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Your current IP address is 8.222.208.146. </p> <div class="paragraphbreak" style="margin-top:0.5em"></div><div style="font-size: 16px;"> <p>Even while globally blocked, you will <i>usually</i> still be able to edit pages on <a href="https://meta.wikimedia.org/wiki/" class="extiw" title="m:">Meta-Wiki</a>. </p> </div> <div class="paragraphbreak" style="margin-top:0.5em"></div><div style="font-size: 16px;"> <p>If you believe you were blocked by mistake, you can find additional information and instructions in the <a href="https://meta.wikimedia.org/wiki/Special:MyLanguage/No_open_proxies" class="extiw" title="m:Special:MyLanguage/No open proxies">No open proxies</a> global policy. Otherwise, to discuss the block please <a href="https://meta.wikimedia.org/wiki/Steward_requests/Global" class="extiw" title="m:Steward requests/Global">post a request for review on Meta-Wiki</a>. You could also send an email to the <a href="https://meta.wikimedia.org/wiki/Special:MyLanguage/Stewards" class="extiw" title="m:Special:MyLanguage/Stewards">stewards</a> <a href="https://meta.wikimedia.org/wiki/Special:MyLanguage/VRT" class="extiw" title="m:Special:MyLanguage/VRT">VRT</a> queue at <kbd>stewards@wikimedia.org</kbd> including all above details. </p> </div> <p>Other useful links: <a href="https://meta.wikimedia.org/wiki/Global_blocks" class="extiw" title="m:Global blocks">Global blocks</a> · <a href="/wiki/Help:I_have_been_blocked" title="Help:I have been blocked">Help:I have been blocked</a> </p> </div></li></ul><hr /> <div id="viewsourcetext">You can view and copy the source of this page:</div><textarea readonly="" accesskey="," id="wpTextbox1" cols="80" rows="25" style="" class="mw-editfont-monospace" lang="en" dir="ltr" name="wpTextbox1">{{Short description|Stellar classification distinguished by bright blue luminosity}} {{Star nav}} A '''B-type main-sequence star''' (B V) is a [[main sequence|main-sequence]] ([[hydrogen]]-burning) [[star]] of [[Stellar classification#Type B|spectral type B]] and luminosity class V. These stars have from 2 to 16 times the [[solar mass|mass]] of the [[Sun]] and [[effective temperature|surface temperature]]s between 10,000 and 30,000 [[Kelvin|K]].<ref>{{cite journal | author=Habets, G. M. H. J. | author2=Heintze, J. R. W. | title=Empirical bolometric corrections for the main-sequence | journal=Astronomy and Astrophysics Supplement | volume=46 |date=November 1981 | pages=193–237 | bibcode=1981A&AS...46..193H }}, Tables VII and VIII.</ref> B-type stars are extremely luminous and blue. Their spectra have strong neutral [[helium]] [[absorption line]]s, which are most prominent at the B2 subclass, and moderately strong hydrogen lines. Examples include [[Regulus]], [[Algol A]] and [[Acrux]].<ref>[[SIMBAD]], entries on [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Regulus Regulus], [http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Algol%20A Algol A] and [[Acrux]] accessed on June 19, 2007.</ref> ==History== This class of stars was introduced with the Harvard sequence of stellar spectra and published in the [[Harvard Revised Photometry Catalogue|''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 [[A-type main-sequence star|type A]].<ref>{{cite journal | last=Pickering | first=Edward Charles | date=1908 | title=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 | journal=Annals of the Astronomical Observatory of Harvard College | volume=50 | page=1 | bibcode=1908AnHar..50....1P | access-date=2009-09-21 |url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1908AnHar..50....1P&link_type=ARTICLE&db_key=AST&high= }}</ref><ref name="gray_corbally">{{cite book | author=Gray, C. Richard O. | author2=Corbally, J. | title=Stellar Spectral Classification | date=2009 | publisher=[[Princeton University Press]] | pages=115–122 | isbn=978-0691125114 }}</ref> 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&nbsp;nm being stronger than the line at 420&nbsp;nm.