The Helium and heavy elements enrichment of the Galactic Disk

Abstract

We present chemical evolution models for the Galactic disk. We also present a new determination of X, Y , and Z for M17 a Galactic metal-rich H II region. We compare our models for the Galactic disk with the Galactic H II regions  abundances.
The ΔY/ΔO ratio predicted from the Galactic chemical evolution model is in very good agreement with the ΔY/ΔO value derived from M17 and the primordial helium abundance, Yp, taking into account the presence of temperature variations in this H II region. From the M17 observations we obtain that ΔY/ΔZ = 1.97±0.41, in excellent agreement with two ΔY/ΔZ determinations derived from K dwarf stars of the solar vicinity that amount to 2.1 ± 0.4 and 2.1 ± 0.9 respectively. We also compare our models with the solar abundances. The solar and Orion nebula O/H values are in good agreement with our chemical evolution model.