Code to measure the strength of the calcium triplet (CaT) spectral feature by fitting stellar templates using the method described in Foster et al. (2010) and Usher et al. (2019).
As described in Usher et al. (2018), the code measures the strength of the CaT by fitting a linear combination of stellar templates using the pPXF code of Cappellari & Emsellem (2004), normalising the fitted templates using a polynomial fit to regions of low line opacity, and then measure the index strength on the normalised templates. Some of the code was written to be a more general wrapper around pPXF.
Any publication resulting from the use of this software should cite Usher et al., 2019 and Cappellari & Emsellem (2004). Although modification of this code is encouraged, any publication resulting from the modified code should state that the code has been modified and explain how the code has been modified.
Besides pPXF (available from http://www-astro.physics.ox.ac.uk/~mxc/software/#ppxf), this code requires Numpy, SciPy and optionally Matplotlib to run. Running this code requires no installation - just put src/ in your Python path and set the PPXF_TEMPLATE environment variable to the location of the templates/ directory.
The code can be used in two different ways. From the command line run measure_CaT.py . This script can handle spectra in FITS format, ascii or as a pickled ppxf_data object.
From within a Python script
input_datum = ppxf_data.ppxf_data(wavelengths, fluxes, sigmas)
output_datum = ppxf_lib.ppxf_CaT(input_datum)
where wavelengths, fluxes and sigmas are 1d Numpy arrays contain the wavelengths, fluxes and (optionally) uncertainties of the spectra to be fit.
Christopher Usher
2018-09-19 Liverpool