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B-type main-sequence star

January 10, 2023

A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K.[1] B-type stars are extremely luminous and blue. Their spectra have strong neutral helium absorption lines, which are most prominent at the B2 subclass, and moderately strong hydrogen lines. Examples include Regulus and Algol A.[2]

History

This class of stars was introduced with the Harvard sequence of stellar spectra and published in the Revised Harvard photometry catalogue. The definition of type B-type stars was the presence of non-ionized helium lines with the absence of singly ionized helium in the blue-violet portion of the spectrum. All of the spectral classes, including the B type, were subdivided with a numerical suffix that indicated the degree to which they approached the next classification. Thus B2 is 1/5 of the way from type B (or B0) to type A.[3][4]

Later, however, more refined spectra showed lines of ionized helium for stars of type B0. Likewise, A0 stars also show weak lines of non-ionized helium. Subsequent catalogues of stellar spectra classified the stars based on the strengths of absorption lines at specific frequencies, or by comparing the strengths of different lines. Thus, in the MK Classification system, the spectral class B0 has the line at wavelength 439 nm being stronger than the line at 420 nm.[5] The Balmer series of hydrogen lines grows stronger through the B class, then peak at type A2. The lines of ionized silicon are used to determine the sub-class of the B-type stars, while magnesium lines are used to distinguish between the temperature classes.[4]

Properties

Properties of typical B-type main-sequence stars[6][7]
Spectral
type 		Mass (M☉) Radius (R☉) Luminosity (L☉) Effective
temperature
(K) 		Color
index
(B − V)
B0V 17.70 7.16 44,668 31,400 -0.301
B1V 11.00 5.71 13,490 26,000 -0.278
B2V 7.30 4.06 2,692 20,600 -0.215
B3V 5.40 3.61 977 17,000 -0.178
B4V 5.10 3.46 776 16,400 -0.165
B5V 4.70 3.36 589 15,700 -0.156
B6V 4.30 3.27 372 14,500 -0.140
B7V 3.92 2.94 302 14,000 -0.128
B8V 3.38 2.86 155 12,300 -0.109
B9V 2.75 2.49 72 10,700 -0.070

Type-B stars don't have a corona and lack a convection zone in their outer atmosphere. They have a higher mass loss rate than smaller stars such as the Sun, and their stellar wind has velocities of about 3,000 km/s.[8] The energy generation in main-sequence B-type stars comes from the CNO cycle of thermonuclear fusion. Because the CNO cycle is very temperature sensitive, the energy generation is heavily concentrated at the center of the star, which results in a convection zone about the core. This results in a steady mixing of the hydrogen fuel with the helium byproduct of the nuclear fusion.[9] Many B-type stars have a rapid rate of rotation, with an equatorial rotation velocity of about 200 km/s.[10]

Be and B[e] stars

Main article: B[e] stars

Spectral objects known as "Be stars" are massive yet non-supergiant entities that notably have, or had at some time, 1 or more Balmer lines in emission, with the hydrogen-related electromagnetic radiation series projected out by the stars being of particular scientific interest. Be stars are generally thought to feature unusually strong stellar winds, high surface temperatures, and significant attrition of stellar mass as the objects rotate at a curiously rapid rate, all of this in contrast to many other main-sequence star types.[11]

Objects known as B[e] stars are distinct from Be stars in having unusual neutral or low ionization emission lines that are considered to have 'forbidden mechanisms', something denoted by the use of the square brackets. In other words, these particular stars' emissions appear to undergo processes not normally allowed under 1st-order perturbation theory in quantum mechanics. The definition of a B[e] star can include blue giants and blue supergiants.

Spectral standard stars

 
Part of the constellation of Carina, Epsilon Carinae is an example of a double star featuring a main-sequence B-type star. The primary is an evolved giant star with a stellar classification of K0 III, hence its yellowish color. The secondary is a typical core hydrogen-fusing B-type main sequence star of spectral class B2 Vp.

The revised Yerkes Atlas system (Johnson & Morgan 1953)[12] listed a dense grid of B-type dwarf spectral standard stars, however not all of these have survived to this day as standards. The "anchor points" of the MK spectral classification system among the B-type main-sequence dwarf stars, i.e. those standard stars that have remain unchanged since at least the 1940s, are upsilon Orionis (B0 V), eta Aurigae (B3 V), eta Ursae Majoris (B3 V).[13][14] Besides these anchor standards, the seminal review of MK classification by Morgan & Keenan (1973)[14] listed "dagger standards" of Tau Scorpii (B0 V), Omega Scorpii (B1 V), 42 Orionis (B1 V), 22 Scorpii (B2 V), Rho Aurigae (B5 V), and 18 Tauri (B8 V). The Revised MK Spectra Atlas of Morgan, Abt, & Tapscott (1978)[15] further contributed the standards Beta2 Scorpii (B2 V), 29 Persei (B3 V), HD 36936 (B5 V), and HD 21071 (B7 V). Gray & Garrison (1994)[16] contributed two B9 V standards: Omega Fornacis and HR 2328. The only published B4 V standard is 90 Leonis, from Lesh (1968).[17] There has been little agreement in the literature on choice of B6 V standard.

