On the Interpretation of Sub-Giant Branch Morphologies of
  Intermediate-Age Star Clusters with Extended Main Sequence Turnoffs
  Recent high-quality photometry of many star clusters in the Magellanic Clouds
with ages of 1$\,-\,$2 Gyr revealed main sequence turnoffs (MSTOs) that are
significantly wider than can be accounted for by a simple stellar population
(SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age
spread of several $10^8$ yr, challenging the traditional view of star clusters
as being formed in a single star formation episode. Li et al. and Bastian &
Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651,
NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC)
that exhibit an eMSTO. They argued that the SGB of these star clusters can be
explained only by a SSP. We study these and two other similar star clusters in
the LMC, using extensive simulations of SSPs including unresolved binaries. We
find that the shapes of the cross-SGB profiles of all star clusters in our
sample are in fact consistent with their cross-MSTO profiles when the latter
are interpreted as age distributions. Conversely, SGB morphologies of star
clusters with eMSTOs are found to be inconsistent with those of simulated SSPs.
Finally, we create PARSEC isochrones from tracks featuring a grid of convective
overshoot levels and a very fine grid of stellar masses. A comparison of the
observed photometry with these isochrones shows that the morphology of the red
clump (RC) of such star clusters is also consistent with that implied by their
MSTO in the age spread scenario. We conclude that the SGB and RC morphologies
of star clusters featuring eMSTOs are consistent with the scenario in which the
eMSTOs are caused by a distribution of stellar ages.
