Prestellar core's chemistry: Modelling of the methanol emission in the prestelar core L1689B
IPAG, Grenoble, FR
The recent detections in prestellar cores of carbon chain molecules with six or more atoms, more commonly known as complex organic molecules (COMs), has provided a big challenge for the astrochemical community in the recent years. COMs are believed to be synthesised in the very first phases of star formation on the surface of dust grains. Simple molecules are hydrogenated and COMs form with the aid of mobile radicals (e.g. HCO) in the warm up phase at temperatures of 30-40 K. In the following stages and with the increase of the temperature (around 100 K), the content of the iced mantles is released to the gas phase. However, the low temperatures found in prestellar cores (close to 10 K) have cast doubts on this scenario; the mobility of radicals under this temperatures should be almost negligible. Recently, new astrochemical models have appeared. Non-thermal desorption processes like secondary UV photons, cosmic rays and chemical desorption reactions among others can provide radicals with enough mobility.
Beside the formation routes, there are still lot of open questions about the COMs formation in prestellar cores. In this contribution, we present the detailed modelling of the methanol (CH3OH) emission (one of the most simple COMs) in the prestellar core L1689B. The emission is study using RATRAN, a 1-D non-LTE open code that calculates both the radiative transfer and the excitation of molecular lines based on the Monte Carlo method. We find that the methanol emission is better reproduced with profiles that present a higher density (> 106 cm-3) and a lower temperature (< 7 K) in the central position of the cores. However, we discuss the effect of different source models and how the variation of this two parameters affects the modelling.
A. Bacmann, IPAG, FR
A. Faure, IPAG, FR