Chemical peculiarities

Some of the B-type stars of stellar class B0–B3 exhibit unusually strong lines of non-ionized helium. These chemically peculiar stars are termed helium-strong stars. These often have strong magnetic fields in their photosphere. In contrast, there are also helium-weak B-type stars with understrength helium lines and strong hydrogen spectra. Other chemically peculiar B-types stars are the mercury-manganese stars with spectral types B7-B9. Finally, the aforementioned Be stars show a prominent emission spectrum of hydrogen.[18]

Planets

B-type stars known to have planets include the main-sequence B-type HIP 78530.

See also

References

  1. ^ Habets, G. M. H. J.; Heintze, J. R. W. (November 1981). "Empirical bolometric corrections for the main-sequence". Astronomy and Astrophysics Supplement. 46: 193–237. Bibcode:1981A&AS...46..193H., Tables VII and VIII.
  2. ^ SIMBAD, entries on Regulus and Algol A, accessed June 19, 2007.
  3. ^ Pickering, Edward Charles (1908). "Revised Harvard photometry : a catalogue of the positions, photometric magnitudes and spectra of 9110 stars, mainly of the magnitude 6.50, and brighter observed with the 2 and 4 inch meridian photometers". Annals of the Astronomical Observatory of Harvard College. 50: 1. Bibcode:1908AnHar..50....1P. Retrieved 2009-09-21.
  4. ^ a b Gray, C. Richard O.; Corbally, J. (2009). Stellar Spectral Classification. Princeton University Press. pp. 115–122. ISBN 978-0691125114.
  5. ^ Morgan, William Wilson; Keenan, Philip Childs; Kellman, Edith (1943). An atlas of stellar spectra, with an outline of spectral classification. Chicago, Ill: The University of Chicago press. Bibcode:1943assw.book.....M.
  6. ^ Pecaut, Mark J.; Mamajek, Eric E. (1 September 2013). "Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars". The Astrophysical Journal Supplement Series. 208 (1): 9. arXiv:1307.2657. Bibcode:2013ApJS..208....9P. doi:10.1088/0067-0049/208/1/9. ISSN 0067-0049. S2CID 119308564.
  7. ^ Mamajek, Eric (2 March 2021). "A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence". University of Rochester, Department of Physics and Astronomy. Retrieved 5 July 2021.
  8. ^ Aschenbach, B.; Hahn, Hermann-Michael; Truemper, Joachim (1998). Hermann-Michael Hahn (ed.). The invisible sky: ROSAT and the age of X-ray astronomy. Springer. p. 76. ISBN 0387949283.
  9. ^ Böhm-Vitense, Erika (1992). Introduction to stellar astrophysics. Vol. 3. Cambridge University Press. p. 167. ISBN 0521348714.
  10. ^ McNally, D. (1965). "The distribution of angular momentum among main sequence stars". The Observatory. 85: 166–169. Bibcode:1965Obs....85..166M.
  11. ^ Slettebak, Arne (July 1988). "The Be Stars". Publications of the Astronomical Society of the Pacific. 100: 770–784. Bibcode:1988PASP..100..770S. doi:10.1086/132234.
  12. ^ Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313
  13. ^ MK ANCHOR POINTS, Robert F. Garrison
  14. ^ a b Spectral Classification, W.W. Morgan & P.C. Keenan, 1973, Annual Review of Astronomy and Astrophysics, vol. 11, p.29
  15. ^ Revised MK Spectral Atlas for stars earlier than the sun, W.W. Morgan, W. W., H.A. Abt, J.W. Tapscott, 1978, Williams Bay: Yerkes Observatory, and Tucson: Kitt Peak National Observatory
  16. ^ The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation, R.F. Gray & R.O. Garrison, 1994, The Astronomical Journal, vol. 107, no. 4, p. 1556-1564
  17. ^ The Kinematics of the Gould Belt: an Expanding Group? J.R. Lesh, 1968, Astrophysical Journal Supplement, vol. 17, p.371 (Table 1)
  18. ^ Gray, Richard O.; Corbally, C. J. (2009). Stellar Spectral Classification. Princeton University Press. pp. 123–136. ISBN 978-0691125114.

