Direct Imaging of an Asymmetric Debris Disk in the Hd 106906 Planetary System

Abstract

We present the first scattered light detections of the HD 106906 debris disk using Gemini/GPI in the infrared and HST/ACS in the optical. HD 106906 is a 13 Myr old F5V star in the Sco-Cen association, with a previously detected planet-mass candidate HD 106906b projected 650 AU from the host star. Our observations reveal a near edge-on debris disk that has a central cleared region with radius ∼50 AU, and an outer extent >500 AU. The HST data show the outer regions are highly asymmetric, resembling the "needle" morphology seen for the HD 15115 debris disk. The planet candidate is oriented ∼21 • away from the position angle of the primary's debris disk, strongly suggesting non-coplanarity with the system. We hypothesize that HD 106906b could be dynamically involved in the perturbation of the primary's disk, and investigate whether or not there is evidence for a circumplanetary dust disk or cloud that is either primordial or captured from the primary. We show that both the existing optical properties and near-infrared colors of HD 106906b are weakly consistent with this possibility, motivating future work to test for the observational signatures of dust surrounding the planet.

HD 106906: A Case Study for External Perturbations of a Debris Disk

“…The inner disk has little to no vertical extension. While Kalas et al (2015) tentatively suggested the presence of a "warp" in the disk's vertical structure on the west side of the disk, this warp was not confirmed by Lagrange et al (2016). This lack of vertical extension indicates that the inclinations of the disk particles have not been excited.…”

“…4. Kalas et al (2015) observed a faint extension on the west side of the disk out to nearly 500 au, but only diffuse emission on the east side.…”

“…The initial semimajor axis range of 65-85 au for the 10,000 superparticles in the simulated disk was chosen in anticipation that the disk would spread during the 15 Myr course of the simulation. The radial extent of the HD 106906 ring as observed in scattered-light imaging is -50 100 au (Kalas et al 2015;Lagrange et al 2016). The orbital parameters of the companion were chosen such that the gravitational perturbations from the companion would excite the eccentricities of the disk particles without causing a vertical extension of the disk on the timescale of the system's age, and such that the simulated companion's orbit could reproduce the position of the observed companion.…”

“…Following Lee & Chiang (2016), we used g=0.5. Figure 2 shows the simulated brightness of the dust produced by SMACK after 5 Myr, scaled for comparison with Figure 1 of Lagrange et al (2016) and Figure 3 of Kalas et al (2015). The SMACK-produced dust population exhibits a brightness asymmetry at pericenter (Figure 2(a)) as well as a faint extension on the apocenter side (Figure 2(b)), although it does not reproduce the diffuse emission on the eastern side of the disk suggested by Kalas et al (2015).…”

“…Scattered-light imaging of the disk with the Gemini Planet Imager (GPI), the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS), and SPHERE has revealed that the disk is a ring viewed nearly edge-on (inclination~ 85 ), with a inner region cleared of small dust grains (Kalas et al 2015;Lagrange et al 2016). These observations noted four major features of the disk morphology and system geometry:…”