Dust Segregation
Further evidence for planet-building activity
in the V4046 Sgr disk comes from a comparison of the GPI and SMA data (Figure 3). GPI
imaging traces light scattered off small dust
grains, which appear to prevail within 10-45
AU of the central stars. Data from the SMA
traces thermal emission from larger centimeter- to millimeter-sized dust grains, revealing
emission concentrated in a ring whose inner
edge lies at ~ 30 AU. Thus, the GPI data confirm the earlier Spitzer and Herschel spectroscopic observations, which show that the
gap seen at submillimeter wavelengths is indeed partially filled with small dust particles.
Modeling of planet formation in disks suggests that we should see this phenomenon
of grain size segregation. When a gas giant
planet forms in a disk, it creates local density waves that trap larger (mm- to cm-sized)
particles outside the planet-forming regions
of the disk. Smaller (micron-sized) grains
freely pass through these pressure traps, resulting in strong dust particle size gradients.
Our comparison of the GPI and submillimeter imaging of the V4046 Sgr disk provides
vivid evidence in support of these so-called
“dust filtration” models by describing the
structure of a circumbinary disk captured in
the process of actively forming planets.
In summary, our GPI images appear to provide powerful tests of two planet-forming
processes in the V4046 Sgr disk: (1) That
one or more young giant planets following
orbits similar to those of Saturn or Uranus
have simultaneously carved out a disk gap
and an inner disk hole; and (2) these gas-giant planets have generated large-scale density waves, resulting in dust particle filtration
and segregation by size. Together these results offer two possible ways giant planets
can form in de