IRES Echelle spectrometer 

The IRES instrument (Intermediate Resolution Echelle Spectrometer) is a fiber-fed echelle spectrometer with a resolution (R ~ 7,000, Δλ~ 0.5A) over the range 400 nm — 700 nm. It is currently (Fall 2017) in beta-test mode. It is fully functional, but the robotic operation and calibration software is under active development.

Equipment Description 

1. Echelle optical design

The optical design is a ‘gamma’ configuration as shown below (Update: The current design has two 60-degree prisms for increased dispersion).

A photo of the system is shown below (correction June 2017: The camera is currently a FLI Proline 9000).

2. Spectrometer computer control

The echelle spectrometer is controlled by a Windows PC labeled ESC in the illustration below. It runs the echelle imaging camera (currently a FLI Proline 9000), the flip mirror, and the calibration lamps (halogen, Ne-Ar laser, RELCO starter lamp). The telescope control computer (labeled TCC) communicates with the ESC using a network socket. Once an acquisition command is sent, the ESC initiates a series of three images: a flat field, a spectral line calibration image, and a science image. These are transferred to the TCC which runs a scheduling daemon that archives  all images and transfers copies to the file server at the University of Iowa every few minutes. 

3. Pickoff mirror assembly

The pickoff mirror assembly contains  a 90/10 optical cube beam splitter. There is a small camera that images the target field. The field is plated-solved using WCS and the target is then centered precisely on the fiber. The assembly was 3-d printed.

4. Sample spectra

A sample 10s raw echellogram of the star Aldebaran (K5III), which has 100’s of lines, is shown below.


A line plot of the sodium 5889/5895 doublet, taken in the Aldebaran echellogram above,, illustrates the spectral resolution, which is ~0.5 Angstrom (R ~ 7,000).

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