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takyon writes:

http://www.astronomy.com/news/2016/10/astronomers-find-a-planet-through-a-never-before-used-method

A-type stars are bigger and hotter than most stars in the Kepler catalog and tend to be noisy, changing brightness at regular intervals. This dimming and brightening can be hard to untangle from, for instance, a planet transiting and dimming its light. As such, while there's no reason for A-type stars not to have planets, it's been difficult for astronomers to identify them. So far, the few exoplanets found around A-type stars are either from direct imaging (which can only [be done] where the planets are very far from their star, or from transits where the planets are very close to the star, where the signal is strong.

But astronomers came up with a novel idea to use the variability of the star itself as a way to look for exoplanets. The star pulses because of helium changes in its lower layers. It puffs up, cools and dims, shrinks, heats and brightens, and then repeats the process multiple times in a day. In a Kepler light curve, this shows up as a periodic dimming and brightening, like clockwork. But this clock shows a delay. The pulsations appear a little early or late, and by calculating this delay, astronomers can measure that the star is actually moving in a back-and-forth, orbital motion. And this movement is due to the gravitational tug of a nearby planet.

The delays in KIC 7917485's pulsations revealed a planet about 12 Jupiter masses with a period of 840 days, which is close to the habitable zone of such a hot star. While 12 Jupiter masses makes this planet nearly a brown dwarf, and certainly a gas giant, the study's authors point out that potential moons keep the question of habitability an intriguing one.

An abstract and full report (pdf) are available on arXiv.org.

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