J/A+A/702/A23 TMC-1 analysis of C and S isotopologues (Fuentetaja+, 2025)
Analysis of the isotopologues of CS, CCS, CCCS, HCS+, HCCS+, and H2CS in
TMC-1 with the QUIJOTE line survey.
Fuentetaja R., Cabezas C., Endo Y., Agundez M., Godard Palluet A., Lique F.,
Tercero B., Marcelino N., de Vicente P., Cernicharo J.
<Astron. Astrophys. 702, A23 (2025)>
=2025A&A...702A..23F 2025A&A...702A..23F (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Spectroscopy ; Radio lines
Keywords: astrochemistry - line: identification - molecular data -
ISM: molecules - ISM: individual objects: TMC-1
Abstract:
We performed a detailed analysis of the isotopologues with 13C,
34S, 33S, and 36S of the sulphur-bearing molecules CS, CCS,
CCCS, HCS+, HCCS+, and H2CS towards the starless core TMC-1 using
the QUIJOTE line survey. The observations were obtained with the Yebes
40m radio telescope, and the sensitivity of the data varied between
0.08 and 0.2mK in the 31-50GHz range. Observations with the IRAM 30m
radio telescope of the most abundant isotopologues of these species
are also presented and used to estimate volume densities and to
constrain the excitation conditions of these molecules. Among these
species, we report the first detection in space of C13C34S,
CC33S, CCC33S, HC33S+, and HCC34S+. C36S is also detected for
the first time in a cold starless object. These data were complemented
with sensitive maps that provide the spatial distribution of most of
these species. Using the available collisional rate coefficients for
each species, we modeled the observed line intensities using the large
velocity gradient method for the radiative transfer. The results
allowed us to report the most complete analysis of the column
densities of the CnS family and to compare the abundance ratios of all
detected isotopologues. Adopting a kinetic temperature for TMC-1 of
9K, we found that n(H2)=0.9-1.5x104cm-3 can explain the observed
decline in intensity with increasing rotational levels J for all
observed molecules. We derived the rotational constants for the
C13C34S, CC33S, CCC33S, HC33S+, and HCC34S+ isotopologues
from new laboratory data and complemented them with the frequencies of
the observed lines. We find that all sulphur isotopologues are
consistent with solar isotopic abundance ratios. Accurate 12C/13C
abundances were derived and, as previously suggested, the 13C
isotopologues of CCS and CCCS show strong abundance anomalies
depending on the position of the substituted carbon. Nevertheless, the
12C/13C abundance ratio is practically identical to the solar
value for CS, HCS+, and H2CS. We also searched for the isotopologues
of other S-bearing molecules in the 31-50 GHz domain (HCS, HSC, NCS,
H2CCS, HCSCN, HCCCS+, C4S, and C5S). The expected intensities for
their 34S and 13C isotopologues are too low to be detected with
the present sensitivity of the QUIJOTE line survey, however. The
results presented in this work provide new insights into the molecular
composition, isotopic abundances, and physical conditions of the cold
starless core TMC-1
Description:
The data of the QUIJOTE line survey presented here were gathered in
several observing runs between November 2019 and July 2023. The
measured sensitivity by July 2023 varied between 0.08mK at 32GHz and
0.2mK at 49.5GHz, and it is better by about 50 times than that of
previous line surveys in the Q band of TMC-1.
Observed line parameters for S-bearing species and their isotopologues
in this study.
Objects:
---------------------------------------------
RA (ICRS) DE Designation(s)
---------------------------------------------
04 41 45.89 +25 41 27.0 TMC-1 = HCL 2
---------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 101 188 Observed line parameters for S-bearing species
and their isotopologues in this study
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Mol Molecule
9 A1 --- n_Mol [*#] Note on Mol (1)
11- 21 A11 --- Trans Transition
26- 35 A10 --- Fu-Fl Transition (Fu-Fl)
36- 45 F10.3 MHz nurest Adopted rest frequency (see text)
47- 51 F5.3 MHz e_nurest Adopted rest frequency error (1sigma)
53- 56 F4.2 km/s vLSR ? Local standard of rest (LSR) velocity
of the line (2)
58- 61 F4.2 km/s e_vLSR ? Local standard of rest (LSR) velocity
of the line error (1sigma)
63- 69 F7.2 mK/km.s Int(T*Adv) ? Integrated line intensity
71- 74 F4.2 mK/km.s e_Int(T*Adv) ? Integrated line intensity error (1sigma)
76- 79 F4.2 km/s Deltav ? Linewidth at half intensity derived by
fitting a Gaussian function to the
observed line profile
81- 84 F4.2 km/s e_Deltav ? Linewidth at half intensity derived by
fitting a Gaussian function to the
observed line profile error (1sigma)
86- 87 A2 --- l_T*A [≤ ] Limit flag on T*A (3sigma)
88- 94 F7.2 mK T*A ? Antenna temperature
96- 99 F4.2 mK e_T*A ? Antenna temperature error (1sigma)
101 A1 --- n_T*A [fg] Note on T*A (3)
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Note (1): Note as follows:
* = Lines have been fitted using three gaussians
# = Molecule for which new rotational constants are provided (see Appendix A)
Note (2): If the uncertainty is not given, then the velocity has been fixed to
5.83km/s and the derived frequency has been used to improve the rotational
constants of the molecule (see Appendix A).
Note (3): Note as follows:
f = Blended with HCO. Line parameters are uncertain
g = Fully blended with a line of similar intensity from CC13CO J=5-4.
The frequency difference between both features is 10kHz. Several lines of
the 13C isotopologues of CCCO are detected with QUIJOTE.
Around 50% of the observed intensity can be attributed to CC13CO.
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Acknowledgements:
Raul Fuentetaja, r.fuentetaja(at)iff.csic.es
(End) Patricia Vannier [CDS] 23-Sep-2025