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From the Grammy Nominated album The Truth About Love available now - http://smarturl.it/tal Music video by P!nk featuring Nate Ruess performing Just Give Me ...
Watch judges' comments at http://itv.com/XFactor (UK ONLY) Watch James Arthur sing Impossible by Shontelle Sweeeeet! As potential Winner's Singles go, this o...
WATCH BLOOPERS & MORE: http://bit.ly/ZELDAxtras DOWNLOAD THE SONG: http://smo.sh/13NrBp8 DOWNLOAD UNCENSORED SONG: http://smo.sh/WMYpsf GET LEGEND OF SMOSH T...
From the album Nothing But The Beat Ultimate - Download on iTunes here: http://smarturl.it/NBTBiTunes?IQid=vevo Featuring Sia, Ne-Yo, Akon, Nicki Minaj, Flo ...
Thrift Shop on iTunes: http://itunes.apple.com/us/album/thrift-shop-feat.-wanz-single/id556955707 The Heist physical deluxe edition: http://www.macklemoremer...
Music video by Rihanna performing Rehab. YouTube view counts pre-VEVO: 19591123. (C) 2007 The Island Def Jam Music Group.
http://manofsteel.com http://www.facebook.com/manofsteel In theaters June 14th. From Warner Bros. and Legendary Pictures comes "Man of Steel", starring Henry...
BLOOPERS: http://bit.ly/FiretruckBloopers GET THE SONG: http://smo.sh/WMZv7l MILKSHAKE MUSIC VIDEO: http://bit.ly/MilkyMilkshake CHECK OUT THIS FIRETRUCK TEE...
The adorable 4-year-old crooner was back to put the moves on our host, and to make everybody in the audience melt. This kid is too adorable!
Download on iTunes: http://goo.gl/gcVR7 THREE T-Shirt designs!: http://goo.gl/jr4sY So many things to throw on the ground! Featuring Ryan Reynolds and Elijah...
Music video by P!nk performing Try (The Truth About Love - Live From Los Angeles). (C) 2012 RCA Records, a division of Sony Music Entertainment.
Download "Stay" from Unapologetic now: http://smarturl.it/UnapologeticDlx Music video by Rihanna performing Stay ft. Mikky Ekko. © 2013 The Island Def Jam Mu...
YOLO is available on iTunes now! http://smarturl.it/lonelyIslandYolo THE LONELY ISLAND - THE WACK ALBUM - JUNE 11th! Pre-order THE WACK ALBUM DIRECT: http://...
Macklemore & Ryan Lewis present the official music video for Can't Hold Us feat. Ray Dalton. Can't Hold Us on iTunes: https://itunes.apple.com/us/album/cant-...
Learn Magic at http://www.penguinmagic.com Instagram: http://instagram.com/themagicofrahat Twitter: http://twitter.com/magicofrahat Facebook Group: http://ww...
This video accidentally turned out kind of sad, ME SO SOWWY IT NOT POSED TO BE SAD WHO WANTS HUGS AND COOKIES? Also, FYI for anyone attempting this, it takes...
Pre-order new album Unapologetic, out worldwide Monday, November 19: http://smarturl.it/UnapologeticDlx Music video by Rihanna performing Diamonds. ©: The Is...
Music video by Rihanna performing Pon de Replay. YouTube view counts pre-VEVO: 4166822. (C) 2005 The Island Def Jam Music Group.
Please subscribe to my channel and my vlog channel! I make new videos here every Wednesday and make vlogs during my majestical daily life. JennaMarbles Jenna...
Ellen weighed in on the conversation surrounding the policies of Abercrombie & Fitch.
Young stellar object
T Tauri star
Herbig Ae/Be star
|Initial mass function
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.
- 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". http://www.mpia-hd.mpg.de. Retrieved 2008-10-16.