by Cheikh Bop, on

Presentation of the conference

The conference talks will cover science, outreach, communication, development and education activities originating from astronomy in Africa. The purpose of the gathering is to enhance further collaborations among African countries as well as the rest of the world.

C. T. Bop presented his work during this conference.

Non-LTE modeling of the HCCNC and HNCCC abundance in astrophysical environments - C. T. Bop, A. Faure, E. Quintas-Sanchez, R. Dawes, and F. Lique

The isomers of HCCCN, namely HCCNC and HNCCC, are widely observed in the interstellar medium and in circumstellar envelopes. Their abundance has been determined under the assumption of local thermodynamic equilibrium (LTE) conditions or non-LTE radiative transfer models, but considering the collisional excitation of HCCCN as the same for all isomers [1].

Chemical models for the prototypical cold cores, TMC-1 and L1544, reproduced the abundance of HCCCN fairly well, but they tend to overestimate the abundances of HCCNC and HNCCC with respect to the observations [2]. It is therefore worth revisiting the interpretation of the observational spectra of these isomers using a rigorous non-LTE modelling. The abundance of HCCNC and HNCCC were then determined using non-LTE radiative transfer calculations based on the proper rate coefficients for the first time in this work. Modeling the brightness temperature of HCCNC and HNCCC when using their proper collision rate coefficients shows that models based on LTE or non-LTE with approximate collision data may lead to deviations of up to a factor of ∼1.5 [3].

Reinterpreting the observational spectra led us to significant differences relative to the observed abundances previously determined. Our findings suggest quite similar abundance ratios for the TMC-1 and L1544 cold cores as well as the L483 protostar [4]. This work will encourage further modelling with more robust non-LTE radiative transfer calculations and future studies to revisit the chemistry of HCCCN and its isomers in cold molecular clouds.

[1]. Cernicharo, J., Marcelino, N., Agúndez, M., et al. 2020a, Astronomy & Astro-physics, 642, L8
[2]. Quénard, D., Vastel, C., Ceccarelli, C., et al. 2017, Monthly Notices of the RoyalAstronomical Society, 470, 3194
[3]. Bop, C. T., Lique, F., Faure, A., Quintas-Sánchez, E., & Dawes, R. 2021,Monthly Notices of the Royal Astronomical
Society, 501, 1911
[4]. Bop, C. T., Desrousseaux, B & Lique, F. 2022, Astronomy and Astrophysics, 662, A102