Guide to CISCO imaging exposure times
Background-limited operation
The following table lists the times for background-limited performance (BLIP) to be achieved with CISCO (OHS is not an imaging instrument), i.e. for the sky counts to equal three times the square of the read noise (16 e- rms). Numbers in italics are preliminary.
| Filter | Background | Min BLIP time (s) |
|
|---|---|---|---|
| (mag/arcsec2) | (e-/s/pixel) | ||
| z | 17.3 | 60 | 10 |
| J | 15.6 | 260 | 3 |
| H | 13.6 | 1800 | -(1) |
| K' | 13.1 | 2000 | -(1) |
| K | 12.7 | 2500 | -(1) |
Saturation magnitudes
This table gives the saturation magnitudes for different exposure times in good seeing (~0.3'', when about 12% of the total flux from an unresolved source falls in the peak pixel). For the narrow-band filters, saturation occurs approximately 2.5 mag brighter.
| Filter | Saturation magnitude | Max exposure time (s) |
||||
|---|---|---|---|---|---|---|
| 1.5 s | 5 s | 10 s | 30 s | 60 s | ||
| z | 12.7 | 14.1 | 14.9 | 16.0 | 16.9 | 1200 |
| J | 12.1 | 13.5 | 14.5 | 15.8 | 16.7 | 230 |
| H | 12.5 | 13.9 | 14.8 | 17.2 | - | 45 |
| K' | 12.1 | 13.5 | 14.5 | 17.2 | - | 30 |
| K | 12.0 | 13.5 | 14.5 | - | - | 20 |
Overhead
Since CISCO imaging is done without the auto guiding, there is no overhead
due to setting the auto guider.
The overhead due to resetting the detector, saving the FITS file and dithering
is from 27% (40 s exposure typically used for J-band observations)
to 40% (20 s exposure for H, and K-band ).
Added 2003 Apr. 10