[Virginia Tech Department of

The Virginia Tech Spectral-Line Survey

Spectral Line Imaging Camera (SLIC)

This system is used to image faint Galactic H-alpha emission over wide fields. It consists of a cryogenically-cooled Tektronix 512x512 CCD with 27 micron pixels in the focal plane of a fast (f/1.2) Noct-Nikkor lens. The pixel size is 1.6 arcminutes. A filter wheel ahead of the lens enables imaging with a narrow bandpass H-alpha interference filter (1.75 nm bandpass), various wider continuum filters, and a [SII] doublet filter (6717, 6731 angstroms). A rotatable polarizer has been attached ahead of the filter wheel, on occasion, to explore the polarization of the H-alpha emission. The CCD package, including dewar, and control and image acquisition systems, is manufactured by Photometrics Ltd. We use metal oxide filters with very small thermal shift, produced by Barr Associates of Westford, MA.

The camera is optimized for brightness sensitivity. The system can detect emission of about 1 rayleigh for line-of-sight hydrogen velocities between plus and minus 100 km/s (1 rayleigh = 1 R = 10to the sixth power/4pi photons per square cm per second per steradian). A brightness of 1 rayleigh corresponds to an emission measure of about 2 pc per cmto the sixth power.

The imaging system is equatorially mounted. Tracking to arcsecond precision is assured through the use of a separate Santa Barbara Instruments Group ST-4 auto-tracking CCD attached to a five-inch Celestron telescope mounted in tandem with the camera. The system is mounted on an enclosed concrete pier at the Martin Observatory on the grounds of the Miles C. Horton, Sr. Research Center, located in an isolated region of southwestern Virginia.

[Picture of front of SLIC]

This image shows the front of SLIC. On the left is a filter wheel, through which light passes before entering the f/1.2 58mm lens and arriving at the 512x512 CCD. On the right is mounted a Celestron-5 telescope which utilizes the ST-4 auto-tracking CCD to maintain accurate pointing during an integration. The instrument cradle is mounted on a Celestron CG-11 equatorial head produced by Losmandy. The mount is bolted to a concrete pier.

[Picture of back of SLIC]
This image shows another view of SLIC's instrument cradle showing the C5 tracking telescope (foreground) and the Photometrics CCD dewar (background).

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