An Etymological Dictionary of Astronomy and Astrophysics
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Same as → double-lined binary.

→ double; → line; → spectroscopic; → binary.

Of or relating to → spectroscopy.

→ spectro-; → -scopy; → -ic.

A binary system that cannot be resolved by a telescope, but can be identified by means of the Doppler shift of the spectral lines. As stars revolve, they alternately approach and recede in the line of sight. This motion is shown up in their spectra as a periodic oscillation or doubling of spectral lines.

→ spectroscopic; → binary.

The situation in which spectroscopic features in a certain optical region are not sensitive enough to distinguish adjacent → luminosity classes, for instance → dwarf stars from → giant stars.

→ spectroscopic; → degeneracy.

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.

→ spectroscopic; → H-R diagram.

The stellar mass derived from → gravity (g) and radius (R), expressed by M = gR²/G, where G is the → gravitational constant. Spectroscopic mass conveys the actual mass of the star, in contrast with its → initial mass.

→ spectroscopic; → mass.

The measurement of a stellar distance by the absolute magnitude derived from the luminosity criteria of the spectrum and the apparent magnitude of the star.

→ spectroscopic; → parallax.

A → variable star that displays changes in its → spectrum. In such stars line intensities may vary and new lines may appear. Examples include → AG Carinae, HD 108, HD 191612, and HD 148937.

→ spectroscopic; → variable.