Introduction to StokesPy

StokesPy provides several classes to represent different slices of spectropolarimetric data and its inversion products. For spectropolarimetric data, the highest dimensionality object is the StokesCube, which contains dimensions of (stokes, wavelength, coord1, coord2), i.e. a map on the Sun of full Stokes profiles. StokesPy data objects uses the ndcube project’s ndcube.NDCube object as a base class. In StokesPy, as in ndcube, data and coordinates are contained in a single object, allowing array-like slicing operations to modify both the data and coordinate systems simultanously. This object can be constructed by providing a properly ordered data array and World Coordinate System (WCS) as follows:

>>> stokes = StokesCube(data, wcs)

Where data should have dimensions (stokes, wavelength, coord1, coord2) and wcs should describe those dimensions in physical (world) coordinates. The provided wcs should be APE-14 compliant, which in practice generally means being a properly constructed astropy.wcs.WCS object or a gwcs.wcs.WCS. The interested user should consult the following references to better understand the astropy WCS and how it is used by ndcube, StokesPy’s base class:

• NDCube Introduction

• WCS APE-14

• AstroPy WCS

• gWCS WCS

However, one of the goals of the StokesPy project is to take advantage of the WCS while insulating the user from the complexities of setting up a valid WCS. This is accomplished through custom-built instrument loader functions.

>>> stokes = stokespy.instload.load_HMI_stokes()

In this way, the user can immediately begin working with StokesPy objects in their analysis.

A comprehensive example notebook has been developed demonstrating loading StokesPy objects from HMI and Hinode SOT/SP data files, using the slicing functions, and plotting the objects.