Editing Stellar classification (section)

===Class B===
{{See also|B-type main-sequence star|Blue giant|Blue supergiant}}
[[File:B3V star spectrum.png|thumb|Spectrum of a hypothetical B3V star]]
B-type stars are very luminous and blue. Their spectra have neutral helium lines, which are most prominent at the B2 subclass, and moderate hydrogen lines. As [[OB star|O- and B-type stars]] are so energetic, they only live for a relatively short time. Thus, due to the low probability of kinematic interaction during their lifetime, they are unable to stray far from the area in which they formed, apart from [[runaway star]]s.

The transition from class&nbsp;O to class&nbsp;B was originally defined to be the point at which the [[Helium|He]]&nbsp;II λ4541 disappears. However, with modern equipment, the line is still apparent in the early B-type stars. Today for main-sequence stars, the B class is instead defined by the intensity of the He&nbsp;I violet spectrum, with the maximum intensity corresponding to class&nbsp;B2. For supergiants, lines of [[silicon]] are used instead; the Si&nbsp;IV λ4089 and Si&nbsp;III λ4552 lines are indicative of early B. At mid-B, the intensity of the latter relative to that of Si&nbsp;II λλ4128-30 is the defining characteristic, while for late B, it is the intensity of Mg&nbsp;II λ4481 relative to that of He&nbsp;I λ4471.<ref name="Walborn"/>

These stars tend to be found in their originating [[OB association]]s, which are associated with giant [[molecular cloud]]s. The Orion OB1 association occupies a large portion of a [[spiral arm]] of the [[Milky Way]] and contains many of the brighter stars of the [[Orion constellation|constellation Orion]]. About 1 in 800 (0.125%) of the main-sequence stars in the solar neighborhood are [[B-type main-sequence star]]s.<ref group=lower-alpha name="proportions"/><ref name="LeDrew2001"/> B-type stars are relatively uncommon and the closest is Regulus, at around 80 light years.<ref>{{Cite web |author1=Elizabeth Howell |date=2013-09-21 |title=Regulus: The Kingly Star |url=https://www.space.com/22890-regulus.html |access-date=2022-04-13 |website=Space.com |language=en}}</ref>

Massive yet non-[[supergiant]] stars known as [[Be&nbsp;star]]s have been observed to show one or more [[Balmer lines]] in emission, with the [[hydrogen]]-related [[electromagnetic radiation]] [[Hydrogen spectral series|series]] projected out by the stars being of particular 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.<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]] – or B(e) stars for typographic reasons – possess distinctive neutral or low ionisation [[emission lines]] that are considered to have [[forbidden mechanism]]s, undergoing processes not normally allowed under current understandings of [[quantum mechanics]].

'''Example spectral standards:'''<ref name="Garrison"/>
* B0V – [[Upsilon Orionis]]
* B0Ia – [[Alnilam]]
* B2Ia – [[Chi2 Orionis|Chi<sup>2</sup> Orionis]]
* B2Ib – [[9 Cephei]]
* B3V – [[Eta Ursae Majoris]]
* B3V – [[Eta Aurigae]]
* B3Ia – [[Omicron2 Canis Majoris|Omicron<sup>2</sup> Canis Majoris]]
* B5Ia – [[Eta Canis Majoris]]
* B8Ia – [[Rigel]]