星际尘埃的光学性质

We propose to study the optical properties of three types of interstellar grains: metallic needles, conducting fractalsm and dust with impurities.The optical properties of these grains are unusual compared to that of classical silicate and graphite grains: in the ultraviolet and optical, the extinction of these grains exhibit little variation with wavelength or is “gray”; in the far-infrared and millimeter, the emissivity of these grains is much higher and varies much more gradual than that of silicate and graphite. As a result, these grains are much cold in the interstellar medium. We will study the absorption, scattering, and emission properties of these grains and compare with the so-called “very cold emission” or “submm excess” observed in the interstellar medium both of the Milky Way and external galaxies. We think it is very important to investigate the optical properties of three types of interstellar grains to realize their physical structure and chemical composition.

本项目拟研究星际空间中三类光学性质特异的尘埃：（1）针状金属尘埃（metallic needles）,（2）分形导电尘埃（conducting fractals）,（3）掺杂尘埃（dust with impuritites）。在紫外和光学波段，这些尘埃的消光随波长变化缓慢，即“灰色”（gray）消光，而在远红外和毫米波，这些尘埃的发射系数比经典的石墨和硅酸盐大，而且随波长变化比石墨和硅酸盐来得平缓，因此，这类尘埃在星际空间的温度会很低。我们将研究这些尘埃的吸收，散射和红外辐射，并与天文观测的星系"极冷辐射"(very cold emission)以及“亚毫米剩余”（submm excess）比对。我们认为研究这三类星际尘埃光学性质有助于认识际空间中尘埃的物理结构及化学成分。本项目的研究结果将对于宇宙学、星系、恒星、太阳和太阳系以及基本天文等领域的观测和理论发展都有非常重要的意义。

在研究期间，1）我们使用DDA方法已完成计算针状金属铁尘粒的电磁散射特性与红化、使用DDA方法计算分形尘埃的电磁散射特性和计算针状金属铁尘粒的散射和吸收截面，并得到由这类尘埃所产生的红化；2）我们使用DDA计算含掺杂原子的尘埃电磁散射特性，已经计算完成针状掺杂尘埃的散射和吸收截面,计算完成其热平衡温度及其辐射能谱并与观测到的“极冷辐射”和“亚毫米富余”比较。本项目的研究结果对于开展的宇宙学、星系、恒星、太阳和太阳系以及基本天文等领域的观测和理论发展都有非常重要的意义。