Alpha Trianguli Australis (K2 II-III) : hybrid or composite ?

Abstract

The prototype "hybrid-spectrum" giant, α Trianguli Australis, exhibits a far-ultraviolet continuum which is considerably bluer than would be expected of a star of its optical colors, suggesting the presence of a previously unrecognized companion. If the K type primary is as luminous as indicated by the widths of its Ca II and Hα lines, the companion could be an early F type dwarf that only recently has arrived on the main sequence. Indeed, the flux of C IV from α TrA - an important measure of "hybridness" - would not be inconsistent with that expected from a very young, chromospherically active F star.