The <sup>12</sup>C/<sup>13</sup>C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Halfen, D. T.; Woolf, N. J.; Ziurys, L. M.

doi:10.3847/1538-4357/aa816b

Cited by 36 publications

(46 citation statements)

References 42 publications

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“…The average HCN/H 13 CN, 86±4, is significantly higher than the 12 C/ 13 C ratio of 65 ± 10 in the local ISM (Halfen et al 2017), but agrees surprisingly well with the value of 89±1 in the PSN (Clayton & Nittler 2004). This indicates that HCN is slightly depleted in 13 C in TW Hya, opposite to what was found in the L1498 pre-stellar core (Magalhães et al 2018), suggesting that the underlying process may not be the same in these two environments.…”

Section: Discussionsupporting

confidence: 72%

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Hily-Blant

Souza

Kastner

et al. 2019

A&A

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The isotopic ratio of nitrogen measured in primitive Solar System bodies shows a broad range of values, the origin of which remains unknown. One key question is whether these isotopic reservoirs of nitrogen predate the comet formation stage or are posterior to it. Another central question is elucidating the processes that can produce the observed variations in the 14 N/ 15 N isotopic ratio. Disks that orbit pre-main-sequence (TTauri) stars provide unique opportunities for observing the chemical content of analogs of the protosolar nebula and therefore for building a comprehensive scenario that can explain the origin of nitrogen in the Solar System and in planetforming disks. With ALMA, it has become possible to measure isotopic ratios of nitrogen-bearing species in such environments. We present spectrally and spatially resolved observations of the hyperfine structure of the 4-3 rotational transition of HCN and its main isotopologs H 13 CN and HC 15 N in the disk orbiting the 8 Myr old TTauri star TW Hya. The sensitivity allows directly measuring the HCN/H 13 CN and HCN/HC 15 N abundance ratios with minimal assumptions. Averaged spatially over the disks, the ratios are 86±4 and 223±21, respectively. The latter value is significantly lower than the CN/C 15 N ratio of 323±30 in this disk and thus provides the first evidence that two isotopic reservoirs of nitrogen are present in a disk at the stage of giant planet and comet formation. Furthermore, we find clear evidence for an increase in the ratio of HCN to HC 15 N with radius. The ratio in the outer disk, at 45 au, is 339±28, in excellent agreement with direct measurements in the local interstellar medium, and with the bulk nitrogen isotopic ratio predicted from galactic evolution calculations. In the comet formation region at r = 20 au, the ratio is a factor ≈ 3 lower, 121±11. This radial increase qualitatively agrees with the scenario in which selective photodissociation of N 2 is the dominant fractionation process. However, our isotopic ratios and kinetic temperature of the HCN-emitting layers quantitatively disagree with models of nitrogen chemistry in disks.

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Section: Discussionsupporting

confidence: 72%

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Hily-Blant

Souza

Kastner

et al. 2019

A&A

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“…The non-detection of vinyl alcohol with ALMA along with its non-detection with the IRAM 30 m telescope (Belloche et al 2013) confirms that if vinyl alcohol were present in the Sgr B2(N) star forming region at the level reported by Turner & Apponi (2001), whose observations with the Kitt Peak 12 m telescope did not resolve the multiple hot cores embedded in Sgr B2(N), then its emission must arise from the source envelope on large scales (> 1 pc) and not from the much more compact hot cores, as already stated by Belloche et al (2013). Surveys like PRIMOS (Prebiotic Interstellar Molecular Survey, Neill et al (2012)) or the one performed at the Arizona Radio Observatory (ARO) (Halfen et al 2017) may shed more light on the presence and distribution of vinyl alcohol toward Sgr B2(N).…”

