Rocket observations of far-ultraviolet dust scattering in NGC 2023

The reflection nebula NGC 2023 was observed by a rocket-borne long-slit imaging spectrograph in the 900-1400 Angstrom bandpass on 2000 February 11. A spectrum of the star, as well as that of the nebular scattered light, was recorded. Through the use of a Monte Carlo modeling process, the scattering properties of the dust were derived. The albedo is low, 0.2-0.4, and decreasing toward shorter wavelengths, while the phase function asymmetry parameter is consistent with highly forward-scattering grains, g similar to 0.85. The decrease in albedo, while the optical depth increases to shorter wavelengths, implies that the far-UV rise in the extinction curve is due to an increase in absorption efficiency.