Beta Pictoris' Inner Disk in Polarized Light and New Orbital Parameters for Beta Pictoris b

We present H-band observations of β Pic with the Gemini Planet Imager’s (GPI’s) polarimetry mode that reveal the debris disk between ∼0.″3 (6 AU) and ∼1.″7 (33 AU), while simultaneously detecting β Pic b. The polarized disk image was fit with a dust density model combined with a Henyey-Greenstein scattering phase function. The best-fit model indicates a disk inclined to the line of sight (φ =85\buildrel{\circ}\over{.} {27}_-0.19^+0.26) with a position angle (PA) {θ }_{PA}=30\buildrel{\circ}\over{.} {35}_-0.28^+0.29 (slightly offset from the main outer disk, {θ }_{PA}≈ 29^\circ ), that extends from an inner disk radius of {23.6}_-0.6^+0.9 {AU} to well outside GPI’s field of view. In addition, we present an updated orbit for β Pic b based on new astrometric measurements taken in GPI’s spectroscopic mode spanning 14 months. The planet has a semimajor axis of a={9.2}_-0.4^+1.5 {AU}, with an eccentricity e≤slant 0.26. The PA of the ascending node is {{Ω }}=31\buildrel{\circ}\over{.} 75+/- 0\buildrel{\circ}\over{.} 15, offset from both the outer main disk and the inner disk seen in the GPI image. The orbital fit constrains the stellar mass of β Pic to 1.60+/- 0.05 {M}_⊙ . Dynamical sculpting by β Pic b cannot easily account for the following three aspects of the inferred disk properties: (1) the modeled inner radius of the disk is farther out than expected if caused by β Pic b; (2) the mutual inclination of the inner disk and β Pic b is ∼ 4^\circ , when it is expected to be closer to zero; and (3) the aspect ratio of the disk ({h}₀={0.137}_-0.006^+0.005) is larger than expected from interactions with β Pic b or self-stirring by the disk’s parent bodies.