Section: Astronomical Searchesmentioning

confidence: 99%

Submillimeter spectroscopy and astronomical searches of vinyl mercaptan, C₂H₃SH

Martin‐Drumel

Lee

Беллоче

et al. 2019

A&A

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Context. New laboratory investigations of the rotational spectrum of postulated astronomical species are essential to support the assignment and analysis of current astronomical surveys. In particular, considerable interest surrounds sulfur analogs of oxygencontaining interstellar molecules and their isomers. Aims. To enable reliable interstellar searches of vinyl mercaptan, the sulfur-containing analog to the astronomical species vinyl alcohol, we have investigated its pure rotational spectrum at millimeter wavelengths. Methods. We have extended the pure rotational investigation of the two isomers syn and anti vinyl mercaptan to the millimeter domain using a frequency-multiplication spectrometer. The species were produced by a radiofrequency discharge in 1,2-ethanedithiol. Additional transitions have been re-measured in the centimeter band using Fourier-transform microwave spectroscopy to better determine rest frequencies of transitions with low-J and low-K a values. Experimental investigations were supported by quantum chemical calculations on the energetics of both the [C 2 ,H 4 ,S] and [C 2 ,H 4 ,O] isomeric families. Interstellar searches for both syn and anti vinyl mercaptan as well as vinyl alcohol were performed in the EMoCA (Exploring Molecular Complexity with ALMA) spectral line survey carried out toward Sagittarius (Sgr) B2(N2) with the Atacama Large Millimeter/submillimeter Array (ALMA). Results. Highly accurate experimental frequencies (to better than 100 kHz accuracy) for both syn and anti isomers of vinyl mercaptan have been measured up to 250 GHz; these deviate considerably from predictions based on extrapolation of previous microwave measurements. Reliable frequency predictions of the astronomically most interesting millimeter-wave lines for these two species can now be derived from the best-fit spectroscopic constants. From the energetic investigations, the four lowest singlet isomers of the [C 2 ,H 4 ,S] family are calculated to be nearly isoenergetic, which makes this family a fairly unique test bed for assessing possible reaction pathways. Upper limits for the column density of syn and anti vinyl mercaptan are derived toward the extremely molecule-rich star-forming region Sgr B2(N2) enabling comparison with selected complex organic molecules.

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“…The assignment was in part based on the 12 C 13 C isotopic ratio of 22 determined by Gardner & Whiteoak (1982) which is consistent with the Galactic centre value and not with the higher ratio that characterises local clouds. Indeed, the 12 C 13 C isotopic ratio shows a gradient with galactocentric distance, increasing from about 20 in the GC to about 60-70 for local gas (Milam et al 2005;Halfen et al 2017). As a further verification, we used the EMoCA data to measure the 12 C 13 C isotopic ratio of the velocity components at −2.6, 3.7, and 8 km s −1 (covering the velocity range from −5 to 10 km s −1 ).…”

Section: Meaning Of the Cloud Categoriesmentioning

confidence: 99%

Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2

Thiel

Беллоче

Menten

et al. 2019

A&A

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Context. The diffuse and translucent molecular clouds traced in absorption along the line of sight to strong background sources have so far been investigated mainly in the spectral domain because of limited angular resolution or small sizes of the background sources. Aims. We aim to resolve and investigate the spatial structure of molecular clouds traced by several molecules detected in absorption along the line of sight to Sgr B2(N). Methods. We have used spectral line data from the EMoCA survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA), taking advantage of its high sensitivity and angular resolution. The velocity structure across the field of view is investigated by automatically fitting synthetic spectra to the detected absorption features, which allows us to decompose them into individual clouds located in the Galactic centre (GC) region and in spiral arms along the line of sight. We compute opacity maps for all detected molecules. We investigated the spatial and kinematical structure of the individual clouds with statistical methods and perform a principal component analysis to search for correlations between the detected molecules. To investigate the nature of the molecular clouds along the line of sight to Sgr B2, we also used archival Mopra data. Results. We identify, on the basis of c-C 3 H 2 , 15 main velocity components along the line of sight to Sgr B2(N) and several components associated with the envelope of Sgr B2 itself. The c-C 3 H 2 column densities reveal two categories of clouds. Clouds in Category I (3 kpc arm, 4 kpc arm, and some GC clouds) have smaller c-C 3 H 2 column densities, smaller linewidths, and smaller widths of their column density PDFs than clouds in Category II (Scutum arm, Sgr arm, and other GC clouds). We derive opacity maps for the following molecules: c-C 3 H 2 , H 13 CO + , 13 CO, HNC and its isotopologue HN 13 C, HC 15 N, CS and its isotopologues C 34 S and 13 CS, SiO, SO, and CH 3 OH. These maps reveal that most molecules trace relatively homogeneous structures that are more extended than the field of view defined by the background continuum emission (about 15 , that is 0.08 to 0.6 pc depending on the distance). SO and SiO show more complex structures with smaller clumps of size ∼5-8 . Our analysis suggests that the driving of the turbulence is mainly solenoidal in the investigated clouds. Conclusions. On the basis of HCO + , we conclude that most line-of-sight clouds towards Sgr B2 are translucent, including all clouds where complex organic molecules were recently detected. We also conclude that CCH and CH are good probes of H 2 in both diffuse and translucent clouds, while HCO + and c-C 3 H 2 in translucent clouds depart from the correlations with H 2 found in diffuse clouds.

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The ¹²C/¹³C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Cited by 36 publications

References 42 publications

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Submillimeter spectroscopy and astronomical searches of vinyl mercaptan, C₂H₃SH

Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2

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The 12C/13C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Cited by 36 publications

References 42 publications

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Submillimeter spectroscopy and astronomical searches of vinyl mercaptan, C2H3SH

Small-scale physical and chemical structure of diffuse and translucent molecular clouds along the line of sight to Sgr B2

Contact Info

Product

Resources

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The ¹²C/¹³C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

Submillimeter spectroscopy and astronomical searches of vinyl mercaptan, C₂H₃SH