NaCo
Cube Mode
The Cube Mode is a variant of the of the burst mode already offered with VISIR and ISAAC.
In this mode, a data-cube with each single DIT frame is saved. This mode is particularly
interesting for lucky-imaging type of observations, where one wants to select the best frames
out of a set before co-adding them. The mode is not suited for time resolved applications
since we have no way to time-stamp each single DIT frame and we occasionally lose frames.
There are stringent limitations to the use of this mode, in particular it will only be offered in p82 in combination with basic imaging and NGS (i.e. no LGS observations).
Users will be allowed to specify different window formats (e.g. 64x64 up to full frame - 1024x1024) with increasing minimum DIT, once the window size gets bigger. The maximum number of DIT frames that can be saved in a cube is limited by the need to have file sizes smaller than 512 Mb.
Preliminary tests have shown that in most cases the system is able to deliver 100% of the DIT frames, even when one selects the minimum DIT. This is yet not the case for the full frame option with DIT=0.35, which occasionally drops 5-10 frames/100. 0.5 sec DIT is a safe choice. The number of parameters involved is large and till we can improve the performance of this mode, the feasibility of cube-mode observations will be done on a case by case basis. Given the great interest shown for this mode by the community, we will offer it despite it not being fully characterized. The following table lists minimum DIT and maximum NDIT (number of planes in the cube) allowed when one uses a Double_RdRstRd:
| Window size (pixels) | Min DIT | Max NDIT |
|---|---|---|
| 1024x1026 | 0.35 | 127 |
| 512x514 | 0.1091 | 508 |
| 256x258 | 0.0389 | 2032 |
| 128x130 | 0.0158 | 8065 |
| 64x66 | 0.0072 | 31775 |
A preliminary test on noise performance in Double_RdRstRd (DCR) has shown that temporal noise (i.e.
variation of noise across the cube) is similar to the spatial noise already quoted for the
CONICA detector (from 3.8 to 4.2 ADUs RMS). It is expected, but not yet tested, that with FowlerNsamp the noise will be
at the same level of what currently quoted. The minimum DIT in this mode will vary differently with
window size (and be longer, of course) than in DCR.
Very small windows (64x66, 128x130) show larger noise than bigger windows, mostly due to the presence of fixed pattern
noise (such as 8-pixe fixed patern noise). The cosmetic of the detector is also different, with more blemishes with smaller windows.
Interested users shuld check these webpges for the latest news on cube moe characterization, or contact the NaCo Team at naco@eso.org. Given the need for real-time decisions, this mode will only be offered in VM.