Steady-state logarithmic spiral potential

class galpy.potential.SteadyLogSpiralPotential(amp=1.0, omegas=0.65, A=-0.035, alpha=-7.0, m=2, gamma=0.7853981633974483, p=None, tform=None, tsteady=None, ro=None, vo=None)[source]

Class that implements a steady-state spiral potential

\[\Phi(R,\phi) = \frac{\mathrm{amp}\times A}{\alpha}\,\cos\left(\alpha\,\ln R - m\,(\phi-\Omega_s\,t-\gamma)\right)\]

Can be grown in a similar way as the DehnenBarPotential, but using \(T_s = 2\pi/\Omega_s\) to normalize \(t_{\mathrm{form}}\) and \(t_{\mathrm{steady}}\). If the pattern speed is zero, \(t_\mathrm{form}\) and \(t_\mathrm{steady}\) are straight times, not times divided by the spiral period.

__init__(amp=1.0, omegas=0.65, A=-0.035, alpha=-7.0, m=2, gamma=0.7853981633974483, p=None, tform=None, tsteady=None, ro=None, vo=None)[source]

NAME:

__init__

PURPOSE:

initialize a logarithmic spiral potential

INPUT:

amp - amplitude to be applied to the potential (default: 1., A below)

gamma - angle between sun-GC line and the line connecting the peak of the spiral pattern at the Solar radius (in rad; default=45 degree; or can be Quantity)

A - amplitude (alpha*potential-amplitude; default=0.035; can be Quantity

omegas= - pattern speed (default=0.65; can be Quantity)

m= number of arms

Either provide:

  1. alpha=

  2. p= pitch angle (rad; can be Quantity)

tform - start of spiral growth / spiral period (default: -Infinity)

tsteady - time from tform at which the spiral is fully grown / spiral period (default: 2 periods)

OUTPUT:

(none)

HISTORY:

2011-03-27 - Started - Bovy (NYU)