Figure 2.
Left: Total polarized
intensity of the V4046
Sgr disk. Right: Total
polarized intensity
multiplied by r2,to
account for dilution of
incident starlight.
rendering of the V4046 Sgr disk based on
these data).
On the other hand, our analysis of infrared
observations from the Spitzer Space Telescope and Herschel Space Observatory suggests that the apparent “hole” at submillimeter wavelengths is actually partially filled with
gas and dust. Since probing this inner-disk
material directly requires imaging at resolutions near the diffraction limit of an 8-meter telescope, we turned to the new Gemini
Planet Imager (GPI) on the Gemini South Telescope to achieve this extreme resolution.
GPI Imaging of V4046 Sgr
GPI is a state-of-the-art, near-infrared instrument dedicated to directly detecting and
characterizing young, self-luminous exoplanets and the dusty circumstellar disks in
which they form. GPI combines high-order
adaptive optics, a diffraction-suppressing
coronagraph, and an integral field spectrograph to obtain near-diffraction-limited images. GPI allows us to observe these targets
with unprecedentedly short integration
times of just a few minutes.
We obtained Early Science observations
of V4046 Sgr with GPI in April 2014, using
its coronagraphic+polarimetric modes to
6
GeminiFocus
trace light scattered off micron-sized (or
smaller) dust grains in the disk. Our data
consist of images through the J- and K2band filters, at wavelengths of 1.24 and 2.25
microns, respectively.
Figure 2 shows the resulting images of the
disk at J-band, which (thanks to the proximity of V4046 Sgr and the exquisite resolution
and sensitivity of GPI) probe down to ~ 7 AU
from the central binary at ~ 2 AU resolution.
The left image is the total polarized intensity;
the right image is total polarized intensity
multiplied by the square of the deprojected
distance from each pixel to the star (r2) — to
account for the fact that the light reaching
the disk from the central star drops off as 1/r2.
The GPI images reveal a distinct double ring
structure, with a bright inner ring centered at
~ 14 AU, and an outer halo extending out to
~ 45 AU. Two gaps appear in the disk: One between the two rings at ~ 20 AU, and one interior to the bright ring. These gaps roughly
correspond to the orbital radii of Uranus and
Saturn in our own Solar System. The gap/
ring structure revealed by the GPI images of
V4046 Sgr hence provides the first strong evidence for ongoing planet formation in a circumbinary disk within giant-planet-hosting
regions similar to that of our Sun’s.
July 2015