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arXiv 2023年

作者： Fried, Zachary T.P. Lee, Kin Long Kelvin Byrne, Alex N. McGuire, Brett A. Department of Chemistry Massachusetts Institute of Technology CambridgeMA02139 United States Accelerated Computing Systems and Graphics Group Intel Corporation 2111 NE 25th Ave. HillsboroOR97124 United States National Radio Astronomy Observatory CharlottesvilleVA22903 United States

Machine learning techniques have been previously used to model and predict column densities in the TMC-1 dark molecular cloud. In interstellar sources further along the path of star formation, such as those where a protostar itself has been formed, the chemistry is known to be drastically different from that of largely quiescent dark clouds. To that end, we have tested the ability of various machine learning models to fit the column densities of the molecules detected in source B of the Class 0 protostellar system IRAS 16293-2422. By including a simple encoding of isotopic composition in our molecular feature vectors, we also examine for the first time how well these models can replicate the isotopic ratios. Finally, we report the predicted column densities of the chemically relevant molecules that may be excellent targets for radioastronomical detection in IRAS 16293-2422B. Copyright © 2023, The Authors. All rights reserved.

关键词： Molecules

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Astronomical Detection of the Interstellar Anion C10H – towards TMC-1 from the GOTHAM Large Program on the GBT

arXiv

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arXiv 2023年

作者： Remijan, Anthony Scolati, Haley N. Burkhardt, Andrew M. Changala, P. Bryan Charnley, Steven B. Cooke, Ilsa R. Cordiner, Martin A. Gupta, Harshal Herbst, Eric Lee, Kin Long Kelvin Loomis, Ryan Shingledecker, Christopher N. Siebert, Mark A. Xue, Ci McCarthy, Michael C. McGuire, Brett A. National Radio Astronomy Observatory CharlottesvilleVA22903 United States Department of Chemistry University of Virginia CharlottesvilleVA22904 United States Department of Physics Wellesley College WellesleyMA02481 United States Center for Astrophysics Harvard & Smithsonian CambridgeMA02138 United States Astrochemistry Laboratory The Goddard Center for Astrobiology NASA Goddard Space Flight Center GreenbeltMD20771 United States Department of Chemistry University of British Columbia 2036 Main Mall VancouverBCV6T 1Z1 Canada Institute for Astrophysics and Computational Sciences The Catholic University of America WashingtonDC20064 United States National Science Foundation AlexandriaVA22314 United States Department of Astronomy University of Virginia CharlottesvilleVA22904 United States Accelerated Computing Systems and Graphics Group Intel Corporation 2111 NE 25th Ave HillsboroOR97124 United States Department of Chemistry Massachusetts Institute of Technology CambridgeMA02139 United States Department of Physics and Astronomy Benedictine College AtchisonKS66002 United States

Using data from the GOTHAM (GBT Observations of TMC-1: Hunting for Aromatic Molecules) survey, we report the first astronomical detection of the C10H– anion. The astronomical observations also provided the necessary data to refine the spectroscopic parameters of C10H– . From the velocity stacked data and the matched filter response, C10H– is detected at >9σ confidence level at a column density of 4.04−+102.2367 × 1011 cm−2. A dedicated search for the C10H radical was also conducted towards TMC-1. In this case, the stacked molecular emission of C10H was detected at a ∼3.2σ confidence interval at a column density of 2.02−+20.8268 ×1011 cm−2. However, since the determined confidence level is currently – /C10H column density ratio is ∼2.0+5−1-.96the highest value measured between an anion and neutral species to date. Such a high ratio is at odds with current theories for interstellar anion chemistry. For the radical species, both models can reproduce the measured abundances found from the survey;however, the machine learning analysis matches the detected anion abundances much better than the gas/grain chemical model, suggesting that the current understanding of the formation chemistry of molecular anions is still highly *** Codes 85-11 Copyright © 2023, The Authors. All rights reserved.

关键词： Matched filters

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Detection of Interstellar E-1-cyano-1,3-butadiene in GOTHAM Observations of TMC-1

arXiv

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arXiv 2023年

作者： Cooke, Ilsa R. Xue, Ci Changala, P. Bryan Shay, Hannah Toru Byrne, Alex N. Tang, Qi Yu Fried, Zachary T.P. Lee, Kin Long Kelvin Loomis, Ryan A. Lamberts, Thanja Remijan, Anthony Burkhardt, Andrew M. Herbst, Eric McCarthy, Michael C. McGuire, Brett A. Department of Chemistry University of British Columbia 2036 Main Mall VancouverBCV6T 1Z1 Canada Department of Chemistry Massachusetts Institute of Technology CambridgeMA02139 United States Center for Astrophysics|Harvard & Smithsonian CambridgeMA02138 United States Accelerated Computing Systems and Graphics Group Intel Corporation 2111 25th NE Ave HillsboroOR97124 United States National Radio Astronomy Observatory CharlottesvilleVA22903 United States Leiden Institute of Chemistry Gorlaeus Laboratories Leiden University P.O. Box 9502 Leiden2300 RA Netherlands Leiden Observatory Leiden University P.O. Box 9513 Leiden2300 RA Netherlands Department of Physics Wellesley College WellesleyMA02481 United States Department of Chemistry University of Virginia CharlottesvilleVA22904 United States Department of Astronomy University of Virginia CharlottesvilleVA22904 United States Center for Astrophysics Harvard & Smithsonian CambridgeMA02138 United States National Radio Astronomy Observatory CharlottesvilleVA22903 United States

