J/A+A/617/A7 Nitrogen isotopic ratio in prestellar cores (Redaelli+, 2018)
14N/15N ratio measurements in prestellar cores with N2H+ :
new evidence of 15N-antifractionation.
Redaelli E., Bizzocchi L., Caselli P., Harju J. Chacon-Tanarro A.,
Leonardo E., Dore L.
<Astron. Astrophys. 617, A7 (2018)>
=2018A&A...617A...7R 2018A&A...617A...7R (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Radio lines ; Spectroscopy
Keywords: ISM: clouds - ISM: molecules - ISM: abundances - radio lines: ISM -
stars: formation
Abstract:
The 15N fractionation has been observed to show large variations
among astrophysical sources, depending both on the type of target and
on the molecular tracer used. These variations cannot be reproduced by
the current chemical models.
Until now, the 14N/15N ratio in N2H+ has been accurately
measured in only one prestellar source, L1544, where strong levels of
fractionation, with depletion in 15N, are found (14N/15N∼1000).
In this paper we extend the sample to three more bona fide prestellar
cores, in order to understand if the antifractionation in N2H+ is
a common feature of this kind of sources. Methods. We observed
N2H+ , N15NH+ and 15NNH+ in L183, L429 and L694-2 with the
IRAM 30m telescope. We modeled the emission with a non-local radiative
transfer code in order to obtain accurate estimates of the molecular
column densities, including the one for the optically thick N2H+ .
We used the most recent collisional rate coefficients available, and
with these we also re-analysed the L1544 spectra previously published.
The obtained isotopic ratios are in the range 630-770 and
significantly differ with the value, predicted by the most recent
chemical models, of ∼440, close to the protosolar value. Our
prestellar core sample shows high level of depletion of 15N in
diazenylium, as previously found in L1544. A revision of the N
chemical networks is needed in order to explain these results.
Description:
Analysis of the N2H+, 15NNH+ and N15NH+ spectra of three
prestellar core s (L183, L429, L694-2). The lines are modeled with
non-LTE approach in order to derive the column density of each
isotopologue. From the ratios between the column density of the main
isotopologue and of the rare species, the 14N/15N isotopic ratio is
inferred.
Objects:
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RA (2000) DE Designation(s)
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15 54 08.32 -02 52 23 L183 = LDN 183
18 16 06.40 -08 14 00 L429 = LDN 429
19 41 04.50 +10 57 02 L694-2 = [LM99] L694-2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
183n2hp.dat 36 521 N2H+ spectra (x=Vlsr, y=TA*) in L183
183nqnhp.dat 36 521 N15NH+ spectra (x=Vlsr, y=TA*) in L183
429n2hp.dat 36 521 N2H+ spectra (x=Vlsr, y=TA*) in L429
429nqnhp.dat 36 521 N15NH+ spectra (x=Vlsr, y=TA*) in L429
694n2hp.dat 36 555 N2H+ spectra (x=Vlsr, y=TA*) in L694-2
694nqnhp.dat 36 555 N15NH+ spectra (x=Vlsr, y=TA*) in L694-2
694qnnhp.dat 36 555 15NNH+ spectra (x=Vlsr, y=TA*) in L694-2
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See also:
J/A+A/472/519 : N2H+(1-0) maps of Ophiuchus main cloud (Andre+, 2007)
J/A+A/587/A118 : N2H+, N2D+ and C17O spectra in Ophiuchus (Punanova+, 2016)
J/A+A/610/A77 : Orion Integral Filament ALMA+IRAM30m N2H+(1-0) data
(Hacar+, 2018)
Byte-by-byte Description of file: 183*.dat 429*.dat 694*.dat
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Bytes Format Units Label Explanations
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6- 18 E13.7 km/s Vlsr Velocity
24- 36 E13.7 K TA* Antenna temperature
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Acknowledgements:
Alexander Kopylov, akop(at)sao.ru
References:
Kopylova & Kopylov, 1998PAZh...24..573K 1998PAZh...24..573K, (1998AstL...24..491K 1998AstL...24..491K)
Structure and dynamic state of the Corona Borealis supercluster
(End) Alexander Kopylov [SAO, Russia], Patricia Vannier [CDS] 05-Jun-2018