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Showing 1-20 of about 27 results.
Ubiquitous aromatic carbon chemistry at the earliest stages of star formationBurkhardt, Andrew M.Loomis, Ryan A.Shingledecker, Christopher N.Lee, Kin Long KelvinRemijan, Anthony J.McCarthy, Michael C.McGuire, Brett A.DOI: info:10.1038/s41550-020-01253-4v. 5181–187
Burkhardt, Andrew M., Loomis, Ryan A., Shingledecker, Christopher N., Lee, Kin Long Kelvin, Remijan, Anthony J., McCarthy, Michael C., and McGuire, Brett A. 2021. "Ubiquitous aromatic carbon chemistry at the earliest stages of star formation." Nature Astronomy 5:181– 187. https://doi.org/10.1038/s41550-020-01253-4
ID: 159642
Type: article
Authors: Burkhardt, Andrew M.; Loomis, Ryan A.; Shingledecker, Christopher N.; Lee, Kin Long Kelvin; Remijan, Anthony J.; McCarthy, Michael C.; McGuire, Brett A.
Abstract: Benzonitrile (c-C6H5CN, where `c' indicates a cyclic structure), a polar proxy for benzene (c-C6H6), has the potential to serve as a highly convenient radio probe for aromatic chemistry, provided that this ring can be found in other astronomical sources beyond the molecule-rich prestellar cloud TMC-1. Here we present radio astronomical evidence of benzonitrile in four other prestellar, and possibly protostellar, sources: Serpens 1A, Serpens 1B, Serpens 2 and MC27/L1521F. These detections establish that benzonitrile is not unique to TMC-1; rather, aromatic chemistry appears to be widespread throughout the earliest stages of star formation, probably persisting at least until the initial formation of a protostar. The abundance of benzonitrile far exceeds predictions from models that well reproduce the abundances of carbon chains such as HC7N, a cyanpolyyne with the same heavy atoms, indicating that the chemistry responsible for planar carbon structures (as opposed to linear ones) in primordial sources is favourable but not well understood. The abundance of benzonitrile relative to carbon chain molecules displays sizable variations between sources within the Taurus and Serpens clouds, implying the importance of physical conditions and initial elemental reservoirs of the clouds themselves.
The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Strong Increase in Mid-Infrared Continuum EmissionHunter, T. R.Brogan, C. L.De Buizer, J. M.Towner, A. P. M.Dowell, C. D.MacLeod, G. C.Stecklum, B.Cyganowski, C. J.El-Abd, S. J.McGuire, B. A.DOI: info:10.3847/2041-8213/abf6d9v. 912No. 1
Hunter, T. R., Brogan, C. L., De Buizer, J. M., Towner, A. P. M., Dowell, C. D., MacLeod, G. C., Stecklum, B., Cyganowski, C. J., El-Abd, S. J., and McGuire, B. A. 2021. "The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Strong Increase in Mid-Infrared Continuum Emission." Astrophysical Journal Letters 912 (1):https://doi.org/10.3847/2041-8213/abf6d9
ID: 159529
Type: article
Authors: Hunter, T. R.; Brogan, C. L.; De Buizer, J. M.; Towner, A. P. M.; Dowell, C. D.; MacLeod, G. C.; Stecklum, B.; Cyganowski, C. J.; El-Abd, S. J.; McGuire, B. A.
Abstract: In recent years, dramatic outbursts have been identified toward massive protostars via infrared and millimeter dust continuum and molecular maser emission. The longest lived outburst (>6 yr) persists in NGC 6334 I-MM1, a deeply embedded object with no near-IR counterpart. Using FORCAST and HAWC+ on SOFIA, we have obtained the first mid-IR images of this field since the outburst began. Despite being undetected in pre-outburst ground-based 18 mu m images, MM1 is now the brightest region at all three wavelengths (25, 37, and 53 mu m), exceeding the UCHII region MM3 (NGC 6334 F). Combining the SOFIA data with ALMA imaging at four wavelengths, we construct a spectral energy distribution of the combination of MM1 and the nearby hot core MM2. The best-fit Robitaille radiative transfer model yields a luminosity of (4.9 +/- 0.8) x 10(4) L (circle dot). Accounting for an estimated pre-outburst luminosity ratio MM1:MM2 = 2.1 +/- 0.4, the luminosity of MM1 has increased by a factor of 16.3 +/- 4.4. The pre-outburst luminosity implies a protostar of mass 6.7 M (circle dot), which can produce the ionizing photon rate required to power the pre-outburst HCHII region surrounding the likely outbursting protostar MM1B. The total energy and duration of the outburst exceed the S255IR-NIRS3 outburst by a factor of greater than or similar to 3, suggesting a different scale of event involving expansion of the protostellar photosphere (to greater than or similar to 20 R (circle dot)), thereby supporting a higher accretion rate (greater than or similar to 0.0023 M (circle dot) yr(-1)) and reducing the ionizing photon rate. In the grid of hydrodynamic models of Meyer et al., the combination of outburst luminosity and magnitude (3) places the NGC 6334 I-MM1 event in the region of moderate total accretion (similar to 0.1-0.3 M (circle dot)) and hence long duration (similar to 40-130 yr).
