System Sensitivity and Observing Strategies - Abu

Currently, Abu is background-limited by instrumental effects rather than by the atmosphere/telescope. Based on observations of 30 Dor, sensitivity for a 4 hour on target integration time at L band is conservatively estimated at L = 14 for S/N = 5.

For planning purposes, one can assume 1/3 time off target on sky and 2/3 time on target during a typical observing sequence.

Prior to the coming observing season, modifications to the system are planned which should reduce the background dramatically. We anticipate a corresponding improvement in sensitivity of better than 0.8 mag. Since we will not know the actual background until after the observing season is underway, proposers should emphasise the limiting magnitudes which are a) essential, and b) desired, for the success of their program. The queue observing team may request additional information for accepted programs in order to make best use of the available telescope time.

The night sky is remarkably stable: L observations of two and three minutes were routinely obtained during the first season, limited more by the inability of the telescope to track for longer periods. In practice, several schemes were tried, using different integration times and numbers of coadds to reach these exposure times (e.g. 9s times 20 coadds; 1s times 145 coadds; and so on). The optimal combination is still being defined. The current instrument control software performs co-adding in situ, so that such combinations do not incur excessive readout-time overhead. The guider should be functional for the second season, and L integrations of five, or even as much as fifteen, minutes may be possible. Extremely long total exposure times, by "relentless observing", are the strength of this system.

Ian Gatley and his team at the Rochester Institute of Technology will lead the observing program, including scheduling, communications with the queue observing team, the data pipeline, and the transfer of data to investigators. The pipeline image processing, based on software from Mike Merrill (NOAO), means that proposers can receive their final data, such as these, without needing to pay attention to the details, if they so wish. Data are returned from the South Pole over a NASA-maintained satellite link which runs for a few hours a day (when the satellite is visible from the pole), allowing distribution of results with almost the same timeliness as queue and service observing programs elsewhere. All South Pole experimenters are very grateful to NASA networking and the South Pole TDRS Relay team for this service.

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Updated: 26Oct98