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Overheads

Acquisition overheads associated with setting up on each new target include time for slewing the telescope, configuring the guiding for sources fainter than V~12, and finding and centering the target. These sum to be ~10 minutes for targets with V<12 and 12 minutes for targets with V>12 (Table 1).

Read out overheads are ~200% when using the 256x256 ROI (2.8 arcsecond field of view) and ~320% for the full-frame (512x512 pix, 5.6 arcsecond field of view). Thus a single set of 60ms x 1000 images (1 minute total) will take ~180 seconds to complete using the 256 ROI and ~250 seconds using the full detector (Table 2).

Point source standards (bright stars known to be single) will be observed at each sky location with a minimum of one per hour. These take 15 minutes (including acquisition overheads) and must be included in time requests. Groups of science targets closer than ~ 15 degrees may share point source standards.

Programs wishing to do photometry must include 15 minutes (including acquisition overheads) per night for calibrators (wide binaries).

Filter changes are not supported during the night. If observations using multiple filter pairs are required they must be submitted as separate observations and they will be executed on different nights.


ActionOverhead (min)
Acquisition (V<12) 10
Acquisition (V>12) 12
Point Source Standard15
Photometric Standard15

Table 1. DSSI overheads. Each target must include an acquisition, and a point source standard must be included for every group of science targets within 15 degrees and/or every hour. A photometric standard must be included once/night when doing photometry.



ROI Integration Overhead Total Time
256 x 25660ms x 1000200%180s
512 x 51260ms x 1000320%250s

Table 2. DSSI readout modes and associated overheads.