Properties of the δ Scorpii Circumstellar Disk from Continuum Modeling

Abstract

We present optical $WBVR$ and infrared $JHKL$ photometric observations of the\nBe binary system $\\delta$ Sco, obtained in 2000--2005, mid-infrared (10 and $18\n\\mu$m) photometry and optical ($\\lambda\\lambda$ 3200--10500 \\AA)\nspectropolarimetry obtained in 2001. Our optical photometry confirms the\nresults of much more frequent visual monitoring of $\\delta$ Sco. In 2005, we\ndetected a significant decrease in the object's brightness, both in optical and\nnear-infrared brightness, which is associated with a continuous rise in the\nhydrogen line strenghts. We discuss possible causes for this phenomenon, which\nis difficult to explain in view of current models of Be star disks. The 2001\nspectral energy distribution and polarization are succesfully modeled with a\nthree-dimensional non-LTE Monte Carlo code which produces a self-consistent\ndetermination of the hydrogen level populations, electron temperature, and gas\ndensity for hot star disks. Our disk model is hydrostatically supported in the\nvertical direction and radially controlled by viscosity. Such a disk model has,\nessentially, only two free parameters, viz., the equatorial mass loss rate and\nthe disk outer radius. We find that the primary companion is surrounded by a\nsmall (7 $R_\\star$), geometrically-thin disk, which is highly non-isothermal\nand fully ionized. Our model requires an average equatorial mass loss rate of\n$1.5\\times 10^{-9} M_{\\sun}$ yr$^{-1}$.\n