# LSR¶

class astropy.coordinates.builtin_frames.LSR(*args, copy=True, representation_type=None, differential_type=None, **kwargs)[source]

A coordinate or frame in the Local Standard of Rest (LSR).

This coordinate frame is axis-aligned and co-spatial with ICRS, but has a velocity offset relative to the solar system barycenter to remove the peculiar motion of the sun relative to the LSR. Roughly, the LSR is the mean velocity of the stars in the solar neighborhood, but the precise definition of which depends on the study. As defined in Schönrich et al. (2010): “The LSR is the rest frame at the location of the Sun of a star that would be on a circular orbit in the gravitational potential one would obtain by azimuthally averaging away non-axisymmetric features in the actual Galactic potential.” No such orbit truly exists, but it is still a commonly used velocity frame.

We use default values from Schönrich et al. (2010) for the barycentric velocity relative to the LSR, which is defined in Galactic (right-handed) cartesian velocity components $$(U, V, W) = (11.1, 12.24, 7.25)~{{\rm km}}~{{\rm s}}^{{-1}}$$. These values are customizable via the v_bary argument which specifies the velocity of the solar system barycenter with respect to the LSR.

The frame attributes are listed under Other Parameters.

Parameters
dataBaseRepresentation subclass instance

A representation object or None to have no data (or use the coordinate component arguments, see below).

raAngle, optional, keyword-only

The RA for this object (dec must also be given and representation must be None).

decAngle, optional, keyword-only

The Declination for this object (ra must also be given and representation must be None).

distanceQuantity [:ref: ‘length’], optional, keyword-only

The Distance for this object along the line-of-sight. (representation must be None).

pm_ra_cosdecQuantity [:ref: ‘angular speed’], optional, keyword-only

The proper motion in Right Ascension (including the cos(dec) factor) for this object (pm_dec must also be given).

pm_decQuantity [:ref: ‘angular speed’], optional, keyword-only

The proper motion in Declination for this object (pm_ra_cosdec must also be given).

radial_velocityQuantity [:ref: ‘speed’], optional, keyword-only

The radial velocity of this object.

representation_typeBaseRepresentation subclass, str, optional

A representation class or string name of a representation class. This sets the expected input representation class, thereby changing the expected keyword arguments for the data passed in. For example, passing representation_type='cartesian' will make the classes expect position data with cartesian names, i.e. x, y, z in most cases unless overridden via frame_specific_representation_info. To see this frame’s names, check out <this frame>().representation_info.

differential_typeBaseDifferential subclass, str, dict, optional

A differential class or dictionary of differential classes (currently only a velocity differential with key ‘s’ is supported). This sets the expected input differential class, thereby changing the expected keyword arguments of the data passed in. For example, passing differential_type='cartesian' will make the classes expect velocity data with the argument names v_x, v_y, v_z unless overridden via frame_specific_representation_info. To see this frame’s names, check out <this frame>().representation_info.

copybool, optional

If True (default), make copies of the input coordinate arrays. Can only be passed in as a keyword argument.

Other Parameters
v_baryCartesianDifferential

The velocity of the solar system barycenter with respect to the LSR, in Galactic cartesian velocity components.

Attributes Summary

 default_differential Default representation for differential data (e.g., velocity) default_representation Default representation for position data frame_attributes frame_specific_representation_info Mapping for frame-specific component names name v_bary

Attributes Documentation

default_differential

Default representation for differential data (e.g., velocity)

default_representation

Default representation for position data

frame_attributes = {'v_bary': <astropy.coordinates.attributes.DifferentialAttribute object>}
frame_specific_representation_info

Mapping for frame-specific component names

name = 'lsr'
v_bary = <CartesianDifferential (d_x, d_y, d_z) in km / s     (11.1, 12.24, 7.25)>