Study of the chemo-dynamical coupling in the formation of solar-like stars

Abstract

Astrochemistry is the study of the chemical composition of interstellar objects and the chemical reactions occurring in space. How species interact have a great impact in the process ofstar formation. In fact, determining aspects for the dynamical behavior of interstellar matterare the gas cooling rate and the ionization degree, highly influenced by the gas chemistryand molecular abundances. Indeed, efficient gas cooling diminishes thermal supportagainst gravity, leading to fragmentation and collapse of molecular filaments into pre-stellarcores. Here, elemental depletions of Carbon (C) and Oxygen (O) are key to determine thecooling rate of the gas, as CO and CII are the main coolants in molecular clouds. The ionizationfraction of the gas is involved in gas dynamics as well, since it controls the couplingof the gas with the magnetic fields. Magnetic fields thus drive the dissipation of turbulenceand angular momentum transfer in the cloud collapse and the dynamics of accretion disks.The ionization fraction of the gas is, in absence of other ionization agents like X-rays, UVphotons, and shocks, proportional to ³H2 , the cosmic-ray ionization rate for H2 molecules.Other factors that affect the ionization degree of the gas are the molecular abundances andelemental depletion factors. Towards the surface of a cloud (Av Ç 4 mag), Carbon is the maindonor of electrons. Deeper into the cloud however, in the range Av » 4¡7 mag, Sulphur (S)becomes the main donor of electrons. This range of extinctions encompasses a large fractionof the molecular cloud’s mass...