AAS 205th Meeting, 9-13 January 2005
Session 48 Visible-Light Telescopes, Instruments, and Technology
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[48.12] An Economical High Resolution Spectrograph Optimized for Radial Velocity Measurements at 5000 Angstroms.

D. Lyons, D. N. Arion (Carthage College)

A high resolution spectrometer was built and calibrated on an optical bench. The target resolution of the instrument was designed to allow accurate measurement of the Doppler shifts of the 5007 Angstrom O III line in planetary nebulae due to their expansion. The optical components of the instrument include two Meade ETX 90 Maksutov-Cassegrain telescopes, a Richardson Grating Laboratory reflection diffraction grating, nickel-plated glass slides used as slit apertures, and an SBIG ST-8E CCD imaging camera. The mounts for each of the optical components were machined out of aluminum bar and plate stock. The instrument was calibrated using He and Hg gas discharge tubes generating spectra of known wavelengths. A total of four sets of lines were imaged and analyzed to calibrate the instrument. The line shapes in the images were manually fit with functions approximating the pressure and Doppler broadening of the lines, as expected for the behavior of the lines emitted by the spectrum tubes. These fits were used to identify the line peak positions, which were then compared to standard line wavelengths to determine the instrument calibration. The He I line at 5015.678 Angstrom line was carefully analyzed to determine the system wavelength uncertainty, which determines the smallest resolvable difference in wavelength that the instrument can determine. The resulting operating resolution at 5007 Angstroms was found to be 206474, making the instrument capable of resolving Doppler shifts at 5007 Angstroms corresponding to +/- 1.4 kilometers per second. The program was thus successful in developing an instrument suitable for a variety of relatively low velocity Doppler measurements, especially those associated with planetary nebula expansions. Future work entails developing a mounting system to rigidly hold the instrument on a suitable telescope, while maintaining the necessary precision to retain the instrumental resolution.

This work was supported in part by Carthage College through the Summer Undergraduate Research Program, and by a Small Research Grant of the American Astronomical Society.

The author(s) of this abstract have provided an email address for comments about the abstract: darion@carthage.edu

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