2020A&A...640A..51C


C.D.S. - SIMBAD4 rel 1.7 - 2020.10.26CET13:56:29

2020A&A...640A..51C - Astronomy and Astrophysics, volume 640A, 51-51 (2020/8-1)

Carbon isotopic fractionation in molecular clouds.

COLZI L., SIPILA O., ROUEFF E., CASELLI P. and FONTANI F.

Abstract (from CDS):


Context. Carbon fractionation has been studied from a theoretical point of view with different models of time-dependent chemistry, including both isotope-selective photodissociation and low-temperature isotopic exchange reactions.
Aims. Recent chemical models predict that isotopic exchange reactions may lead to a depletion of 13C in nitrile-bearing species, with 12C/13C ratios two times higher than the elemental abundance ratio of 68 in the local interstellar medium. Since the carbon isotopic ratio is commonly used to evaluate the 14N/15N ratios with the double-isotope method, it is important to study carbon fractionation in detail to avoid incorrect assumptions.
Methods. In this work, we implemented a gas-grain chemical model with new isotopic exchange reactions and investigated their introduction in the context of dense and cold molecular gas. In particular, we investigated the 12C/13C ratios of HNC, HCN, and CN using a grid of models, with temperatures and densities ranging from 10 to 50 K and 2x103 to 2x107cm–3, respectively.
Results. We suggest a possible 13C exchange through the 13C+C3-12C+13CC2 reaction, which does not result in dilution, but rather in 13C enhancement, for molecules that are formed starting from atomic carbon. This effect is efficient in a range of time between the formation of CO and its freeze-out on grains. Furthermore, the parameter-space exploration shows, on average, that the 12C/13C ratios of nitriles are predicted to be a factor 0.8-1.9 different from the local 12C/13C of 68 for high-mass star-forming regions. This result also affects the 14N/15N ratio: a value of 330 obtained with the double-isotope method is predicted to vary in the range 260-630, up to 1150, depending on the physical conditions. Finally, we studied the 12C/13C ratios of nitriles by varying the cosmic-ray ionisation rate, ζ: the 12C/13C ratios increase with ζ because of secondary photons and cosmic-ray reactions.

Abstract Copyright: © ESO 2020

Journal keyword(s): astrochemistry - methods: numerical - ISM: molecules - molecular processes

Simbad objects: 13

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Number of rows : 13

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 [HKM99] B1-b cor 03 33 20.32 +31 07 21.5           ~ 164 0
2 LDN 1498 DNe 04 11.0 +24 58           ~ 250 0
3 NAME [BM89] L1521B cor 04 24 12.7 +26 36 53           ~ 62 0
4 LDN 1527 DNe 04 39 53 +25 45.0           ~ 508 0
5 TMC-1 MoC 04 41 45.9 +25 41 27           ~ 1378 0
6 V* V2457 Ori Or* 05 35 26.97000 -05 09 54.4644         18.858 ~ 117 0
7 IRAS 05358+3543 mul 05 39 10.4 +35 45 19           ~ 136 1
8 LDN 183 MoC 15 54 12.2 -02 49 42           ~ 690 1
9 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11760 0
10 NAME Sgr B2 MoC 17 47 20.4 -28 23 07           ~ 1943 1
11 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 337 1
12 W 51e2 Rad 19 23 43.90 +14 30 34.8           ~ 184 0
13 HD 210121 * 22 08 11.9025501667 -03 31 52.770012247   7.84 7.68     B7II 152 0

    Equat.    Gal    SGal    Ecl

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2020.10.26-13:56:29

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