SX Phoenicis Stars in the Globular Cluster NGC 5466

Through time-series CCD photometry of the globular cluster NGC 5466, we have detected nine SX Phoenicis stars, including three new ones. All the SX Phoenicis stars are located in the blue straggler region in the color-magnitude diagram of NGC 5466. Five of them clearly show double-radial mode features, the periods of which are consistent with the theoretical ratio of the first-overtone mode to the fundamental mode (P_1H/P_F). Normally, it has not been easy to secure a P-L relation for the SX Phoenicis stars because their pulsational mode has been difficult to determine. The existence of five SX Phoenicis stars in NGC 5466 with double-radial modes allows us to reliably derive a P-L relation for the fundamental mode of SX Phoenicis stars. Using seven SX Phoenicis stars, including five stars with double-radial modes, we derive a P-L relation for the fundamental mode in NGC 5466, ⟨V⟩ = -3.25(±0.46) log P + 14.70(±0.06),(σ = ±0.04), corresponding to ⟨M_V⟩ = -3.25(±0.46) log P - 1.30(±0.06) for an adopted distance modulus of (m - M)₀ = 16.00 and zero reddening.