Interstellar Detection of 2-cyanocyclopentadiene, C5H5CN, a Second Five-membered Ring toward TMC-1Lee, Kin Long KelvinChangala, P. BryanLoomis, Ryan A.Burkhardt, Andrew M.Xue, CiCordiner, Martin A.Charnley, Steven B.McCarthy, Michael C.McGuire, Brett A.DOI: info:10.3847/2041-8213/abe764v. 910L2
Lee, Kin Long Kelvin, Changala, P. Bryan, Loomis, Ryan A., Burkhardt, Andrew M., Xue, Ci, Cordiner, Martin A., Charnley, Steven B., McCarthy, Michael C., and McGuire, Brett A. 2021. "Interstellar Detection of 2-cyanocyclopentadiene, C5H5CN, a Second Five-membered Ring toward TMC-1." The Astrophysical Journal 910:L2. https://doi.org/10.3847/2041-8213/abe764
ID: 159425
Type: article
Authors: Lee, Kin Long Kelvin; Changala, P. Bryan; Loomis, Ryan A.; Burkhardt, Andrew M.; Xue, Ci; Cordiner, Martin A.; Charnley, Steven B.; McCarthy, Michael C.; McGuire, Brett A.
Abstract: Using radio observations with the Green Bank Telescope, evidence has now been found for a second five-membered ring in the dense cloud Taurus Molecular Cloud-1 (TMC-1). Based on additional observations of an ongoing, large-scale, high-sensitivity spectral line survey (GOTHAM) at centimeter wavelengths toward this source, we have used a combination of spectral stacking, Markov Chain Monte Carlo (MCMC), and matched filtering techniques to detect 2-cyanocyclopentadiene, a low-lying isomer of 1-cyanocyclopentadiene, which was recently discovered there by the same methods. The new observational data also yield a considerably improved detection significance for the more stable isomer and evidence for several individual transitions between 23-32 GHz. Through our MCMC analysis, we derive cospatial, total column densities of 8.3 × 1011 and 1.9 × 1011 cm-2 for 1- and 2-cyanocyclopentadiene, respectively, corresponding to a ratio of ∼4.4 favoring the former. The derived abundance ratios point toward a common formation pathway-most likely being cyanation of cyclopentadiene by analogy to benzonitrile.
Discovery of Interstellar trans-cyanovinylacetylene (HC ≡ CCH = CHC ≡ N) and vinylcyanoacetylene (H2C = CHC3N) in GOTHAM Observations of TMC-1Lee, Kin Long KelvinLoomis, Ryan A.Burkhardt, Andrew M.Cooke, Ilsa R.Xue, CiSiebert, Mark A.Shingledecker, Christopher N.Remijan, AnthonyCharnley, Steven B.McCarthy, Michael C.McGuire, Brett A.DOI: info:10.3847/2041-8213/abdbb9v. 908L11
Lee, Kin Long Kelvin, Loomis, Ryan A., Burkhardt, Andrew M., Cooke, Ilsa R., Xue, Ci, Siebert, Mark A., Shingledecker, Christopher N., Remijan, Anthony, Charnley, Steven B., McCarthy, Michael C., and McGuire, Brett A. 2021. "Discovery of Interstellar trans-cyanovinylacetylene (HC ≡ CCH = CHC ≡ N) and vinylcyanoacetylene (H2C = CHC3N) in GOTHAM Observations of TMC-1." The Astrophysical Journal 908:L11. https://doi.org/10.3847/2041-8213/abdbb9
ID: 159619
Type: article
Authors: Lee, Kin Long Kelvin; Loomis, Ryan A.; Burkhardt, Andrew M.; Cooke, Ilsa R.; Xue, Ci; Siebert, Mark A.; Shingledecker, Christopher N.; Remijan, Anthony; Charnley, Steven B.; McCarthy, Michael C.; McGuire, Brett A.
Abstract: We report the discovery of two unsaturated organic species, trans-(E)-cyanovinylacetylene and vinylcyanoacetylene, using the second data release of the GOTHAM deep survey toward TMC-1 with the 100 m Green Bank Telescope. For both detections, we performed velocity stacking and matched filter analyses using Markov Chain Monte Carlo simulations, and for trans-(E)-cyanovinylacetylene, three rotational lines were observed at low signal-to-noise (∼3σ). From this analysis, we derive column densities of 2 × 1011 and 3 × 1011 cm-2 for vinylcyanoacetylene and trans-(E)-cyanovinylacetylene, respectively, and an upper limit of for vinylcyanoacetylene and trans-(E)-cyanovinylacetylene, respectively, and an upper limit of 11 cm-2 for trans-(Z)-cyanovinylacetylene. Comparisons with G3//B3LYP semiempirical thermochemical calculations indicate abundances of the [H3C5N] isomers are not consistent with their thermodynamic stability, and instead their abundances are mainly driven by dynamics. We provide a discussion on how these species may be formed in TMC-1, with reference to related molecules like vinyl cyanide (CH2 = CHC ≡ N). As part of this discussion, we performed the same analysis for ethyl cyanide (CH3CH2C ≡ N), the hydrogenation product of CH2 = CHC ≡ N. This analysis provides evidence-at 4.2σ significance-of an upper limit to the column density of = CHC ≡ N. This analysis provides evidence-at 4.2σ significance-of an upper limit to the column density of 11 cm-2; an order of magnitude lower than previous upper limits toward this source.
