Most of our knowledge of extrasolar planets rests on precise radial-velocity measurements , either for direct detection or for confirmation of the planetary origin of photometric transit signals .
This has limited our exploration of the parameter space of exoplanet hosts to solar- and later-type , sharp-lined stars .
Here we extend the realm of stars with known planetary companions to include hot , fast-rotating stars .
Planet-like transits have previously been reported in the lightcurve obtained by the SuperWASP survey of the A5 star HD15082 ( WASP-33 ; V = 8.3 , v \sin i = 86 km s ^ { -1 } ) .
Here we report further photometry and time-series spectroscopy through three separate transits , which we use to confirm the existence of a gas giant planet with an orbital period of 1.22d in orbit around HD15082 .
From the photometry and the properties of the planet signal travelling through the spectral line profiles during the transit we directly derive the size of the planet , the inclination and obliquity of its orbital plane , and its retrograde orbital motion relative to the spin of the star .
This kind of analysis opens the way to studying the formation of planets around a whole new class of young , early-type stars , hence under different physical conditions and generally in an earlier stage of formation than in sharp-lined late-type stars .
The reflex orbital motion of the star caused by the transiting planet is small , yielding an upper mass limit of 4.1 M _ { Jupiter } on the planet .
We also find evidence of a third body of sub-stellar mass in the system , which may explain the unusual orbit of the transiting planet .
In HD 15082 , the stellar line profiles also show evidence of non-radial pulsations , clearly distinct from the planetary transit signal .
This raises the intriguing possibility that tides raised by the close-in planet may excite or amplify the pulsations in such stars .