The sub-Jupiter mass transiting exoplanet WASP-11b

We report the discovery of a sub-Jupiter mass exoplanet transiting a magnitude V = 11.6 host star 1SWASP J030928.54+304024.7. A simultaneous fit to the transit photometry and radial-velocity measurements yield a planet mass $M_{\rm p}$ = 0.53 $\pm$ 0.07 ${M_{\rm J}}$, radius $R_{\rm p} = 0.91^_~{R_{\rm J}}$ and an orbital period of $3.722465^{\rm +0.000006}_$ days. The host star is an early to mid-K dwarf, with a spectral analysis yielding an effective temperature of 4800 $\pm$ 100 K and log g = 4.45 $\pm$ 0.2. It is amongst the smallest, least massive and lowest luminosity stars known to harbour a transiting exoplanet. WASP-11b is the third least strongly irradiated transiting exoplanet discovered to date, experiencing an incident flux $F_{\rm p}$ = 1.9$\times$108  erg s-1 cm-2 and having an equilibrium temperature $T_{\rm eql}$ = 960 $\pm$ 70 K.