SkyEllipticalAnnulus#

class photutils.aperture.SkyEllipticalAnnulus(positions, a_in, a_out, b_out, b_in=None, theta=<Quantity 0. deg>)[source]#

Bases: SkyAperture

An elliptical annulus aperture defined in sky coordinates.

The aperture has a single fixed size/shape, but it can have multiple positions (see the positions input).

Parameters:

positionsSkyCoord: The celestial coordinates of the aperture center(s). This can be either scalar coordinates or an array of coordinates.
a_inscalar Quantity: The inner semimajor axis in angular units.
a_outscalar Quantity: The outer semimajor axis in angular units.
b_outscalar Quantity: The outer semiminor axis in angular units.
b_inNone or scalar Quantity: The inner semiminor axis in angular units. If None, then the inner semiminor axis is calculated as:

\[b_{in} = b_{out} \left(\frac{a_{in}}{a_{out}}\right)\]
thetascalar Quantity, optional: The position angle (in angular units) of the ellipse semimajor axis. For a right-handed world coordinate system, the position angle increases counterclockwise from North (PA=0).

Examples

>>> from astropy.coordinates import SkyCoord
>>> import astropy.units as u
>>> from photutils.aperture import SkyEllipticalAnnulus
>>> positions = SkyCoord(ra=[10.0, 20.0], dec=[30.0, 40.0], unit='deg')
>>> aper = SkyEllipticalAnnulus(positions, 0.5*u.arcsec, 2.0*u.arcsec,
...                             1.0*u.arcsec)

Attributes Summary

`a_in`	The inner semimajor axis in angular units.
`a_out`	The outer semimajor axis in angular units.
`b_in`	The inner semiminor axis in angular units.
`b_out`	The outer semiminor axis in angular units.
`isscalar`	Whether the instance is scalar (i.e., a single position).
`positions`	The center position(s) in sky coordinates.
`shape`	The shape of the instance.
`theta`	The position angle in angular units of the ellipse semimajor axis.

Methods Summary

`copy`()	Make a deep copy of this object.
`to_pixel`(wcs)	Convert the aperture to an `EllipticalAnnulus` object defined in pixel coordinates.

Attributes Documentation

a_in#: The inner semimajor axis in angular units.

a_out#: The outer semimajor axis in angular units.

b_in#: The inner semiminor axis in angular units.

b_out#: The outer semiminor axis in angular units.

isscalar#: Whether the instance is scalar (i.e., a single position).

positions#: The center position(s) in sky coordinates.

shape#: The shape of the instance.

theta#: The position angle in angular units of the ellipse semimajor axis.

Methods Documentation

copy()#

Make a deep copy of this object.

Returns:

resultAperture: A deep copy of the Aperture object.

to_pixel(wcs)[source]#

Convert the aperture to an EllipticalAnnulus object defined in pixel coordinates.

Parameters:

wcsWCS object: A world coordinate system (WCS) transformation that supports the astropy shared interface for WCS (e.g., astropy.wcs.WCS, gwcs.wcs.WCS).

Returns:

apertureEllipticalAnnulus object: An EllipticalAnnulus object.

Notes

The aperture shape parameters are converted using the local WCS properties (pixel scale, rotation angle) evaluated at the first aperture position. Because aperture objects require scalar shape parameters, only a single reference position is used for the conversion. For apertures with multiple positions used with a WCS that has spatially-varying distortions, this may produce inaccurate results for positions far from the first position.