This page contains advice on how to organise HiPERCAM reduction in terms of directory structure and file names.

Night-by-night directories

Since HiPERCAM file names repeat from night-to-night (i.e. you can get ‘run0023.fits’ on multiple nights), reduction should always be organised into directories with one per night. e.g. somewhere there should be a top-level directory with a series of directories like so:


(or if you prefer, you could have underscores ‘_’ rather than hyphens ‘-‘). This is how I organise the raw data in Warwick, and I recommend the same layout for reduction. Thus when starting on a new night’s-worth of data, the first steps are typically as follows:

mkdir 2018-01-03
cd 2018-01-03
ln -s <path_to_raw_data>/2018-01-03 data

then within the sub-directory 2018-01-03, all the raw data will be found inside ‘data’, a soft-link to the raw data directory.

File naming within a night directory

Typically a given night has several biases, a flat field and possibly some dark runs. I always stick to the run name when making single calibration frames out of such runs. Thus the raw HiPERCAM run ‘run0003.fits’ (or equivalently run003.xml, run003.dat for ULTRACAM) will be combined in some way to make a single HiPERCAM frame called ‘run0003.hcm’ (or ‘run003.hcm’). However, then I make a soft link which defines its fundamental purpose. e.g.:

ln -s run003.hcm bias_1x1_cdd.hcm

which says this is a bias frame taken with 1x1 binning with cdd readout speed (ULTRACAM). If you set up ‘ls’ right, soft links appear distinct from ordinary files and ‘ls -l’ should tell you where it points. Soft links always carry the danger of being broken of course, so one must take care not to move or delete the target file. It helps also always to use relative path names (as long as one does not change the directory structure), so I commonly make links to bias frames taken on later nights e.g. within 2018-01-03 I might write:

ln -s ../2018-01-04/bias_arsco.hcm

where in 2018-01-04, bias_arsco.hcm is itself a link to perhaps ‘run011.hcm’, a bias run taken specifically to match the format of a run on ‘AR Sco’ the previous night. (NB without a link name specified in the previous line, the link is simply created with the target name, i.e. ‘bias_arsco.hcm’ in this case.)

Always start bias frames with ‘bias_’ then add enough information to make it obvious what it can be used for. The binning is important, hence the ‘1x1’ above, but readout speeds must match as well, hence the ‘cdd’. I adopt the convention that I don’t say when biases are full frame (no ‘ff’) because that’s the default bias, so the bias above is full frame.

For flat fields, the main issue is what filters were used, so I call them names like ‘flat_ugr.hcm’ or ‘flat_ugi.hcm’. Sometimes calibration frames are affected by issues, but maybe you have no choice bu to use what is available. Then a name like ‘flat_ugr_caution.hcm’ might be warranted.

Reduction file names

Once all set with calibrations, then for a given run, I use the root name (‘run023’ or ‘run0034’ or whatever) for all files associated with that run. The pipeline defines a set of standard extensions that will be added to any given file to allow this. Thus you will end up with multiple files of the form ‘run023.XXX’, with ‘XXX’ being the file extension. A full set of such files and their likely meanings are:





Binary FITS

Representative image of the run, probably from its start using averun


JSON text

File of photometric apertures (JSON text file)

ASCII text

Reduction driver file for reduce


ASCII text

Output log file from a run of reduce


Binary FITS

FITS version of a reduce log file made with hlog2fits

If you find such a set, within a directory, then assuming the pipeline version used to make the log file still applies, you should be able to re-reduce using the aperture (‘.ape’) and reduction (‘.red’) files. A run of setaper with the hcm (‘.hcm’) and (‘.ape’) files will show the apertures selected. If the reduction fails, then you may want to re-generate the reduction driver file using genred.