# SkyEllipticalAnnulus¶

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

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, either in angular or pixel units.

a_outscalar Quantity

The outer semimajor axis, either in angular or pixel units.

b_outscalar Quantity

The outer semiminor axis, either in angular or pixel units.

b_inNone or scalar Quantity

The inner semiminor axis, either in angular or pixel 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). The default is 0 degrees.

Examples

>>> from astropy.coordinates import SkyCoord
>>> import astropy.units as u
>>> from photutils import SkyEllipticalAnnulus
>>> positions = SkyCoord(ra=[10., 20.], dec=[30., 40.], unit='deg')
>>> aper = SkyEllipticalAnnulus(positions, 0.5*u.arcsec, 2.0*u.arcsec,
...                             1.0*u.arcsec)


Attributes Summary

 a_in Check that value is either an angular or a pixel scalar Quantity. a_out Check that value is either an angular or a pixel scalar Quantity. b_in Check that value is either an angular or a pixel scalar Quantity. b_out Check that value is either an angular or a pixel scalar Quantity. positions Check that value is a SkyCoord. theta Check that value is either an angular scalar Quantity.

Methods Summary

 to_pixel(wcs) Convert the aperture to an EllipticalAnnulus object defined in pixel coordinates.

Attributes Documentation

a_in

Check that value is either an angular or a pixel scalar Quantity.

a_out

Check that value is either an angular or a pixel scalar Quantity.

b_in

Check that value is either an angular or a pixel scalar Quantity.

b_out

Check that value is either an angular or a pixel scalar Quantity.

positions

Check that value is a SkyCoord.

theta

Check that value is either an angular scalar Quantity.

Methods Documentation

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
aperture

An EllipticalAnnulus object.