An investigation of spectral line stacking techniques and application to the detection of HC11NLoomis, Ryan A.Burkhardt, Andrew M.Shingledecker, Christopher N.Charnley, Steven B.Cordiner, Martin A.Herbst, EricKalenskii, SergeiLee, Kin Long KelvinWillis, Eric R.Xue, CiRemijan, Anthony J.McCarthy, Michael C.McGuire, Brett A.DOI: info:10.1038/s41550-020-01261-4v. 5188–196
Loomis, Ryan A., Burkhardt, Andrew M., Shingledecker, Christopher N., Charnley, Steven B., Cordiner, Martin A., Herbst, Eric, Kalenskii, Sergei, Lee, Kin Long Kelvin, Willis, Eric R., Xue, Ci, Remijan, Anthony J., McCarthy, Michael C., and McGuire, Brett A. 2021. "An investigation of spectral line stacking techniques and application to the detection of HC11N." Nature Astronomy 5:188– 196. https://doi.org/10.1038/s41550-020-01261-4
ID: 159355
Type: article
Authors: Loomis, Ryan A.; Burkhardt, Andrew M.; Shingledecker, Christopher N.; Charnley, Steven B.; Cordiner, Martin A.; Herbst, Eric; Kalenskii, Sergei; Lee, Kin Long Kelvin; Willis, Eric R.; Xue, Ci; Remijan, Anthony J.; McCarthy, Michael C.; McGuire, Brett A.
Abstract: As the inventory of interstellar molecules continues to grow, the gulf between small species, whose individual rotational lines can be observed with radio telescopes, and large ones, such as polycyclic aromatic hydrocarbons best studied in bulk via infrared and optical observations, is slowly being bridged. Understanding the connection between these two molecular reservoirs is critical to understanding the interstellar carbon cycle, but will require pushing the boundaries of how far we can probe molecular complexity while still retaining observational specificity. Towards this end, we present a method for detecting and characterizing new molecular species in single-dish observations towards sources with sparse line spectra. We have applied this method to data from the ongoing GOTHAM (GBT Observations of TMC-1: Hunting Aromatic Molecules) Green Bank Telescope large programme, discovering six new interstellar species. Here we highlight the detection of HC11N, the largest cyanopolyyne in the interstellar medium.
Interstellar detection of the highly polar five-membered ring cyanocyclopentadieneMcCarthy, Michael C.Lee, Kin Long KelvinLoomis, Ryan A.Burkhardt, Andrew M.Shingledecker, Christopher N.Charnley, Steven B.Cordiner, Martin A.Herbst, EricKalenskii, SergeiWillis, Eric R.Xue, CiRemijan, Anthony J.McGuire, Brett A.DOI: info:10.1038/s41550-020-01213-yv. 5176–180
McCarthy, Michael C., Lee, Kin Long Kelvin, Loomis, Ryan A., Burkhardt, Andrew M., Shingledecker, Christopher N., Charnley, Steven B., Cordiner, Martin A., Herbst, Eric, Kalenskii, Sergei, Willis, Eric R., Xue, Ci, Remijan, Anthony J., and McGuire, Brett A. 2021. "Interstellar detection of the highly polar five-membered ring cyanocyclopentadiene." Nature Astronomy 5:176– 180. https://doi.org/10.1038/s41550-020-01213-y
ID: 159354
Type: article
Authors: McCarthy, Michael C.; Lee, Kin Long Kelvin; Loomis, Ryan A.; Burkhardt, Andrew M.; Shingledecker, Christopher N.; Charnley, Steven B.; Cordiner, Martin A.; Herbst, Eric; Kalenskii, Sergei; Willis, Eric R.; Xue, Ci; Remijan, Anthony J.; McGuire, Brett A.
Abstract: Much like six-membered rings, five-membered rings are ubiquitous in organic chemistry, frequently serving as the building blocks for larger molecules, including many of biochemical importance. From a combination of laboratory rotational spectroscopy and a sensitive spectral line survey in the radio band toward the starless cloud core TMC-1, we report the astronomical detection of 1-cyano-1,3-cyclopentadiene (1-cyano-CPD, c-C5H5CN), a highly polar, cyano derivative of cyclopentadiene. The derived abundance of 1-cyano-CPD is far greater than predicted from astrochemical models that well reproduce the abundance of many carbon chains. This finding implies that either an important production mechanism or a large reservoir of aromatic material may need to be considered. The apparent absence of its closely related isomer, 2-cyano-1,3-cyclopentadiene, may arise from that isomer's lower stability or may be indicative of a more selective pathway for formation of the 1-cyano isomer, perhaps one starting from acyclic precursors. The absence of N-heterocycles such as pyrrole and pyridine is discussed in light of the astronomical finding of 1-cyano-CPD.
Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filteringMcGuire, Brett A.Loomis, Ryan A.Burkhardt, Andrew M.Lee, Kin Long KelvinShingledecker, Christopher N.Charnley, Steven B.Cooke, Ilsa R.Cordiner, Martin A.Herbst, EricKalenskii, SergeiSiebert, Mark A.Willis, Eric R.Xue, CiRemijan, Anthony J.McCarthy, Michael C.DOI: info:10.1126/science.abb7535v. 3711265–1269
McGuire, Brett A., Loomis, Ryan A., Burkhardt, Andrew M., Lee, Kin Long Kelvin, Shingledecker, Christopher N., Charnley, Steven B., Cooke, Ilsa R., Cordiner, Martin A., Herbst, Eric, Kalenskii, Sergei, Siebert, Mark A., Willis, Eric R., Xue, Ci, Remijan, Anthony J., and McCarthy, Michael C. 2021. "Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering." Science 371:1265– 1269. https://doi.org/10.1126/science.abb7535
ID: 159345
Type: article
Authors: McGuire, Brett A.; Loomis, Ryan A.; Burkhardt, Andrew M.; Lee, Kin Long Kelvin; Shingledecker, Christopher N.; Charnley, Steven B.; Cooke, Ilsa R.; Cordiner, Martin A.; Herbst, Eric; Kalenskii, Sergei; Siebert, Mark A.; Willis, Eric R.; Xue, Ci; Remijan, Anthony J.; McCarthy, Michael C.
Abstract: Unidentified infrared emission bands are ubiquitous in many astronomical sources. These bands are widely, if not unanimously, attributed to collective emissions from polycyclic aromatic hydrocarbon (PAH) molecules, yet no single species of this class has been identified in space. Using spectral matched filtering of radio data from the Green Bank Telescope, we detected two nitrile-group–functionalized PAHs, 1- and 2-cyanonaphthalene, in the interstellar medium. Both bicyclic ring molecules were observed in the TMC-1 molecular cloud. In this paper, we discuss potential in situ gas-phase PAH formation pathways from smaller organic precursor molecules.
The Family of Amide Molecules toward NGC 6334ILigterink, Niels F. W.El-Abd, Samer J.Brogan, Crystal L.Hunter, Todd R.Remijan, Anthony J.Garrod, Robin T.McGuire, BrettDOI: info:10.3847/1538-4357/abad38v. 90137
Ligterink, Niels F. W., El-Abd, Samer J., Brogan, Crystal L., Hunter, Todd R., Remijan, Anthony J., Garrod, Robin T., and McGuire, Brett. 2020. "The Family of Amide Molecules toward NGC 6334I." The Astrophysical Journal 901:37. https://doi.org/10.3847/1538-4357/abad38
ID: 157763
Type: article
Authors: Ligterink, Niels F. W.; El-Abd, Samer J.; Brogan, Crystal L.; Hunter, Todd R.; Remijan, Anthony J.; Garrod, Robin T.; McGuire, Brett
Abstract: Amide molecules produced in space could play a key role in the formation of biomolecules on a young planetary object. However, the formation and chemical network of amide molecules in space is not well understood. In this work, Atacama Large Millimeter/submillimeter Array observations are used to study a number of amide(-like) molecules toward the high-mass star-forming region NGC 6334I. The first detections of cyanamide (NH2CN), acetamide (CH3C(O)NH2), and N-methylformamide (CH3NHCHO) are presented for this source. These are combined with analyses of isocyanic acid (HNCO) and formamide (NH2CHO), and a tentative detection of urea (carbamide; NH2C(O)NH2). Abundance correlations show that most amides are likely formed in related reactions occurring in ices on interstellar dust grains in NGC 6334I. However, in an expanded sample of sources, large abundance variations are seen for NH2CN that seem to depend on the source type, which suggests that the physical conditions within the source heavily influence the production of this species. The rich amide inventory of NGC 6334I strengthens the case that interstellar molecules can contribute to the emergence of biomolecules on planets.
Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH2CN) in TMC-1McGuire, Brett A.Burkhardt, Andrew M.Loomis, Ryan A.Shingledecker, Christopher N.Lee, Kin Long KelvinCharnley, Steven B.Cordiner, Martin A.Herbst, EricKalenskii, SergeiMomjian, EmmanuelWillis, Eric R.Xue, CiRemijan, Anthony J.McCarthy, Michael C.DOI: info:10.3847/2041-8213/aba632v. 900L10
McGuire, Brett A., Burkhardt, Andrew M., Loomis, Ryan A., Shingledecker, Christopher N., Lee, Kin Long Kelvin, Charnley, Steven B., Cordiner, Martin A., Herbst, Eric, Kalenskii, Sergei, Momjian, Emmanuel, Willis, Eric R., Xue, Ci, Remijan, Anthony J., and McCarthy, Michael C. 2020. "Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH2CN) in TMC-1." The Astrophysical Journal 900:L10. https://doi.org/10.3847/2041-8213/aba632
ID: 157685
Type: article
Authors: McGuire, Brett A.; Burkhardt, Andrew M.; Loomis, Ryan A.; Shingledecker, Christopher N.; Lee, Kin Long Kelvin; Charnley, Steven B.; Cordiner, Martin A.; Herbst, Eric; Kalenskii, Sergei; Momjian, Emmanuel; Willis, Eric R.; Xue, Ci; Remijan, Anthony J.; McCarthy, Michael C.
