""" 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", "SagittariusVasiliev21"]
[docs]
class SagittariusLaw10(coord.BaseCoordinateFrame):
"""
A Heliocentric spherical coordinate system defined by the orbit
of the Sagittarius dwarf galaxy, as described in
http://adsabs.harvard.edu/abs/2003ApJ...599.1082M
and further explained in http://www.stsci.edu/~dlaw/Sgr/.
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) * u.degree
theta = (90 - 13.46) * u.degree
psi = (180 + 14.111534) * u.degree
# 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
# -------------------------------------------------------------------------------------
[docs]
class SagittariusVasiliev21(coord.BaseCoordinateFrame):
"""
A Heliocentric, right-handed spherical coordinate system defined by the orbit of the
Sagittarius dwarf galaxy, as described in Vasiliev et al. 2021,
https://ui.adsabs.harvard.edu/abs/2021MNRAS.501.2279V/abstract
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__
# Galactic to Sgr coordinates
@frame_transform_graph.transform(
coord.StaticMatrixTransform, coord.Galactic, SagittariusVasiliev21
)
def galactic_to_sgr_v21():
"""Compute the transformation from ICRS to Sagittarius coordinates"""
if not hasattr(SagittariusVasiliev21, "_R"):
R = np.diag([1.0, -1.0, -1.0]) @ B @ C @ D
SagittariusVasiliev21._R = R
return SagittariusVasiliev21._R
# Sgr to Galactic coordinates
@frame_transform_graph.transform(
coord.StaticMatrixTransform, SagittariusVasiliev21, coord.Galactic
)
def sgr_to_galactic_v21():
"""Compute the inverse transformation from Sagittarius coordinates to ICRS"""
return galactic_to_sgr_v21().T
