""" Astropy coordinate class for the Palomar 5 stream 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__ = ["Pal5PriceWhelan18"]
[docs]class Pal5PriceWhelan18(coord.BaseCoordinateFrame):
"""
A Heliocentric spherical coordinate system defined by the orbit
of the Pal 5 stream by A. Price-Whelan (2018).
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 Pal 5's orbit.
phi2 : angle_like, optional, must be keyword
The latitude-like angle corresponding to Pal 5'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 Pal 5 stream's orbit.
pm_phi2 : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in the latitude-like direction perpendicular to the
Pal 5 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 defined by trying to align the stream to the equator
R = np.array(
[
[-0.65019243, -0.75969758, -0.01045969],
[-0.62969142, 0.54652698, -0.55208422],
[0.42513354, -0.3523746, -0.83372274],
]
)
# Extra rotation to put the cluster center at (0, 0)
R2 = np.array(
[
[9.99938314e-01, 1.57847502e-03, -1.09943927e-02],
[-1.57837962e-03, 9.99998754e-01, 1.73543959e-05],
[1.09944064e-02, 0.00000000e00, 9.99939560e-01],
]
)
R = R2 @ R
@frame_transform_graph.transform(
coord.StaticMatrixTransform, coord.ICRS, Pal5PriceWhelan18
)
def icrs_to_pal5():
"""Compute the transformation from Galactic spherical to
heliocentric Pal 5 coordinates.
"""
return R
@frame_transform_graph.transform(
coord.StaticMatrixTransform, Pal5PriceWhelan18, coord.ICRS
)
def pal5_to_icrs():
"""Compute the transformation from heliocentric Pal 5 coordinates to
spherical Galactic.
"""
return icrs_to_pal5().T