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;