# Lopsided disk potential¶

Like in Kuijken & Tremaine, but for m=1. See galpy.potential.CosmphiDiskPotential for a more general version that allows for a break radius within which the radial dependence of the potential changes from R^p to R^-p (lopsided disk corresponds to m=1).

class galpy.potential.LopsidedDiskPotential(amp=1.0, phib=0.4363323129985824, p=1.0, phio=0.01, r1=1.0, cp=None, sp=None, ro=None, vo=None)[source]

Class that implements the disk potential

$\Phi(R,\phi) = \mathrm{amp}\,\phi_0\,\left(\frac{R}{R_1}\right)^p\,\cos\left(\phi-\phi_b\right)$

Special case of CosmphiDiskPotential with m=1; see documentation for CosmphiDiskPotential

__init__(amp=1.0, phib=0.4363323129985824, p=1.0, phio=0.01, r1=1.0, cp=None, sp=None, ro=None, vo=None)[source]

Initialize a CosmphiDiskPotential.

Parameters:
• amp (float, optional) – Amplitude to be applied to the potential (default: 1.), degenerate with phio below, but kept for overall consistency with potentials.

• m (int, optional) – m in cos(m * phi - m * phib).

• p (float) – Power-law index of the phi(R) = (R/Ro)^p part.

• r1 (float or Quantity, optional) – Normalization radius for the amplitude (can be Quantity); amp x phio is only the potential at (R,phi) = (r1,pib) when r1 > rb; otherwise more complicated.

• rb (float or Quantity, optional) – If set, break radius for power-law: potential R^p at R > Rb, R^-p at R < Rb, potential and force continuous at Rb.

• phib (float or Quantity, optional) – Angle (in rad; default=25 degree).

• phio (float or Quantity, optional) – Potential perturbation (in terms of phio/vo^2 if vo=1 at Ro=1; or can be Quantity).

• cp (float or Quantity, optional) – m * phio * cos(m * phib); can be Quantity with units of velocity-squared.

• sp (float or Quantity, optional) – m * phio * sin(m * phib); can be Quantity with units of velocity-squared.

• ro (float or Quantity, optional) – Distance scale for translation into internal units (default from configuration file).

• vo (float or Quantity, optional) – Velocity scale for translation into internal units (default from configuration file).

Notes

• Either specify (phib, phio) or (cp, sp).

• 2011-10-27 - Started - Bovy (IAS)