What makes it special?

This package provides the following tools for the analysis of measured spectra:

  • calculation of the spectral correlation between channels of an IFS datacube;

  • calculation of empirical spectral indices for MLT-dwarfs;

  • fitting of input spectra to different grids of models, including additional parameters such as (extra) black body component(s) and extinction;

  • using either the MCMC (emcee) or nested (nestle) sampler to infer posterior distributions on spectral model parameters;

  • searching for the best-fit template spectrum within a given template library, with up to two free parameters (flux scaling and relative extinction).

The MCMC and nested sampler routines have been adapted to:

  • be flexible, as they are usable on any grid of models provided by the user (along with a snippet function specifying the format of the input);

  • sample the effect of (additional) blackbody components;

  • sample the effect of extinction;

  • sample different extinction laws than ISM (parametrised using RV);

  • accept either uniform or Gaussian priors for each model parameter;

  • accept a prior on the mass of the object (if surface gravity is one of the model parameters, and for the MCMC sampler only);

  • consider convolution with the spectral PSF, photometric filters transmission and/or resampling of the model for consistency with the input spectrum.

  • use a log-likelihood expression that can include i) spectral correlation between measurements of adjacent channels of a given instrument, and ii) additional weights that are proportional to the relative spectral bandwidth of each measurement, in case these are obtained from different instruments (e.g. photometry+spectroscopy).

More details are available in Christiaens et al. (2021) (note it was originally implemented as specfit, a former module of the VIP package).