The ultraviolet phase function of interstellar grains.

A reanalysis of NGC 1435, the reflection nebula near Merope, shows that the best fit of the ultraviolet surface brightness map is given if interstellar grains scatter nearly isotropically. However, there is sufficient uncertainty in the distribution of dust in this nebula that this conclusion is by no means certain. The average intensity of the high-latitude, diffuse ultraviolet light also can serve as a measure of the phase function of interstellar grains. Unfortunately, the different observations of the intensity of this light disagree with each other significantly so that no firm conclusions can be reached. When the diffuse background is definitively measured, it should be possible to estimate with confidence the ultraviolet phase function of interstellar grains. This result will be important for determining the intensity of the extragalactic ultraviolet background.