Detection of vibrationally excited C6H in the cold prestellar core TMC-1 with the QUIJOTE line survey
Abstract
In this work, we present the detection of twelve doublets with quantum numbers of N = 12-11 to N = 17-16 of the ν11(μ2Σ) vibrationally excited state of C6H towards TMC-1. This marks the first time that an excited vibrational state of a molecule has been detected in a cold starless core. The data are part of the QUIJOTE line survey gathered with the Yebes 40m radio telescope. The line intensities have been aptly reproduced with a rotational temperature of 6.2 ± 0.4 K and a column density of (1.2 ± 0.2)×1011 cm−2. We also analysed the ground state transitions of C6H, detecting fourteen lines with quantum numbers of J = 23/2-21/2 to J = 35/2 for each of the two 2Π3/2 and 2Π1/2 ladders. It is not possible to model the intensities of all the transitions of the ground state simultaneously using a single column density. We considered the two ladders as two different species and found that the rotational temperature is the same for both ladders, Trot(2Π3/2)=Trot(2Π1/2)=6.2 ± 0.2, achieving a result that is comparable to that of the ν11(2μΣ) state. The derived column densities are N(2Π3/2) = (6.2 ± 0.3)×1012 cm−2 and N(2Π1/2) = (8.0 ± 0.4)×1010 cm−2. The fraction of C6H molecules in its 2Π3/2, 2Π1/2, and ν11(μ2Σ) states is 96.8%, 1.3%, and 1.9%, respectively. Finally, we report that this vibrational mode has also been detected towards the cold cores Lupus-1A and L1495B, as well as the low-mass star forming cores L1527 and L483, with fractions of C6H molecules in this mode of 3.8%, 4.1%, 14.8%, and 6%, respectively.
Based on observations carried out with the Yebes 40m telescope (projects 19A003, 20A014, 20D023, 21A011, 21D005, and 23A024). The 40m radio telescope at Yebes Observatory is operated by the Spanish Geographic Institute (IGN, Ministerio de Transportes, Movilidad y Agenda Urbana).- Publication:
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Astronomy and Astrophysics
- Pub Date:
- December 2023
- DOI:
- 10.1051/0004-6361/202348495
- arXiv:
- arXiv:2311.13860
- Bibcode:
- 2023A&A...680L...4C
- Keywords:
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- astrochemistry;
- line: identification;
- molecular data;
- ISM: molecules;
- ISM: individual objects: TMC-1;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted as a Letter in Astronomy &