The study of cometary composition is important for understanding our solar system's early evolutionary processes. Carbon dioxide (CO₂) is a common hypervolatile in comets that can drive activity but is more difficult to study than other hypervolatiles owing to severe telluric absorption. CO₂ can only be directly observed from space-borne assets. Therefore, a proxy is needed to measure CO₂ abundances in comets using ground-based observations. The flux ratio of the [O i] λ5577 line to the sum of the [O i] λ6300 and [O i] λ6364 lines (hereafter referred to as the [O i] line ratio) has, with some success, been used in the past as such a proxy. We present an [O i] line ratio analysis of comet 45P/Honda-Mrkos-Pajdušáková (HMP), using data obtained with the Tull Coudé Spectrograph on the 2.7 m Harlan J. Smith Telescope at McDonald Observatory, taken from UT 2017 February 21–23, when the comet was at heliocentric distances of 1.12–1.15 au. HMP is a hyperactive Jupiter-family comet (JFC). Icy grains driven out by CO₂ sublimation have been proposed as a driver of hyperactivity, but the CO₂ abundance of HMP has not been measured. From our [O i] line ratio measurements, we find a CO₂/H₂O ratio for HMP of 22.9% ± 1.4%. We compare the CO₂/H₂O ratios to the active fractions of the nine comets (including HMP) in the literature that have data for both values. We find no correlation. These findings imply that CO₂ sublimation driving out icy grains is not the only factor influencing active fractions for cometary nuclei.

中文翻译：

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根据 [O i] 观测推断 45P/Honda-Mrkos-Pajdušáková 彗星中的 CO2 丰度：对彗星彗发中冰粒来源的影响

彗星成分的研究对于理解太阳系的早期演化过程非常重要。二氧化碳 (CO ₂ ) 是彗星中常见的高挥发物，可以驱动彗星活动，但由于严重的大地吸收，比其他高挥发物更难研究。CO ₂只能从星载资产直接观测到。因此，需要一个代理来使用地面观测来测量彗星中的CO _2丰度。[O 的通量比我]λ5577 行到[O]的总和我]λ6300 和 [O我]λ6364行（以下简称[O我] 线路比率）过去曾被用作这样的代理，并取得了一些成功。我们提出一个[O我] 彗星 45P/Honda-Mrkos-Pajdušáková (HMP) 的线比分析，使用麦克唐纳天文台 2.7 m Harlan J. Smith 望远镜上的 Tull Coudé 摄谱仪获得的数据，取自 UT 2017 年 2 月 21-23 日，当时彗星日心距离为 1.12–1.15 个天文单位。HMP 是一颗异常活跃的木星家族彗星 (JFC)。_{CO 2}升华排出的冰颗粒已被认为是多动症的驱动因素，但 HMP 的 CO ₂丰度尚未测量。来自我们的[O我] 线比率测量，我们发现HMP 的CO ₂ /H ₂ O 比率为22.9% ± 1.4%。我们将 CO ₂ /H ₂ O 比率与文献中九颗彗星（包括 HMP）的活跃部分进行比较，该文献中有这两个值的数据。我们发现没有相关性。这些发现意味着CO ₂升华驱除冰晶颗粒并不是影响彗星核活性分数的唯一因素。