The extinction curve of interstellar dust in the dense molecular cloud cores is crucial for understanding dust properties, particularly size distribution and composition. We investigate the infrared extinction law in four nearby isolated molecular cloud cores—L429, L483, L673, and L1165—across the 1.2–8.0 μm wavelength range, using deep near-infrared and mid-infrared photometric data from UKIRT Infrared Deep Sky Survey and Spitzer Space Telescope. These observations probe an unprecedented extinction depth, reaching AV ∼ 40–60 mag in these dense cloud cores. We derive color-excess ratios E(K − λ)/E(H − K) by fitting color–color diagrams of (K − λ) versus (H − K), which are subsequently used to calculate the extinction law Aλ/AK. Our analysis reveals remarkably similar and exceptionally flat infrared extinction curves for all four cloud cores, exhibiting the most pronounced flattening reported in the literature to date. This flatness is consistent with the presence of large dust grains, suggesting significant grain growth in dense environments. Intriguingly, our findings align closely with the Astrodust model for a diffuse interstellar environment proposed by Hensley and Draine. This agreement between dense core observations and a diffuse medium model highlights the complexity of dust evolution and the need for further investigation into the processes governing dust properties in different interstellar environments.

中文翻译：

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四个孤立的致密分子云核心中最平坦的红外消光曲线


致密分子云核心中星际尘埃的消光曲线对于理解尘埃特性至关重要，特别是尺寸分布和组成。我们使用来自 UKIRT 红外深空巡天和斯皮策太空望远镜的深近红外和中红外光度数据，研究了附近四个孤立分子云核心（L429、L483、L673 和 L1165）在 1.2–8.0 μm 波长范围内的红外消光规律。这些观测探测到了前所未有的消光深度，在这些密集的云芯中达到了 AV ∼ 40-60 等。我们通过拟合 （K − λ） 与 （H − K） 的颜色-颜色图来得出颜色过剩比 E（K − λ）/E（H − K），这些图随后用于计算消光定律 Aλ/AK。我们的分析揭示了所有四个云芯的红外消光曲线非常相似且异常平坦，表现出迄今为止文献中报道的最明显的平坦化。这种平整度与大尘埃颗粒的存在一致，表明在密集环境中颗粒显着生长。有趣的是，我们的发现与 Hensley 和 Draine 提出的弥散星际环境的 Astrodust 模型密切相关。致密核心观测和漫射介质模型之间的这种一致性突出了尘埃演化的复杂性，以及进一步研究不同星际环境中控制尘埃特性的过程的必要性。