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 viewref
: 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