Astrometry of the resolved binary target Alhena (= γ Gem). a) Overview the orbit of Alhena B relative to Alhena A, as reported in Drummond (2014). The black rectangular frame indicates the area shown at larger magnification in the following panels. The position of Alhena A is marked with a star. b) Observed relative positions of Alhena B (crosses) and their predicted positions (squares) on the assumed orbit for each of the three epochs (2011.98, 2013.17: this work; 2012.26: Drummond 2014). The sizes of the crosses correspond to the astrometric error bars in the azimuthal and radial directions. Note that the observed positions are systematically and significantly offset to the north (χ2 = 31.4). c) The same for an adjusted orbit with , leading to a good fit the data (χ2 = 6.8).
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