  In order to look for signs of on-going planet formation in young disks, we
carried out the first J-band polarized emission imaging of the Herbig Ae/Be
stars HD 150193, HD 163296, and HD 169142 using the Gemini Planet Imager (GPI),
along with new H band observations of HD 144432. We confirm the complex "double
ring" structure for the nearly face-on system HD 169142 first seen in H-band,
finding the outer ring to be substantially redder than the inner one in
polarized intensity. Using radiative transfer modeling, we developed a physical
model that explains the full spectral energy distribution (SED) and J- and
H-band surface brightness profiles, suggesting that the differential color of
the two rings could come from reddened starlight traversing the inner wall and
may not require differences in grain properties. In addition, we clearly detect
an elongated, off-center ring in HD 163296 (MWC 275), locating the scattering
surface to be 18 AU above the midplane at a radial distance of 77 AU,
co-spatial with a ring seen at 1.3mm by ALMA linked to the CO snow line.
Lastly, we report a weak tentative detection of scattered light for HD 150193
(MWC 863) and a non-detection for HD 144432; the stellar companion known for
each of these targets has likely disrupted the material in the outer disk of
the primary star. For HD 163296 and HD 169142, the prominent outer rings we
detect could be evidence for giant planet formation in the outer disk or a
manifestation of large-scale dust growth processes possibly related to
snow-line chemistry.
