The Elginfield Observatory & Coudé Spectrograph


In 1969 the 1.2 meter telescope was erected by Boller & Chivens at our Elginfield site 25 km north of the University of Western Ontario campus: Longitude = 5h 25m 16s west Latitude = + 43º 12.0'.  Funding for the facility came from the Natural Sciences and Engineering Research Council of Canada and from the province of Ontario.  The project was spearheaded by W.H. Wehlau with assistance from J.M. Moorhead, G.S. Symonds, and me.

The Ritchey-Chretien optics give the telescope a large 1.25-degree field at the Cassegrain focus. The secondary mirror is figured on both sides; f/8.3 for the Cassegrain focus and f/30.5 for the coudé focus. The instrument also has a Nasmyth focus (the Nasmyth mounting ring is the black disk, just barely visible, on top of the polar axle in the picture). The reflecting surface of the primary mirror is bare aluminum, while the secondary and the coudé mirrors have over-coated silver that reach 98% reflectivity across much of the spectrum.

The large coudé spectrograph is located at ground level and occupies the right portion of the building.

The resolving power (λ/Δλ) is about 100000. The higher the resolving power, the more detail one can see in the spectrum.  The more detail we see, the more we learn about the stars.  The visible window (3800 to 10000 Angstroms) is covered in the 7th through the 17th orders of a 316 l/mm grating, but only a few tens of Angstroms is recorded in each exposure. The narrow wavelength range reduces scattered light to a minimum thereby avoiding one of the major faults of spectrographs.

The entrance aperture is a Richardson image slicer that admits 4 x 7 arc seconds of the sky, or really the seeing disk (image) of the star.  This increases the amount of light and shortens the exposure times while maintaining high resolving power.  It looks like this:

Details of how a slicer works can be found in my book Photospheres, Chapter 12.

Inside the coudé spectrograph, with a 669 mm focal-length Schmidt camera on the left and a 2000 mm focal-length camera on the right.  The diffraction grating is hidden behind the short camera and the collimator is out of the field of view to the right (From Photospheres, Figure 12.1.)

A Reticon detector with 1872 diodes is mounted on the short camera and a CCD with 4096 pixels in the direction of dispersion is mounted on the long camera.

Here us a sample of the data:

The red line is the α Hya spectrum (a K3 II-III giant star); the thin blue line is the solar spectrum (a G2 V dwarf star).

The Elginfield Observatory was closed at the end of 2010.

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