A B[e] star, frequently called a B[e]-type star, is a B-type star with distinctive forbidden neutral or low ionisation emission lines in its spectrum. The designation results from combining the spectral class B, the lowercase e denoting emission in the spectral classification system, and the surrounding square brackets signifying forbidden lines. These stars frequently also show strong hydrogen emission lines, but this feature is present in a variety of other stars and is not sufficient to classify a B[e] object. Other observational characteristics include optical linear polarization and often infrared radiation that is much stronger than in ordinary B-class stars, called infrared excess. As the B[e] nature is transient, B[e]-type stars might exhibit a normal B-type spectrum at times, and hitherto normal B-type stars may become B[e]-type stars.
Many Be stars were discovered to have spectral peculiarities. One of these peculiarities was the presence of forbidden spectral lines of ionised iron and occasionally other elements.[1]
In 1973 a study of one of these stars, HD 45677 or FS CMa, showed an infrared excess as well as forbidden lines of [OI], [SII], [FeII], [NiII], and many more.[2]
In 1976 a study of Be stars with infrared excesses identified a subset of stars which showed forbidden emission lines from ionised iron and some other elements. These stars were all considered to be distinct from the classical main sequence Be stars, although they appeared to consist of a wide range of different types of star. The term B[e] star was coined to group these stars.[3]
One type of B[e] star was readily identified as being highly luminous supergiants. By 1985, eight dust-shrouded B[e] supergiants were known in the Magellanic Clouds.[4] Others were found to be definitely not supergiants. Some were binaries, others proto-planetary nebulae, and the term "B[e] phenomenon" was used to make it clear that different types of star could produce the same type of spectrum.[5]
Classificationedit
Following the recognition that the B[e] phenomenon could occur in several distinct types of star, four sub-types were named:[6]
Around half of the known B[e] stars could not be placed in any of these groups and were called unclassified B[e] stars (unclB[e]). The unclB[e] stars have since been re-classified as FS CMa stars, a type of variable named for one of the earliest known B[e] stars.[7]
Natureedit
The forbidden emission, infrared excess, and other features indicative of the B[e] phenomenon, themselves provide strong hints at the nature of the stars. The stars are surrounded by ionised gas which produces intense emission lines in the same way as Be stars. The gas must be sufficiently extended to allow the formation of forbidden lines in the outer low density region, and also for dust to form which produces the infrared excess. These features are common to all the types of B[e] star.[8]
The sgB[e] stars have hot fast winds which produce extended circumstellar material, plus a denser equatorial disc. HAeB[e] are surrounded by the remains of the molecular clouds which are forming the stars. Binary B[e] stars can produce discs of material as it is transferred from one star to another through roche lobe overflow. cPNB[e] are post-AGB stars that have shed their entire atmospheres after reaching the end of their lives as actively fusing stars. The FS CMa stars appear to be binaries with a rapidly rotating mass-losing component.[8]
^Burbidge, E. Margaret; Burbidge, G. R. (1954). "A Group of Peculiar Shell Stars". Astrophysical Journal. 119: 501. Bibcode:1954ApJ...119..501B. doi:10.1086/145856.
^Swings, J. P. (1973). "Spectrographic observations of the peculiar Be star with infrared excess HD 45677". Astronomy and Astrophysics. 26: 443. Bibcode:1973A&A....26..443S.
^Allen, D. A.; Swings, J. P. (1976). "The spectra of peculiar Be stars with infrared excesses". Astronomy and Astrophysics. 47: 293. Bibcode:1976A&A....47..293A.
^Zickgraf, F.-J.; Wolf, B.; Leitherer, C.; Appenzeller, I.; Stahl, O. (1986). "B(e)-supergiants of the Magellanic Clouds". Astronomy and Astrophysics. 163: 119. Bibcode:1986A&A...163..119Z.
^Cidale, L.; Zorec, J.; Tringaniello, L. (2001). "BCD spectrophotometry of stars with the B[e] phenomenon". Astronomy and Astrophysics. 368: 160–174. Bibcode:2001A&A...368..160C. doi:10.1051/0004-6361:20000409.
^Lamers, Henny J. G. L. M.; Zickgraf, Franz-Josef; de Winter, Dolf; Houziaux, Leo; Zorec, Janez (1998). "An improved classification of B[e]-type stars". Astronomy and Astrophysics. 340: 117. Bibcode:1998A&A...340..117L.
^Miroshnichenko, A.S.; Zharikov, S.V.; Danford, S.; Manset, N.; Korčáková, D.; KřÍček, R.; Šlechta, M.; Omarov, Ch.T.; Kusakin, A.V.; Kuratov, K.S.; Grankin, K.N. (2015). "Toward understanding the B[e] phenomenon. V. Nature and spectral variations of the MWC 728 binary system". The Astrophysical Journal. 809 (2): 129. arXiv:1508.00950. Bibcode:2015ApJ...809..129M. doi:10.1088/0004-637X/809/2/129. S2CID 27971806.
^ abMiroshnichenko, A.S. (2007). "Toward Understanding the B[e] Phenomenon. I. Definition of the Galactic FS CMa Stars". The Astrophysical Journal. 667 (1): 497–504. Bibcode:2007ApJ...667..497M. CiteSeerX10.1.1.548.81. doi:10.1086/520798. S2CID 40320323.
^"The Wings of the Seagull Nebula" (Press release). ESO. 6 February 2013. press release for Seagull Nebula image
External linksedit
"Hot and Active Stars Research". Philippe Stee's homepage.
Thizy, Olivier. . Archived from the original on 2012-07-24.
