Uncertainties in separation and position angle of historic measures – Alpha Centauri AB case study

Graeme White, Roderick Letchford, Allan Ernest

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Abstract

Accurate uncertainties in the Separations and Position Angles of historic measures of double stars are needed for the study of the motion (rectilinear or orbit) of the individual members of the pair. As a guide for workers in this field, we present an assessment of these uncertainties for the most well studied pair α Cen AB, over a period of some 260 years, that shows the accuracy of both the Separation and Position Angle measures has improved. Standard Deviation estimates of Separations falls from about 0.5 arcsec in the mid-1800s to 0.07 arcsec by the late twentieth century. Standard Deviation estimates of Position Angles fall from about 2 degree in the mid-1800s to about 0.3 degree by the late twentieth century. In addition, there seems to be a falling away of accuracy in the twenty first century data. As expected, here is an increase in the spread of uncertainties, and a bias, apparent at small separations.
Original languageEnglish
Pages (from-to)432-442
Number of pages11
JournalJournal of Double Star Observations
Volume14
Issue number3
Publication statusPublished - 01 Jul 2018

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