Far-UV Dust Scattering Properties within $10\deg$ of $\rho$ Oph

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Session 8 -- General ISM, Dust
Display presentation, Monday, 9:20-6:30, Pauley Room

[8.10] Far-UV Dust Scattering Properties within $10\deg$ of $\rho$ Oph

K.D.Gordon, A.N.Witt (U. of Toledo), G.R.Carruthers, S.A.Christensen, B.C.Dohne (NRL)

The far-UV scattering properties, the albedo and scattering phase function asymmetry, of dust in the region within $10\deg$ of $\rho$ Oph were investigated. Ultraviolet images of this region were obtained during the Far UV Cameras' experiment (NRL-803), part of the Air Force Space Test Program's AFP-675 payload, which flew aboard the Space Shuttle in May 1991 (STS-39). Camera \#1 observed in the wavelength region 1230-1600 \AA\ ($\lambda_{eff} = 1415$ \AA\) and Camera \#2 observed in the wavelength region 1650-2000 \AA\ ($\lambda_{eff} = 1825$ \AA\). Each camera possessed a $20\deg$ field of view with an angular resolution of approximately $3'$. In both bandpasses, the $\rho$ Oph region appears as an extended reflection nebula filling a substantial fraction of the field of view, with some foreground dark nebulae silhouetted against the scattered light background. Typical intensities for the $\rho$ Oph nebula at 1415 \AA\ range from $2\times10^4$ to $1\times10^5$ photons/($\mbox{cm}^2$ s sr \AA\). Using four UV images of the $\rho$ Oph region (two from each camera) and the fluxes of the region's 31 brightest B-type stars, the nebular to stellar flux ratio was calculated. After subtracting an appropriate amount of sky background, the ratios were $1.10 \pm 0.12$ (@1415 \AA\) and $0.96 \pm 0.16$ (@1825 \AA\). Using a Monte Carlo model which assumes a spherically symmetric distribution of dust and an extended stellar emission region, the dust scattering properties matching the observed nebular to stellar flux ratio were determined. These results, specifically the albedo (a) and the scattering phase function asymmetry (g), will be presented.

Program support was made available by the Office of Naval Research, the flight opportunity was provided by the DoD Space Test Program, and additional support was derived from NASA LTSA Grant NAGW-3168.

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