About

Several ideas proposed in literature suggest that homogeneous evolution or quasi-homogeneous evolution can be applicable to some evolutionary phases of stars (Beech and Mitalas (1939) and Maeder (1980). Besides, massive stars have a radiation pressure dominance that allows an inspection into their closeness to homogeneity, and therefore polytropic approximations. To afford the same, mixing must occur inside the star such that the core and envelope compositions do not differ largely. This study explored homogeneous evolution, illustrated the stated relevance of homogeneity to massive stars and briefly skimmed through literature that explores the sources of such mixing. The development of a model that maps the evolution of completely homogeneous stars is done for masses of 30, 60 and 120M ☉ . This model is built on the lines of Beech and Mitalas (1989), incorporated with few modifications and interpretations. The main differences lie in the computation of luminosity with mass loss rates and possibly the route of estimation followed for obtaining a constant term in the L-Tc relation. An attempt is made to simplify the computation, with the aid of literature in Chandrasekhar (1939), Prialnik (2009) and Pols (2011). An excellent agreement is found with the results of Beech and Mitalas (1989), a study that has further explored the correlation of its results with Klapp (1982) and El Eid et al. (1983).

Results

The model is computationally swift and traces the evolution of homogeneously evolving stars with and without mass loss rates by varying the hydrogen mass fraction (X). For all mass loss rates and all values of initial masses, homogeneous evolution uniformly proceeds to the blue. This attraction to higher effective temperatures is fueled by mixing and is independent of the mass loss rate until extreme values are input. Luminosity, on the other hand, is a sensitive function of the mass loss rate and decreases with increasing mass loss. Aligning with expectations, models concerning more massive stars lose a greater amount of mass to stellar winds than their less massive counterparts. Additionally, nucleosynthesis from homogeneously evolving stars is explored by making estimates of the mass of helium ejected by the star throughout the course of its evolution. More helium is lost by stars with greater initial masses and greater mass loss rates. This helium ejection from nucleosynthesis impacts the enrichment of the surrounding medium (Woody and Richads, 1979) and reveals inner layers in cases of quasi-homogeneous evolution. Such quasi-homogeneous evolution holds the scope to explain observations of select OBN blue stragglers and Wolf-Rayet stars (Mathys (1987) and Maeder (1987)). Although, it is quite debatable whether mass loss can be the only mechanism in massive stars that leads to such evolution (Maeder, 1987). A clear mathematical description of the mixing mechanisms along with their range of applicability might be a fruitful direction to take up in further studies. At the present, I conclude with a decent model for mapping the homogeneous evolution of stars and its possible consequence(s) for nucleosynthesis from homogeneously evolving stars.