The First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli–Bernstein) at 16.6 au from the Sun

Nathan X. Roth, Stefanie N. Milam, Martin A. Cordiner, Dominique Bockelée-Morvan, Nicolas Biver, Michael S. P. Kelley, Anthony J. Remijan, Steven B. Charnley, Carrie E. Holt, Kiernan D. Foster, Joseph Chatelain, Edward Gomez, Sarah Greenstreet, Tim Lister and Helen Usher
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Abstract

We report observations of comet C/2014 UN271 (Bernardinelli–Bernstein) carried out on UT 2024 March 8 and 17 at a heliocentric distance (rH) of 16.6 au using the Atacama Large Millimeter/submillimeter Array (ALMA). The CO (J = 2–1) line at 230 GHz was detected along with continuum emission from its dust coma and large (∼140 km) nucleus, revealing the nature of the activity drivers and outgassing kinematics of the largest Oort cloud comet discovered to date. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for CO and a stringent upper limit for the H2CO production rate. CO outgassing displayed multiple active jets that evolved from one epoch to the next. The continuum emission was compact and spatially unresolved and is consistent with thermal emission from the large nucleus and a tentative detection of a dust coma. Complementary optical observations provided activity context for the ALMA epochs, indicating that UN271 underwent an outburst in late February before returning to a quiescent brightness in mid- to late March. These results represent the first secure detection of molecular activity reported in the literature for C/2014 UN271 and highlight the dynamic nature of this distantly active small world.
首次探测到已知最大的奥尔特云彗星的分子活动:距离太阳16.6 au的C/2014 UN271 (Bernardinelli-Bernstein)的ALMA成像
我们报告了在UT 2024年3月8日和17日使用阿塔卡马大型毫米/亚毫米阵列(ALMA)在日心距离(rH)为16.6 au的地方观测到的C/2014 UN271 (Bernardinelli-Bernstein)彗星。230 GHz的CO (J = 2-1)谱线与它的尘埃彗发和大彗核(约140公里)的连续辐射一起被探测到,揭示了迄今为止发现的最大奥尔特云彗星的活动驱动因素和排气运动的性质。这项工作提出了CO的光谱集成通量图、自相关光谱、产量和母尺度长度,以及H2CO产量的严格上限。CO放出气体显示了从一个时代到下一个时代演变的多个活跃喷流。连续辐射紧凑且空间未解析,与大核的热发射和尘埃昏迷的初步探测一致。补充光学观测提供了ALMA时代的活动背景,表明UN271在2月下旬经历了一次爆发,然后在3月中下旬恢复到静止亮度。这些结果代表了文献中首次安全检测到C/2014 UN271的分子活性,并突出了这个遥远活跃的小世界的动态性质。
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