<ref>{{cite book|title=An atlas of stellar spectra, with an outline of spectral classification|date=1943|publisher=The University of Chicago press|location=Chicago, Ill|bibcode=1943assw.book.....M|author=Morgan, William Wilson|author2=Keenan, Philip Childs|author3=Kellman, Edith}}</ref> 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.<ref name="gray_corbally" /> ==Properties== {| class="wikitable floatright" style="text-align:center; font-size:smaller;" |+ Properties of typical B-type main-sequence stars<ref>{{cite journal |last1=Pecaut |first1=Mark J. |last2=Mamajek |first2=Eric E. |title=Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars |journal=The Astrophysical Journal Supplement Series |date=1 September 2013 |volume=208 |issue=1 |pages=9 |doi=10.1088/0067-0049/208/1/9 |url=https://ui.adsabs.harvard.edu/abs/2013ApJS..208....9P/abstract |issn=0067-0049|arxiv=1307.2657 |bibcode=2013ApJS..208....9P |s2cid=119308564 }}</ref><ref>{{cite web |last1=Mamajek |first1=Eric |title=A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence |url=http://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt |publisher=University of Rochester, Department of Physics and Astronomy |access-date=5 July 2021 |date=2 March 2021}}</ref> |- ![[Spectral type|Spectral<br/>type]] ![[Stellar mass|Mass]] ({{Solar mass|link=y}}) ![[Stellar radius|Radius]] ({{Solar radius|link=y}}) ![[Luminosity]] ({{Solar luminosity|link=y}}) ![[Effective temperature|Effective<br/>temperature]]<br/>(K) ![[Color index|Color<br/>index]]<br/>{{nowrap|(B − V)}} |- | B0V | 17.70 | 7.16 | 44,668 | style="background-color:#{{Color temperature|31400|hexval}}"|31,400 | -0.301 |- | B1V | 11.00 | 5.71 | 13,490 | style="background-color:#{{Color temperature|26000|hexval}}"|26,000 | -0.278 |- | B2V | 7.30 | 4.06 | 2,692 | style="background-color:#{{Color temperature|20600|hexval}}"|20,600 | -0.215 |- | B3V | 5.40 | 3.61 | 977 | style="background-color:#{{Color temperature|17000|hexval}}"|17,000 | -0.178 |- | B4V | 5.10 | 3.46 | 776 | style="background-color:#{{Color temperature|16400|hexval}}"|16,400 | -0.165 |- | B5V | 4.70 | 3.36 | 589 | style="background-color:#{{Color temperature|15700|hexval}}"|15,700 | -0.156 |- | B6V | 4.30 | 3.27 | 372 | style="background-color:#{{Color temperature|14500|hexval}}"|14,500 | -0.140 |- | B7V | 3.92 | 2.94 | 302 | style="background-color:#{{Color temperature|14000|hexval}}"|14,000 | -0.128 |- | B8V | 3.38 | 2.86 | 155 | style="background-color:#{{Color temperature|12300|hexval}}"|12,300 | -0.109 |- | B9V | 2.75 | 2.49 | 72 | style="background-color:#{{Color temperature|10700|hexval}}"|10,700 | -0.070 |} Type-B stars do not have a [[stellar corona|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&nbsp;km/s.<ref>{{cite book | author=Aschenbach, B. | author2=Hahn, Hermann-Michael | author3=Truemper, Joachim | editor=Hermann-Michael Hahn | title=The invisible sky: ROSAT and the age of X-ray astronomy | publisher=Springer | date=1998 | page=76 | isbn=0387949283 }}</ref> 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.<ref>{{cite book | first=Erika | last=Böhm-Vitense | date=1992 | title=Introduction to stellar astrophysics | page=167 | volume=3 | publisher=[[Cambridge University Press]] | isbn=0521348714 }}</ref> Many B-type stars have a rapid rate of [[stellar rotation|rotation]], with an equatorial rotation velocity of about 200&nbsp;km/s.<ref>{{cite journal | last = McNally | first = D. | title=The distribution of angular momentum among main sequence stars | journal=The Observatory | date=1965 | volume=85 | pages=166–169 | bibcode=1965Obs....85..166M }}</ref> ==Be and B[e] stars== {{main|Be star|B(e) star{{!}}B[e] star}} 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]] [[Hydrogen spectral series|series]] projected out by the stars being of particular scientific interest. Be stars are generally thought to feature unusually strong [[stellar wind]]s, high surface temperatures, and significant attrition of [[stellar mass]] as the objects [[Stellar rotation|rotate]] at a curiously rapid rate, all of this in contrast to many other main-sequence star types.