2014 programme

Poster
Poster

An Astronomical Calculator for Double Stars

Andrew James

Non-Affiliated Independent Amateur Astronomer (NAIAA)

One of the most interesting aspects of visual double stars is the main desire in learning if their component stars are gravitationally attached as binary stars. Only a few systems have been established in the last two centuries or so, but the vast majority remain indeterminate, or have such long orbital periods that we have no way of discovering a connection by motion alone.

Yet there are other indirect mathematical or astrophysical methods of estimating probabilities of true association. These methods require using available data sets from both the Washington Double Star Catalogue (WDS) and the various Hipparcos Star Catalogues (HiP, HIP2, HIPX), plus other information from the CDS's on-line SIMBAD database. Moreover, when this data is combined, we can learn more about these systems and basic derived stellar parameters.

For several years, I have used and developing a spreadsheet named "DSCalc" that is mostly helpful in writing double star observational texts. This enables me to make quick and simple calculations of distances, absolute magnitudes, apparent or true separations, dynamic parallaxes, and orbital periods. It also finds general estimates of their mutual stellar masses, radii, surface temperatures, etc., recently extending to provide basic information of stellar ages, if metallicity data is available.

One of the main strengths is that useful results may be compared to other published methods of theoretical analysis, so that the accuracies can be examined and commented upon. Contrasting the apparent motions of the visual double star with the expectant predicted motions helps finds the probability of true attachment. Importantly, this allows selection of critical pairs to measure and the overall frequency of successive examination of double stars at the telescope.

This poster paper gives a general rundown of the calculation methods and presents some recently worked on examples that have been usefully applied to southern double stars.

Andrew is a Sydney amateur astronomer who has made several presentations to NACAA since the 1980. His specialist interests are in southern double stars, southern planetary nebulae and towards historical astronomy. He is continuing to work on the original double star observations made by Australian astronomers in the 19th Century, and presents his general works through the website Southern Astronomical Delights. Although a 34 year member and a past president of the ASNSW, Andrew's given presentation is as an independent free-lance amateur astronomer, deliberately distanced from the astronomical society system or commercial interests.