SPARO: Recent Progress

On Oct. 12th, 1999, SPARO was installed on Viper by Austral Winter 1999 winter-overs Greg Griffin and John Davis. The installation had been planned for July, but had to be postponed due a failure of Viper's azimuth motor that rendered the telescope inoperable for several months. During the remaining few weeks of the winter season, successful cryogenic operation of SPARO was demonstrated: Helium-4 and Helium-3 hold times were five days and four days, respectively. Other system tests were successfully carried out, including measurements of amplifier noise due to the JFET amplifiers in the SPARO cryostat. Due to a computer malfunction and other minor setbacks, no observations were possible before station opening.

Novak, Chuss, and Matt Newcomb of Carnegie-Mellon arrived at Pole on Nov. 3, 1999. After some days of debugging computer problems, "first-light at Pole" was obtained on Nov. 11, by observing the Moon. SPARO was operated through the third week of November. Tests that were carried out during this SPARO run include

(1) Pointing: Both the Moon and the bright Galactic cloud RCW-57 were found to be within a few tenths of a degree of the nomimal Viper pointing.
(2) Beam-size: The beam's FWHM was found to be approximately 4-6 arcminutes, close to the nominal size of 4 arcminutes.
(3) Signal strength: Observations of the Moon indicate that the coupling of SPARO's beam to the sky is reasonably high - the Moon signal was approximately equal to the expected value. Further analysis is underway and should produce an accurate measurement of the optical efficiency of the instrument-plus-telescope system.
(4) Synchronous offsets: These were found to be extremely small, as expected for this under-illuminated optical design.
(5) Noise: the mechanical pump that sits out on the telescope and pumps on SPARO's 1.5 K stage was found to be causing occasional microphonics noise. To eliminate this problem, the pump will be moved off the telescope for winter 2000 observations. We will pump through the new, more rugged Helium pressure hoses that are currently being installed in Viper's cable wrap for use with the Corona instrument. Aside from these occasional microphonics due to the pump, we were at all times limited by fundamental bolometer and photon noise, as expected.
(6) System operation: Data acquistion and analysis operations were successfully and repeatedly tested for mapping, photometric, and polarimetric modes.

We are now preparing for SPARO's 2000 winter-over by purchasing spares for critical parts, and by refining SPARO's documentation and observing plan. Renbarger is analysing the test results from Nov. 1999. Chuss and Novak will be returning to Pole in late January to cool SPARO and reinstall it onto the telescope. Greg Griffin of Carnegie-Mellon University and Dave Pernic of the University of Chicago's Yerkes Observatory will operate SPARO during Winter 2000. Observations are scheduled for February through May.