import astropy.coordinates as coord
import astropy.units as u
import numpy as np
from astropy.coordinates import frame_transform_graph
__all__ = ["JhelumBonaca19"]
[docs]
class JhelumBonaca19(coord.BaseCoordinateFrame):
"""
A Heliocentric spherical coordinate system defined by the orbit of the Jhelum
stream, as described in Bonaca et al. 2019.
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 aligned with the stream.
phi2 : angle_like, optional, must be keyword
The latitude-like angle aligned perpendicular to the stream.
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 Jhelum stream's orbit.
pm_phi2 : :class:`~astropy.units.Quantity`, optional, must be keyword
The proper motion in the latitude-like direction perpendicular to the
Jhelum stream's orbit.
radial_velocity : :class:`~astropy.units.Quantity`, optional, must be keyword
The radial velocity 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 Bonaca+2019
R = np.array(
[
[0.6173151074, -0.0093826715, -0.7866600433],
[-0.0151801852, -0.9998847743, 0.0000135163],
[-0.7865695266, 0.0119333013, -0.6173864075],
]
)
@frame_transform_graph.transform(
coord.StaticMatrixTransform, coord.ICRS, JhelumBonaca19
)
def icrs_to_jhelum():
"""
Compute the transformation from ICRS spherical to heliocentric Jhelum
coordinates.
"""
return R
@frame_transform_graph.transform(
coord.StaticMatrixTransform, JhelumBonaca19, coord.ICRS
)
def jhelum_to_icrs():
"""
Compute the transformation from heliocentric Jhelum coordinates to spherical ICRS.
"""
return icrs_to_jhelum().T
