the surface brightness profiles (Figs. \[fig:brightnessprof\] and \[fig:spiralpeak\]). The spectral differences between S1 and S2 and within S1 could indicate that the surface dust grains might have different optical properties according to their location, which can be [a]{} sign of different composition or size.]{} The SPHERE reflectance spectra of SAO 206462 look somewhat different from the SPHERE spectra of HR 4796A [@Milli2017], which show an increasing slope at $\sim$1–1.1 $\muup$m [and]{} then a plateau in the $J$ band.

Summary
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The analysis of the SPHERE total intensity images confirm the red colors for the dust grains and the presence of the shadow lanes [(though at lower significance)]{} found by @Stolker2016 in SPHERE polarized-light images. They also indicate [sharp variations [($\sim$40%)]{} in the S1 width]{}, while the S2 width does not show strong variations. Finally, the reflectance spectra suggest [local spectral differences between S1 and S2 and within S1]{}, which might be a hint [of]{} different composition or sizes of the dust grains.

Detection limits on putative giant protoplanets {#sec:detectionlimits}
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Archival NaCo/$L^{\prime}$ imaging data {#sec:nacodata}
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We reduced and analyzed archival NaCo/$L^{\prime}$ imaging data (ESO program 090.C-0443, P.I. Currie) using a custom pipeline for the reduction steps (cosmetics, frame registering) 