Equipment

dome-at-night

The VAO consists of a f/6.8 Cassegrain reflector with a 0.43m (17 inch) primary mirror and Dall-Kirkham correction lens. The telescope is mounted on an Paramount German equatorial mount. The imaging camera is a SBIG 6303E with a 2K x 3K cooled CCD sensor and a 32' x 21' field of view. 

The available filter set include L, R, G, and B photometric color filters, and a narrowband [5 nm width] at Halpha [656.3nm] filter. There is a also a 2048 -channel fiber-fed spectrometer with a spectral range 350 nm - 750 nm and a resolution 1.2 nm. 

The telescope is located on the roof of the Van Allen Hall [geodetic: 41°41’12" N, 91° 31’55"W, elevation 200 m] on the campus of the University of Iowa in Iowa City. It was installed in August 2014 with funding from the Carver Trust. 

Equipment Summary

Component Make, Model Specification Comments
Optical tube assembly Planewave CDK17 0.43 m f/6.8 Corrected Dall-Kirkham With dew heaters
Mount Bisque Paramount II German Equatorial, max. slew 6 deg/s N.B. Paramount II no longer manufactured)
Focus Controller Planewave EFA The EFA Kit automates focusing , monitors temperature (Delta T Dew Heater), controls fans Controlled by PWI3 software
Focuser Hedrick 1.3 inch travel Controlled by PWI3 software
Dew Heater Planewave Delta-T Primary, secondary mirror heater Controlled by PWI3 software
Camera SBIG STXL 6303E 3072 x 2048, 9 micron pixels, 32'x 21.5' FOV plate scale 14.2 micron/arcsec
Filter wheel SBIG FW8G 8 position 50mm round filters With autoguider camera (KAI 430)
Filters Custom Scientific LRGB, Halpha [5 nm]
Spectrometer Ocean Optics Maya 2000 Pro Fiber-fed, 2048 channels, 50 micron slit, 350-750 nm, 1.2 nm spectral resolution Sample spectrum
Off-axis guider Astrodon MMOAG Feeds spectrometer optical fiber
Dome Astrohaven 18-ft diameter clamshell design Control software written by K. Ivarsen

The major components of the telescope system are shown below.

VAO-telescope-labeled


Cabling guide


VAO cabling guide

Performance specifications

1. Seeing

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. 

seeing-3nights-june

2. Tracking

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. 

tracking-test-30-60-120


3. Sensitivity (Signal-to-noise ratio)

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 a standard Landolt field using L, R, G, and B filters. 

For unfiltered [filter L] images, the SNR as a function of apparent magnitude at three exposure times [10s, 60s, 300s]  is given in the plot below. The observing conditions were nomimal (1.8 arcsec seeing, 60 deg elevation).

snr-vs-magnitude


For individual B, G (=V), and R filter images, the SNR at 60 sec exposure is given below. Note that the SNR scales as inverse square-root time). 

snr-by-filter-60sec



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