Astro 920 / Fixing the WIYN Bench Spectrograph

Topics covered in this course

• Spectral Resolution:   resolution loss with collimator f.l. decrease: effects of of undersampling; study via simulatioins trades in resolution and througnbput between smaller fibers and shorter collimator f.l.

  Status: Soeren Meibom in preliminary phase of acquiring high-resolution solar spectrum. Here are some data files for a high-resolution solar spectrum:

  • ASCII data file
  • FITS image
  • postscript plot of subregion of spectrum

• Performance Simulator:   GUI interface (java) to simulate
  • basic setups as function of central wave and resolution, allowing camera-collimator angle to be a free parameter [done]
  • vignetting from collimator, grating and camera as function of alpha and beta
  • grating efficiency as function of off-littrow condition

  Status: Steve Crawford has alpha version of most capabilties. Starting to add in physical optical layout to model vignetting; has collimator, grating, camera objective, and foot done; needs to add vignetting from toes, foot mount (at current pupil), and camera objective as it obscures the inintial collimated beam (collimator-to-grating) as a function of camera-collimator angle and camera-grating distance. Has added good analytic approximattion to real SparsePak input beam profile next; needs to add the same for the other cables. Added calculation of vignetting as off-blaze efficiency at fixed central wavelength as a function of camera-collimator angle; maybe add off-axis case later. Needs to add absolute values for filter throughputs and and grating peak efficiencies. Needs more theory or data to handle off-littrow condition. Needs hooks for MAB to write comments/notes. Consider option for adding field lens.

  1. Web version: www.astro.wisc.edu/~crawford/Spectrograph/intro.html, with the associated documentation pages.
  2. or: /d/www/crawford/Spectrograph/, % java BenchSetupApp, and
  /d/tatum/crawford/programs/Java/Spectrograph/docs/spec.tex 3. Development version: /d/tatum/crawford/programs/Java/Spectrograph/, % java BenchSetupApp
  4. Fixed "alpha.1 version" of source-code for down-loading: /d/tatum/crawford/programs/Java/Spectrograph/version0.5

• Total system throughput:
  • calibration with existing standard-star data
  • design and conduct new calibration measurements on extended sources

  Status: Kyle Westfall has preliminary zeropoint for echelle H-alpha region based on one measurement; lamp color-terms are found to be negligible; needs to finalize numbers for atmospheric losses, spectral aperture extraction losses and focal plane losses; needs to perform measurment for remaining data for which focal plane losses will require modeling. Separate effort by Crawford to model vignetting to help understand throughput budget.

• Optimize X15 filter   for xcor studies of MgI and Fe region near 5200 A.

  Status: Not started (Westfall?); some stellar data in hand; may be able to use solar spectrum from Meibom.

• Scattered light:   understand cause of scattered light at 8600 A using echelle and X23 filter: grating, filter, or camera coatings? Design and conduct new experiment.

  Status: Analysis completed in MgI and CaII regions by MAB; Ha echelle data just acquired. New tests drafted.

• WIYN simulator:   a hardware project to design, build, test WIYN simulator.

  Status: Initial design only. Some relevant numbers are listed here.

• On-site Testing:   at-telescope tests of current optical design.

  Status: Plannng not yet started

From WIYN Facts page, the following relevant numbers are derived:

The primary has a 17.1% central obstruction from the baffle for the tertiary. This comes from the ratio of diameters (squared) of the primary (D_P = 3498.85 mm) and baffle (D_B = 1446.2 mm). The baffle diameter is larger than the secondary diameter (D_S = 1200 mm), and so the baffle is the effective limit for the central stop for an on-axis source.

For the f/6.3 beam at the WIYN, MOS, and folded-Cass ports, 17.1% of a uniform beam corresponds to f/15.2. Hence a beam which simulates the true beam for these ports should consist of a uniformly filled beam (a cone with uniform cross-sectional surface-brightness) for apex angles between 7.5 deg (f/15.2) and 17.6 deg (f/6.3).