GBT astronomical commissioning got underway with a regular schedule of activities on January 8. The commissioning included the first attempt at a real pointing observation with the GBT (see accompanying figure). The telescope was scanned in right ascension at a rate of three degrees per minute over a total range of three degrees. The observation was made with prime focus receiver one at a frequency of 800 MHz (the nominal beamwidth of the GBT at 800 MHz is 15 arcminutes). The received signal was transmitted over optical fiber to the electronics room in the Jansky laboratory and recorded with the digital continuum receiver (DCR). The antenna and all NRAO electronics were controlled by version 3.2 of the GBT monitor and control software. The telescope observer's interface, GO, was used to execute the pointing scans, and the operator's interface, CLEO, was used to monitor the observations. The observer was Dana Balser and the telescope operator was Greg Monk for the initial pointing observation.

Because of the continued work on the azimuth track, most of the other data-taking activities have been done with the telescope fixed in position. This has been very productive, and the staff is proceeding with characterizations, tests, and debugging. Some of the other commissioning activities of the week of January 15-21 are listed below.

• IF Stability Tests. This is a program to measure the total power stability of the GBT IF chain. A few problems in the IF router and optical fiber system were found and are being addressed. Some quantitative measures of the IF stability will be available shortly.
• Frequency accuracy tests. In these tests, a precise frequency was injected into the front end receiver and was measured with the Spectral Processor backend. This tests the accuracy of the down-conversion steps and the validity of the LO equations. The results of these tests were very good: a line fell precisely in a 78 Hz frequency channel, and +/- 7 Hz steps to either side produced the expected line shape change.
• Software work. Monitor and Control System version 3.2.0 was released on 19 January. Data from the Digital Continuum Receiver were recorded using the AIPS++ data filler and will be used for AIPS++ development and debugging.
• GBT Spectrometer. Further observations were taken with the GBT Spectrometer and control and interface work on the Spectrometer is continuing.

P. R. Jewell

M. M. McKinnon

22 January 2001