SIMBAD references

We introduce SNAPSHOT, a technique to systematically compute stellar structure models in hydrostatic and thermal equilibrium based on three 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 = 8-60 M_☉ 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 = 2-9 M_☉, M_env = 0-50 M_☉, 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 (RSGs). 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 RSG masses from luminosities and T_eff alone. We derive the following relationship between M_core and the total luminosity of an RSG during core He burning: log M_core ≃ 0.44log L/L_☉ - 1.38. At M_core/M_total ≃ 0.2, our models exhibit a bistability and jump from an 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.