S21B0056
S21B0056
A million visual binaries identified from recent Gaia data releases have revealed a mysterious excess of “twin" binaries, whose two component stars separated by 50–5000 au have nearly identical physical properties. We propose to use REACH (SCExAO+IRD) to obtain high-resolution (R∼100,000), spatially resolved spectra of the twin binaries with <∼ 1" angular separations, which correspond to physical separations of 50–500 au. We will measure projected spin velocity vsini of each component star from absorption line broadening and use their difference in each binary to assess the spin (mis)alignment of the twin stars. The measurements will provide critical information for uncovering the origin of the twin phenomenon, which may also bring key insights into more generic star/binary-forming processes such as circumbinary accretion and dynamical orbit evolution in dense star-forming clusters. The same spectra will also be used to probe the difference of chemical abundances in the component stars and to search for potential signatures of planets engulfed by the stars.
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