always working in Littrow (angle
between incident and diffracted beams = 0.0). When you change the operating
wavelength the grating is automatically tilted to put the central wavelength
at the center of the detector.