The<sup>12</sup>C/<sup>13</sup>C Isotope Gradient Derived from Millimeter Transitions of CN: The Case for Galactic Chemical Evolution

Milam, Stefanie N.; Savage, C. M.; Brewster, M. A.; Ziurys, L. M.; Wyckoff, S.

doi:10.1086/497123

Cited by 536 publications

(748 citation statements)

References 37 publications

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“…For the oxygen isotopes, we adopt a ratio of X[ 16 O/ 18 O] = 100. These values are smaller than the broad Galactic scale values (Milam et al 2005), but taken into account of fractionation observed in cold dense core (Mladenović & Roueff 2014) and are consistent with Carolan et al (2008) and Wiles et al (2015). Assuming these values, we see from the Detection Equation that τ 13 CO = T * A ( 13 CO)/T * A ( 12 CO), with τ 12 CO then determined by the preceding formula (and similarly for τ C 18 O ).…”

Section: Molecular Lines: Optical Depthssupporting

confidence: 89%

Infall, outflow, and turbulence in massive star-forming cores in the G333 giant molecular cloud

Wiles

Redman

et al. 2015

Mon. Not. R. Astron. Soc.

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We present molecular line imaging observations of three massive molecular outflow sources, G333.6-0.2, G333.1-0.4, and G332.8-0.5, all of which also show evidence for infall, within the G333 giant molecular cloud (GMC). All three are within a beam size (36 arcseconds) of IRAS sources, 1.2-mm dust clumps, various masing species and radio continuum-detected Hii regions and hence are associated with high-mass star formation. We present the molecular line data and derive the physical properties of the outflows including the mass, kinematics, and energetics and discuss the inferred characteristics of their driving sources. Outflow masses are of 10 to 40 M ⊙ in each lobe, with core masses of order 10 3 M ⊙ . outflow size scales are a few tenth of a parsec, timescales are of several ×10 4 years, mass loss rates a few ×10 −4 M ⊙ /yr. We also find the cores are turbulent and highly supersonic.

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Section: Molecular Lines: Optical Depthssupporting

confidence: 89%

Infall, outflow, and turbulence in massive star-forming cores in the G333 giant molecular cloud

Wiles

Redman

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Isotopic ratios have proven extremely powerful in providing quantitative constraints on the composition of the protosolar disk from which the solar system formed (Chaussidon & Gounelle 2007;Jehin et al 2009). For carbon, the isotopic ratio 12 C/ 13 C measured in comets shows a remarkable homogeneity, with a mean value of 91 that agrees with the solar value of 90, and is also very close to the value of 70 determined in the local ISM (Milam et al 2005;Asplund et al 2009;Manfroid et al 2009). For oxygen, measurements in comets lead to 16 O/ 18 O ratios between 500 and 600, which again are in good agreement with the solar and local ISM value of 500 (Wilson & Rood 1994).…”

Section: Introductionsupporting

confidence: 78%

“…If we now assume that 12 CN/ 13 CN= 12 C/ 13 C and adopt for the latter the value of 68 from Milam et al (2005), we derive an isotopic ratio CN/C 15 N = 476 ± 70 in L1498 and CN/C 15 N = 510 ± 70 in L1544, where conservative uncertainties are applied (see Table 2). Altogehter, these values give CN/C 15 N = 500 ± 75.…”

Section: Resultsmentioning

confidence: 99%

“…The most important changes regard the dissociative recombinations of ions such as NH + 2 , NH + 3 , and NH + 4 , which are critical (Milam et al 2005). for the production of hydrides. Following Dislaire et al (2012), the dissociative recombination of N 2 H + possesses a channel producing NH with a branching ratio of ≈ 5% (Vigren et al 2012).…”

Section: Model Calculationsmentioning

confidence: 99%

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The CN/C¹⁵N isotopic ratio towards dark clouds

