A Herbig Ae/Be star (HAeBe) 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 are sometimes accompanied by circumstellar disks.[1] Hydrogen and calcium emission lines are observed in their spectra. They are 2-8 Solar mass (M☉) 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).
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,
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 M☉) – F, G, K, M spectral type pre-main-sequence stars – are called T Tauri stars. More massive (>8 M☉) 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.
Planets
Planets around Herbig Ae/Be stars include:
HD 95086 b around an A-type star
Gallery
IRAS 12196-6300 is located just under 2300 light-years from Earth.[2]
Herbig Ae/Be Star V1025 Tauri from the Mount Lemmon SkyCenter
References
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
"A stellar fingerprint". Retrieved 29 February 2016.
Sources
Thé P.S., de Winter D., Pérez M.R. (1994) [1] 0
Pérez M.R., Grady C.A. (1997), Observational Overview of Young Intermediate-Mass Objects: Herbig Ae/Be Stars, Space Science Reviews, Vol 82, p. 407-450
Waters L. B. F. M., Waelkens, C. (1998), HERBIG Ae/Be STARS, Annual Review of Astronomy and Astrophysics, Vol. 36, p. 233-266
Herbig Ae/Be stars
"Molecular Hydrogen In The Circumstellar Environment Of Herbig Ae/Be Stars" (PDF). mpia-hd.mpg.de. Retrieved 2008-10-16.
vte
Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track
Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova
Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]
White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary
Burster
Hypothetical
Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar
Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova
Structure
Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism
Properties
Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram
Star systems
Binary
Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system
Earth-centric
observations
Sun
Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard
Lists
Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy
Related articles
Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event
vte
Variable stars
Pulsating
Cepheids and
cepheid-like
Type I (Classical cepheids, Delta Scuti) Type II (BL Herculis, W Virginis, RV Tauri) RR Lyrae Rapidly oscillating Ap SX Phoenicis
Blue-white with
early spectra
Alpha Cygni Beta Cephei Slowly pulsating B-type PV Telescopii Blue large-amplitude pulsator
Long-period
Mira Semiregular Slow irregular
Other
Gamma Doradus Solar-like oscillations White dwarf
Eruptive
Protostar and PMS
Herbig Ae/Be Orion
FU Orionis T Tauri
Giants and
supergiants
Luminous blue variable R Coronae Borealis (DY Persei) Yellow hypergiant
Eruptive binary
Double periodic FS Canis Majoris RS Canum Venaticorum
Other
Flare Gamma Cassiopeiae Lambda Eridani Wolf–Rayet
Cataclysmic
AM Canum Venaticorum Dwarf nova Luminous red nova Nova Polar Intermediate polar Supernova
Hypernova SW Sextantis Symbiotic
Symbiotic nova Z Andromedae
Rotating
Non-spherical
Rotating ellipsoidal
Stellar spots
BY Draconis FK Comae Berenices
Magnetic fields
Alpha² Canum Venaticorum Pulsar SX Arietis
Eclipsing
Algol Beta Lyrae Planetary transit W Ursae Majoris
He1523a.jpg Star portal * List
vte
Star formation
Object classes
Interstellar medium Molecular cloud Bok globule Dark nebula Young stellar object Protostar T Tauri star Pre-main-sequence star Herbig Ae/Be star Herbig–Haro object
Theoretical concepts
Initial mass function Jeans instability Kelvin–Helmholtz mechanism Nebular hypothesis Planetary migration
Hellenica World - Scientific Library
Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License
