======= Specter

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Introduction

A 2D CCD pixel-level simulation and extraction toolkit for multi-object spectrographs.

Directories included here:

doc/ Documentation (data model, overview, ...)

py/specter/ Python classes and modules

py/specter/psf/
    modeling the spectrograph point spread functions

py/specter/extract/
    extract spectra from CCD images given a PSF

bin/ executable scripts

dev/ Code under initial development, before it moves into py/

Basic Concepts

Specter is designed to simulate astronomical multi-object spectrographs, and extract spectra from the 2D CCD images. The user provides a model of the point-spread-function (PSF) of how light from spectrum i at wavelength w is dispersed on the CCD::

pixels, xx, yy = psf.pix(i, w)

where xx and yy are the slices defining the CCD pixel coordinates where those pixels appear on the CCD image. doc/datamodel/psf.md lists multiple file formats for parameterizing different PSFs, or users can subclass specter.psf.PSF to provide their own parameterization.

Using this PSF model, specter provides pixel-level simulations of the CCD images produced by the spectrograph given input spectra.

The inverse of simulating photons on the CCD is extracting the photons back off of the CCD to provide a model of spectra given an input image and noise model of that image. Specter uses the PSF model and the "spectroperfectionism" methodology of Bolton & Schlegel 2009.

Command Line Tools

Run bin/specter -h to see command line options for the CCD pixel-level simulator. It accepts input spectra, a spectrograph point-spread-function (PSF) model, and generates output CCD images.

bin/exspec performs 2D PSF extractions given an input image, image noise model, and PSF. It subdivides the problem into overlapping regions and then reassembles them, thus making the O(N^2) problem tractable by doing many small extractions instead of a single large one.

Python Tools

Run python setup.py build_sphinx to see python library documentation for both the simulator and extractor.

Example usage of the Python toolkit::

#- Load PSF file for some spectrograph
from specter.psf import load_psf
psf = load_psf('psf.fits')

#- Get PSF spot for fiber 10 and wavelength 5000 Angstroms:
spot = psf.pix(10, 5000)

#- Project photons[nspec, nw] at wavelength[nw] onto the CCD:
image = psf.project(photons, wavelength)

#- Extract spectra 0:10
from specter.extract import ex2d
xphot, ivar, R = ex2d(image, image_ivar, psf, specrange=[0,10], \
                      wavelengths=wavelength)

Full Documentation

Please visit specter on Read the Docs_

.. _specter on Read the Docs: https://desi-specter.readthedocs.io/en/latest/

License

specter is free software licensed under a 3-clause BSD-style license. For details see the LICENSE.rst file.

Specter

Install / Use

README