Editing Subdwarf (section)

== Hot (blue) subdwarfs<span class="anchor" id="hot subdwarf anchor"></span><span class="anchor" id="hot subdwarf"></span><span class="anchor" id="hot subdwarfs"></span><span class="anchor" id="hot subdwarf star"></span><span class="anchor" id="hot subdwarf stars"></span> ==
{{Main|B-type subdwarf|O-type subdwarf}}
Hot subdwarfs, of bluish spectral types&nbsp;O and B are an entirely different class of object than cool subdwarfs; they are also called ''"extreme [[horizontal branch|horizontal-branch]] stars"''.
Hot subdwarf stars represent a late stage in the evolution of some stars, caused when a [[red giant]] star loses its outer [[hydrogen]] layers before the core begins to fuse [[helium]].

The reasons for their premature loss of their hydrogen envelope are unclear, but the interaction of stars in a [[binary star]] system is thought to be one of the main mechanisms. Single subdwarfs may be the result of a merger of two [[white dwarf]]s or gravitational influence from substellar companions. B-type subdwarfs, being more luminous than white dwarfs, are a significant component in the hot star population of old stellar systems, such as [[globular cluster]]s and [[elliptical galaxy|elliptical galaxies]].<ref>{{cite journal |last1=Jeffery |first1=C. Simon |year=2005 |title=Pulsations in Subdwarf B Stars |journal=[[Journal of Astrophysics and Astronomy]] |volume=26 |issue=2–3 |pages=261–271 |bibcode=2005JApA...26..261J |doi=10.1007/BF02702334 |s2cid=13814916}}</ref><ref>{{cite journal |last1=Geier |first1=S. |last2=Edelmann |first2=H. |last3=Heber |first3=U. |last4=Morales-Rueda |first4=L. |year=2009 |title=Discovery of a close substellar companion to the hot subdwarf star HD&nbsp;149382 — the decisive influence of substellar objects on late stellar evolution |journal=[[The Astrophysical Journal Letters]] |volume=702 |issue=1 |pages=L96–L99  |arxiv=0908.1025 |bibcode=2009ApJ...702L..96G |doi=10.1088/0004-637X/702/1/L96 |s2cid=119282460}}</ref>

===Heavy metal subdwarfs===
{{anchor|heavy metal subdwarfs|heavy metal subdwarf star|heavy metal subdwarf stars}}
{{expand section|date=March 2024}}
The heavy metal subdwarfs are a type of hot subdwarf star with high concentrations of [[heavy metals]]. The metals detected include [[germanium]], [[strontium]], [[yttrium]], [[zirconium]] and [[lead]]. Known heavy metal subdwarfs include [[HE 2359-2844]], [[LS IV-14 116]], and [[HE 1256-2738]].<ref>{{cite news |title=Astronomers discover two heavy metal stars |date=2 August 2013 |department=Astronomy |website=Sci-News.com |url=http://www.sci-news.com/astronomy/science-heavy-metal-stars-01283.html |access-date=5 November 2016}}</ref>