Production of Helium by Stellar Evolution

Stellar Rotation in Young Clusters. Ii. Evolution of Stellar Rotation and Surface Helium Abundance

We derive the effective temperatures and gravities of 461 OB stars in 19 young clusters by fitting the H profile in their spectra. We use synthetic model profiles for rotating stars to develop a method to estimate the polar gravity for these stars, which we argue is a useful indicator of their evolutionary status. We combine these results with projected rotational velocity measurements obtained...

The Chemical Evolution of Helium

We report on measurements of the He abundance toward the outer Galaxy H II region S 206 with the NRAO Green Bank telescope. Observations of hydrogen and helium radio recombination lines between 8 − 10GHz were made toward the peak radio continuum position in S 206. We derive He/H = 0.08459 ± 0.00088 (random)± 0.0010 (known systematic), 20% lower than optical recombination line results. It is dif...

The cosmic production of helium.

We estimate the cosmic production rate of helium relative to metals (DeltaY/DeltaZ) using K dwarf stars in the Hipparcos catalog with accurate spectroscopic metallicities. The best fitting value is DeltaY/DeltaZ = 2.1 +/- 0.4 at the 68% confidence level. Our derived value agrees with determinations from H II regions and with theoretical predictions from stellar yields with standard assumptions ...

Stellar Structure and Evolution

Stellar Evolution Presenting

Stars “evolve” with time in a predicable manner. Our theory of stellar evolution is one of the foundations of astrophysics, is well tested and verified, and has enabled great advances in many fields of astrophysics. As such, stellar evolution is a cornerstone of any astronomy course, from the 100 level up through graduate levels. One of the leading software to model a star’s evolution in detail...