  We report the discovery of a transiting exoplanet, KELT-11b, orbiting the
bright ($V=8.0$) subgiant HD 93396. A global analysis of the system shows that
the host star is an evolved subgiant star with $T_{\rm eff} = 5370\pm51$ K,
$M_{*} = 1.438_{-0.052}^{+0.061} M_{\odot}$, $R_{*} = 2.72_{-0.17}^{+0.21}
R_{\odot}$, log $g_*= 3.727_{-0.046}^{+0.040}$, and [Fe/H]$ = 0.180\pm0.075$.
The planet is a low-mass gas giant in a $P = 4.736529\pm0.00006$ day orbit,
with $M_{P} = 0.195\pm0.018 M_J$, $R_{P}= 1.37_{-0.12}^{+0.15} R_J$, $\rho_{P}
= 0.093_{-0.024}^{+0.028}$ g cm$^{-3}$, surface gravity log ${g_{P}} =
2.407_{-0.086}^{+0.080}$, and equilibrium temperature $T_{eq} =
1712_{-46}^{+51}$ K. KELT-11 is the brightest known transiting exoplanet host
in the southern hemisphere by more than a magnitude, and is the 6th brightest
transit host to date. The planet is one of the most inflated planets known,
with an exceptionally large atmospheric scale height (2763 km), and an
associated size of the expected atmospheric transmission signal of 5.6%. These
attributes make the KELT-11 system a valuable target for follow-up and
atmospheric characterization, and it promises to become one of the benchmark
systems for the study of inflated exoplanets.
