The ADF and the t2 Formalism in H II Regions Based on the Upper Mass Limit of the IMF for the MW

Abstract

We study in depth the abundance discrepancy problem in H II regions, this time from a different perspective than the usual one: by studying the effect of the upper mass limit (M_up) of the initial mass function (IMF) on the O, C, and He predicted by chemical evolution models for the Milky Way. We use abundances determined with the direct method (DM) and with the temperature independent method (TIM). We compare the predicted abundances at the present time with observations of Orion, M17, and M8 to determine the M_up value of the galactic IMF. From the DM abundances, the models predict an M_up = 25 - 45 M_⊙, while from the TIM, CEMs derive an M_up = 70 - 110 M_⊙. Spiral galaxies with the stellar mass and star formation rate of the MW are predicted to have an M_up ≈ 100 M_⊙. These results support that abundances derived from the TIM are better than those derived from the DM.