Star formation
Object classes
Interstellar medium Molecular cloud Bok globule Dark nebula Young stellar object Protostar T Tauri star Herbig Ae/Be star Herbig–Haro object
Theoretical concepts
Initial mass function Jeans instability Kelvin–Helmholtz mechanism Nebular hypothesis
Star portal
v t e

A Herbig Ae/Be star (HABe) is a pre-main-sequence star – a young (<10Myr) star of spectral types A or B. These stars are still embedded in gas-dust envelopes and may be surrounded 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). In the Hertzsprung–Russell diagram these 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 (in order to exclude T Tauri stars),
• Balmer emission lines in the stellar spectrum (in order to be similar to T Tauri stars),
• Projected location within the boundaries of a dark interstellar cloud (in order to select really young stars near their birthplaces),
• Illumination of a nearby bright reflection nebula (in order to guarantee physical link with star formation region).

Nowadays there are known several 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,
• Infrared radiation excess (in comparison with normal stars) due to circumstellar dust (in order to distinguish from classical Be 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 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 (<2 Solar mass) - F, G, K, M spectral type pre-main-sequence stars, are called T Tauri stars. More massive (>8 Solar mass) 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 are main-sequence objects.

References [edit]

• "Molecular Hydrogen In The Circumstellar Environment Of Herbig Ae/Be Stars". http://www.mpia-hd.mpg.de. Retrieved 2008-10-16. 

v t e Star Evolution Formation Pre-main-sequence star Main sequence Horizontal branch Asymptotic giant branch Dredge-up Instability strip Red clump PG1159 star Mira variable Planetary nebula Protoplanetary nebula Luminous red nova Luminous blue variable Wolf–Rayet star Supernova impostor Supernova Hypernova Hertzsprung–Russell diagram Color–color diagram Protostars Molecular cloud H II region Bok globule Young stellar object Herbig–Haro object Hayashi track Hayashi limit Henyey track Orion T Tauri FU Orionis Herbig Ae/Be Luminosity class Subdwarf Dwarf Blue Red White Black Brown Subgiant Giant Blue Red Bright giant Supergiant Blue Red Yellow Hypergiant Yellow Blue straggler Spectral classification O B A F G K M Be OB Subdwarf B Late-type Peculiar Am Ap/Bp Oscillating Barium Carbon CH Extreme helium Lambda Boötis Lead Mercury-manganese S Shell Technetium Remnants White dwarf Black dwarf Helium planet Neutron star Pulsar Magnetar Stellar black hole Compact star Quark Exotic Stellar core: EF Eridani B Theoretical stars Dark-matter star Quasi-star Thorne–Żytkow object Iron star Nucleosynthesis Alpha process Triple-alpha process Proton–proton chain Helium flash CNO cycle Lithium burning Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova Remnants Structure Core Convection zone Microturbulence Oscillations Radiation zone Atmosphere Photosphere Starspot Chromosphere Corona Stellar wind Bubble Asteroseismology Eddington luminosity Kelvin–Helmholtz mechanism Properties Designation Dynamics Effective temperature Kinematics Magnetic field Magnitude Absolute Mass Metallicity Rotation UBV color Variability Star systems Binary Contact Common envelope Multiple Accretion disc Planetary system Earth's Solar System Earth-centric observation of Pole star Circumpolar star Magnitude Apparent Extinction Photographic Color Radial velocity Proper motion Parallax Photometric-standard star Lists Star names Arabic Chinese Most massive Least massive Largest Brightest Historical Most luminous Nearest Nearest bright Stars with exoplanets Brown dwarfs Collapsars Planetary nebulae Novae Notable supernovae Supernova remnants Supernova candidates Timeline of stellar astronomy Related articles Substellar object Brown dwarf Sub-brown dwarf Planet Star cluster Association Open cluster Globular cluster Super star cluster Galaxy Supercluster Helioseismology Guest star Constellation Asterism Gravity Intergalactic star Infrared dark cloud Star portal

v t e Variable stars Pulsating Cepheids and cepheid-like Classic Cepheid Type II Cepheids RR Lyrae Delta Scuti SX Phoenicis Blue-white with earlyspectra Beta Cephei PV Telescopii Long Period and Semiregular Mira Semiregular Slow irregular Other RV Tauri Alpha Cygni Pulsating white dwarf Eruptive Protostar Herbig Ae/Be Orion FU Orionis Main Sequence Wolf–Rayet Flare Giants and supergiants Luminous blue Gamma Cassiopeiae R Coronae Borealis Betelgeuse Eruptive binary RS Canum Venaticorum Cataclysmic or explosive Cataclysmic variable star Dwarf nova Nova Supernova Z Andromedae Rotating Non-spherical Ellipsoidal Stellar spots FK Comae Berenices BY Draconis Magnetic fields Alpha-2 Canum Venaticorum SX Arietis Pulsar Eclipsing Algol Beta Lyrae W Ursae Majoris The Star Portal