Abstract: We present an overview of the GBT Observations of TMC-1: Hunting Aromatic Molecules Large Program on the Green Bank Telescope. This and a related program were launched to explore the depth and breadth of aromatic chemistry in the interstellar medium at the earliest stages of star formation, following our earlier detection of benzonitrile (c-C6H5CN) in TMC-1. In this work, details of the observations, use of archival data, and data reduction strategies are provided. Using these observations, the interstellar detection of propargyl cyanide (HCCCH2CN) is described, as well as the accompanying laboratory spectroscopy. We discuss these results, and the survey project as a whole, in the context of investigating a previously unexplored reservoir of complex, gas-phase molecules in pre-stellar sources. A series of companion papers describe other new astronomical detections and analyses.
The Submillimeter Rotational Spectrum of Ethylene Glycol up to 890 GHz and Application to ALMA Band 10 Spectral Line Data of NGC 6334IMelosso, MattiaDore, LucaTamassia, FilippoBrogan, Crystal L.Hunter, Todd R.McGuire, Brett A.DOI: info:10.1021/acs.jpca.9b10803v. 124240–246
Melosso, Mattia, Dore, Luca, Tamassia, Filippo, Brogan, Crystal L., Hunter, Todd R., and McGuire, Brett A. 2020. "The Submillimeter Rotational Spectrum of Ethylene Glycol up to 890 GHz and Application to ALMA Band 10 Spectral Line Data of NGC 6334I." Journal of Physical Chemistry A 124:240– 246. https://doi.org/10.1021/acs.jpca.9b10803
ID: 158250
Type: article
Authors: Melosso, Mattia; Dore, Luca; Tamassia, Filippo; Brogan, Crystal L.; Hunter, Todd R.; McGuire, Brett A.
Abstract: The rotational spectrum of the most stable conformer of ethylene glycol (HO(CH$_2$)$_2$OH) has been recorded between 360-890 GHz using a frequency-modulation sub-millimeter spectrometer. The refinement and extension of the spectroscopic parameters over previous efforts provides predicted catalog frequencies for ethylene glycol with sufficient accuracy for comparison to high-frequency astronomical data. The improvement in the cataloged line positions, and the need for improved accuracy enabled by high-frequency laboratory work, is demonstrated by an analysis of ethylene glycol emission at 890 GHz in the high-mass star-forming region NGC 6334I in ALMA Band 10 observations. The need for accurate rotational spectra at sub-millimeter wavelengths/THz frequencies is discussed.
A Search for Light Hydrides in the Envelopes of Evolved StarsSiebert, Mark A.Simon, IgnacioShingledecker, Christopher N.Carroll, P. BrandonBurkhardt, Andrew M.Booth, Shawn ThomasRemijan, Anthony J.McGuire, Brett A.Aladro, RebecaDuran, Carlos A.DOI: info:10.3847/1538-4357/abac0ev. 90122
Siebert, Mark A., Simon, Ignacio, Shingledecker, Christopher N., Carroll, P. Brandon, Burkhardt, Andrew M., Booth, Shawn Thomas, Remijan, Anthony J., McGuire, Brett A., Aladro, Rebeca, and Duran, Carlos A. 2020. "A Search for Light Hydrides in the Envelopes of Evolved Stars." The Astrophysical Journal 901:22. https://doi.org/10.3847/1538-4357/abac0e
ID: 157694
Type: article
Authors: Siebert, Mark A.; Simon, Ignacio; Shingledecker, Christopher N.; Carroll, P. Brandon; Burkhardt, Andrew M.; Booth, Shawn Thomas; Remijan, Anthony J.; McGuire, Brett A.; Aladro, Rebeca; Duran, Carlos A.
Abstract: We report a search for the diatomic hydrides SiH, PH, and FeH along the line of sight toward the chemically rich circumstellar envelopes of IRC+10216 and VY Canis Majoris. These molecules are thought to form in high-temperature regions near the photospheres of those stars, and may then further react via gas-phase and dust-grain interactions leading to more complex species, but have yet to be constrained by observation. We used the German Receiver for Astronomy at Terahertz Frequencies spectrometer on the Stratospheric Observatory for Infrared Astronomy to search for rotational emission lines of these molecules in four spectral windows ranging from 600 to 1500 GHz. Although none of the targeted species was detected in our search, we report their upper limit abundances in each source and discuss how they influence the current understanding of hydride chemistry in dense circumstellar media. We attribute the nondetections of these hydrides to their compact source sizes, high barriers of formation, and proclivity to react with other molecules in the winds.
Detection of Interstellar HC4NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 ConditionsXue, CiWillis, Eric R.Loomis, Ryan A.Lee, Kin Long KelvinBurkhardt, Andrew M.Shingledecker, Christopher N.Charnley, Steven B.Cordiner, Martin A.Kalenskii, SergeiMcCarthy, Michael C.Herbst, EricRemijan, Anthony J.McGuire, Brett A.DOI: info:10.3847/2041-8213/aba631v. 900L9
Xue, Ci, Willis, Eric R., Loomis, Ryan A., Lee, Kin Long Kelvin, Burkhardt, Andrew M., Shingledecker, Christopher N., Charnley, Steven B., Cordiner, Martin A., Kalenskii, Sergei, McCarthy, Michael C., Herbst, Eric, Remijan, Anthony J., and McGuire, Brett A. 2020. "Detection of Interstellar HC4NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions." The Astrophysical Journal 900:L9. https://doi.org/10.3847/2041-8213/aba631
ID: 157670
Type: article
Authors: Xue, Ci; Willis, Eric R.; Loomis, Ryan A.; Lee, Kin Long Kelvin; Burkhardt, Andrew M.; Shingledecker, Christopher N.; Charnley, Steven B.; Cordiner, Martin A.; Kalenskii, Sergei; McCarthy, Michael C.; Herbst, Eric; Remijan, Anthony J.; McGuire, Brett A.