January 10, 2023
type, main, sequence, star, hertzsprung, russell, diagram, spectral, type, brown, dwarfs, white, dwarfs, dwarfs, subdwarfs, main, sequence, dwarfs, subgiants, giants, giants, blue, giants, bright, giants, supergiants, supergiant, hypergiants, absolutemagni, tu. Hertzsprung Russell diagram Spectral type O B A F G K M L T Brown dwarfs White dwarfs Red dwarfs Subdwarfs Main sequence dwarfs Subgiants Giants Red giants Blue giants Bright giants Supergiants Red supergiant Hypergiants absolutemagni tude MV A B type main sequence star B V is a main sequence hydrogen burning star of spectral type B and luminosity class V These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10 000 and 30 000 K 1 B type stars are extremely luminous and blue Their spectra have strong neutral helium absorption lines which are most prominent at the B2 subclass and moderately strong hydrogen lines Examples include Regulus and Algol A 2 Contents 1 History 2 Properties 3 Be and B e stars 4 Spectral standard stars 5 Chemical peculiarities 6 Planets 7 See also 8 ReferencesHistory EditThis class of stars was introduced with the Harvard sequence of stellar spectra and published in the Revised Harvard photometry catalogue The definition of type B type stars was the presence of non ionized helium lines with the absence of singly ionized helium in the blue violet portion of the spectrum All of the spectral classes including the B type were subdivided with a numerical suffix that indicated the degree to which they approached the next classification Thus B2 is 1 5 of the way from type B or B0 to type A 3 4 Later however more refined spectra showed lines of ionized helium for stars of type B0 Likewise A0 stars also show weak lines of non ionized helium Subsequent catalogues of stellar spectra classified the stars based on the strengths of absorption lines at specific frequencies or by comparing the strengths of different lines Thus in the MK Classification system the spectral class B0 has the line at wavelength 439 nm being stronger than the line at 420 nm 5 The Balmer series of hydrogen lines grows stronger through the B class then peak at type A2 The lines of ionized silicon are used to determine the sub class of the B type stars while magnesium lines are used to distinguish between the temperature classes 4 Properties EditProperties of typical B type main sequence stars 6 7 Spectraltype Mass M Radius R Luminosity L Effectivetemperature K Colorindex B V B0V 17 70 7 16 44 668 31 400 0 301B1V 11 00 5 71 13 490 26 000 0 278B2V 7 30 4 06 2 692 20 600 0 215B3V 5 40 3 61 977 17 000 0 178B4V 5 10 3 46 776 16 400 0 165B5V 4 70 3 36 589 15 700 0 156B6V 4 30 3 27 372 14 500 0 140B7V 3 92 2 94 302 14 000 0 128B8V 3 38 2 86 155 12 300 0 109B9V 2 75 2 49 72 10 700 0 070Type B stars don t have a corona and lack a convection zone in their outer atmosphere They have a higher mass loss rate than smaller stars such as the Sun and their stellar wind has velocities of about 3 000 km s 8 The energy generation in main sequence B type stars comes from the CNO cycle of thermonuclear fusion Because the CNO cycle is very temperature sensitive the energy generation is heavily concentrated at the center of the star which results in a convection zone about the core This results in a steady mixing of the hydrogen fuel with the helium byproduct of the nuclear fusion 9 Many B type stars have a rapid rate of rotation with an equatorial rotation velocity of about 200 km s 10 Be and B e stars EditMain article B e stars Spectral objects known as Be stars are massive yet non supergiant entities that notably have or had at some time 1 or more Balmer lines in emission with the hydrogen related electromagnetic radiation series projected out by the stars being of particular scientific interest Be stars are generally thought to feature unusually strong stellar winds high surface temperatures and significant attrition of stellar mass as the objects rotate at a curiously rapid rate all of this in contrast to many other main sequence star types 11 Objects known as B e stars are distinct from Be stars in having unusual neutral or low ionization emission lines that are considered to have forbidden mechanisms something denoted by the use of the square brackets In other words these particular stars emissions appear to undergo processes not normally allowed under 1st order perturbation theory in quantum mechanics The definition of a B e star can include blue giants and blue supergiants Spectral standard stars Edit Part of the constellation of Carina Epsilon Carinae is an example of a double star featuring a main sequence B type star The primary is an evolved giant star with a stellar classification of K0 III hence its yellowish color The secondary is a typical core hydrogen fusing B type main sequence star of spectral class