The aim of this work is to characterize HCN and CH$_3$OH emission from recent comets.
We used the Onsala 20-m telescope to search for millimetre transitions of HCN towards a sample of 11 recent and mostly bright comets in the period December 2016 to November 2019. Also CH$_3$OH was searched for in two comets. The HCN sample includes the interstellar comet 2I/Borisov. For the short-period comet 46P/Wirtanen we could monitor the variation of HCN emission over a time span of about one month. We performed radiative transfer modelling for the observed molecular emission by also including time-dependent effects due to the outgassing of molecules.
HCN was detected in 6 comets. Two of these are short-period comets and 4 of them are long-period. Six methanol transitions were detected in 46P/Wirtanen, enabling us to determine the gas kinetic temperature. From the observations, we determined the molecular production rates using time-dependent radiative transfer modelling. For 5 comets, we could determine that the HCN mixing ratios lie near 0.1% using contemporary water production rates, $Q_\mathrm{H_2O}$, taken from other studies. This HCN mixing ratio was also found typical in our monitoring observations of 46P/Wirtanen but here we notice deviations, on a daily time scale, up to 0.2% which could indicate short-time changes in the outgassing activity. From our radiative transfer modelling of cometary comae, we found that time-dependent effects on the HCN level populations are of the order 5-15% when $Q_\mathrm{H_2O}$ is around $2\times 10^{28}\,\mathrm{mol\, s^{-1}}$. The effects may be relatively stronger for comets with lower $Q_\mathrm{H_2O}$. The exact details of the time-dependent effects depend on the amount of neutral and electron collisions, radiative pumping, and molecular parameters such as the spontaneous rate coefficient.
The cyano radical (CN) is one of the most frequently remotely observed species in space, also in comets. Data from the high-resolution Double Focusing Mass Spectrometer (DFMS) on board the Rosetta orbiter, collected in the inner coma of comet 67P/Churyumov-Gerasimenko, revealed an unexpected chemical complexity, and, recently, also more CN than expected from photodissociation of its most likely parent hydrogen cyanide (HCN). This work is dedicated to the derivation of abundances relative to HCN of three cometary nitriles (including structural isomers) from DFMS data. Mass spectrometry of compl…
Single-dish observations and non-LTE analysis of CH3OH, HCN, and CO line emission in the Oort cloud comet C/2017 K2 (PANSTARRS)
Institute of Astronomy of the Russian Academy of Sciences（俄罗斯科学院天文研究所）；Department of Physics and Astronomy, Chalmers University of Technology（查尔姆斯理工大学物理与天文系）
The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful tool for high-resolution mapping of comets, but the main interferometer (comprised of 50x12-m antennas) is insensitive to the largest coma scales due to a lack of very short baselines. In this work, we present a new technique employing ALMA autocorrelation data (obtained simultaneously with the interferometric observations), effectively treating the entire 12-m array as a collection of single-dish telescopes. Using combined autocorrelation spectra from 28 active antennas, we recovered extended HCN coma emission from comet C/…
CH$_3$OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH$_3$OH/HCN Production Rate Ratio
NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；American University（美国大学）；The Catholic University of America（美利坚天主教大学）；LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台，PSL大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）
Cometary comae are generally depleted in nitrogen. The main carriers for volatile nitrogen in comets are NH3 and HCN. It is known that ammonia readily combines with many acids like e.g. HCN, HNCO, HCOOH, etc. encountered in the interstellar medium as well as in cometary ice to form ammonium salts (NH4+X-) at low temperatures. Ammonium salts, which can play a significant role in prebiotic chemistry, are hard to detect in space as they are unstable in the gas phase and their infrared signature is often hidden by thermal radiation or by e.g. OH in minerals. Here we report the presence of all poss…
Comets spend most of their lives at large distances from any star, during which time their interior compositions remain relatively unaltered. Cometary observations can therefore provide direct insight into the chemistry that occurred during their birth at the time of planet formation. To-date, there have been no confirmed observations of parent volatiles (gases released directly from the nucleus) of a comet from any planetary system other than our own. Here we present high-resolution, interferometric observations of 2I/Borisov, the first confirmed interstellar comet, obtained using the Atacama…
