J. D. Cline1, M. W. Castelaz1, A. Castelaz2,3 1PARI 2Summer Research Student at PARI 3Webb Institute

1
Two 26 Meter Radio Telescopes for Long-Term
Monitoring Programs and Surveys
Not-for-profit public foundationwww.pari.edu
J. D. Cline1, M. W. Castelaz1, A.
Castelaz2,31PARI 2Summer Research Student at
PARI 3Webb Institute of Naval Architecture
Introduction
Session 49.04 Tuesday, January 11, 2005. AAS
205th Meeting

• The 26 m radio telescopes
• Installed by NASA for the Gemini and Apollo
  programs.
• In excellent condition because of rigorous and
  consistent periodic maintenance since that time.
• Motion controls have been upgraded for
  astronomical use.
• This poster presents
• The new control system
• The pointing models
• FeedBox infrastructure support
• Current research
• New research initiative

Pisgah Astronomical Research Institute is a
not-for-profit public foundation located on 200
acres in Western North Carolina in the Pisgah
National Forest.
Pointing Models

• Pointing Models Correct for
• Non-perpendicularity of radio axis to minor axis
  
• Non-perpendicularity of minor to major axes
• Elevation misalignment in both axes
• Azimuth misalignment in both axes
• Encoder eccentricity and phase angle
• Tube flexure in both axes

• Procedure for Pointing Model
• Point the telescope at radio point sources
  throughout the sky and record observed Major and
  Minor axis positions.
• Difference Observed and Catalog Positions.
• Plot differences with catalog positions.
• Fit the plots with second order polynomials
  coefficients are pointing model parameters

26 East Antenna
26 West Antenna
EMIN difference between Minor axis observed and
catalog position EMAJ difference between Major
axis observed and catalog position TMIN Minor
Axis Observed Position TMAJ Major Axis Observed
Position
EMAJ vs. TMAJ Curve tube flexure for major
axis 0.036 Slope major axis scale factor
23.76 arcsec
Scale factor and nearly zero flexure for major
axis
Two 26 m radio telescopes on a 300 m nearly
east-west baseline
EMIN vs. TMAJ Curve elevation misalignment in
0.144 Slope azimuth misalignment in -10.08
arcsec
The New Control System
Major axis azimuthal and elevation corrections
are small

• Each telescope follows an alt-alt coordinate
  system.
• The major axis moves the telescope East-West.
• The minor axis moves the telescope
  North-South.
• DFM Engineering telescope control system.
• Installed on 26 East antenna in 2001 and 26
  West antenna in 2002.

Current Research
EMAJ vs. TMIN Curve collimation 0.144 Slope
non- perpendicularity of the axes -2.88

• Pulsars
• Dr. David Moffett, Furman University, PI.
• 327 MHz receiver installed on 26 East antenna.
• Timings of a dozen pulsars.
• Methanol Maser Survey
• Dr. Mel Blake, PARI, PI.
• 6.7 GHz receiver installed on 26 West antenna.
• Unbiased single-dish survey of northern
  hemisphere sky.
• Currently in the process of receiver calibration.

Little correction is needed for collimation and
for non-perpendicularity of the major and minor
axes.
Minor Axis
EMIN vs. TMIN Curve tube flexure for minor axis
-0.360 Slope minor scale factor 15.48 arcsec
Major Axis
Scale factor and correction for flexure of the
minor axis
Using the models, both telescopes now Point to
within 2 arcminutes and Track to better than
within 1 arcminute per hour

• Control of both antenna are linked to a central
  computer which
• Controls the telescopes separately or as a common
  pair.
• Drives a telescope in raster scan mode for
  mapping.
• Allows user-defined catalogs.
• Uses either Equatorial or Galactic coordinates.
• Define track rates.

• Telecontrol on the central computer. Features
  standard telescope control items including
• Equatorial and GalacticCoordinates
• Time
• Telescope Status
• User Catalog
• Weather

New Research Initiative
FeedBox Infrastructure

• Extreme Scattering Events (ESEs) and Intra-Day
  Variables (IDVs). Brian Dennison, UNC-Asheville,
  PI.
• Long-term monitoring of interstellar turbulence
  via its effect on scattering of radio waves over
  a large sample of compact sources.
• Two element interferometer to reduce noise
  confusion and measure point sources.
• Two frequencies, 2.4 GHz and 8.4 GHz.

26 E Feedbox
26 W Feedbox
Feedboxes have AC power, coax, fiber and
appropriate cabling as required by receiver
configuration.
See http//www.pari.edu/ for more information