RHOTHETA
Name
RHOTHETA
Purpose
Calculate the separation and position angle of a binary star
Explanation
This function will return the separation rho and position angle
theta of a visual binary star derived from its orbital elements.
The algorithms described in the following book will be used:
Meeus J., 1992, Astronomische Algorithmen, Barth.
Compared to the examples given at p. 400 and no discrepancy found.
Input parameters will never be changed.
Calling Sequence
Result = RHOTHETA ( P, T, e, a, i, Omega, omega2, t2)
Input
P - Period [year]
T - Time of periastron passage [year]
e - eccentricity of the orbit
a - semi-major axis [arc second]
i - inclination [degree]
Omega - node [degree]
omega2 - longitude of periastron [degree]
t2 - epoch of observation [year]
Output
structure containing
rho - separation [arc second]
theta - position angle [degree]
In case of errors rho and theta are -1.
Restrictions
All input parameters have to be scalars and floating point numbers.
Example
Find the position of Eta Coronae Borealis at the epoch 1980.0
IDL> test=rhotheta(41.623,1934.008,0.2763,0.907,59.025,23.717,219.907,1980.0)
rho= 0.411014 theta= 318.42307
Procedures Called
CIRRANGE - from IDL Astronomy Library
Modification History
Written by: Sebastian Kohl Hamburg Observatory, November, 2012