Detection probability of a low-mass planet for triple lens events: implication of properties of binary-lens superposition

Abstract

In view of the assumption that any planetary system is likely to be composed of more than one planet, and the multiple planet system with a large mass planet has more chance of detailed follow-up observations, the multiple planet system may be an efficient way to search for sub-Jovian planets. We compare the magnification pattern of the triple lens system with that of a best-fitted binary system composed of a star and a Jovian mass planet, and check the probability in detecting the low-mass secondary planet whose signature will be superposed on that of the primary Jovian mass planet. Detection probabilities of the low-mass planet in the triple lens system are quite similar to the probability in detecting such a low-mass planet in a binary system with a star and only a low-mass planet, which shows that the signature of a low-mass planet can be effectively detected even when it is concurrent with the signature of the more massive planet, implying that the binary superposition approximation works over a relatively broad range of planet mass ratio and separations, and the inaccuracies thereof do not significantly affect the detection probability of the lower mass secondary planet. Since the signature of the Jovian mass planet will be larger and lasts longer, thereby warranting more intensive follow-up observations, the actual detection rate of the low-mass planet in a triple system with a Jovian mass can be significantly higher than that in a binary system with a low-mass planet only. We conclude that it may be worthwhile to develop an efficient algorithm to search for `super-Earth' planets in the paradigm of the triple lens model for high-magnification microlensing events.