Studies of Interstellar Processes

普林斯顿大学的布鲁斯·德雷恩博士将领导对星际介质中各种过程的研究。他将研究非常小的星际颗粒的尺寸分布。有了观测到的与波长相关的星际灭绝所提供的限制，德雷恩博士希望能获得迄今为止关于星际颗粒大小分布的最佳确定。将开发新的光解离区模型，使用改进的光电加热率估计，以及对分子氢(H2)的辐射和碰撞激发/去激发的详细建模。他将扩展之前对球形颗粒的研究，考虑非球形颗粒的形状，以便获得对不规则星际颗粒的净力的现实估计。他将研究在致密的分子云中发生伽马射线暴(GRB)时的可观察后果，包括尘埃的破坏、热尘埃的热发射、由于振动激发的氢气而出现的吸收特征，以及氢气发出的紫外线荧光。我们将研究“热翻转”和“热陷陷”在星际颗粒排列物理中的作用。德雷恩博士将尝试改进离散偶极子近似(DDA)中强吸收材料的处理方法。这将允许使用DDA来计算由无定形碳等材料组成的不规则颗粒的红外吸收截面。他还希望继续支持和维护便携程序DDSCAT，该程序被多个学科的研究人员用来计算不规则目标的散射和吸收。

Dr. Bruce Draine of Princeton University will lead studies of a variety of processes in the interstellar medium. He will investigate the size distribution of very small interstellar grains. With the constraints provided by the observed wavelength-dependent interstellar extinction, Dr. Draine expects to obtain the best determination to date of the size distribution of interstellar grains. New models of photo-dissociation regions will be developed, using improved estimates of photoelectric heating rates, and detailed modeling of radiative and collisional excitation/de-excitation of molecular hydrogen (H2). He will extend previous studies on spherical grains to consider nonspherical grain shapes in order to obtain realistic estimates for the net force on irregular interstellar grains. He will study the observable consequences if a gamma ray burst (GRB) takes place in a dense molecular cloud, including the destruction of dust, thermal emission from hot dust, the appearance of absorption features due to vibrationally-excited H2, and ultraviolet fluorescent emission from H2. Studies will be conducted into the role of "thermal flipping" and "thermal trapping" in the physics of interstellar grain alignment. Dr. Draine will attempt to improve the treatment of strongly-absorbing materials in the discrete dipole approximation (DDA). This would allow the DDA to be used to calculate the infrared absorption cross sections of irregular grains composed of materials like amorphous carbon. He also expects to continue to support and maintain the portable program DDSCAT, which is used by researchers in a number of disciplines to compute scattering and absorption by irregular targets.