""" Astropy coordinate class for the Sagittarius coordinate system """
# Third-party
import numpy as np
import astropy.units as u
import astropy.coordinates as coord
from astropy.coordinates import frame_transform_graph
__all__ = ["GD1Koposov10"]
[docs]
class GD1Koposov10(coord.BaseCoordinateFrame):
"""
A Heliocentric spherical coordinate system defined by the orbit of the GD1 stream,
as described in Koposov et al. 2010 (see: `<http://arxiv.org/abs/0907.1085>`_).
For more information about this class, see the Astropy documentation on coordinate
frames in :mod:`~astropy.coordinates`.
Parameters
----------
representation : :class:`~astropy.coordinates.BaseRepresentation` or None
A representation object or None to have no data (or use the other keywords)
phi1 : angle_like, optional, must be keyword
The longitude-like angle corresponding to GD-1's orbit.
phi2 : angle_like, optional, must be keyword
The latitude-like angle corresponding to GD-1's orbit.
distance : :class:`~astropy.units.Quantity`, optional, must be keyword
The Distance for this object along the line-of-sight.
pm_phi1_cosphi2 : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in the longitude-like direction corresponding to
the GD-1 stream's orbit.
pm_phi2 : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in the latitude-like direction perpendicular to the
GD-1 stream's orbit.
radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword
The Distance for this object along the line-of-sight.
"""
default_representation = coord.SphericalRepresentation
default_differential = coord.SphericalCosLatDifferential
frame_specific_representation_info = {
coord.SphericalRepresentation: [
coord.RepresentationMapping("lon", "phi1"),
coord.RepresentationMapping("lat", "phi2"),
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__
# Rotation matrix as defined in the Appendix of Koposov et al. (2010)
R = np.array(
[
[-0.4776303088, -0.1738432154, 0.8611897727],
[0.510844589, -0.8524449229, 0.111245042],
[0.7147776536, 0.4930681392, 0.4959603976],
]
)
@frame_transform_graph.transform(coord.StaticMatrixTransform, coord.ICRS, GD1Koposov10)
def icrs_to_gd1():
"""
Compute the transformation from Galactic spherical to heliocentric GD1 coordinates.
"""
return R
@frame_transform_graph.transform(coord.StaticMatrixTransform, GD1Koposov10, coord.ICRS)
def gd1_to_icrs():
"""
Compute the transformation from heliocentric GD1 coordinates to spherical Galactic.
"""
return icrs_to_gd1().T