Abstract: We report an astronomical detection of HC4NC for the first time in the interstellar medium with the Green Bank Telescope toward the TMC-1 molecular cloud with a minimum significance of 10.5σ. The total column density and excitation temperature of HC4NC are determined to be ${3.29}_{-1.20}^{+8.60}\times {10}^{11}$ cm-2 and ${6.7}_{-0.3}^{+0.3}\ {\rm{K}}$ , respectively, using Markov chain Monte Carlo analysis. In addition to HC4NC, HCCNC is distinctly detected whereas no clear detection of HC6NC is made. We propose that the dissociative recombination of the protonated cyanopolyyne, HC5NH+, and the protonated isocyanopolyyne, HC4NCH+, are the main formation mechanisms for HC4NC while its destruction is dominated by reactions with simple ions and atomic carbon. With the proposed chemical networks, the observed abundances of HC4NC and HCCNC are reproduced satisfactorily.
The Laboratory Millimeter and Submillimeter Rotational Spectrum of Lactaldehyde and an Astronomical Search in Sgr B2(N), Orion-KL, and NGC 6334IAlonso, Elena R.McGuire, Brett A.Kolesniková, LucieCarroll, P. BrandonLeón, IkerBrogan, Crystal L.Hunter, Todd R.Guillemin, Jean-ClaudeAlonso, Jose L.DOI: info:10.3847/1538-4357/ab3463v. 88318
Alonso, Elena R., McGuire, Brett A., Kolesniková, Lucie, Carroll, P. Brandon, León, Iker, Brogan, Crystal L., Hunter, Todd R., Guillemin, Jean-Claude, and Alonso, Jose L. 2019. "The Laboratory Millimeter and Submillimeter Rotational Spectrum of Lactaldehyde and an Astronomical Search in Sgr B2(N), Orion-KL, and NGC 6334I." The Astrophysical Journal 883:18. https://doi.org/10.3847/1538-4357/ab3463
ID: 154398
Type: article
Authors: Alonso, Elena R.; McGuire, Brett A.; Kolesniková, Lucie; Carroll, P. Brandon; León, Iker; Brogan, Crystal L.; Hunter, Todd R.; Guillemin, Jean-Claude; Alonso, Jose L.
Abstract: We present a laboratory rotational study of, and astronomical search for, lactaldehyde (CH3CH(OH)CH(O)), one of the simplest chiral molecules that could reasonably be seen in the interstellar medium (ISM), in the millimeter and submillimeter wave regions from 80 to 460 GHz. More than 5000 transitions were assigned to the most stable conformer, and a set of spectroscopic constants was accurately determined. Lactaldehyde is involved in numerous metabolic pathways used by life on Earth, and is a logical step up in complexity from glycolaldehyde (CH(O)CH2OH) which is being detected with increasing regularity in the ISM. We present an accompanying radio astronomical search for lactaldehyde in three high-mass star-forming regions (NGC 6334I, Sgr B2(N), and Orion-KL) as well as in the publicly available data from the ASAI Large Project. Neither molecule is detected in these sources, and we report corresponding upper limits to the column densities. We discuss the potential utility of lactaldehyde in combination with other members of the [C3,H6,O2] isomeric family in probing pathways of chemical evolution in the ISM.
Modeling C-shock Chemistry in Isolated Molecular OutflowsBurkhardt, Andrew M.Shingledecker, Christopher N.Le Gal, RomaneMcGuire, Brett A.Remijan, Anthony J.Herbst, EricDOI: info:10.3847/1538-4357/ab2be8v. 88132
Burkhardt, Andrew M., Shingledecker, Christopher N., Le Gal, Romane, McGuire, Brett A., Remijan, Anthony J., and Herbst, Eric. 2019. "Modeling C-shock Chemistry in Isolated Molecular Outflows." The Astrophysical Journal 881:32. https://doi.org/10.3847/1538-4357/ab2be8
ID: 154247
Type: article
Authors: Burkhardt, Andrew M.; Shingledecker, Christopher N.; Le Gal, Romane; McGuire, Brett A.; Remijan, Anthony J.; Herbst, Eric
Abstract: Shocks are a crucial probe for understanding the ongoing chemistry within ices on interstellar dust grains, where many complex organic molecules (COMs) are believed to be formed. However, previous work has been limited to the initial liberation into the gas phase through nonthermal desorption processes such as sputtering. Here we present results from the adapted three-phase gas-grain chemical network code NAUTILUS, with the inclusion of additional high-temperature reactions, nonthermal desorption, collisional dust heating, and shock physics parameters. This enhanced model is capable of reproducing many of the molecular distributions and abundance ratios seen in our prior observations of the prototypical shocked outflow L1157. In addition, we find that, among others, NH2CHO, HCOOCH3, and CH3CHO have significant post-shock chemistry formation routes that differ from those of many other COMs observed in shocks. Finally, a number of selected species and phenomena are studied here with respect to their usefulness as shock tracers in various astrophysical sources.
