In some polar coronal holes, previous studies have identified a coronal hole boundary layer (CHBL), which is different in composition from the coronal hole core region. However, compositionally distinct CHBL structure at low heliographic latitudes remains underexplored. Using solar wind composition measurements from the Advanced Composition Explorer (ACE), we study two particular low-latitude coronal holes of 2003: a large polar hole extension with outward magnetic polarity and a smaller equatorial hole with inward magnetic polarity. For both of these coronal holes, we examine the distribution of two composition parameters, the O⁷⁺ to O⁶⁺ charge state density ratio (n(O⁷⁺)/n(O⁶⁺)) and the Fe to O abundance ratio (n(Fe)/n(O)), and find that each hole has an identifiable CHBL based on an anticorrelation of solar wind speed and n(O⁷⁺)/n(O⁶⁺). We also examine the FIP (first ionization potential) effect in the CHBL using n(Fe)/n(O), and find that there is no significant change from the CHBL to the core region for one of the coronal holes we study, while the other coronal hole has a noticeable decrease in n(Fe)/n(O) values in its core. Finally, we discuss our results in the context of previous work studying CHBL structure.

中文翻译：

---

低日照纬度日冕孔边界层的组成

在一些极地日冕洞中，先前的研究已经确定了日冕洞边界层（CHBL），其成分与日冕洞核心区域不同。然而，在低日光纬度下成分不同的 CHBL 结构仍未得到充分探索。使用高级成分探索器 (ACE) 的太阳风成分测量，我们研究了 2003 年两个特殊的低纬度日冕洞：一个具有向外磁极的大极洞延伸和一个具有向内磁极的较小赤道洞。对于这两个冕洞，我们检查了两个组成参数的分布，即 O ⁷⁺与 O ⁶⁺电荷态密度比 (n(O ⁷⁺ )/n(O ⁶⁺)) 和 Fe 与 O 的丰度比 (n(Fe)/n(O))，并基于太阳风速和 n(O ⁷⁺ )/n(O ^{6 +} )。我们还使用 n(Fe)/n(O) 检查了 CHBL 中的 FIP（第一电离势）效应，发现我们研究的一个日冕孔从 CHBL 到核心区域没有显着变化，而另一个日冕洞在其核心的 n(Fe)/n(O) 值显着下降。最后，我们在先前研究 CHBL 结构的工作的背景下讨论我们的结果。