Editing White dwarf (section)

== Discovery ==
{{See also|List of white dwarfs}}
The first white dwarf discovered was in the [[triple star system]] of [[40 Eridani]], which contains the relatively bright [[main sequence]] star [[40 Eridani A]], orbited at a distance by the closer [[binary star|binary system]] of the white dwarf [[40 Eridani B]] and the [[main sequence]] [[red dwarf]] [[40 Eridani C]]. The pair 40 Eridani B/C was discovered by [[William Herschel]] on 31 January 1783.<ref>
{{cite journal
 |last=Herschel |first=W.  |author-link=William Herschel
 |year=1785
 |title=Catalogue of Double Stars
 |journal=[[Philosophical Transactions of the Royal Society of London]]
 |volume=75  |pages=40–126
 |bibcode=1785RSPT...75...40H  |jstor=106749
 |doi=10.1098/rstl.1785.0006 |doi-access=free |s2cid=186209747
}}
</ref> In 1910, [[Henry Norris Russell]], [[Edward Charles Pickering]] and [[Williamina Fleming]] discovered that, despite being a dim star, 40&nbsp;Eridani&nbsp;B was of [[stellar classification|spectral type]]&nbsp;A, or white.<ref name=holberg>
{{cite conference
 |last=Holberg |first=J. B.
 |year=2005
 |title=How degenerate stars came to be known as 'white dwarfs'
 |volume=207 |page=1503
 |conference=[[American Astronomical Society]] meeting&nbsp;207
 |bibcode=2005AAS...20720501H
}}
</ref> In 1939, Russell looked back on the discovery and noted that Pickering had suggested that such exceptions lead to breakthroughs and in this case it led to the discovery of white dwarfs.<ref name="schatzman">
{{cite book | author = Evry L. Schatzman | date = 1958 | title = White Dwarfs | publisher = North-Holland Publishing Company | isbn = 978-0-598-58212-6 | url = https://books.google.com/books?id=PrixAAAAIAAJ}}</ref>{{rp|page=1}}
The spectral type of 40 Eridani B was officially described in 1914 by [[Walter Sydney Adams|Walter Adams]].<ref>
{{cite journal
 |last=Adams |first=W.S. |author-link=Walter Sydney Adams
 |year=1914
 |title=An A-type star of very low luminosity
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=26 |issue= 155 |page=198
 |bibcode=1914PASP...26..198A
 |doi= 10.1086/122337  |doi-access=free
}}
</ref>

The white dwarf companion of Sirius, Sirius&nbsp;B, was next to be discovered. During the nineteenth century, positional measurements of some stars became precise enough to measure small changes in their location. [[Friedrich Wilhelm Bessel|Friedrich Bessel]] used position measurements to determine that the stars Sirius (α&nbsp;Canis Majoris) and [[Procyon]] (α&nbsp;Canis Minoris) were changing their positions periodically. In 1844 he predicted that both stars had unseen companions.<ref name="fwbessel">
{{cite journal
 |last1=Bessel |first1=F.W.  |author-link=Friedrich Wilhelm Bessel
 |year=1844
 |title=On the variations of the proper motions of Procyon and Sirius
 |journal=[[Monthly Notices of the Royal Astronomical Society]]
 |volume=6 |issue=11 |pages=136–141
 |bibcode=1844MNRAS...6R.136B
 |doi=10.1093/mnras/6.11.136a  |doi-access=free
}}
</ref>

Bessel roughly estimated the period of the companion of Sirius to be about half a century;<ref name=fwbessel/> [[Christian August Friedrich Peters|C.A.F. Peters]] computed an orbit for it in 1851.<ref name=flammarion>
{{cite journal
 |last=Flammarion |first=Camille
 |title=The companion of Sirius
 |year=1877
 |volume=15 |page=186
 |journal=[[Astronomical Register]]
 |bibcode=1877AReg...15..186F
}}
</ref> It was not until 31&nbsp;January 1862 that [[Alvan Graham Clark]] observed a previously unseen star close to Sirius, later identified as the predicted companion.<ref name=flammarion/> [[Walter Sydney Adams|Walter Adams]] announced in 1915 that he had found the spectrum of Sirius&nbsp;B to be similar to that of Sirius.<ref>
{{cite journal
 |last=Adams  |first=W.S.  |author-link=Walter Sydney Adams
 |year=1915
 |title=The spectrum of the companion of Sirius
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=27  |issue=161  |page=236
 |bibcode=1915PASP...27..236A
 |doi= 10.1086/122440  |doi-access=free
}}
</ref>

