Alma Observations of HCN and Its Isotopologues on Titan

Molter, Edward; Nixon, C. A.; Cordiner, Martin; Serigano, Joseph; Irwin, Patrick; Teanby, N. A.; Charnley, Steven B.; Lindberg, Johan E.

doi:10.3847/0004-6256/152/2/42

Cited by 68 publications

(67 citation statements)

References 44 publications

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“…More specifically, the modeled 14 N/ 15 N values for CH 3 CN and C 2 H 5 CN are ∼80 at high altitudes (∼800 km) and increase to ∼120 in the lower stratosphere (∼200 km), while those for HCN and HC 3 N are expected to be relatively constant at ∼80 altitudes below 800 km. These modeled values for HCN and HC 3 N are in good agreement with previous observation results of 94±13 (Gurwell 2004) and 72.2±2.2 (Molter et al 2016) for HCN, and 67±14 (Cordiner et al 2018) for HC 3 N. Interestingly, there is another photochemical model showing different 14 N/ 15 N values for nitriles. Vuitton et al (2019) modeled nitrile chemistry including isotopic fractionation processes, which indicated that 14 N/ 15 N for CH 3 CN at high (>1000 km) altitude is smaller than that of HCN and HC 3 N because they proposed that CH 3 CN is produced from N( 2 D) which is enriched in 15 N. In turn, in the lower stratosphere (at 200 km), three nitriles are expected to exhibit similar 14 N/ 15 N values of ∼55 because non-fractionated N-atoms produced by GCR collision with N 2 homogenizes 14 N/ 15 N in nitriles via recycling processes.…”

Section: Introductionsupporting

confidence: 92%

¹⁴N/¹⁵N Isotopic Ratio in CH₃CN of Titan’s Atmosphere Measured with ALMA

Iino

Sagawa

Tsukagoshi

2020

ApJ

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Each of the nitriles present in the atmosphere of Titan can be expected to exhibit different 14 N/ 15 N values depending on their production processes, primarily because of the various N 2 dissociation processes induced by different sources such as ultraviolet radiation, magnetospheric electrons, and galactic cosmic rays. For CH 3 CN, one photochemical model predicted a 14 N/ 15 N value as 120-130 in the lower stratosphere. This is much higher than that for HCN and HC 3 N, ∼67-94. By analyzing archival data obtained by the Atacama Large Millimeter/submillimeter Array (ALMA), we successfully detected submillimeter rotational transitions of CH 3 C 15 N (J = 19-18) locate at the 338 GHz band in Titan's atmospheric spectra. By comparing those observations with the simultaneously observed CH 3 CN (J = 19-18) lines at the 349 GHz band, which probe from 160 to ∼400 km altitude, we then derived 14 N/ 15 N in CH 3 CN as 125 +145 −44 . Although the range of the derived value shows insufficient accuracy due to data quality limitations, the best-fit value suggests that 14 N/ 15 N for CH 3 CN is higher than values that have been previously observed and theoretically predicted for HCN and HC 3 N. This may be explained by the different N 2 dissociation sources according to the altitudes, as suggested by a recent photochemical model.

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Section: Introductionsupporting

confidence: 92%

¹⁴N/¹⁵N Isotopic Ratio in CH₃CN of Titan’s Atmosphere Measured with ALMA

Iino

Sagawa

Tsukagoshi

2020

ApJ

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“…36489corr been used extensively as a dense gas tracer in external galaxies (e.g., Schirm et al 2016;Sliwa & Downes 2017;Johnson et al 2018). HCN is also very abundant in the atmosphere of Titan, and has been used to measure nitrogen fractionation there (e.g., Molter et al 2016). CH 3 CN is regularly used to determine kinetic temperature in star-forming regions (Bell et al 2014), and HC 3 N has been shown to be important in observations of ultraluminous infrared galaxies (Costagliola et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Exploring molecular complexity with ALMA (EMoCA): complex isocyanides in Sgr B2(N)

Willis

Garrod

Беллоче

et al. 2020

A&A

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Context. The Exploring Molecule Complexity with ALMA (EMoCA) survey is an imaging spectral line survey using the Atacama Large Millimeter/submillimeter Array (ALMA) to study the hot-core complex Sagittarius B2(N). Recently, EMoCA revealed the presence of three new hot cores in this complex (N3-N5), in addition to providing detailed spectral data on the previously known hot cores in the complex (N1 and N2). The present study focuses on N2, which is a rich and interesting source for the study of complex molecules whose narrow line widths ameliorate the line confusion problem. Aims. We investigate the column densities and excitation temperatures of cyanide and isocyanide species in Sgr B2(N2). We then use state-of-the-art chemical models to interpret these observed quantities. We also investigate the effect of varying the cosmic-ray ionization rate (ζ) on the chemistry of these molecules. Methods. We used the EMoCA survey data to search for isocyanides in Sgr B2(N2) and their corresponding cyanide analogs. We then used the coupled three-phase chemical kinetics code MAGICKAL to simulate their chemistry. Several new species, and over 100 new reactions have been added to the network. In addition, a new single-stage simultaneous collapse/warm-up model has been implemented, thus eliminating the need for the previous two-stage models. A variable, visual extinction-dependent ζ was also incorporated into the model and tested. Results. We report the tentative detection of CH 3 NC and HCCNC in Sgr B2(N2), which represents the first detection of both species in a hot core of Sgr B2. In addition, we calculate new upper limits for C 2 H 5 NC, C 2 H 3 NC, HNC 3 , and HC 3 NH + . Our updated chemical models can reproduce most observed NC:CN ratios reasonably well depending on the physical parameters chosen. The model that performs best has an extinction-dependent cosmic-ray ionization rate that varies from ∼2 × 10 −15 s −1 at the edge of the cloud to ∼1 × 10 −16 s −1 in the center. Models with higher extinction-dependent ζ than this model generally do not agree as well, nor do models with a constant ζ greater than the canonical value of 1.3 × 10 −17 s −1 throughout the source. Radiative transfer models are run using results of the best-fit chemical model. Column densities produced by the radiative transfer models are significantly lower than those determined observationally. Inaccuracy in the observationally determined density and temperature profiles is a possible explanation. Excitation temperatures are well reproduced for the true "hot core" molecules, but are more variable for other molecules such as HC 3 N, for which fewer lines exist in ALMA Band 3. Conclusions. The updated chemical models do a very good job of reproducing the observed abundances ratio of CH 3 NC:CH 3 CN towards Sgr B2(N2), while being consistent with upper limits for other isocyanide/cyanide pairs. HCCNC:HC 3 N is poorly reproduced, however. Our results highlight the need for models with A V -depdendent ζ. However, there is still much to be understood about...

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“…Dashed green lines plotted for the DM Tau (Teague et al 2015) and TW Hya ) disks represent the range of values derived for various radii. Purple squares represent values for the following individual sources: TMC-1 (Wootten 1987), low-mass protostar IRAS 16293-2422 (Schöier et al 2002), the TW Hya disk (Öberg et al 2012), comet HaleBopp (Meier et al 1998), and Titan (Molter et al 2016).…”

Section: Comparison To Disk Modelsmentioning

confidence: 99%