Binary Star Orbits. III. In which we Revisit the Remarkable Case of Tweedledum and Tweedledee

TL;DR

This paper revisits the complex binary star system 'Tweedledum and Tweedledee', correcting previous data errors and determining their orbits through archival and new observations, addressing historical ambiguities in interferometric measurements.

Contribution

The study provides the first corrected orbital elements for the 'Tweedledum and Tweedledee' system, resolving quadrant ambiguities and introducing a novel software filter for archival speckle data.

Findings

Corrected orbital elements for the binary system

Resolved the 180-degree quadrant ambiguity

Confirmed co-planarity of the multiple system

Abstract

Two of the most challenging objects for optical interferometry in the middle of the last century were the close components (FIN 332) of the wide visual binary STF2375 (= WDS 18455+0530 = HIP 92027 = ADS 11640). Each component of the wide pair was found to have subcomponents of approximately the same magnitude, position angle and separation and, hence, were designated by the tongue in cheek monikers "Tweedledum and Tweedledee" by the great visual interferometrist William S. Finsen in 1953. They were later included in a list of "Double Stars that Vex the Observer" by W.H. van den Bos (1958a). While speckle interferometry has reaped a rich harvest investigating the close inteferometric binaries of Finsen, the "Tweedles" have continued to both fascinate and exasperate due to both the great similarity of the close pairs as well as the inherent 180 degree ambiguity associated with interferometry. Detailed analysis of all published observations of the system have revealed several errors which are here corrected, allowing for determination of these orbital elements which resolve the quadrant ambiguity. A unique software filter was developed which allowed subarrays from archival ICCD speckle data from 1982 to be re-reduced. Those data, combined with new and unpublished observations obtained in 2001-9 from NOAO 4m telescopes, the Mt. Wilson 100in telescope and the Naval Observatory Flagstaff Station 61in telescope as well as high quality unresolved measures all allow for the correct orbits to be determined. Co-planarity of the multiple system is also investigated.