标题： 星际消光曲线的形状分析。 第六章 近红外消光定律 显示英文标题

标题： An Analysis of the Shapes of Interstellar Extinction Curves. VI. The Near-IR Extinction Law

摘要： 我们结合新的哈勃空间望远镜/先进巡天相机（HST/ACS）观测数据和现有数据来研究近红外消光的波长依赖性。先前的研究表明，消光曲线可以用幂律形式表示，并且具有“普遍”的指数值，尽管一些近期的观测指出可能存在显著的视线间变化。我们展示出幂律模型能够很好地拟合大多数近红外消光曲线，但幂指数β的值在不同视线之间存在显著差异。因此，“普遍的近红外消光定律”似乎不可能成立。相反，我们发现随着β减小，R(V)[=A(V)/E(B-V)]有增大的趋势，这表明曾被认为是“异常”的近红外消光曲线实际上可能是对于不同的R(V)值来说典型的。我们还展示出幂律参数可能依赖于用于推导它们的波长区间，即随着更长波长被包括进来，β会增加。这一结果意味着通过外推幂律拟合来确定R(V)是不可靠的。为了避免这个问题，我们采用了近红外消光的一种不同函数形式。这种新形式模仿了一个幂律，其指数随波长增加，只有两个自由参数，可以更精确地拟合所有我们的曲线，并且产生的R(V)值与独立估算和常用的估计R(V)的方法一致。此外，与幂律模型不同，它给出的R(V)值独立于用于推导它们的波长区间。它还表明关系式R(V) = -1.36 E(K-V)/E(B-V) - 0.79 可以估计R(V)到±0.12的精度。最后，我们使用模型消光曲线表明我们的消光曲线符合理论预期。 显示英文摘要

摘要： We combine new HST/ACS observations and existing data to investigate the wavelength dependence of NIR extinction. Previous studies suggest a power-law form, with a "universal" value of the exponent, although some recent observations indicate that significant sight line-to-sight line variability may exist. We show that a power-law model provides an excellent fit to most NIR extinction curves, but that the value of the power, beta, varies significantly from sight line-to-sight line. Therefore, it seems that a "universal NIR extinction law" is not possible. Instead, we find that as beta decreases, R(V) [=A(V)/E(B-V)] tends to increase, suggesting that NIR extinction curves which have been considered "peculiar" may, in fact, be typical for different R(V) values. We show that the power law parameters can depend on the wavelength interval used to derive them, with the beta increasing as longer wavelengths are included. This result implies that extrapolating power law fits to determine R(V) is unreliable. To avoid this problem, we adopt a different functional form for NIR extinction. This new form mimics a power law whose exponent increases with wavelength, has only 2 free parameters, can fit all of our curves over a longer wavelength baseline and to higher precision, and produces R(V) values which are consistent with independent estimates and commonly used methods for estimating R(V). Furthermore, unlike the power law model, it gives R(V)'s that are independent of the wavelength interval used to derive them. It also suggests that the relation R(V) = -1.36 E(K-V)/E(B-V) - 0.79 can estimate R(V) to +/-0.12. Finally, we use model extinction curves to show that our extinction curves are in accord with theoretical expectations.