We report the detection of the lowest energy conformer of E-1-cyano-1,3-butadiene (E-1-C4H5CN), a linear isomer of pyridine, using the fourth data reduction of the GOTHAM deep spectral survey toward TMC-1 with the 100 m Green Bank Telescope. We performed velocity stacking and matched filter analyses using Markov chain Monte Carlo simulations and find evidence for the presence of this molecule at the 5.1σ level. We derive a total column density of 3.8+1.0−0.9 × 1010 cm−2, which is predominantly found toward two of the four velocity components we observe toward TMC-1. We use this molecule as a proxy for constraining the gas-phase abundance of the apolar hydrocarbon 1,3-butadiene. Based on the three-phase astrochemical modeling code NAUTILUS and an expanded chemical network, our model underestimates the abundance of cyano-1,3-butadiene by a factor of 19, with a peak column density of 2.34 × 1010 cm−2 for 1,3-butadiene. Compared to the modeling results obtained in previous GOTHAM analyses, the abundance of 1,3-butadiene is increased by about two orders of magnitude. Despite this increase, the modeled abundances of aromatic species do not appear to change and remain underestimated by 1–4 orders of magnitude. Meanwhile, the abundances of the five-membered ring molecules increase proportionally with 1,3-butadiene by two orders of magnitudes. We discuss implications for bottom-up formation routes to aromatic and polycyclic aromatic molecules. Copyright © 2023, The Authors. All rights reserved.

关键词： Polycyclic aromatic hydrocarbons

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Discovery of Interstellar 2-Cyanoindene (2-C9H7CN) in GOTHAM Observations of TMC-1

arXiv

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arXiv 2022年

作者： Sita, Madelyn L. Changala, P. Bryan Xue, Ci Burkhardt, Andrew M. Shingledecker, Christopher N. Lee, Kin Long Kelvin Loomis, Ryan A. Momjian, Emmanuel Siebert, Mark A. Gupta, Divita Herbst, Eric Remijan, Anthony J. McCarthy, Michael C. Cooke, Ilsa R. McGuire, Brett A. Department of Chemistry University of Virginia CharlottesvilleVA22904 United States Center for Astrophysics Harvard & Smithsonian CambridgeMA02138 United States Department of Chemistry Massachusetts Institute of Technology CambridgeMA02139 United States Department of Physics Wellesley College WellesleyMA02481 United States Department of Physics and Astronomy Benedictine College AtchisonKS66002 United States Accelerated Computing Systems and Graphics Group Intel Corporation 2111 NE 25th Ave HillsboroOR97124 United States National Radio Astronomy Observatory CharlottesvilleVA22903 United States National Radio Astronomy Observatory SocorroNM87801 United States Department of Astronomy University of Virginia CharlottesvilleVA22904 United States I. Physikalisches Institut Universität zu Köln Zülpicher Str. 77 Köln50937 Germany Department of Chemistry University of British Columbia 2036 Main Mall VancouverBCV6T 1Z1 Canada

We present laboratory rotational spectroscopy of five isomers of cyanoindene (2-, 4-, 5-, 6-, and 7-cyanoindene) using a cavity Fourier-transform microwave spectrometer operating between 6–40 GHz. Based on these measurements, we report the detection of 2-cyanoindene (1H-indene-2-carbonitrile;2-C9H7CN) in GOTHAM line survey observations of the dark molecular cloud TMC-1 using the Green Bank Telescope at centimeter wavelengths. Using a combination of Markov Chain Monte Carlo (MCMC), spectral stacking, and matched filtering techniques, we find evidence for the presence of this molecule at the 6.3σ level. This provides the first direct observation of the ratio of a cyano-substituted polycyclic aromatic hydrocarbon (PAH) to its pure hydrocarbon counterpart, in this case indene, in the same source. We discuss the possible formation chemistry of this species, including why we have only detected one of the isomers in TMC-1. We then examine the overall hydrocarbon:CN-substituted ratio across this and other simpler species, as well as compare to those ratios predicted by astrochemical models. We conclude that while astrochemical models are not yet sufficiently accurate to reproduce absolute abundances of these species, they do a good job at predicting the ratios of hydrocarbon:CN-substituted species, further solidifying -CN tagged species as excellent proxies for their fully-symmetric counterparts. Copyright © 2022, The Authors. All rights reserved.

关键词： Polycyclic aromatic hydrocarbons

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