THE MARS MANUAL
(The Multi-Aperture Red Spectometer)
Kitt Peak National Observatory
National Optical Astronomy Observatory
Staff Contacts: Daryl Willmarth (email@example.com) and Arjun Dey (dey@ noao.edu)
- Programs that need low-to-moderate dispersion spectra in the red
- Programs requiring high throughput
- Programs requiring a high density of multislits
- Programs that need nod-n-shuffle observing mode
Click here for the MARS optical diagram (Figure 1).
Multi-slit masks are individual masks fabricated for each target field. They require substantial effort to prepare, since good astrometric prositions are required for each object. To maximize the number of objects that can be observed without overlapping their spectra, an ancient UNIX-Fortran77 program, MSLIT, designs the mask pattern*. In this observing mode, one can typically observe up to 30 objects simultaneously. Refer to the manual "Multi-Slits at Kitt Peak" which is available from the KPNO documents website for details on design and construction. Please note that the multi-slit design software is being significantly updated with an anticipated release date of summer 2002
* Soon to be upgraded.
Data measured through a XX -arcsec slit, with YY seeing,
etc...... Spline fit.
Any of these modes can optionally use the "nod-and-shuffle" technique for accurate sky-subtraction. See the section below for more details on using this technique.
|Mask #||Width- Arcsecs||Width-mm||Length-arcmins||Length-mm|
--- SETUP MASKS --- #19 Lynds Test line of holes, 32 holes, 380 micron diam. #20 Knife-edge Hole 1.95mm diameter #21 Knife-edge Hole 2.05mm diameter --- TEST MASKS --- #22 Test Centroid 6 holes #23 Garth No.I alternating double hole pattern #24 Garth No.II another double hole pattern #25 Fowler Test X-pattern centered at 45 deg., 200 micron holes --- MISCELLANEOUS MASKS --- #26 1 hole, 2.5" diam. centered #27 2 holes, 2.5" diam. (star/sky) #28 2.5" slit with 2" center occultation #29 2.5" slit with 4" center occultati
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Atmospheric Dispersion Compensation - The ADC or Risley PrismsA set of Risley Prisms is available for atmospheric dispersion correction at the RC focus of the 4-meter telescope. This ADC covers a field slightly larger than MARS field (~5 arcminutes) and is automatically controlled by the telescope control system. One inconvenience caused by the Risleys is difficulty of locating guide stars. The Telescope Operator must be aware that suitable guide stars must fall inside the annular area just outside the instrument FOV but inside the field of the prisms. Choosing a guide star in or too close to the MARS FOV will result in vignetting the instrument field. The ADC is used at the option of the observer and may not be suitable for all types of observations.
Click here for a plot of the ADC throughput in the 5500-10,000A spectral region.
The Collimator LensThe collimator optics consist of a re-imaging field lens, located just beneath the aperture plate near the focal plane of the telescope, and a collimating doublet. The field lens is a simple plano-convex lens that images the pupil of the telescope onto the collimating doublet and also reduces vignetting when the full 50mm spectrograph aperture is used.The plano-side of the lens goes upward (skyward).
The doublet collimating lens is a classical crown-flint cemented lens with the achromatic range centered at a wavelength of 0.63 microns. The clear aperture of the lens is 4.2 inches, and the effective focal length is 31.5inches. The flint element faces the incoming beam. Both the field lens and collimator are anti-reflection coated. The flint element is not a good UV transmitter and contributes to the poor throughput below 4000A.
The Grism Dispersive ElementThe dispersive element consists of a transmission grating replicated on the hypotenuse exit face of a right angle prism. The grism follows the collimator and was chosen for this application because of its high efficiency. The purpose of the grism is to obtain dispersion without deviation at the center of the spectral range. The instrument performs as a direct-vision spectrograph with the ``zero" order of the grism falling outside the field of view of the detector. The grism is fixed and there is no provision for adjusting the central wavelength by tilting the assembly. Adjustments of a few hundred Angstroms are possible by using offset slits as described in an earlier section of this manual.
This instrument uses two types of grisms, a "conventional" grism, shown below, and a new volume-phase holographic grism (see NOAO Newsletter, 67, Sept. 2001, p 32). The new "VPH" grism employs a sinusodial varying index of refraction medium produced by holographic interference as the disperser.
The undeviated central wavelength (UDCW) depends upon the wedge-angle and refractive index of the prism, and the particular ruling used. When the vertex of the prism equals the groove angle of the rulings, maximum energy throughput is obtained.
Grism Number 4950-400 5970-300 6560-150 8050-450** 9700-300 9700-300 7300-300 Old Grism Number 650 770 810 none 780-1 780-1 780-2 g/mm 400 300 150 450 300 300 300 Order 1 1 1 1 1 2 1 UDCW* - Angstroms 4950 5970 6360 8050 9700 4850 7300 Resolution - Angstroms@ 12 15 30 8 15 8 15 Dispersion - A/Pixel 3.2 4.3 9.1 2.0 4.3 2.2 4.3 Spectral Range - Angstroms ~4000-
* Undeviated central wavelength
@ With a 2.5" aperture
** New Volume-Phase Holographic Grism, see NOAO Newsletter #67, September 2001, p. 32. Has a built-in OG-550 filter.
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The Upper Filter BoltThe upper filter bolt is normally reserved for up to four order separation filters. These filters are 3-1/2 inches square and are NOT interchangeable with the lower filter bolt.
Order Separation Filter List
ORDER SEPARATION FILTERS FOR MARS/RCSP
Filter Transmission Curves
Some important parameters of the system are:
Click here for a system DQE curve.
Click here for measured DQE values
Click here for a link to the LBNL
|observe||Take an object, zero, dark, flat, or comp image|
|more <n>||Repeat the last 'observe' n times|
|flpr||Flush the process after a control-c abort|
|zero||Take a series of zero or bias images|
|object||Take a series of object images|
|flat||Take a series of flat images|
|comp||Take a series of comparison spectra images|
|dark||Take a series of darks|
|test||Take a test image and overwrite previous test image|
|detpars||Set the detector parameters for CCD format and gain|
|instrpars||Set the instrument parameters & header keywords,
such as grism, filters and DISPAXIS=1
|obspars||Set observing paramenter; image root name and sequence number|
|ccdinfo||Display current CCD format, gain, binning, temperatures etc.|
|wfits||Write FITS format data frames to tape|
|tele||Test TCS link for transmission of telescope header data|