The Gemini telescope consists of a f/6.8 Cassegrain reflector with a 0.51m (20") primary mirror and Dall-Kirkham correction lens. The telescope is mounted on an equatorial fork mount with high-resolution encoders that provide accurate tracking, even with long (several minute) exposures. The imaging camera is a cooled, back-illuminated 2K x 2K CCD sensor with a 28' x 28' field of view.
The available filter set include Astrodon Tru-color R, G, and B color filters, Sloan g’ and r’ filters, and narrowband [5 nm width] filters centered at Hα [656.3nm], OIII [500.7 nm] , and SII [672 nm]. There are also two spectrometer systems: A low-resolution grism spectral range 350 nm - 750 nm and a resolution 1.0 nm, and a medium resolution echelle with R~7,000 (resolution 0.05 nm).
The telescope is located the Winer Observatory in southern Arizona [31.6656° N, 110.6018° W, elevation 1500 m] and is operated robotically using a high-speed Internet connection. It was installed in May 2015 with funding from the Carver Trust. Gemini replaces the venerable Rigel telescope, a 37 cm diameter robotic telescope operated from May 2002 - May 2015.
The major components of the telescope system are shown below.
During several days of tests in June 2015, median seeing varied from 1.5 arc second to 1.8 arc seconds as shown below. The tests were made by taking images of the north celestial pole (constant airmass) and repeatedly performing a focus sequence using the Planewave PWI3 program. The observed FWHM angular sizes were corrected to one airmass.
Telescope tracking was tested by taking a series of images with increasing exposure times, from 30 sec to 960 sec in multiples of two. The resulting images, shown below, show subimages of the original images with exposure time, FWHM star sizes, and roundness in the insets. The tracking is excellent, even for 480 sec exposures. There is a significant increase in FWHM and ellipticity at 960 sec, probably as a result of a non-ideal mount model.
3. Sensitivity (Signal-to-noise ratio) and zero-point magnitudes
To test the signal-to-noise ration (SNR) of an unresolved target (e.g., a star) as a function of magnitude, filter, and exposure time, we observed star fields that contained SDSS survey stars with very accurate magnitudes. Photometry of the Sloan g' and r’ images were done using Sextractor, and the resulting star lists were compared with star positions and magnitudes in the SDSS catalog. The resulting zero-point magnitudes were determined by a best-fit least-squares fit.
Sloa g’ filter: Zero-point magnitude 21.1
Sloan r’ filter: Zero-point magnitude 21.1