Interstellar Glycolaldehyde, Methyl Formate, and Acetic Acid. I. A Bimodal Abundance Pattern in Star-forming RegionsEl-Abd, Samer J.Brogan, Crystal L.Hunter, Todd R.Willis, Eric R.Garrod, Robin T.McGuire, Brett A.DOI: info:10.3847/1538-4357/ab3646v. 883129
El-Abd, Samer J., Brogan, Crystal L., Hunter, Todd R., Willis, Eric R., Garrod, Robin T., and McGuire, Brett A. 2019. "Interstellar Glycolaldehyde, Methyl Formate, and Acetic Acid. I. A Bimodal Abundance Pattern in Star-forming Regions." The Astrophysical Journal 883:129. https://doi.org/10.3847/1538-4357/ab3646
ID: 154698
Type: article
Authors: El-Abd, Samer J.; Brogan, Crystal L.; Hunter, Todd R.; Willis, Eric R.; Garrod, Robin T.; McGuire, Brett A.
Abstract: The relative column densities of the structural isomers methyl formate, glycolaldehyde, and acetic acid are derived for a dozen positions toward the massive star-forming regions MM1 and MM2 in the NGC 6334I complex, which are separated by ̃4000 au. Relative column densities of these molecules are also gathered from the literature for 13 other star-forming regions. In this combined data set, a clear bimodal distribution is observed in the relative column densities of glycolaldehyde and methyl formate. No such distribution is evident with acetic acid. The two trends are comprised of star-forming regions with a variety of masses, suggesting that there must be some other common parameter that is heavily impacting the formation of glycolaldehyde. This is indicative of some demonstrable differentiation in these cores; studying the abundances of these isomers may provide a clue as to the integral chemical processes ongoing in a variety of protostellar environments.
Orion SrcI's Disk Is SaltyGinsburg, AdamMcGuire, Brett A.Plambeck, RichardBally, JohnGoddi, CiriacoWright, MelvynDOI: info:10.3847/1538-4357/aafb71v. 87254
Ginsburg, Adam, McGuire, Brett A., Plambeck, Richard, Bally, John, Goddi, Ciriaco, and Wright, Melvyn. 2019. "Orion SrcI's Disk Is Salty." The Astrophysical Journal 872:54. https://doi.org/10.3847/1538-4357/aafb71
ID: 155452
Type: article
Authors: Ginsburg, Adam; McGuire, Brett A.; Plambeck, Richard; Bally, John; Goddi, Ciriaco; Wright, Melvyn
Abstract: We report the detection of NaCl, KCl, and their 37Cl and 41K isotopologues toward the disk around Orion SrcI. About 60 transitions of these molecules were identified. This is the first detection of these molecules in the interstellar medium not associated with the ejecta of evolved stars. It is also the first ever detection of the vibrationally excited states of these lines in the ISM above v = 1, with firm detections up to v = 6. The salt emission traces the region just above the continuum disk, possibly forming the base of the outflow. The emission from the vibrationally excited transitions is inconsistent with a single temperature, implying the lines are not in LTE. We examine several possible explanations of the observed high excitation lines, concluding that the vibrational states are most likely to be radiatively excited via rovibrational transitions in the 25-35 μ {{m}} (NaCl) and 35-45 μ {{m}} (KCl) range. We suggest that the molecules are produced by destruction of dust particles. Because these molecules are so rare, they are potentially unique tools for identifying high-mass protostellar disks and measuring the radiation environment around accreting young stars.
Gas phase detection and rotational spectroscopy of ethynethiol, HCCSHLee, Kin Long KelvinMartin-Drumel, Marie-AlineLattanzi, ValerioMcGuire, Brett A.Caselli, PaolaMcCarthy, Michael C.DOI: info:10.1080/00268976.2018.1552028v. 1171381–1391
Lee, Kin Long Kelvin, Martin-Drumel, Marie-Aline, Lattanzi, Valerio, McGuire, Brett A., Caselli, Paola, and McCarthy, Michael C. 2019. "Gas phase detection and rotational spectroscopy of ethynethiol, HCCSH." Molecular Physics 117:1381– 1391. https://doi.org/10.1080/00268976.2018.1552028
ID: 152909
Type: article
Authors: Lee, Kin Long Kelvin; Martin-Drumel, Marie-Aline; Lattanzi, Valerio; McGuire, Brett A.; Caselli, Paola; McCarthy, Michael C.
Abstract: We report the gas-phase detection and spectroscopic characterisation of ethynethiol (?), a metastable isomer of thioketene (?) using a combination of Fourier-transform microwave and submillimetre-wave spectroscopies. Several a-type transitions of the normal species were initially detected below 40 GHz using a supersonic expansion-electrical discharge source, and subsequent measurement of higher-frequency, b-type lines using double resonance provided accurate predictions in the submillimetre region. With these, searches using a millimetre-wave absorption spectrometer equipped with a radio frequency discharge source were conducted in the range 280-660 GHz, ultimately yielding nearly 100 transitions up to ? and ?. From the combined data set, all three rotational constants and centrifugal distortion terms up to the sextic order were determined to high accuracy, providing a reliable set of frequency predictions to the lower end of the THz band. Isotopic substitution has enabled both a determination of the molecular structure of HCCSH and, by inference, its formation pathway in our nozzle discharge source via the bimolecular radical-radical recombination reaction ?, which is calculated to be highly exothermic (-477 kJ/mol) using the HEAT345(Q) thermochemical scheme.
