apertures

ApertureList

A list of apertures, useful for IFU or MOS instruments

Parameters

Examples

File format

Much like an ApertureMask, an ApertureList can be initialised by either of the three standard DataContainer methods. The easiest is however to make an ASCII file with the following columns:

id   left    right   top     bottom  angle  conserve_image  shape
     arcsec  arcsec  arcsec  arcsec  deg
int  float   float   float   float   float  bool            str/int

Acceptable shape entries are: round, rect, hex, oct, or an integer describing the number of corners the polygon should have.

A polygonal mask is generated for a given shape and will be scaled to fit inside the edges of each aperture list row. The corners of each aperture defined by shape are found by finding equidistant positions around an ellipse constrained by the edges (left, …, etc). An additional optional column offset may be added. This column describes the offset from 0 deg to the angle where the first corner is set.

Additionally, the filename of an ApertureMask polygon file can be given. The geometry of the polygon defined in the file will be scaled to fit inside the edges of the row.

Note

shape values "rect" and 4 do not produce equal results

Both use 4 equidistant points around an ellipse constrained by [left, …, etc]. However "rect" aims to fill the contraining area, while 4 simply uses 4 points on the ellipse. Consequently, 4 results in a diamond shaped mask covering only half of the constraining area filled by "rect".

ApertureMask

Only provides the on-sky window coords of the Aperture

  • Case: Imaging

    • Covers the whole FOV of the detector

    • Round (with mask), square (without mask)

  • CaseLS Spec

    • Covers the slit FOV

    • Polygonal (with mask), square (without mask)

  • CaseIFU Spec

    • Covers the on-sky FOV of one slice of the IFU

    • Square (without mask)

  • CaseMOS Spec

    • Covers a single MOS fibre FOV

    • Round, Polygonal (with mask), square (without mask)

The geometry of an ApertureMask can be initialised with the standard DataContainer methods (see Parameters below). Regardless of which method is used, the following columns must be present:

x       y
arcsec  arcsec
float   float

Certain keywords need to also be included in the ascii header:

# id: <int>
# conserve_image: <bool>
# x_unit: <str>
# y_unit: <str>

If conserve_image is False, the flux from all sources in the aperture is summed and distributed uniformly over the aperture area.

Parameters

filenamestr

Path to ASCII file containing the columns listed above

tableastropy.Table

An astropy Table containing the columns listed above

array_dictdict

A dictionary containing the columns listed above: {x: [...], y: [...], id: <int>, conserve_image: <bool>}

Other Parameters

pixel_scalefloat

[arcsec] Defaults to "!INST.pixel_scale" from the config

idint

An integer to identify the ApertureMask in a list of apertures

RectangularApertureMask

SlitWheel

A selection of predefined spectroscopic slits and possibly other field masks

It should contain an open position. A user can define a non-standard slit by directly using the Aperture effect.

Parameters

slit_names : list of str

filename_formatstr

A f-string for the path to the slit files

current_slitstr

Default name

Examples

This Effect assumes a folder full of ASCII files containing the edges of each slit. Each file should be names the same except for the slit’s name or identifier.

This example assumes a folder masks containing the slit ASCII files with the naming convention: slit_A.dat, slit_B.dat, etc.

name: slit_wheel
class: SlitWheel
kwargs:
    slit_names:
        - A
        - B
        - C
    filename_format: "masks/slit_{}.dat
    current_slit: "C"