  We present early laboratory simulations and extensive on-sky tests validating
of the performance of a shaped pupil coronagraph (SPC) behind an extreme-AO
corrected beam of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO)
system. In tests with the SCExAO internal source/wavefront error simulator, the
normalized intensity profile for the SPC degrades more slowly than for the Lyot
coronagraph as low-order aberrations reduce the Strehl ratio from extremely
high values (S.R. $\sim$ 0.93--0.99) to those characteristic of current
ground-based extreme AO systems (S.R. $\sim$ 0.74--0.93) and then slightly
lower values down to S.R. $\sim$ 0.57. On-sky SCExAO data taken with the SPC
and other coronagraphs for brown dwarf/planet-hosting stars HD 1160 and HR 8799
provide further evidence for the SPC's robustness to low-order aberrations.
From H-band Strehl ratios of 80% to 70%, the Lyot coronagraph's performance vs.
that of the SPC may degrade even faster on sky than is seen in our internal
source simulations. The 5-$\sigma$ contrast also degrades faster (by a factor
of two) for the Lyot than the SPC. The SPC we use was designed as a technology
demonstrator only, with a contrast floor, throughput, and outer working angle
poorly matched for SCExAO's current AO performance and poorly tuned for imaging
the HR 8799 planets. Nevertheless, we detect HR 8799 cde with SCExAO/CHARIS
using the SPC in broadband mode, where the S/N for planet e is within 30% of
that obtained using the vortex coronagraph. The shaped-pupil coronagraph is a
promising design demonstrated to be robust in the presence of low-order
aberrations and may be well-suited for future ground and space-based direct
imaging observations, especially those focused on follow-up exoplanet
characterization and technology demonstration of deep contrast within
well-defined regions of the image plane.
