A B [e] star is a star of spectral class B, in the spectrum of which there are forbidden emission lines . The designation is a combination of the name of the spectral class B , the letter e means radiation ( English emission ), square brackets indicate forbidden lines. Such stars often also have strong hydrogen emission lines, but this feature is also found in other types of stars. Other observational manifestations of B [e] stars are optical linear polarization and, often, infrared radiation is stronger than that of ordinary B stars. Since B [e] stars have a transitional nature, in some periods they may possess the spectrum of an ordinary B star; in turn, ordinary B stars can become B [e] stars.
Opening
Many Be stars have specific spectral features. One of these features was the presence of forbidden lines of ionized iron and, sometimes, other elements [1] . In the study in 1973 of one of such stars, HD 45677 or FS CMa, an infrared excess of radiation and the presence of forbidden lines [O I ], [S II ], [Fe II ], [Ni II ] [2] were revealed.
A study of Be stars with an infrared excess carried out in 1976 revealed the presence of a group of stars in the spectrum of which there were forbidden emission lines of ionized iron and some other elements. These stars were considered different from ordinary main sequence Be-stars, and could belong to different types of stars. This group of stars was given the name B [e] stars [3] .
One of the varieties of B [e] stars is supergiants of high luminosity. By 1985, 8 B [e] supergiants surrounded by a dust envelope in the Magellanic Clouds were known [4] . Other B [e] stars are definitely not supergiants. Some are binary stars , protoplanetary nebulae ; the concept of a B [e] -phenomenon means that different types of stars can have the spectrum of the same type [5] .
Classification
Since it was revealed that the spectrum of type B [e] can belong to different types of stars, four subtypes of objects were identified [6] :
- B [e] supergiants (sgB [e]),
- B [e] stars to the main sequence (HAeB [e]), a subset of Herbig’s Ae / Be stars ,
- compact planetary nebulae of B [e] stars (cPNB [e]),
- symbiotic B [e] stars (SymB [e]).
About half of the known B [e] stars cannot be attributed to any of the above subtypes; such objects are classified as unclassified B [e] stars (unclB [e]). unclB [e] stars have recently been classified as FS CMa stars by the name of one of the first known B [e] stars [7] .
The nature of B [e] stars
Radiation in forbidden lines, infrared excess, and other features of the radiation of such objects help to reveal the nature of objects. B [e] stars are surrounded by ionized gas, creating intense emission lines in the same way as Be stars. The gaseous medium must be sufficiently long for the appearance of forbidden lines in the external low-density region, as well as for the existence of dust, which creates an excess of infrared radiation. These features are inherent in all types of B [e] stars [8] .
The sgB [e] subtype stars have a hot fast stellar wind creating an extended region of circumstellar matter and a dense equatorial disk. HAeB [e] subtype stars are surrounded by remnants of molecular clouds forming stars. Double B [e] stars can create disks from a substance flowing from one binary component to another after filling the Roche lobe . The cPNB [e] subtype stars are stars after the asymptotic branch of giants , which have lost the atmosphere after the completion of their existence in the form of stars with intensely occurring nuclear reactions. Stars like FS CMa are considered binary with a rapidly rotating and mass-losing component [8] .
See also
- Shell star
Notes
- ↑ E. Margaret; Burbidge, GR A Group of Peculiar Shell Stars (Eng.) // The Astrophysical Journal : journal. - IOP Publishing 1954. - Vol. 119 . - P. 501 . - DOI : 10.1086 / 145856 . - .
- ↑ Swings, JP Spectrographic observations of the peculiar Be star with infrared excess HD 45677 (Eng.) // Astronomy and Astrophysics : journal. - 1973. - Vol. 26 . - P. 443 . - .
- ↑ Allen, DA; Swings, JP The spectra of peculiar Be stars with infrared excesses ( Astronomy and Astrophysics : journal. - 1976. - Vol. 47 . - P. 293 . - .
- ↑ Zickgraf, F.-J .; Wolf, B .; Leitherer, C .; Appenzeller, I .; Stahl, O. B (e) -supergiants of the Magellanic Clouds (Eng.) // Astronomy and Astrophysics : journal. - 1986. - Vol. 163 . - P. 119 . - .
- ↑ Cidale, L .; Zorec, J .; Tringaniello, L. BCD spectrophotometry of stars with the B [e] phenomenon (Eng.) // Astronomy and Astrophysics : journal. - 2001. - Vol. 368 . - P. 160 . - DOI : 10.1051 / 0004-6361: 20000409 . - .
- ↑ Henny JGLM; Lamers; Zickgraf, Franz-Josef; De Winter, Dolf; Houziaux, Leo; Zorec, Janez. An improved classification of B [e] -type stars (Eng.) // Astronomy and Astrophysics : journal. - 1998. - Vol. 340 . - P. 117 . - .
- ↑ Miroshnichenko, AS; Zharikov, SV; Danford, S .; Manset, N .; KorčÁková, D .; KřÍčEk, R .; Šlechta, M .; Omarov, Ch. T .; Kusakin, AV; Kuratov, KS; Grankin, KN TOWARD UNDERSTANDING THE B [e] PHENOMENON. V. NATURE AND SPECTRAL VARIATIONS OF THE MWC 728 BINARY SYSTEM (German) // The Astrophysical Journal : magazin. - IOP Publishing 2015. - Bd. 809 , Nr. 2 . - S. 129 . - DOI : 10.1088 / 0004-637X / 809/2/129 . - . - arXiv : 1508.00950 .
- ↑ 1 2 Miroshnichenko, AS Toward Understanding the B [e] Phenomenon. I. Definition of the Galactic FS CMa Stars (Eng.) // The Astrophysical Journal : journal. - IOP Publishing 2007. - Vol. 667 . - P. 497 . - DOI : 10.1086 / 520798 . - .
Links
- Philippe Stee's homepage: Hot and Active Stars Research
- Article from Olivier Thizy: Be Stars
- ESO press release for Seagull Nebula image The Wings of the Seagull Nebula