Hily-Blant

Forêts

Fauré

et al. 2013

A&A

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Understanding the origin of the composition of solar system cosmomaterials is a central question, not only in the cosmochemistry and astrochemistry fields, and requires various approaches to be combined. Measurements of isotopic ratios in cometary materials provide strong constraints on the content of the protosolar nebula. Their relation with the composition of the parental dark clouds is, however, still very elusive. In this paper, we bring new constraints based on the isotopic composition of nitrogen in dark clouds, with the aim of understanding the chemical processes that are responsible for the observed isotopic ratios. We have observed and detected the fundamental rotational transition of C 15 N towards two starless dark clouds, L1544 and L1498. We were able to derive the column density ratio of C 15 N over 13 CN towards the same clouds, and obtain the CN/C 15 N isotopic ratios, which were found to be 500 ± 75 for both L1544 and L1498. These values are therefore marginally consistent with the protosolar value of 441. Moreover, this ratio is larger than the isotopic ratio of nitrogen measured in HCN. In addition, we present model calculations of the chemical fractionation of nitrogen in dark clouds, which make it possible to understand how CN can be deprived of 15 N and HCN can simultaneously be enriched in heavy nitrogen. The non-fractionation of N 2 H + , however, remains an open issue and we propose some chemical way of alleviating the discrepancy between model predictions and the observed ratios.

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“…The discrepancy of isotope abundance ratios between our sources and the local ISM might arise from Galactic chemical evolution, because the solar value represents the ISM 4.5 Gyr ago. The 12 C/ 13 C ratios can also be affected by isotope selective photodissociation from UV photons because both 12 C and 13 C have different self-shielding (Wilson & Rood 1994;Milam et al 2005). The 13 C is more easily photodissociated than 12 C, which can result in a lower 12 C/ 13 C ratio in the star-forming region compared with the local ISM (e.g.…”

Section: Isotopic Abundancesmentioning

confidence: 99%

Millimetre spectral line mapping observations towards four massive star-forming H ii regions

Wang

Zhang

et al. 2017

Mon. Not. R. Astron. Soc.

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We present spectral line mapping observations towards four massive star-forming regionsCepheus A, DR21S, S76E and G34.26+0.15 -with the IRAM 30-m telescope at the 2 and 3 mm bands. In total, 396 spectral lines from 51 molecules, one helium recombination line, 10 hydrogen recombination lines and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 14 0, 14 -13 0, 13 ) was detected in G34.26+0.15, as the first detection in massive star-forming regions. We found that c-C 3 H 2 and NH 2 D show enhancement in shocked regions, as suggested by the evidence of SiO and/or SO emission. The column density and rotational temperature of CH 3 CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of 12 C/ 13 C were derived using HC 3 N and its 13 C isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value (∼65). The 14 N/ 15 N and 16 O/ 18 O abundance ratios in these sources were also derived using the double isotopic method, which were slightly lower than in the local interstellar medium. Except for Cep A, the 33 S/ 34 S ratios in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N(DCO + )/N(HCO + ) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5 × 10 −5 . Our results show that the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage sources. Evidence of shock activity is seen in all stages studied.

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The¹²C/¹³C Isotope Gradient Derived from Millimeter Transitions of CN: The Case for Galactic Chemical Evolution

Cited by 536 publications

References 37 publications

Infall, outflow, and turbulence in massive star-forming cores in the G333 giant molecular cloud

Infall, outflow, and turbulence in massive star-forming cores in the G333 giant molecular cloud

The CN/C¹⁵N isotopic ratio towards dark clouds

Millimetre spectral line mapping observations towards four massive star-forming H ii regions

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The12C/13C Isotope Gradient Derived from Millimeter Transitions of CN: The Case for Galactic Chemical Evolution

Cited by 536 publications

References 37 publications

Infall, outflow, and turbulence in massive star-forming cores in the G333 giant molecular cloud

Infall, outflow, and turbulence in massive star-forming cores in the G333 giant molecular cloud

The CN/C15N isotopic ratio towards dark clouds

Millimetre spectral line mapping observations towards four massive star-forming H ii regions

Contact Info

Product

Resources

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The¹²C/¹³C Isotope Gradient Derived from Millimeter Transitions of CN: The Case for Galactic Chemical Evolution

The CN/C¹⁵N isotopic ratio towards dark clouds