SIMBAD references

Through time-series CCD photometry of the metal-poor globular cluster M53 we have discovered eight new SX Phoenicis-type stars (labeled ``SXP1'' to ``SXP8''). All the new SX Phoenicis stars are located in the blue straggler star region of the color-magnitude diagram of M53. One of these stars (SXP2) is found to have very closely separated pulsation frequencies: f₁/f₂=0.9595, where f₁and f₂are the primary and secondary frequencies, respectively. This may be due to excitation of nonradial modes. Six of these SX Phoenicis stars are considered to be pulsating in the fundamental mode. They show a tight linear correlation between the period and luminosity. We derive a period-luminosity relation for the fundamental mode for the period range of -1.36<logP(days)←1.15: <V>=-3.010(±0.262)logP+15.310(±0.048) with an rms scatter of 0.038, corresponding to <M_V>=-3.010logP-1.070 for an adopted distance modulus of (m-M)_V=16.38.