Herbig Ae/Be star
Pre-main-sequence stars of spectral types A or B, still embedded in gas and dust.
A Herbig Ae/Be star (HAeBe) is a pre-main-sequence star – a young star of spectral types A or B. These stars are still embedded in gas-dust envelopes and are sometimes accompanied by circumstellar disks. Hydrogen and calcium emission lines are observed in their spectra. They are 2–8 Solar mass objects, still existing in the star formation (gravitational contraction) stage and approaching the main sequence (i.e. they are not burning hydrogen in their center).
- type
- Pre-main-sequence star
- spectral_types
- A or B
- mass_range
- 2–8 solar masses
- age
- <10 million years
- named_after
- George Herbig
- first_distinguished
- 1960
- location_in_HR_diagram
- Right of the main sequence
Lore & Background
In the Hertzsprung–Russell diagram, Herbig Ae/Be stars are located to the right of the main sequence. They are named after the American astronomer George Herbig, who first distinguished them from other stars in 1960. The original Herbig criteria were: spectral type earlier than F0, Balmer emission lines in the stellar spectrum, projected location within the boundaries of a dark interstellar cloud, and illumination of a nearby bright reflection nebula. There are now several known isolated Herbig Ae/Be stars (i.e. not connected with dark clouds or nebulae). Thus the most reliable criteria now can be: spectral type earlier than F0, Balmer emission lines in the stellar spectrum, and infrared radiation excess due to circumstellar dust.
Reader's Guide
Sometimes Herbig Ae/Be stars show significant brightness variability. They are believed to be due to clumps (protoplanets and planetesimals) in the circumstellar disk. In the lowest brightness stage the radiation from the star becomes bluer and linearly 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 (less than 2 Solar masses) in pre-main-sequence stage are not observed, because they evolve very quickly: when they become visible, the hydrogen in the center is already burning and they are main-sequence objects.
Did You Know?
- Planets around Herbig Ae/Be stars include HD 95086 b around an A-type star, HD 100546 b around a B-type star, and AB Aurigae b around an A-type star.
- Herbig Ae/Be stars are 2–8 Solar mass objects still in the gravitational contraction stage.
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