Source object interface

Input required for a Source object

A ScopeSim Source object is essentially a 2+1D (x, y, lambda) description of an on-sky object. Hence to build one of these objects we need the following data:

  • A spatial description

    Either in table form (point sources) or in image/bitmap form (extended source)

  • A spectral description

    A spectrum with wavelength and flux information

For example we could use two FITS images to describe the spatial flux distribution of the young and old components of a spiral galaxy, and two spectra from a starburst and an elliptical galaxy for the spectral description.

Internally this infor mation is stored in the following attributes:

  • <Source>.fields - the spatial information [Table or ImageHDU from astropy]

  • <Source>.spectra - the spectral information [SourceSpectrum from synphot]

More detailed information about the scopesim.Source object can be found in the scopesim documentation.

Below is a description of how to initialise (create) a Source object

Spatial description

Series of arrays

The most basic method for creating point source Source objects is by passing a series of arrays to the following argument keys:

  • x, y : positions [arcsec] from the centre of the field of view

  • ref : refers to the spectrum associated with a given point source

Optionally, if multiple point sources use the same spectrum, a scaling factor can be applied to each of the degenerate point sources:

  • weight : scaling factor

Code Example:

src = Source(x=[1, 2], y=[-1, 5], ref=[0, 0], weight=[3.14, 0.5])

Astropy Table

astropy.table.Table objects are a handy way to organize the information of the objects. Each column can contain the spatial information and the reference to the spectra used in the table.

FITS ImageHDU

Extended souces should provide an intensity map in the form of an fits.HDUImage object. The header keywords should contain information regarding position or the centre of the image (CRPIXn) relative to the centre of the field of view (CRVALn) [degrees], and pixel scale [CDELTn | CDn_m] [degress / pixel].

Each ImageHDU should also be associated with an appropriate spectrum (synphot.SourceSpectrum) contained in the list <Source>.spectra. The keyword SPEC_REF must be present and refer to the list index of the corresponding spectrum in <Source>.spectra.

Spectral description

Series of arrays

  • wave

  • flux

synphot.SourceSpectrum