Searching transients in large-scale surveys A method based on the Abbe value

Received...; accepted... Aims. A new method is presented to identify transient candidates in large-scale surveys based on the variability pattern in their light curves. Methods. The method is based on the Abbe value,A, that estimates the smoothness of a light curve, and on a newly introduced value called the excess Abbe and denoted EA, that estimates the regularity of the light curve variability pattern over the duration of the observations. Results. Based on simulated light curves, transients are shown to occupy a specific region in theA versus EA diagram, distinct from sources presenting pulsating-like features in their light curves or having featureless light curves. The method is tested on real light curves taken from EROS-2 and OGLE-II surveys in a 0.50 ◦ × 0.17 ◦ field of the sky in the LMC centered at RA(J2000)=5h25m56.5s and DEC(J2000)=-69d29m43.3s. The method identifies 43 EROS-2 transient candidates out of a total of ∼1300 variable stars, and 19 more OGLE-II candidates, 10 of which do not have any EROS-2 variable star matches and which would need further confirmation to assess their reliability. The efficiency of the method is further tested by comparing the list of transient candidates with known Be stars in the literature. It is shown that all Be stars known in the studied field of view with detectable bursts or outbursts are successfully extracted by the method. In addition, four new transient candidates displaying burst