On the stability of nonisothermal Bonnor-Ebert spheres

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Aims. We investigate the stability of non-isothermal Bonnor-Ebert spheres with a model that includes a self-consistent calculation of the gas temperature. This way we can discard the assumption of equality between the dust and gas temperatures, and study the stability as the gas temperature changes with chemical evolution of the gas. Methods. We use a gas-grain chemical model including a time-dependent treatment of depletion onto grain surfaces, which strongly influences the gas temperature as the main coolant, CO, depletes from the gas. Dust and gas temperatures are solved with radiative transfer. For comparison with previous work, we assume that the cores are deeply embedded in a larger external structure, corresponding to visual extinction $A_{\rm V}^{\rm ext}=10$ mag. Results. We find that the critical non-dimensional radius $\xi_1$ derived here is similar to our previous work where we assumed $T_{\rm dust}=T_{\rm gas}$; the $\xi_1$ values lie below the isothermal critical value $\xi_0\sim6.45$, but the difference is less than 10%. Chemical evolution does not affect notably the stability condition of low-mass cores (<0.75 $M_\odot$). For higher masses the decrease of cooling owing to CO depletion causes substantial temporal changes in the temperature and density profiles of the cores. In the mass range 1-2 $M_\odot$ , $\xi_1$ decreases with chemical evolution, whereas above 3 $M_\odot$ , $\xi_1$ instead increases. We also find that decreasing $A_{\rm V}^{\rm ext}$ increases the gas temperature especially when the gas is chemically old, causing $\xi_1$ to increase with respect to models with higher $A_{\rm V}^{\rm ext}$. The derived $\xi_1$ values are close to $\xi_0$. The density contrast between the core center and edge varies between 8 to 16 depending on core mass and the chemical age of the gas, compared to the constant value $\sim$ 14.1 for the isothermal BES.