Infrared radiation excess (in comparison with normal stars) due tocircumstellar dust (in order to distinguish from classicalBe stars, which have infrared excess due to free-free emission).
Sometimes Herbig Ae/Be stars show significant brightness variability. They are believed to be due to clumps (protoplanets andplanetesimals) in the circumstellar disk. In the lowest brightness stage the radiation from the star becomes bluer andlinearly polarized (when the clump obscures direct star light, scattered from disk light relatively increases – it is the same effect as the blue color of our sky).
Analogs of Herbig Ae/Be stars in the smaller mass range (<2M☉) – F, G, K, Mspectral typepre-main-sequence stars – are calledT Tauri stars. More massive (>8M☉)stars in pre-main-sequence stage are not observed, because they evolve very quickly: when they become visible (i.e. disperses surrounding circumstellar gas and dust cloud), the hydrogen in the center is already burning and they aremain-sequence objects.
^V. Mannings & A. Sargent (2000) High-resolution studies of gas and dust around young intermediate-mass stars: II. observations of an additional sample of Herbig Ae/Be systems. Astrophysical Journal, vol. 529, p. 391
![IRAS 12196-6300 is located just under 2300 light-years from Earth.[2]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aA_stellar_fingerprint.jpg)
