# Softened-needle bar potential¶

class galpy.potential.SoftenedNeedleBarPotential(amp=1.0, a=4.0, b=0.0, c=1.0, normalize=False, pa=0.4, omegab=1.8, ro=None, vo=None)[source]

Class that implements the softened needle bar potential from Long & Murali (1992)

$\Phi(x,y,z) = \frac{\mathrm{amp}}{2a}\,\ln\left(\frac{x-a+T_-}{x+a+T_+}\right)$

where

$T_{\pm} = \sqrt{(a\pm x)^2 + y^2+(b+\sqrt{z^2+c^2})^2}$

For a prolate bar, set $$b$$ to zero.

__init__(amp=1.0, a=4.0, b=0.0, c=1.0, normalize=False, pa=0.4, omegab=1.8, ro=None, vo=None)[source]

Initialize a softened-needle bar potential.

Parameters:
• amp (float or Quantity, optional) – Amplitude to be applied to the potential (default: 1); can be a Quantity with units of mass.

• a (float or Quantity, optional) – Bar half-length.

• b (float , optional) – Triaxial softening length (can be Quantity).

• c (float, optional) – Prolate softening length (can be Quantity).

• pa (float or Quantity, optional) – The position angle of the x axis.

• omegab (float or Quantity, optional) – Pattern speed.

• normalize (bool or float, optional) – If True, normalize such that vc(1.,0.)=1., or, if given as a number, such that the force is this fraction of the force necessary to make vc(1.,0.)=1.

• 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

• 2016-11-02 - Started - Bovy (UofT)