<ref name="Slettebak1988">{{cite journal |title=The Be Stars |journal=[[Publications of the Astronomical Society of the Pacific]] |first=Arne |last=Slettebak |volume=100 |pages=770–784 |date=July 1988 |doi=10.1086/132234 |bibcode=1988PASP..100..770S|doi-access=free }}</ref> Objects known as [[B(e) star|B[e] stars]] are distinct from Be stars in having unusual neutral or low ionization [[emission lines]] that are considered to have '[[forbidden mechanism]]s', something denoted by the use of the square brackets. In other words, these particular stars' emissions appear to undergo processes not normally allowed under [[Perturbation theory (quantum mechanics)|1st-order perturbation theory]] in [[quantum mechanics]]. The definition of a B[e] star can include [[blue giant]]s and [[blue supergiant]]s. ==Spectral standard stars== [[File:B-type main sequence star 1.png|thumb|Artist's impression of a B-type star]] [[File:NewAlbireo.jpg|thumb|The secondary component of the double star [[Albireo]] is a B8 [[main sequence]] star, the blue contrasting with the cooler yellow [[giant star|giant]] primary.]] The revised Yerkes Atlas system (Johnson & Morgan 1953)<ref>[http://adsabs.harvard.edu/abs/1953ApJ...117..313J 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</ref> 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|Thabit]] (B0 V), [[Eta Aurigae|Haedus]] (B3 V), and [[Alkaid]] (B3 V).<ref name="Garrison">[http://www.astro.utoronto.ca/~garrison/mkstds.html MK ANCHOR POINTS] {{Webarchive|url=https://web.archive.org/web/20190625094716/http://www.astro.utoronto.ca/~garrison/mkstds.html |date=2019-06-25 }}, Robert F. Garrison</ref><ref name="MK73">[http://adsabs.harvard.edu/abs/1973ARA%26A..11...29M Spectral Classification], W.W. Morgan & P.C. Keenan, 1973, Annual Review of Astronomy and Astrophysics, vol. 11, p.29</ref> Besides these anchor standards, the seminal review of MK classification by Morgan & Keenan (1973)<ref name="MK73"/> listed "dagger standards" of [[Tau Scorpii|Paikauhale]] (B0 V), [[Omega Scorpii]] (B1 V), [[42 Orionis]] (B1 V), [[22 Scorpii]] (B3 V), [[Rho Aurigae]] (B5 V), and [[18 Tauri]] (B8 V). The Revised MK Spectra Atlas of Morgan, Abt, & Tapscott (1978)<ref name="MK78">[http://adsabs.harvard.edu/abs/1978rmsa.book.....M 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</ref> further contributed the standards [[Beta Scorpii|Acrab]] (B2 V), [[29 Persei]] (B3 V), [[HD 36936]] (B5 V), and [[HD 21071]] (B7 V). Gray & Garrison (1994)<ref>[http://adsabs.harvard.edu/abs/1994AJ....107.1556G 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</ref> contributed two B9 V standards: [[Omega Fornacis]] and [[HR 2328]]. The only published B4 V standard is [[90 Leonis]], from Lesh (1968).<ref>[http://adsabs.harvard.edu/abs/1968ApJS...17..371L The Kinematics of the Gould Belt: an Expanding Group?] J.R. Lesh, 1968, Astrophysical Journal Supplement, vol. 17, p.371 (Table 1)</ref> 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&ndash;B3 exhibit unusually strong lines of non-ionized helium. These chemically [[peculiar star]]s 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 star]]s with spectral types B7-B9. == Planets == B-type stars known to have planets include the main-sequence B-type [[HIP 78530 b|HIP 78530]] and [[HD 129116]]. == See also == * [[Herbig Ae/Be star]] * [[Star count]] ==References== {{reflist|30em}} {{Star|state=collapsed}} {{Portal bar|Astronomy|Stars|Outer space}} [[Category:Star types]] [[Category:B-type main-sequence stars| ]] </textarea><div class="templatesUsed"><div class="mw-templatesUsedExplanation"><p><span id="templatesused">Pages transcluded onto the current version of this page<span class="posteditwindowhelplinks"> (<a href="/wiki/Help:Transclusion" title="Help:Transclusion">help</a>)</span>:</span> </p></div><ul> <li><a href="/wiki/Template:Cite_book" title="Template:Cite book">Template:Cite book</a> (<a href="/w/index.php?title=Template:Cite_book&action=edit" title="Template:Cite book">view source</a>) (protected)</li><li><a 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