Gas-phase synthetic pathways to benzene and benzonitrile: a combined microwave and thermochemical investigationLee, Kin Long KelvinMcGuire, Brett A.McCarthy, Michael C.DOI: info:10.1039/C8CP06070Cv. 212946–2956
Lee, Kin Long Kelvin, McGuire, Brett A., and McCarthy, Michael C. 2019. "Gas-phase synthetic pathways to benzene and benzonitrile: a combined microwave and thermochemical investigation." Physical Chemistry Chemical Physics (Incorporating Faraday Transactions) 21:2946– 2956. https://doi.org/10.1039/C8CP06070C
ID: 150505
Type: article
Authors: Lee, Kin Long Kelvin; McGuire, Brett A.; McCarthy, Michael C.
Abstract: Not Available
Searches for Interstellar HCCSH and H2CCSMcGuire, Brett A.Shingledecker, Christopher N.Willis, Eric R.Lee, Kin Long KelvinMartin-Drumel, Marie-AlineBlake, Geoffrey A.Brogan, Crystal L.Burkhardt, Andrew M.Caselli, PaolaChuang, Ko-JuEl-Abd, SamerHunter, Todd R.Ioppolo, SergioLinnartz, HaroldRemijan, Anthony J.Xue, CiMcCarthy, Michael C.DOI: info:10.3847/1538-4357/ab3b01v. 883201
McGuire, Brett A., Shingledecker, Christopher N., Willis, Eric R., Lee, Kin Long Kelvin, Martin-Drumel, Marie-Aline, Blake, Geoffrey A., Brogan, Crystal L., Burkhardt, Andrew M., Caselli, Paola, Chuang, Ko-Ju, El-Abd, Samer, Hunter, Todd R., Ioppolo, Sergio, Linnartz, Harold, Remijan, Anthony J., Xue, Ci, and McCarthy, Michael C. 2019. "Searches for Interstellar HCCSH and H2CCS." The Astrophysical Journal 883:201. https://doi.org/10.3847/1538-4357/ab3b01
ID: 154704
Type: article
Authors: McGuire, Brett A.; Shingledecker, Christopher N.; Willis, Eric R.; Lee, Kin Long Kelvin; Martin-Drumel, Marie-Aline; Blake, Geoffrey A.; Brogan, Crystal L.; Burkhardt, Andrew M.; Caselli, Paola; Chuang, Ko-Ju; El-Abd, Samer; Hunter, Todd R.; Ioppolo, Sergio; Linnartz, Harold; Remijan, Anthony J.; Xue, Ci; McCarthy, Michael C.
Abstract: A longstanding problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and submillimeter regions of the sulfur- containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its b-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high- mass star-forming regions, however, resulted in nondetections. An analogous search for the lowest-energy isomer, {{{H}}}2{CCS}, is presented for comparison, and also resulted in nondetections. Typical upper limits on the abundance of both species relative to hydrogen are 10-9-10-10. We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available.
ALMA Detection of Vibrationally Excited (v t = 1, 2) Acetic Acid toward NGC 6334IXue, CiRemijan, Anthony J.Brogan, Crystal L.Hunter, Todd R.Herbst, EricMcGuire, Brett A.DOI: info:10.3847/1538-4357/ab32e0v. 882118
Xue, Ci, Remijan, Anthony J., Brogan, Crystal L., Hunter, Todd R., Herbst, Eric, and McGuire, Brett A. 2019. "ALMA Detection of Vibrationally Excited (v t = 1, 2) Acetic Acid toward NGC 6334I." The Astrophysical Journal 882:118. https://doi.org/10.3847/1538-4357/ab32e0
ID: 154428
Type: article
Authors: Xue, Ci; Remijan, Anthony J.; Brogan, Crystal L.; Hunter, Todd R.; Herbst, Eric; McGuire, Brett A.
Abstract: Vibrationally excited states of detected interstellar molecules have been shown to account for a large portion of unidentified spectral lines in observed interstellar spectra toward chemically rich sources. Here, we present the first interstellar detection of the first and second vibrationally excited torsional states of acetic acid (v t = 1, 2) toward the high-mass star-forming region NGC 6334I. The observations presented were taken with the Atacama Large Millimeter/submillimeter Array in bands 4, 6, and 7 covering a frequency range of 130-352 GHz. By comparing a single-excitation temperature model to the observations, the best-fit excitation temperature and column density are obtained to be 142(25) K and 1.12(7) × 1017 cm-2, respectively. Based on the intensity maps of the vibrationally excited CH3COOH transitions, we found that the CH3COOH emissions are compact and concentrated toward the MM1 and MM2 regions with a source size smaller than 2″. After locating the emission from different CH3COOH transitions, which cover a large range of excitation energies, we are able to explain the variation of the CH3COOH emission peak within the MM2 core by invoking continuum absorption or outflows.