LinearVelocityField#

class agabpylib.simulation.starclusters.kinematics.LinearVelocityField(v, s, omega, kappa)#

Bases: Kinematics

General linear velocity field for the cluster stars which besides the mean cluster velocity can include a rotation and isotropic expansion/contraction term, both defined with respect to the cluster centre. The velocities are generated according to equations (3) and (4) in Lindegren et al (2000, https://ui.adsabs.harvard.edu/abs/2000A%26A…356.1119L/abstract), where the “dilation” terms are not used.

Specifically the dilation terms \(w_1, w_2, w_3\) are set to zero, while the diagonal terms of the matrix \(T\) are set equal to the expansion rate \(\kappa\) (i.e., \(w_4=w_5=T_{zz}=\kappa\)).

v#

Mean cluster velocity [v_x, v_y, v_z] km/s.

Type:

astropy.units.Quantity 3-vector

s#

Cluster velocity dispersion [s_x. s_y, s_z] in km/s.

Type:

astropy.units.Quantity 3-vector

omega#

Angular speed of the cluster [omega_x, omega_y, omega_z] in km/s/pc

Type:

astropy.units.Quantity 3-vector

kappa#

Cluster expansion/contraction rate in km/s/pc

Type:

astropy.units.Quantity

tmat#

The matrix describing the linear velocity field of the cluster with respect to the cluster barycentre.

Type:

astropy.units.Quantity 3x3 matrix

Methods Summary

addinfo()

returns:

info -- String with specific information about the cluster kinematics.

generate_kinematics(x, y, z, rng)

Generate the velocity vectors of the stars randomly according to the prescribed kinematics of the cluster.

getmeta()

returns:

meta -- Metadata on the kinematics of the cluster stars.

Methods Documentation

addinfo()#
Returns:

info – String with specific information about the cluster kinematics.

Return type:

str

generate_kinematics(x, y, z, rng)#

Generate the velocity vectors of the stars randomly according to the prescribed kinematics of the cluster.

Parameters:

  • x (astropy.units.Quantity arrays) – The x, y, z positions of the stars with respect to the barycentre, in units of pc, where the barycentre of the cluster is assumed to be at (0, 0, 0) pc!

  • y (astropy.units.Quantity arrays) – The x, y, z positions of the stars with respect to the barycentre, in units of pc, where the barycentre of the cluster is assumed to be at (0, 0, 0) pc!

  • z (astropy.units.Quantity arrays) – The x, y, z positions of the stars with respect to the barycentre, in units of pc, where the barycentre of the cluster is assumed to be at (0, 0, 0) pc!

  • rng (numpy.random.Generator) – Random number generator. This is provided separately to enable user control over the random number sequence.

Returns:

v_x, v_y, v_z – The v_x, v_y, v_z velocity components of the stars in units of km/s.

Return type:

astropy.units.Quantity arrays

getmeta()#
Returns:

meta – Metadata on the kinematics of the cluster stars.

Return type:

dict