WASP-4b: a 12th magnitude transiting hot Jupiter in the southern hemisphere

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE collaboration and the first planet orbiting a star brighter than 16th magnitude to be discovered in the southern hemisphere. A simultaneous fit to high-quality light curves and precision radial velocity measurements leads to a planetary mass of 1.22 M and 0.09 a planetary radius of 1.42 0.07 R . The host star is USNO-B1.0 0479 0948995, a G7 V 0.08 Jup 0.04 Jup star of visual magnitude 12.5. As a result of the short orbital period, the predicted surface temperature of the planet is 1761 K, making it an ideal candidate for detections of the secondary eclipse at infrared wavelengths.