利用FAST对12P/庞斯-布鲁克斯彗星和C/2023 A3（紫金山-阿特拉斯）彗星的厘米波OH观测
Centimeter-wave OH observations of comets 12P/Pons-Brooks and C/2023 A3 (Tsuchinshan-ATLAS) with FAST
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中文总结 AI 辅助
利用FAST对两颗彗星开展厘米波OH观测，分析其OH谱线探测结果、低探测率原因，计算OH产率并与文献数据比对，验证了结果的合理性。
中文摘要 AI 辅助
我们利用五百米口径球面射电望远镜（FAST），在2024年两颗明亮彗星12P/庞斯-布鲁克斯（12P/Pons-Brooks）和C/2023 A3（紫金山-阿特拉斯）的出现期，开展了OH 18厘米谱线的厘米波光谱观测。对于哈雷型彗星12P/庞斯-布鲁克斯，共获取5个epoch的OH观测数据；在近日点前的1个epoch中，1665和1667 MHz的主要OH谱线被稳定探测到吸收特征，而在近日点后的2个epoch中得到了上限值。对于动力学新奥尔特云彗星C/2023 A3（紫金山-阿特拉斯），共获取6个epoch的OH观测数据；在该彗星最接近地球后的2个epoch中，1665和1667 MHz谱线被稳定探测到吸收特征，我们还在这两个epoch中的1个里报告了1721 MHz伴线的疑似探测结果。这两颗明亮彗星的低OH探测率，主要归因于观测期间它们不利的日心径向速度，导致OH激发的反脉泽负反转模式。我们计算了两颗彗星的OH产率，在考虑FAST的小波束尺寸和碰撞猝灭效应后，产率与文献数据一致；具体而言，这与12P/庞斯-布鲁克斯彗星OH产率的幂律拟合结果相符，也与C/2023 A3（紫金山-阿特拉斯）彗星及另外4颗动力学新奥尔特云彗星在可比日心距离下的产率相符。
英文摘要
We present centimeter-wave spectroscopic observations of the OH 18-cm lines in two bright comets, 12P/Pons-Brooks and C/2023 A3 (Tsuchinshan-ATLAS), conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during their 2024 apparitions. For the Halley-type comet 12P/Pons-Brooks, five epochs of OH observations were obtained. The main OH lines at 1665 and 1667 MHz were robustly detected in absorption during one pre-perihelion epoch, while upper limits were derived for two post-perihelion epochs. For the dynamically new Oort Cloud comet C/2023 A3 (Tsuchinshan-ATLAS), six epochs of OH observations were obtained. The 1665 and 1667 MHz lines were robustly detected in absorption during two epochs immediately following the comet's closest approach to Earth. We also reported a tentative detection of the 1721 MHz satellite line in one of these two epochs. The low OH detection rates for these two bright comets are primarily attributable to their unfavorable heliocentric radial velocity during the observations, which resulted in the anti-maser negative inversion mode of the OH excitation. We calculated the OH production rates for both comets and found that, after considering the small beam size of FAST and the collisional quenching effect, production rates are consistent with the data from literature. Specifically, this matches the power-law fit of the OH production rates for comet 12P/Pons-Brooks, as well as the production rates at comparable heliocentric distances among comet C/2023 A3 (Tsuchinshan-ATLAS) and four other dynamically new Oort Cloud comets.