Mapping the release of volatiles in the inner comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array
29P/Schwassmann-Wachmann 1 is a distant Centaur/comet, showing persistent CO-driven activity and frequent outbursts. We used the Herschel space observatory in 2010, 2011, and 2013 to observe H$_2$O and NH$_3$ and to image the dust coma. Observations with the IRAM 30 m were undertaken in 2007, 2010, 2011, and 2021 to monitor the CO production rate and to search for HCN. Modeling was performed to constrain the size of the sublimating icy grains and to derive the dust production rate. HCN is detected for the first time in comet 29P (at 5$σ$ in the line area). H$_2$O is detected as well, but not N…
Monitoring Volatile Evolution in Disrupting Comet D/2021 A1 (Leonard) with NOEMA and APEX
California Institute of Technology（加州理工学院）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Virginia Tech（弗吉尼亚理工大学）；American University（美国大学）；Institut de Radioastronomie Millimétrique（毫米波射电天文学研究所）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台、巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎西岱大学）
We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations of the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst. These measurements of HCN, CS, CH$_3$OH, H$_2$CO, and HNC (along with continuum emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrela…
JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS
University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；University of Hawai‘i（夏威夷大学）；Universidad Diego Portales（迭戈波塔莱斯大学）；Planetary Science Institute（行星科学研究所）；Georgia Institute of Technology（佐治亚理工学院）
JCMT detection of HCN emission from 3I/ATLAS at 2.1 AU
East Asian Observatory（东亚天文台）；National Taiwan Normal University（台湾师范大学）；Academia Sinica Institute of Astronomy & Astrophysics（中央研究院天文及天文物理研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Catholic University of America（美国天主教大学）
The Evolution in Coma Molecular Composition of Comet C/2017 K2 (PanSTARRS) Across the H$_2$O Sublimation Zone: ALMA Imaging of an H$_2$O-Dominated Coma
NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；American University（美国大学）；The Catholic University of America（美利坚天主教大学）；National Radio Astronomy Observatory（美国国家射电天文台）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台、巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎西岱大学）
The coma of comet 67P/Churyumov-Gerasimenko has been probed by the Rosetta spacecraft and shows a variety of different molecules. The ROSINA COmet Pressure Sensor and the Double Focusing Mass Spectrometer provide in-situ densities for many volatile compounds including the 14 gas species H2O, CO2, CO, H2S, O2, C2H6, CH3OH, H2CO, CH4, NH3, HCN, C2H5OH, OCS, and CS2. We fit the observed densities during the entire comet mission between August 2014 and September 2016 to an inverse coma model. We retrieve surface emissions on a cometary shape with 3996 triangular elements for 50 separated time inte…
Perihelion observations of interstellar comet 3I/ATLAS with the IRAM 30-m telescope
LIRA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université de Paris（巴黎天文台）；IRAM（红外毫米波天文台）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Department of Physics, Catholic University of America（美利坚天主教大学物理系）；Department of Physics, American University（美利坚大学物理系）
JWST Spatial-Spectral Mapping of Green Comet C/2022 E3 (ZTF)
NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；American University（美国大学）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）；University of California, San Diego（加州大学圣迭戈分校）；University of Maryland, College Park（马里兰大学帕克分校）；University of Virginia（弗吉尼亚大学）；Space Telescope Science Institute（太空望远镜科学研究所）；California Institute of Technology（加州理工学院）；European Space Agency（欧洲空间局）；Association of Universities for Research in Astronomy（大学天文研究协会）
On 31 August 2019, an interstellar comet was discovered as it passed through the Solar System (2I/Borisov). Based on initial imaging observations, 2I/Borisov appeared to be completely similar to ordinary Solar System comets - an unexpected characteristic after the multiple peculiarities of the only previous known interstellar visitor 1I/'Oumuamua. Spectroscopic investigations of 2I/Borisov identified the familiar cometary emissions from CN, C2, O I, NH2, OH, HCN, and CO, revealing a composition similar to that of carbon monoxide-rich Solar System comets. At temperatures >700 K, comets addition…
The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H2O and N2+/H2O ratios}, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high resolution, spatially, spectrally and temporally resolved CO observations using the James Clerk Maxwell Telescope (JCMT) and Submillimeter Array (SMA) to elucidate the outgassing behaviour of C/2016 R2. Resul…
