Spectro-interferometry of the Be Star δ Sco: Near-infrared Continuum and Gas Emission Region Sizes in 2007

We present near-infrared H- and K-band spectro-interferometric observations of the gaseous disk around the primary Be star in the δ Sco binary system, obtained in 2007 (between periastron passages in 2000 and 2011). Observations using the CHARA/MIRC instrument at H band resolve an elongated disk with a Gaussian FWHM 1.18 × 0.91 mas. Using the Keck Interferometer (KI), the source of the K-band continuum emission is only marginally spatially resolved, and consequently we estimate a relatively uncertain K-band continuum disk FWHM of 0.7 ± 0.3 mas. Line emission on the other hand, He I λ2.0583 μm and Brγ λ2.1657 μm, is clearly detected, with ~10% lower visibilities than those of the continuum. When taking into account the continuum/line flux ratio this translates into much larger sizes for the line emission regions: 2.2 ± 0.4 mas and 1.9 ± 0.3 mas for He I and Brγ, respectively. Our KI data also reveal a relatively flat spectral differential phase response, ruling out significant off-center emission. We expect that these new measurements will help constrain dynamical models being actively developed in order to explain the disk formation process in the δ Sco system and Be stars in general.