special 0.0.1

Package for spectral characterization of (sub)stellar objects

specfit (or spectral_fitting on pypi) is a package for the spectral characterization of (sub-)stellar objects.

This package provides the tools for the analysis of measured spectra (e.g. low-res spectra of directly imaged companions, but not exclusively), including:

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

• fitting of input spectra to different grids of models (the code is grid-independent, download of the grids is left to the user);

• MCMC sampling of the model grid parameter space;

• searching for the best-fit template spectrum within a given library.

In particular, the MCMC sampler routine makes use of the emcee package (Foreman-Mackey et al. 2013):

• is flexible, as it is usable on any grid of models downloaded by the user (provided a snippet function specifying the format of the input);

• can fit (additional) blackbody components;

• can sample the effect of extinction;

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

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

• accepts a prior on the mass of the object (if surface gravity is one of the model parameters);

• considers convolution with the spectral PSF and/or resampling of the model for consistency with the input spectrum.

Furthermore, the log-likelihood expression has the option to include:

• spectral correlation between measurements of adjacent channels of a given instrument;

• weights that are proportional to the relative spectral span of each measurement, in case these are obtained from different instruments.

More details are available in Christiaens et al. (2021). Please cite this publication if you use specfit for your research, along with Foreman-Mackey et al. (2013) if you use the MCMC sampler.

Documentation

The documentation for specfit can be found here: TBD

Jupyter notebook tutorial

TBD

TL;DR setup guide

$ pip install spectral_fitting

Installation and dependencies

The benefits of using a Python package manager (distribution), such as (ana)conda or Canopy, are many. Mainly, it brings easy and robust package management and avoids messing up with your system’s default python. An alternative is to use package managers like apt-get for Ubuntu or Homebrew/MacPorts/Fink for macOS. We recommend using Miniconda.

specfit depends on existing packages from the Python ecosystem, such as numpy, scipy, matplotlib, pandas and astropy. There are different ways of installing specfit suitable for different scenarios.

Using pip

The easiest way to install specfit (spectral_fitting on pypi) is through the Python Package Index, aka PyPI, with the pip package manager. Simply run:

$ pip install spectral_fitting

With pip you can easily uninstall, upgrade or install a specific version of specfit. For upgrading the package run:

$ pip install --upgrade spectral_fitting

Alternatively, you can use pip install and point to the GitHub repo:

$ pip install git+https://github.com/VChristiaens/specfit.git

Using the setup.py file

You can download specfit from its GitHub repository as a zip file. A setup.py file (setuptools) is included in the root folder of specfit. Enter the package’s root folder and run:

$ python setup.py install

Using Git

If you plan to contribute or experiment with the code you need to make a fork of the repository (click on the fork button in the top right corner) and clone it:

$ git clone https://github.com/<replace-by-your-username>/specfit.git

If you do not create a fork, you can still benefit from the git syncing functionalities by cloning the repository (but will not be able to contribute):

$ git clone https://github.com/VChristiaens/specfit.git

Before installing the package, it is highly recommended to create a dedicated conda environment to not mess up with the package versions in your base environment. This can be done easily with (replace spec_env by the name you want for your environment):

$ conda create -n spec_env python=3.9 ipython

Note: installing ipython while creating the environment with the above line will avoid a commonly reported issue which stems from trying to import VIP from within a base python2.7 ipython console.

To install specfit, simply cd into the specfit directory and run the setup file in ‘develop’ mode:

$ cd VIP
$ python setup.py develop

If cloned from your fork, make sure to link your specfit directory to the upstream source, to be able to easily update your local copy when a new version comes out or a bug is fixed:

$ git add remote upstream https://github.com/VChristiaenss/specfit

Loading specfit

Finally, start Python or IPython and check that you are able to import specfit:

import spectral_fitting as specfit

If everything went fine with the installation, you will see a welcome message. Now you can start characterizing exoplanets and other (sub)stellar objects!