2006MNRAS.371..957R

The Rapid Temporal Survey (RATS) is a survey to detect objects whose optical intensity varies on time-scales of less than ∼70 min. In our pilot data set taken with the Isaac Newton Telescope and the Wide Field Camera in 2003 November, we discovered nearly 50 new variable objects. Many of these varied on time-scales much longer than 1 h. However, only four objects showed a modulation on a time-scale of 1 h or less. This paper presents followup optical photometry and spectroscopy of these four objects. We find that RATJ0455 + 1305 is a pulsating (on a period of 374 s) subdwarf B star of the EC14026 type. We have modelled its spectrum and determine T_eff= 29200 ± 1900K and logg = 5.2±0.3 which locates it on the cool edge of the EC14026 instability strip. It has a modulation amplitude which is one of the highest of any known EC14026 star. Based on their spectra, photometric variability and their infrared colours, we find that RATJ0449+1756, J0455 + 1254 and J0807+1510 are likely to be SX Phe stars - dwarf δ Sct stars. Our results show that our observing strategy is a good method for finding rare pulsating stars.