Instrument

class poppy.Instrument(name='', *args, **kwargs)

Bases: object

A generic astronomical instrument, composed of

1. an optical system implemented using POPPY, optionally with several configurations such as selectable image plane or pupil plane stops, and

2. some defined spectral bandpass(es) such as selectable filters, implemented using synphot.

This provides the capability to model both the optical and spectral responses of a given system. PSFs may be calculated for given source spectral energy distributions and output as FITS files, with substantial flexibility.

It also provides capabilities for modeling some PSF effects not due to wavefront aberrations, for instance blurring caused by pointing jitter.

This is a base class for Instrument functionality - you cannot easily use this directly, but rather should subclass it for your particular instrument of interest. Some of the complexity of this class is due to splitting up functionality into many separate routines to allow users to subclass just the relevant portions for a given task. There’s a fair amount of functionality here but the learning curve is steeper than elsewhere in POPPY.

You will at a minimum want to override the following class methods:

• get_optical_system

• _get_filter_list

• _get_default_nlambda

• _get_default_fov

• _get_fits_header

For more complicated systems you may also want to override:

• _validate_config

• _get_synphot_bandpass

• _apply_jitter

Attributes Summary

filter	Currently selected filter name (e.g.
filter_list	List of available filter names for this instrument
name
options	A dictionary capable of storing other arbitrary options, for extensibility.
pixelscale	Detector pixel scale, in arcseconds/pixel (default: 0.025)
pupil	Aperture for this optical system.
pupilopd	Pupil OPD for this optical system.

Methods Summary

calc_datacube(wavelengths, *args, **kwargs)	Calculate a spectral datacube of PSFs
calc_psf([outfile, source, nlambda, ...])	Compute a PSF.
display()	Display the currently configured optical system on screen
get_optical_system([fft_oversample, ...])	Return an OpticalSystem instance corresponding to the instrument as currently configured.

Attributes Documentation

filter

Currently selected filter name (e.g. F200W)

filter_list = None

List of available filter names for this instrument

name = 'Instrument'

options = {}

A dictionary capable of storing other arbitrary options, for extensibility. The following are all optional, and may or may not be meaningful depending on which instrument is selected.

Parameters:

source_offset_rfloat

Radial offset of the target from the center, in arcseconds

source_offset_thetafloat

Position angle for that offset

pupil_shift_x, pupil_shift_yfloat

Relative shift of a coronagraphic pupil in X and Y, expressed as a decimal between 0.0-1.0 Note that shifting an array too much will wrap around to the other side unphysically, but for reasonable values of shift this is a non-issue.

jitterstring “gaussian” or None

Type of jitter model to apply. Currently only convolution with a Gaussian kernel of specified width jitter_sigma is implemented. (default: None)

jitter_sigmafloat

Width of the jitter kernel in arcseconds per axis (default: 0.007 arcsec)

paritystring “even” or “odd”

You may wish to ensure that the output PSF grid has either an odd or even number of pixels. Setting this option will force that to be the case by increasing npix by one if necessary.

pixelscale = 0.025

Detector pixel scale, in arcseconds/pixel (default: 0.025)

pupil = None

Aperture for this optical system. May be a FITS filename, FITS HDUList object, or poppy.OpticalElement

pupilopd = None

Pupil OPD for this optical system. May be a FITS filename, or FITS HDUList. If the file contains a datacube, you may set this to a tuple (filename, slice) to select a given slice, or else the first slice will be used.

Methods Documentation

calc_datacube(wavelengths, *args, **kwargs)

Calculate a spectral datacube of PSFs

Parameters:

wavelengthsiterable of floats

List or ndarray or tuple of floating point wavelengths in meters, such as you would supply in a call to calc_psf via the “monochromatic” option

calc_psf(outfile=None, source=None, nlambda=None, monochromatic=None, fov_arcsec=None, fov_pixels=None, oversample=None, detector_oversample=None, fft_oversample=None, overwrite=True, display=False, save_intermediates=False, return_intermediates=False, normalize='first')

Compute a PSF. The result can either be written to disk (set outfile=”filename”) or else will be returned as a FITS HDUlist object.

Output sampling may be specified in one of two ways:

1. Set oversample=. This will use that oversampling factor beyond detector pixels for output images, and beyond Nyquist sampling for any FFTs to prior optical planes.

2. set detector_oversample= and fft_oversample=. This syntax lets you specify distinct oversampling factors for intermediate and final planes.

By default, both oversampling factors are set equal to 2.

Parameters:

sourcesynphot.spectrum.SourceSpectrum or dict

specification of source input spectrum. Default is a 5700 K sunlike star.

nlambdaint

How many wavelengths to model for broadband? The default depends on how wide the filter is: (5,3,1) for types (W,M,N) respectively

monochromaticfloat, optional

Setting this to a wavelength value (in meters) will compute a monochromatic PSF at that wavelength, overriding filter and nlambda settings.

fov_arcsecfloat

field of view in arcsec. Default=5

fov_pixelsint

field of view in pixels. This is an alternative to fov_arcsec.

outfilestring

Filename to write. If None, then result is returned as an HDUList

oversample, detector_oversample, fft_oversampleint

How much to oversample. Default=4. By default the same factor is used for final output pixels and intermediate optical planes, but you may optionally use different factors if so desired.

overwritebool

overwrite output FITS file if it already exists?

displaybool

Whether to display the PSF when done or not.

save_intermediates, return_intermediatesbool

Options for saving to disk or returning to the calling function the intermediate optical planes during the propagation. This is useful if you want to e.g. examine the intensity in the Lyot plane for a coronagraphic propagation.

normalizestring

Desired normalization for output PSFs. See doc string for OpticalSystem.calc_psf. Default is to normalize the entrance pupil to have integrated total intensity = 1.

Returns:

outfitsfits.HDUList

The output PSF is returned as a fits.HDUlist object. If outfile is set to a valid filename, the output is also written to that file.

Notes

More advanced PSF computation options (pupil shifts, source positions, jitter, …) may be set by configuring the options dictionary attribute of this class.

display()

Display the currently configured optical system on screen

get_optical_system(fft_oversample=2, detector_oversample=None, fov_arcsec=2, fov_pixels=None, options=None)

Return an OpticalSystem instance corresponding to the instrument as currently configured.

When creating such an OpticalSystem, you must specify the parameters needed to define the desired sampling, specifically the oversampling and field of view.

Parameters:

fft_oversampleint

Oversampling factor for intermediate plane calculations. Default is 2

detector_oversample: int, optional

By default the detector oversampling is equal to the intermediate calculation oversampling. If you wish to use a different value for the detector, set this parameter. Note that if you just want images at detector pixel resolution you will achieve higher fidelity by still using some oversampling (i.e. not setting oversample_detector=1) and instead rebinning down the oversampled data.

fov_pixelsfloat

Field of view in pixels. Overrides fov_arcsec if both set.

fov_arcsecfloat

Field of view, in arcseconds. Default is 2

optionsdict

Other arbitrary options for optical system creation

Returns:

osyspoppy.OpticalSystem

an optical system instance representing the desired configuration.