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Manuscript Title: Derivation of the orbit of a double star from observations made with an intensity interferometer.
Authors: D. Herbison-Evans
Program title: BIN DYN
Catalogue identifier: AACD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 2(1971)59
Programming language: Algol, Usercode.
Computer: ENGLISH ELECTRIC KDF9.
Operating system: KIDSGROVE ALGOL COMPILER.
RAM: 25K words
Word size: 48
Keywords: Astrophysics, Interferometer, Binary-star, Minimisation, Simplex method.
Classification: 1.7.

Nature of problem:
The data from a stellar intensity interferometer consists of a set of observations of the correlation of the light from two optical reflectors with a given separation (the baseline). If the star is double the data can be used to find the orbit of the double star. This has been done for the star alpha Virginis.

Solution method:
Using a test set of orbital parameters a simplex method is used to minimize the weighted squares of the differences between the corresponding calculated and observed correlations.

Restrictions:
The program can cope with at the most 819 observations made at up to 12 baselines, although this is easily altered. The stars are assumed to present uniform circular discs and not to eclipse. The reflectors are assumed to be negligibly small. The program uses only the first order Newton-Raphson solution for Kepler's equation.

Unusual features:
Two subprograms have been written in USERCODE (machine language). These can be replaced by their ALGOL equivalents.

Running time:
On an English Electric KDF9 (about the speed of an IBM 7090) with 819 observations each residual takes about 5 s to calculate if a machine coded linear loop is used (otherwise 20 s). A full 11 parameter minimisation takes about 1 hour. The time is proportional to the number of observations.