Speaker
Description
Astrochemical observations have revealed a surprisingly high level of chemical complexity, including long carbon chains, in the earliest stages of Sun-like star formation. The origin of these complex species and whether they undergo further growth, possibly contributing to the molecular complexity of planetary systems, remain open questions.
We present recent observations performed using the 100-m Green Bank Telescope in the prestellar core L1544, and the protostellar system IRAS 16293–2422. In L1544, we detected various complex carbon-bearing species, including C$_2$S, C$_3$S, C$_3$N, c-C$_3$H, C$_4$H and C$_6$H, complementing previously reported emission of cyanopolyynes. In IRAS 16293–2422, we detected c-C$_3$H and, for the first time, HC$_7$N. Thanks to the high spectral resolution, we refine the rest frequencies of several c-C$_3$H and C$_6$H transitions. We perform radiative transfer analysis, highlighting a chemical difference between the two sources: IRAS 16293–2422 has column densities 10 to 100 times lower than L1544. We perform astrochemical modeling, employing an up-to-date chemical network with revised reaction rates. The predicted abundances of cyanopolyynes and polyynyl radicals decrease with molecular size, in agreement with observations. However, the models underestimate the abundances of cyanopolyynes longer than HC$_5$N, by up to two orders of magnitude. Current models do not support the hypothesis that elevated cosmic-ray fluxes or strong UV irradiation enhance cyanopolyyne production. This discrepancy suggests that the dominant neutral–neutral formation routes currently included in the network are incomplete. We propose that additional ion–molecule reactions are crucial for the formation of these species. Developing a more comprehensive chemical network for long carbon chains is essential for accurately interpreting present and future observations.
| Topics | Cradle of Life & Our Galaxy |
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