In 1917, [[Adriaan van Maanen]] discovered [[van Maanen's Star]], an isolated white dwarf.<ref name="van Maanen">
{{cite journal
 |last=van&nbsp;Maanen  |first=A.  |author-link=Adriaan van Maanen
 |year=1917
 |title=Two faint stars with large proper motion
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=29  |issue=172  |page=258
 |bibcode=1917PASP...29..258V
 |doi=10.1086/122654  |doi-access=free
}}
</ref> These three white dwarfs, the first discovered, are the so-called ''classical white dwarfs''.<ref name=schatzman/>{{rp|page=2}} Eventually, many faint white stars that had high [[proper motion]] were found, indicating that they could be suspected to be low-luminosity stars close to the Earth, and hence white dwarfs. [[Willem Luyten]] appears to have been the first to use the term ''white dwarf'' when he examined this class of stars in 1922;<ref name="holberg"/><ref>
{{cite journal
 |last=Luyten |first=W.J.  |author-link=Willem Luyten
 |year=1922
 |title=The mean parallax of early-type stars of determined proper motion and apparent magnitude
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=34  |issue=199  |page=156
 |bibcode=1922PASP...34..156L
 |doi= 10.1086/123176  |doi-access=free
}}
</ref><ref>
{{cite journal
 |last=Luyten |first=W.J.  |author-link=Willem Luyten
 |year=1922
 |title=Note on some faint early-type stars with large proper motions
 |journal=Publications of the Astronomical Society of the Pacific
 |volume=34  |issue=197  |page=54
 |bibcode=1922PASP...34...54L
 |doi= 10.1086/123146 |doi-access=free
}}</ref><ref>
{{cite journal
 |last=Luyten |first=W.J.  |author-link=Willem Luyten
 |year=1922
 |title=Additional note on faint early-type stars with large proper motions
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=34  |issue=198  |page=132
 |bibcode=1922PASP...34..132L
 |doi= 10.1086/123168  |doi-access=free
}}
</ref><ref>
{{cite journal
 |last=Aitken |first=R.G.
 |year=1922
 |title=Comet c 1922 (Baade)
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=34  |issue= 202  |page=353
 |bibcode=1922PASP...34..353A
 |doi= 10.1086/123244  |doi-access=free
}}
</ref> the term was later popularized by [[Arthur Eddington]].<ref name=holberg/><ref name=eddington/> Despite these suspicions, the first non-classical white dwarf was not definitely identified until the 1930s. 18&nbsp;white dwarfs had been discovered by 1939.<ref name=schatzman/>{{rp|page=3}} Luyten and others continued to search for white dwarfs in the 1940s. By 1950, over a hundred were known,<ref>
{{cite journal
 |last1=Luyten |first1=W.J. |author-link=Willem Luyten
 |year=1950
 |title=The search for white dwarfs
 |journal=[[The Astronomical Journal]]
 |volume=55  |page=86
 |bibcode=1950AJ.....55...86L
 |doi= 10.1086/106358  |doi-access=free
}}
</ref> and by 1999, over 2000 were known.<ref name=villanovar4>
{{cite journal
 |last1=McCook |first1=George P.
 |last2=Sion   |first2=Edward M.
 |year=1999
 |title=A catalog of spectroscopically identified white dwarfs
 |journal=The Astrophysical Journal Supplement Series
 |volume=121  |issue= 1  |pages=1–130
 |bibcode=1999ApJS..121....1M
 |doi=10.1086/313186  |doi-access=free
}}
</ref> Since then the [[Sloan Digital Sky Survey]] has found over 9000&nbsp;white dwarfs, mostly new.<ref name=sdssr4>
{{cite journal
 |last1=Eisenstein  |first1=Daniel J.  |last2=Liebert     |first2=James
 |last3=Harris      |first3=Hugh C.    |last4=Kleinman    |first4=S. J.
 |last5=Nitta       |first5=Atsuko     |last6=Silvestri   |first6=Nicole
 |last7=Anderson    |first7=Scott A.   |last8=Barentine   |first8=J. C.
 |last9=Brewington  |first9=Howard J.  |last10=Brinkmann  |first10=J.
 |last11=Harvanek   |first11=Michael   |last12=Krzesiński |first12=Jurek
 |last13=Neilsen    |first13=Eric H. Jr.
 |last14=Long       |first14=Dan       |last15=Schneider  |first15=Donald P.
 |last16=Snedden    |first16=Stephanie A.  |author16-link=Stephanie Snedden
 |display-authors=6
 |year=2006
 |title=A catalog of spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey, data release&nbsp;4
 |journal=The Astrophysical Journal Supplement Series
 |volume=167  |issue=1  |pages=40–58
 |s2cid=13829139  |bibcode=2006ApJS..167...40E
 |arxiv=astro-ph/0606700  |doi= 10.1086/507110
}}
</ref>