SNAPSHOT: Connections between Internal and Surface Properties of Massive Stars

Abstract

We introduce, a technique to systematically compute stellar structure models in hydrostatic and thermal equilibrium based on 3 structural properties -core mass M core , envelope mass M env and core composition. This approach allows us to connect these properties of stellar interiors to the luminosity and effective temperature T eff in a more systematic way than with stellar evolution models. We compute core-H burning models with total masses of M total = 8 to 60M and central H mass fractions from 0.70 to 0.05. Using these, we derive an analytical relationship between M core , M total and central H abundance that can be readily used in rapid stellar evolution algorithms. In contrast, core-He burning stars can have a wide range of combinations of M core , M env and core compositions. We compute core-He burning models with M core = 2 − 9M , M env = 0 − 50M and central He mass fractions of 0.50 and 0.01. Models with M core /M total from 0.2 to 0.8 have convective envelopes, low T eff and will appear as red supergiants. For a given M core , they exhibit a small variation in luminosity (0.02 dex) and T eff (∼ 400 K) over a wide range of M env (∼ 2 − 20 M ). This means that it is not possible to derive red supergiant masses from luminosities and T eff alone. We derive the following relationship between M core and the total luminosity of a red supergiant during core He burning: log M core 0.44 log L/L − 1.38. At M core /M total ≈ 0.2, our models exhibit a bi-stability and jump from a RSG to a BSG structure. Our models with M core /M total > 0.8, which correspond to stripped stars produced by mass loss or binary interaction, show that T eff has a strong dependence on M env , M core and the core composition. We constrain the mass of one of these stripped stars in a binary system, HD 45166, and find it to be less than its estimated dynamical mass. When a large observational sample of stripped stars becomes available, our results can be used to constrain their M core , M env , mass-loss rates and the physics of binary interaction.

Grids of stellar models with rotation: V. Models from 1.7 to 120 Msun at zero metallicity

“…Since we only have convection where ∇ rad > ∇ ad , the convective region reduces in size until the H shell becomes radiative. Models from Farrell et al (2020a) support this conclusion in showing that for higher core mass ratios, the value of ∇ rad is lower which tends to disfavour convection. Similarly to the 12 M model, the now radiative H shell moves further towards the stellar surface driving expansion and ends up in a redder part of the HR diagram (Figure 1) than its non-rotating counterpart.…”