Source code for gala.coordinates.sgr

""" Astropy coordinate class for the Sagittarius coordinate system """

# Third-party
import numpy as np

from astropy.coordinates import frame_transform_graph
import astropy.coordinates as coord
import astropy.units as u
from astropy.coordinates.matrix_utilities import rotation_matrix

__all__ = ["SagittariusLaw10"]

[docs]class SagittariusLaw10(coord.BaseCoordinateFrame): """ A Heliocentric spherical coordinate system defined by the orbit of the Sagittarius dwarf galaxy, as described in and further explained in Parameters ---------- representation : `BaseRepresentation` or None A representation object or None to have no data (or use the other keywords). Lambda : `Angle`, optional, must be keyword The longitude-like angle corresponding to Sagittarius' orbit. Beta : `Angle`, optional, must be keyword The latitude-like angle corresponding to Sagittarius' orbit. distance : `Quantity`, optional, must be keyword The Distance for this object along the line-of-sight. pm_Lambda_cosBeta : :class:`~astropy.units.Quantity`, optional, must be keyword The proper motion along the stream in ``Lambda`` (including the ``cos(Beta)`` factor) for this object (``pm_Beta`` must also be given). pm_Beta : :class:`~astropy.units.Quantity`, optional, must be keyword The proper motion in Declination for this object (``pm_ra_cosdec`` must also be given). radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword The radial velocity of this object. """ default_representation = coord.SphericalRepresentation default_differential = coord.SphericalCosLatDifferential frame_specific_representation_info = { coord.SphericalRepresentation: [ coord.RepresentationMapping("lon", "Lambda"), coord.RepresentationMapping("lat", "Beta"), coord.RepresentationMapping("distance", "distance"), ] } _default_wrap_angle = 180 * u.deg def __init__(self, *args, **kwargs): wrap = kwargs.pop("wrap_longitude", True) super().__init__(*args, **kwargs) if wrap and isinstance( self._data, (coord.UnitSphericalRepresentation, coord.SphericalRepresentation), ): self._data.lon.wrap_angle = self._default_wrap_angle # TODO: remove this. This is a hack required as of astropy v3.1 in order # to have the longitude components wrap at the desired angle
[docs] def represent_as(self, base, s="base", in_frame_units=False): r = super().represent_as(base, s=s, in_frame_units=in_frame_units) if hasattr(r, "lon"): r.lon.wrap_angle = self._default_wrap_angle return r
represent_as.__doc__ = coord.BaseCoordinateFrame.represent_as.__doc__
# Define the Euler angles (from Law & Majewski 2010) phi = (180 + 3.75) * theta = (90 - 13.46) * psi = (180 + 14.111534) * # Generate the rotation matrix using the x-convention (see Goldstein) D = rotation_matrix(phi, "z") C = rotation_matrix(theta, "x") B = rotation_matrix(psi, "z") A = np.diag([1.0, 1.0, -1.0]) R = A @ B @ C @ D # Galactic to Sgr coordinates @frame_transform_graph.transform( coord.StaticMatrixTransform, coord.Galactic, SagittariusLaw10 ) def galactic_to_sgr(): """Compute the transformation from Galactic spherical to heliocentric Sagittarius coordinates. """ return R # Sgr to Galactic coordinates @frame_transform_graph.transform( coord.StaticMatrixTransform, SagittariusLaw10, coord.Galactic ) def sgr_to_galactic(): """Compute the transformation from heliocentric Sagittarius coordinates to spherical Galactic. """ return galactic_to_sgr().T