PARAMAGNETIC ALIGNMENT OF SMALL GRAINS: A NOVEL METHOD FOR MEASURING INTERSTELLAR MAGNETIC FIELDS
PARAMAGNETIC ALIGNMENT OF SMALL GRAINS: A NOVEL METHOD FOR MEASURING INTERSTELLAR MAGNETIC FIELDS
复制标题
小颗粒的顺磁排列：测量星际磁场的新方法
作者：
Thiem C. Hoang;A. Lazarian;P. Martin
我们提出了一种新的方法来测量星际磁场的强度，使用紫外线（UV）偏振的星光，部分是由弱排列，小尘埃颗粒。我们开始计算小（尺寸a ≤ 0.01 μm）和非常小（尺寸a ≤ 0.001 μm）的晶粒在星际磁场中由于Davis-Greenstein弛豫和共振弛豫而产生的顺磁排列程度。为了计算顺磁排列的程度，我们使用朗之万方程，并考虑到各种相互作用过程中必不可少的小颗粒的旋转动力学。我们发现，小颗粒的排列是必要的再现所观察到的偏振在紫外线，虽然从这些小颗粒所产生的偏振是可以忽略不计的光学和红外（IR）波长。通过对理论模型与实测消光曲线和偏振曲线的拟合，发现偏振峰值波长λmax < 0.55 μm时的最佳拟合模型比λmax = 0.55 μm时的最佳拟合模型需要更高程度的小晶粒排列。我们解释了UV偏振相对于最大偏振的系统性增加（即，的p（6 μm−1）/pmax），而对于低λmax的情况，通过呼吁小晶粒的更高程度的排列。我们利用小晶粒的顺磁排列与磁场强度B的相关性，提出了一种使用可观测参数λmax和p（6 μm−1）/pmax测量B的新方法。
We present a novel method to measure the strength of interstellar magnetic fields using ultraviolet (UV) polarization of starlight that is in part produced by weakly aligned, small dust grains. We begin with calculating the degrees of the paramagnetic alignment of small (size a ∼ 0.01 μm) and very small (a ∼ 0.001 μm) grains in the interstellar magnetic field due to the Davis–Greenstein relaxation and resonance relaxation. To calculate the degrees of paramagnetic alignment, we use Langevin equations and take into account various interaction processes essential for the rotational dynamics of small grains. We find that the alignment of small grains is necessary to reproduce the observed polarization in the UV, although the polarization arising from these small grains is negligible at the optical and infrared (IR) wavelengths. Based on fitting theoretical models to observed extinction and polarization curves, we find that the best-fit model for the case with the peak wavelength of polarization λmax < 0.55 μm requires a higher degree of alignment of small grains than for the typical case with λmax = 0.55 μm. We interpret the correlation between the systematic increase of the UV polarization relative to maximum polarization (i.e., of p(6 μm−1)/pmax ) with for cases of low λmax by appealing to the higher degree of alignment of small grains. We utilize the correlation of the paramagnetic alignment of small grains with the magnetic field strength B to suggest a new way to measure B using the observable parameters λmax and p(6 μm−1)/pmax .