2175 A bump
quz-e 2175 Å
Fr.: bosse à 2175 Å
The strongest spectral feature in the interstellar → extinction curve occurring in the → ultraviolet and centered at about 2175 Å. The feature is a strong function of the → metallicity of the gas. It appears slightly weaker in the → LMC extinction curve (metallicity about 50% solar), but essentially absent in the → SMC extinction curve (metallicity about 10% solar). Small → interstellar → graphite → dust grains or a mixture of graphite and → polycyclic aromatic hydrocarbons (PAHs) grains have been proposed in → dust models to explain the bump. However, at present the → carrier of the 2175 Å feature is basically unidentified.
big blue bump
quz-e âbi-ye bozorg
Fr.: grande bosse bleue
The broad continuum feature dominating the optical-ultraviolet spectra of AGNs. Most current models attribute the big blue bump to thermal emission from an optically thick accretion disk.
Kefeusi-ye quzâr, ~ zokdâr
Fr.: céphéide à bosse
Bump "a relatively abrupt convexity or bulge on a surface," probably imitative of the sound of a blow; → Cepheid.
Quzdâr, from quz "hump," variant of kuž, → convex, + -dâr "possessing," from dâštan "to have, possess." Zokdâr, from Lori zok "a raised spot, a bulge," cf. Northern Fârs Âbâdé dialect lok " swellimg, knob;" Kefeusi, → Cepheid.