J/A+A/685/A149 Fractionation in young cores (Jensen+, 2024)
Fractionation in young cores:
Direct determination of nitrogen and carbon fractionation in HCN.
Jensen S.S., Spezzano S., Caselli P., Sipilae O., Redaelli E., Giers K.,
Ferrer Asensio J.
<Astron. Astrophys. 685, A149 (2024)>
=2024A&A...685A.149J 2024A&A...685A.149J (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Interstellar medium ; Spectroscopy ;
Millimetric/submm sources
Keywords: astrochemistry - stars: formation - ISM: abundances -
ISM: lines and bands
Abstract:
Nitrogen fractionation is a powerful tracer of the chemical evolution
during star- and planet formation. This requires robust determinations
of the nitrogen fractionation across different evolutionary stages.
We aim to determine the 14N/15N and 12C/13C ratios for HCN in
six starless and prestellar cores and compare the results between the
direct method using radiative transfer modeling and the indirect
double isotope method assuming a fixed 12C/13C ratio.
We present IRAM observations of the HCN 1-0, HCN 3-2, HC15N 1-0 and
H13CN 1-0 transitions toward six embedded cores. The 14N/15N
ratio is derived using both the indirect double isotope method and
directly through non-Local Thermodynamic Equilibrium 1D radiative
transfer modeling of the HCN emission. The latter also provides the
12C/13C ratio, which is compared to the local interstellar value.
The derived 14N/15N ratios using the indirect method are generally in
the range 300-550 and could suggest an evolutionary trend in the
nitrogen fractionation of HCN between starless cores and later stages
of the star formation process. However, the direct method reveals
lower fractionation ratios of around ∼250, mainly resulting from a
lower 12C/13C ratio in the range ∼20-40 compared to the local
interstellar medium value of 68.
This study reveals a significant difference between the nitrogen
fractionation ratio in HCN derived using direct and indirect methods.
This can influence the interpretation of the chemical evolution and
displays the pitfalls of the indirect double isotope method for
fractionation studies. However, the direct method is challenging as it
requires well- constrained source models to produce accurate results.
No trend in the nitrogen fractionation of HCN between earlier and
later stages of the star formation process is evident when the results
of the direct method are considered.
Description:
FTS50 spectra of HCN 1-0, 3-2, H13CN 1-0, HC15N 1-0 toward CB23,
TMC2, L1495, L1495AN, L1512, L1517B. Observatory: IRAM 30m.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 90 6 Observation summary
sp/* . 24 Individual spectra
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Source Source name
9- 10 I2 h RAh Right ascension (J2000)
12- 13 I2 min RAm Right ascension (J2000)
15- 18 F4.1 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
32- 34 F3.1 km/s vLSR LSR velocity
36- 48 A13 --- FileName1 Name of HCN 1-0 spectrum file
in subdirectory sp
50- 62 A13 --- FileName2 Name of HCN 3-2 spectrum file
in subdirectory sp
64- 76 A13 --- FileName3 Name of H13CN 1-0 spectrum file
in subdirectory sp
78- 90 A13 --- FileName4 Name of HC15N 1-0 spectrum file
in subdirectory sp
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Byte-by-byte Description of file: sp/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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1- 20 F20.16 km/s Vlsr Velocity
22- 41 E20.16 K Tmb Main beam temperature
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Acknowledgements:
Sigurd S. Jensen, sigurdsj(at)mpe.mpg.de
(End) Patricia Vannier [CDS] 08-Mar-2024