This is an extension to the reduction pipeline for the HARPS spectrograph, carrying out the demodulation of the spectra from fibers A and B in multiple frames (either 2 or 4).

The input to demod.py is a list of filenames. These need to be the S2D files that are made by the ESPRESSO pipeline, applied to the HARPSPOL raw framed. The fibers A and B are saved in separate files, therefore the number of input files to the script is 4 or 8.

Outputs are saved in the same S2D format, with filenames that share the prefix and timestamp with the first of the files given. The suffixes are

• _S2D_POL_I.fits for the intensity spectrum
• _S2D_POL_STOKES.fits for the Stokes parameters
• _S2D_POL_NULL.fits for the null spectrum (only when 8 files provided)

For usage simply clone this repository and install the dependencies, for example using uv:

uv venv && uv sync
uv run demod.py FILE1 FILE2 [FILE3 FILE4]

The files in old/ are the plugin for the old python-based HARPS reduction pipeline.