An Etymological Dictionary of Astronomy and Astrophysics

A spacial → Hertzsprung-Russell diagram (HRD) which is independent of distance and extinction measurements. The sHRD is derived from the classical HRD by replacing the luminosity (L) to the quantity ℒ = T ⁴_eff/g which is the inverse of the flux-weighted gravity introduced by Kudritzki et al. (2003). The value of ℒ can be calculated from stellar atmosphere analyses without prior knowledge of the distance or the extinction. In contrast to the classical T_eff-log g diagram (→ Kiel diagram), the sHRD sorts stars according to their proximity to the → Eddington limit, because ℒ is proportional to the Eddington factor Γ = L/L_Edd according to the relation

ℒ = (1/4πσG)(L/M) = (c/(σκ)Γ,

where σ is the → Stefan-Boltzmann constant, κ is the electron → scattering  → opacity in the stellar envelope, and the other symbols have their usual meanings

(Langer, N., Kudritzki, R. P., 2014, A&A 564, A52, arXive:1403.2212,

Castro et al., 2014, A&A 570, L13.

See also: → spectroscopic; → H-R diagram.