Name

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    RHOTHETA

Purpose

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    Calculate the separation and position angle of a binary star

Explanation

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    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

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  Result = RHOTHETA ( P, T, e, a, i, Omega, omega2, t2)

Input

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  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

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  structure containing
  rho - separation [arc second]
  theta - position angle [degree]
  In case of errors rho and theta are -1.

Restrictions

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  All input parameters have to be scalars and floating point numbers.
 

Example

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      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

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      CIRRANGE - from IDL Astronomy Library
     

Modification History

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  Written by: Sebastian Kohl Hamburg Observatory, November, 2012