B2 Vp The revised Yerkes Atlas system Johnson amp Morgan 1953 12 listed a dense grid of B type dwarf spectral standard stars however not all of these have survived to this day as standards The anchor points of the MK spectral classification system among the B type main sequence dwarf stars i e those standard stars that have remain unchanged since at least the 1940s are upsilon Orionis B0 V eta Aurigae B3 V eta Ursae Majoris B3 V 13 14 Besides these anchor standards the seminal review of MK classification by Morgan amp Keenan 1973 14 listed dagger standards of Tau Scorpii B0 V Omega Scorpii B1 V 42 Orionis B1 V 22 Scorpii B2 V Rho Aurigae B5 V and 18 Tauri B8 V The Revised MK Spectra Atlas of Morgan Abt amp Tapscott 1978 15 further contributed the standards Beta2 Scorpii B2 V 29 Persei B3 V HD 36936 B5 V and HD 21071 B7 V Gray amp Garrison 1994 16 contributed two B9 V standards Omega Fornacis and HR 2328 The only published B4 V standard is 90 Leonis from Lesh 1968 17 There has been little agreement in the literature on choice of B6 V standard Chemical peculiarities EditSome of the B type stars of stellar class B0 B3 exhibit unusually strong lines of non ionized helium These chemically peculiar stars are termed helium strong stars These often have strong magnetic fields in their photosphere In contrast there are also helium weak B type stars with understrength helium lines and strong hydrogen spectra Other chemically peculiar B types stars are the mercury manganese stars with spectral types B7 B9 Finally the aforementioned Be stars show a prominent emission spectrum of hydrogen 18 Planets EditB type stars known to have planets include the main sequence B type HIP 78530 See also EditHerbig Ae Be star Stellar classification Class B Star countReferences Edit Habets G M H J Heintze J R W November 1981 Empirical bolometric corrections for the main sequence Astronomy and Astrophysics Supplement 46 193 237 Bibcode 1981A amp AS 46 193H Tables VII and VIII SIMBAD entries on Regulus and Algol A accessed June 19 2007 Pickering Edward Charles 1908 Revised Harvard photometry a catalogue of the positions photometric magnitudes and spectra of 9110 stars mainly of the magnitude 6 50 and brighter observed with the 2 and 4 inch meridian photometers Annals of the Astronomical Observatory of Harvard College 50 1 Bibcode 1908AnHar 50 1P Retrieved 2009 09 21 a b Gray C Richard O Corbally J 2009 Stellar Spectral Classification Princeton University Press pp 115 122 ISBN 978 0691125114 Morgan William Wilson Keenan Philip Childs Kellman Edith 1943 An atlas of stellar spectra with an outline of spectral classification Chicago Ill The University of Chicago press Bibcode 1943assw book M Pecaut Mark J Mamajek Eric E 1 September 2013 Intrinsic Colors Temperatures and Bolometric Corrections of Pre main sequence Stars The Astrophysical Journal Supplement Series 208 1 9 arXiv 1307 2657 Bibcode 2013ApJS 208 9P doi 10 1088 0067 0049 208 1 9 ISSN 0067 0049 S2CID 119308564 Mamajek Eric 2 March 2021 A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence University of Rochester Department of Physics and Astronomy Retrieved 5 July 2021 Aschenbach B Hahn Hermann Michael Truemper Joachim 1998 Hermann Michael Hahn ed The invisible sky ROSAT and the age of X ray astronomy Springer p 76 ISBN 0387949283 Bohm Vitense Erika 1992 Introduction to stellar astrophysics Vol 3 Cambridge University Press p 167 ISBN 0521348714 McNally D 1965 The distribution of angular momentum among main sequence stars The Observatory 85 166 169 Bibcode 1965Obs 85 166M Slettebak Arne July 1988 The Be Stars Publications of the Astronomical Society of the Pacific 100 770 784 Bibcode 1988PASP 100 770S doi 10 1086 132234 Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas H L Johnson amp W W Morgan 1953 Astrophysical Journal 117 313 MK ANCHOR POINTS Robert F Garrison a b Spectral Classification W W Morgan amp P C Keenan 1973 Annual Review of Astronomy and Astrophysics vol 11 p 29 Revised MK Spectral Atlas for stars earlier than the sun W W Morgan W W H A Abt J W Tapscott 1978 Williams Bay Yerkes Observatory and Tucson Kitt Peak National Observatory The late B type stars Refined MK classification confrontation with stromgren photometry and the effects of rotation R F Gray amp R O Garrison 1994 The Astronomical Journal vol 107 no 4 p 1556 1564 The Kinematics of the Gould Belt an Expanding Group J R Lesh 1968 Astrophysical Journal Supplement vol 17 p 371 Table 1 Gray Richard O Corbally C J 2009 Stellar Spectral Classification Princeton University Press pp 123 136 ISBN 978 0691125114 Portals Astronomy Spaceflight Outer space Solar System Retrieved from https en wikipedia org w index php title B type main sequence star amp oldid 1131803997, wikipedia, wiki, book, books, library,

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