[ ESO ]
NACO Science Data:
CUBE mode

CAL | HC | refs | QC
Trending & QC1
Data Packages
Data Management
QC links:
  • Frame Type SCIENCE_IMG

description: The cube mode is the mode in which every single DIT frame is saved. Thus, one cube (each "fits" file) includes NDIT frames (e.g. NAXIS3=11). 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 can be used for time resolved applications, provided one selects detector setups that do not lose frames and no single DIT frame time stamping is needed.

The size of each cube is limited by the maximum file size accepted by current version of Linux, 512 MB. Therefore, given a certain detector window, this fixes the maximum number of planes that can be saved in a cube (i.e. NDIT).

Cube mode is offered in combination with 5 different window sizes. Note that since windowing is done on chip (i.e. hardware windowing), NY=NX+2. Another feature of hardware windowing is that one cannot choose the position of the window within the full frame array: each window is centered on pixel (512,512), and the STARTX and STARTY parameters are fixed by the chosen window size.

In terms of data format, cubes are 3-D FITS files (i.e. NAXIS=3), a cube plus the same 3 FITS extensions. The size of the third axis (NAXIS3) is equal to NDIT+1: NDIT is the number of saved DIT frames, and the additional frame at the end of the cube is the combined image, i.e. the frame obtained as a sum of all DIT planes divided by NDIT. This last plane in the cube is the equivalent 2-D image one would obtain in single frame mode. The combined image is used for sanity check and quality control at the observatory. Users are cautioned to use only the first NDIT frames of each cube for their data reduction. Note also that the first frame in the cube may suffer from some reset anomaly and should probably be discarded. Cubes have NAXIS2=NAXIS1+2 as a rule.
For example, if one windows the array to half its size and takes NDIT=200, the size of the cube will be (NAXIS1,NAXIS2,NAXIS3)=(512,514,201). The FITS extensions remain unchanged.

For more information regarding cube mode, available windows, the minimum DIT and the maximum NDIT for various readout and detector modes consult the NACO User Manual and the instrument web pages.

calibrations:The calibration plan includes

  • standard (non-cube) detector darks with readout mode and DIT matching the one used for science;
  • standard (non-cube) sky (twilight) and internal flat fields;
  • standard (non-cube) nightly zero points;

[NACO QC][Observing Facilities and Operations][ESO][Index][Search][Help][News]