January 01, 1970
star, confused, with, star, correct, title, this, article, star, substitution, brackets, technical, restrictions, star, frequently, called, type, star, type, star, with, distinctive, forbidden, neutral, ionisation, emission, lines, spectrum, designation, resul. Not to be confused with Be star The correct title of this article is B e star The substitution of any brackets is due to technical restrictions A B e star frequently called a B e type star is a B type star with distinctive forbidden neutral or low ionisation emission lines in its spectrum The designation results from combining the spectral class B the lowercase e denoting emission in the spectral classification system and the surrounding square brackets signifying forbidden lines These stars frequently also show strong hydrogen emission lines but this feature is present in a variety of other stars and is not sufficient to classify a B e object Other observational characteristics include optical linear polarization and often infrared radiation that is much stronger than in ordinary B class stars called infrared excess As the B e nature is transient B e type stars might exhibit a normal B type spectrum at times and hitherto normal B type stars may become B e type stars Nebulosity around the B e star HD 87643 Contents 1 Discovery 2 Classification 3 Nature 4 See also 5 References 6 External linksDiscovery editMany Be stars were discovered to have spectral peculiarities One of these peculiarities was the presence of forbidden spectral lines of ionised iron and occasionally other elements 1 In 1973 a study of one of these stars HD 45677 or FS CMa showed an infrared excess as well as forbidden lines of OI SII FeII NiII and many more 2 In 1976 a study of Be stars with infrared excesses identified a subset of stars which showed forbidden emission lines from ionised iron and some other elements These stars were all considered to be distinct from the classical main sequence Be stars although they appeared to consist of a wide range of different types of star The term B e star was coined to group these stars 3 One type of B e star was readily identified as being highly luminous supergiants By 1985 eight dust shrouded B e supergiants were known in the Magellanic Clouds 4 Others were found to be definitely not supergiants Some were binaries others proto planetary nebulae and the term B e phenomenon was used to make it clear that different types of star could produce the same type of spectrum 5 Classification editFollowing the recognition that the B e phenomenon could occur in several distinct types of star four sub types were named 6 B e supergiants sgB e pre main sequence B e stars HAeB e a subset of the Herbig Ae Be star stars compact planetary nebulae B e stars cPNB e symbiotic B e stars SymB e Around half of the known B e stars could not be placed in any of these groups and were called unclassified B e stars unclB e The unclB e stars have since been re classified as FS CMa stars a type of variable named for one of the earliest known B e stars 7 Nature editThe forbidden emission infrared excess and other features indicative of the B e phenomenon themselves provide strong hints at the nature of the stars The stars are surrounded by ionised gas which produces intense emission lines in the same way as Be stars The gas must be sufficiently extended to allow the formation of forbidden lines in the outer low density region and also for dust to form which produces the infrared excess These features are common to all the types of B e star 8 nbsp The Seagull Nebula is a roughly circular HII region centred on the Herbig Ae Be star HD 53367 9 The sgB e stars have hot fast winds which produce extended circumstellar material plus a denser equatorial disc HAeB e are surrounded by the remains of the molecular clouds which are forming the stars Binary B e stars can produce discs of material as it is transferred from one star to another through roche lobe overflow cPNB e are post AGB stars that have shed their entire atmospheres after reaching the end of their lives as actively fusing stars The FS CMa stars appear to be binaries with a rapidly rotating mass losing component 8 See also editShell starReferences edit Burbidge E Margaret Burbidge G R 1954 A Group of Peculiar Shell Stars Astrophysical Journal 119 501 Bibcode 1954ApJ 119 501B doi 10 1086 145856 Swings J P 1973 Spectrographic observations of the peculiar Be star with infrared excess HD 45677 Astronomy and Astrophysics 26 443 Bibcode 1973A amp A 26 443S Allen D A Swings J P 1976 The spectra of peculiar Be stars with infrared excesses Astronomy and Astrophysics 47 293 Bibcode 1976A amp A 47 293A Zickgraf F J Wolf B Leitherer C Appenzeller I Stahl O 1986 B e supergiants of the Magellanic Clouds Astronomy and Astrophysics 163 119 Bibcode 1986A amp A 163 119Z Cidale L Zorec J Tringaniello L 2001 BCD spectrophotometry of stars with the B e phenomenon Astronomy and Astrophysics 368 160 174 Bibcode 2001A amp A 368 160C doi 10 1051 0004 6361 20000409 Lamers Henny J G L M Zickgraf Franz Josef de Winter Dolf Houziaux Leo Zorec Janez 1998 An improved classification of B e type stars Astronomy and Astrophysics 340 117 Bibcode 1998A amp A 340 117L Miroshnichenko A S Zharikov S V Danford S Manset N Korcakova D KrIcek R Slechta M Omarov Ch T Kusakin A V Kuratov K S Grankin K N 2015 Toward understanding the B e phenomenon V Nature and spectral variations of the MWC 728 binary system The Astrophysical Journal 809 2 129 arXiv 1508 00950 Bibcode 2015ApJ 809 129M doi 10 1088 0004 637X 809 2 129 S2CID 27971806 a b Miroshnichenko A S 2007 Toward Understanding the B e Phenomenon I Definition of the Galactic FS CMa Stars The Astrophysical Journal 667 1 497 504 Bibcode 2007ApJ 667 497M CiteSeerX 10 1 1 548 81 doi 10 1086 520798 S2CID 40320323 The Wings of the Seagull Nebula Press release ESO 6 February 2013 press release for Seagull Nebula imageExternal links edit Hot and Active Stars Research Philippe Stee s homepage Thizy Olivier Be stars Archived from the original on 2012 07 24 Retrieved from https en wikipedia org w index php title B e star amp oldid 1159429676, wikipedia, wiki, book, books, library,
