Hugues Sana

ESA/AURA Astronomer @ Space Telescope Science Institute

The Liège Orbital Solution Package

This page is dedicated to the Liège Orbital Solution Package (LOSP), a FORTRAN77 numerical package that computes the orbital parameters of spectroscopic binaries. The package deals with SB1 and SB2 systems and is able to adjust either circular or eccentric orbits through a weighted fit. While SB1 solutions are derived using existing algorithms, SB2 orbits are fitted using a new approach.

The SB1 eccentric fit relies on the Wolfe, Horak & Storer method, that uses the Wilsing-Russell approach to obtain an accurate first guess of the solution, followed by a differential correction technique to reach the local minimum. The SB2 eccentric orbits are adjusted using the Li├Ęge Orbital Solution Algorithm for SB2 systems (LOSA2), that uses an orthogonal regression technique and a modified version of the Wolfe at al. algorithm to derive self-consistent solutions for both components of the system. The SB1 circular orbits are fitted through a linear least square technique. SB2 circular systems are addressed using an approach similar to the one used in LOSA2, although adapted to null eccentricities.

The resulting package is light and fast, and robust up to eccentricity of 0.7, although it remains useful above. The LOSA2 algorithm preserves much of the advantage of the original Wolfe et al. method. In particular no fastidious exploration of the 8-dimension parameter space is required. Beyond the standard error computations and thanks to the rapidity of execution of the chosen algorithms, LOSP comes along with a Monte-Carlo simulation package. This additional capability allows an independent and robust check of the accuracy of the determined parameters, and of their error estimates.


Current stable version: 1.0.2.

A tarball containing the code source, installation notes and documentation files can be downloaded here.


- January 2009: version 1.0.1, minor bug in installation script corrected
- November 2008: a preprint describing the LOSP package can be found here. Comments are welcome
- November 2008: version 1.0.0 released
- August 2008: Full set of Monte-Carlo simulations performed to test the performances of the LOSA2 algorithm. The details can be found here.
- August 2006: beta-version 0.9.1 released. Minor bug fixed
- June 2006: beta-version 0.9.0 released


If you are using LOSP, please acknowledge its use by sending me an email, so that I can update the list below.

Papers using LOSP

A list of papers using LOSP or earlier version of the package can be found here.