A He-rich g-mode pulsator on the BHB

We introduce the first g-mode pulsator found to reside on the classical blue horizontal branch. We extend the original discovery dataset to include more than 3 years of continuous photometry of KIC 1718290, which reveals a rich spectrum of low-amplitude modes with periods between one and twelve hours, most of which follow a regular spacing of 276.3 s. This mode structure strongly resembles that of the V1093 Her pulsators, with only a slight shift towards longer periods. Our spectroscopy, however, reveals KIC 1718290 to be quite distinct from the sdB stars that show V1093Her pulsations, which all have surface gravities higher than log g = 5.1 and helium abundances depleted by at least an order of magnitude relative to the solar composition. We find that KIC 1718290 has T_eff = 22 100 K, log g = 4.72, and a supersolar helium abundance (log He/H = -0.45). This places it well above the extreme horizontal branch, and rather on the very blue end of the classical horizontal branch. We conclude that KIC 1718290 must have suffered extreme mass loss during its first giant stage, but not sufficient to reach the extreme horizontal branch.

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Date added: Thu, 10 Oct 13