T3 0.40 meter APT

Observing Program

The T3 0.40m APT operated from November 1987 until July 1996 at the Fairborn Observatory site on Mt. Hopkins. The telescope was relocated during the summer of 1996 to Fairborn's new site at 5500 ft in the Patagonia mountains near Washington Camp, Arizona. Operation of the 0.40m APT has been funded by NASA, NSF, and Tennessee State University.

The 0.40m APT is primarily dedicated to long-term photometric monitoring of chromospherically active single and binary stars. Rapid rotation and deep convection in these stars combine to produce an enhanced dynamo and strong magnetic activity that manifests itself in the light curves of these stars. As a chromospherically active star rotates, large regions of dark starspots are carried into and out of view, resulting in rotational modulation of the star's light by up to 0.5 mag. The growth and decay of these spot regions as well as their redistribution by differential rotation are inferred from the changing shapes and amplitudes of the light curves. Long-term, perhaps cyclic, variations in the total starspot area result in slow variations in the star's mean light. The 0.40m APT is monitoring approximately 100 of these chromospherically active stars to define their long-term behavior. The telescope also monitors a couple dozen additional variable stars of various types each year, especially gamma Doradus candidate stars.


  • Pyrex 16-inch Cassegrain optics from Star Instruments
  • Primary mirror focal ratio is f/3, edge thickness is 1.9 inches
  • Secondary mirror diameter is 4.5 inches, maximum thickness 0.75 inches
  • Effective focal ratio is f/11.6
  • Equatorial fork mount and mechanical tube assembly from DFM Engineering
  • Micro-stepping Berg belt to disk & roller drives on both axes
  • High-precision photometer from Fairborn Observatory
  • Johnson UBV filters
  • Neutral density filters with attenuation of approximately 1.25, 2.5, 3.75, and 5.0 mag.
  • Selectable diaphragm wheel with diameters of 24, 40, 55, 75, & 115 arcseconds
  • EMI 9924B photomultiplier detector running at 1000V and +4 degrees C
  • Photomultiplier, voltage divider, preamp, and filters in sealed environmentally controlled chamber
  • Observes stars between V mag. 3.0 and 11.0 and between declination -35 and +76 degrees
  • ATIS93 automatic control system by Fairborn Observatory
  • External precision of a single observation is typically 0.003--0.004 mag.