We report the discovery by the HATSouth survey of HATS-3b , a transiting extrasolar planet orbiting a V= 12.4 F dwarf star .
HATS-3b has a period of P = 3.5479 d , mass of M _ { p } = 1.07 M _ { J } , and radius of R _ { p } = 1.38 R _ { J } .
Given the radius of the planet , the brightness of the host star , and the stellar rotational velocity ( v \sin { i } = 9.0 km s ^ { -1 } ) , this system will make an interesting target for future observations to measure the Rossiter-McLaughlin effect and determine its spin-orbit alignment .
We detail the low/medium-resolution reconnaissance spectroscopy that we are now using to deal with large numbers of transiting planet candidates produced by the HATSouth survey .
We show that this important step in discovering planets produces \log { g } and T _ { eff } parameters at a precision suitable for efficient candidate vetting , as well as efficiently identifying stellar mass eclipsing binaries with radial velocity semi-amplitudes as low as 1 km s ^ { -1 } .