in @Stolker2016. The IRDIS $K$-band profile does not seem to confirm the increasing trend observed for the IFS data. As discussed in @Stolker2016, the red colors of the dust grains could be explained if they are composed of $\muup$m-sized aggregates [@Min2016].

Then, we registered the spine, photometry, and width of each spiral arm in the [collapsed RDI IFS and IRDIS images]{}. The images were first deprojected assuming for the disk an inclination of 11$^{\circ}$ [@Dent2005; @Pontoppidan2008; @Lyo2011] and a position angle of 62$^{\circ}$ [@Perez2014] and scaled by the square of the distance to the star. Then, [we rotated the images by steps of 2$^{\circ}$ in]{} order to align the spiral parallel to the horizontal direction and [to fit it with a 1D]{} Gaussian function using boxes of $\sim$0.15$''$ width (i.e., 20 pixels for IFS and 12 pixels for IRDIS) width approximately centered on the spiral spine to extract the location of the spine, the intensity at the spine location, and the width of the spiral. The error bars on the data points were assessed using their standard deviation in a [three-bin]{} sliding box.

We [show the width of the spirals as a function of the position angle in Fig. \[fig:widthspirals\]]{}. 