In 1998, the National Science Foundation's Major Research Instrumentation
program granted Yale Southern Observatory $235,000 to develop a CCD detector
system to replace its obsolete photographic plate system. The CCD system
consists of four cameras, one each for the blue- and yellow-optimized 51-cm
aperture lenses and two focus-sensor cameras, again, one for each lens.
The two telescopes are mounted within one tube and the former photographic
plate holders have been replaced with fixtures to hold the CCD cameras.
The CCD camera for the visual telescope is a
camera with a
Chiller cooled (-85 degrees C) 4k x 4k Loral chip with 15 µm
pixels, which translates into a pixel size of 0.83" and a total area of
0.94 x 0.94 degrees or 0.884 square degrees for the plate scale of 55.1"/mm.
The pixel size of 0.83" is well matched to our site where the seeing conditions
usually yield an image FWHM of 2" to 3", corresponding to 3-4 pixels per
FWHM. This is excellent sampling for the derivation of astrometric image
centers, based on our extensive experience with digital image centering.
The unthinned and front-illuminated Loral chip has ~25% quantum efficiency
at 535.0 nm, the lens' minimum focus, and it is fitted with a fixed 100
mm x 100 mm Custom Scientific
V-band filter (Bessell, 1990). Among the figures below is a test exposure
V-band image of Eta Car taken the night after the camera was installed.
This 4k x 4k image covers nearly one square degree.
Pix.Vis. Control Box
The Blue telescope is fitted with an
AP-8 camera that utilizes a thermoelectrically-cooled (-40 degrees C) and
back-illuminated 1k x 1k Site chip with 24 µm pixels (1.32") fitted
with a fixed Custom Scientific
50 mm x 50 mm B-band filter (Bessell, 1990). The blue camera covers a field
of 22.57' x 22.57', or 0.141 square degrees, centered on the field of the
larger PixelVision yellow camera. With a quantum efficiency of approximately
70% at the blue lens' minimum focus of 435.0 nm, we will be able to take
either several short exposures or one deeper exposure during a simultaneous
observation with the yellow camera. Depending on the program, we will take
several short exposures for optimum photometric calibration, or a single
long exposure to reach fainter objects.
Apogee AP-8 Camera
Two SBIG ST5c
CCD cameras are used as focus sensors, one for each telescope. The focus
sensors are based on a new design, which incorporates a Hartmann mask in
the astrograph's converging f/7.3 beam. Additional optics simultaneously
image both the in- and out-of-focus Hartmann images on the same frame without
the need to refocus the telescope to determine the optimum focus. A simple
Hartmann-mask algorithm analyzes the observed relative image positions,
determines the optimum focus and reports that value to the observer who
decides whether or not it is necessary to refocus either the blue or yellow
As diagnostic aids for the interpretation of the observations, we have installed a NovaLynx weather station with temperatature, pressure, relative humidity, wind speed and direction computer inputs as well as additional precision temperature sensors at the astrograph lenses, cameras and external telescope points. These data are all written into the fits headers of each exposure.
The four CCD cameras, the telescope, weather station and temperature sensors are all controlled by a trio of Linux computers and an operating software system written by R. Meyer.
Link to: Astrograph page; Astrometry Research page; Astro. Dept. Home page