On the Selection of Photometric Planetary Transits

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  • 15 January 2003
Abstract
In this paper we present a new method for removing the stellar transits from planetary transit candidate lists based on the presence of gravity darkening in their light curves. This method will greatly reduce the number of transit candidates from future surveys requiring spectroscopic follow up with large telescopes. We show that the presence of this effect can be used to detect stellar secondaries with masses ~0.2 M_sun orbiting sun-like stars at a photometric accuracy level which has already been achieved in transit surveys. Unlike the usual candidate selection method, which are primarily based on the estimated radius of the orbiting object, this technique is not biased against bona-fide planets and brown dwarfs with large radii because the amplitude of the effect depends on the transiting object's mass. We show that many of the recent OGLE-III planetary candidates exhibit the presence of a significant gravity effect and are therefore likely to be due to a stellar secondary. The full transit light curves of white dwarfs will generally not mimic transits of small planets because of the significant gravity darkening effect. We discuss the relative merits of methods used to detect transit candidates which are due to stellar blends rather than planets. We outline how photometric observations taken in two bands can be used to detect the presence of stellar blends.

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