{{Short description|White dwarf star}} {{Starbox begin}} {{Starbox observe | epoch=[[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell=[[Hydra (constellation)|Hydra]] | ra={{RA|11|39|03.1037}}<ref name=s>{{cite simbad|title=Ruiz 439-26|access-date=October 22, 2020}}</ref> | dec={{DEC|-28|52|16.628}}<ref name=s/> | appmag_v=20.52<ref name=ruiz95/> }} {{Starbox character | class=DC9<ref name=ruiz95/> | u-b = 1.03<ref name=blr01/> | b-v = 0.64<ref name=blr01/> | r-i = 1.14<ref name=blr01/> }} {{Starbox astrometry | prop_mo_ra=-397.767 ±0.481<ref name="Gaia DR3"/> | prop_mo_dec=+ 36.869 ±0.441<ref name="Gaia DR3"/> | parallax=9.7390 | p_error=0.5007 | parallax_footnote=<ref name="Gaia DR3"/> | absmag_v=15.46<ref name=ruiz95/><ref name="Gaia DR3"/> }} {{Starbox detail | mass = 0.50 ±0.15<ref name="Gaia EDR3wd"/> | radius = 0.0126<ref>{{Cite journal |last=Ruiz |first=Maria Teresa |last2=Bergeron |first2=P. |last3=Leggett |first3=S. K. |last4=Anguita |first4=Claudio |date=1995-12-01 |title=The Extremely Low Luminosity White Dwarf ESO 439-26 |url=https://ui.adsabs.harvard.edu/abs/1995ApJ...455L.159R |journal=The Astrophysical Journal |volume=455 |pages=L159 |doi=10.1086/309845 |issn=0004-637X|doi-access=free }}</ref> | temperature = {{val|4673|275|fmt=commas}}<ref name="Gaia EDR3wd"/> | gravity = 7.87 ±0.28<ref name="Gaia EDR3wd"/> | luminosity = 1.15 {{e|-5}} <ref name=blr01/> }} {{Starbox catalog | names=Ruiz 439-26, WD 1136-286<ref name=s/> }} {{Starbox reference | Simbad = Ruiz+439-26 }} {{Starbox end}} '''ESO 439-26''' is a [[white dwarf]] star. It was considered the least luminous white dwarf known.<ref name=ruiz95/><ref name="noaoWeb"/> Located 140 light years away from the [[Sun]], it is roughly 10 billion years old and has a temperature of 4560 Kelvin (cooler than the Sun, at 5772 Kelvin). Thus, despite being classified as a "white dwarf", it would actually appear yellowish in color.<ref name="bookKaler"/>
This finding is however based on a too large [[parallax]]. [[Gaia (spacecraft)|Gaia]] measurement of the parallax shows a more distant source and therefore an [[absolute magnitude]] of M<sub>G</sub>=15.0 mag. For example the white dwarf [[WD J2147–4035]] has M<sub>G</sub>=17.7 mag, making this white dwarf less luminous.<ref name="Elms2022"/><ref name="Gaia EDR3wd"/> The updated M<sub>V</sub> is 15.46, using the Gaia parallax<ref name="Gaia DR3"/> and the apparent V-magnitude from Ruiz et al. (see formulae at the article [[Absolute_magnitude#Apparent_magnitude|absolute magnitude]]).<ref name=ruiz95/>
== References == <references>
<ref name="Gaia DR3">{{Cite Gaia DR3|3483746453090944896}}</ref>
<ref name="bookKaler">{{Cite book|url=https://books.google.com/books?id=jmoQBwAAQBAJ&q=ESO+439-26&pg=PA75|title=The Hundred Greatest Stars|first=James B.|last=Kaler|date=May 7, 2006|publisher=Springer Science & Business Media|isbn=9780387216256|via=Google Books}}</ref>
<ref name="noaoWeb">{{Cite web|url=https://www.noao.edu/noao/noaonews/mar96/art3.html|title=The Faintest Known White Dwarf|date=1 March 1996|website=www.noao.edu|access-date=8 May 2020|archive-date=12 March 2021|archive-url=https://web.archive.org/web/20210312011057/https://www.noao.edu/noao/noaonews/mar96/art3.html|url-status=dead}}</ref>
<ref name=ruiz95>{{Cite journal|url=https://iopscience.iop.org/article/10.1086/309845/fulltext/5601.text.html|title=The Extremely Low Luminosity White Dwarf ESO 439-26|journal=The Astrophysical Journal|doi=10.1086/309845|author1=María Teresa Ruiz |author2=P. Bergeron |author3=S. K. Leggett |author4=Claudio Anguita |year=1995 |volume=455 |bibcode=1995ApJ...455L.159R |s2cid=120193018 |doi-access=free }}</ref>
<ref name="Elms2022">{{Cite journal |last1=Elms |first1=Abbigail K. |last2=Tremblay |first2=Pier-Emmanuel |last3=Gänsicke |first3=Boris T. |last4=Koester |first4=Detlev |last5=Hollands |first5=Mark A. |last6=Gentile Fusillo |first6=Nicola Pietro |last7=Cunningham |first7=Tim |last8=Apps |first8=Kevin |date=2022-12-01 |title=Spectral analysis of ultra-cool white dwarfs polluted by planetary debris |journal=Monthly Notices of the Royal Astronomical Society |volume=517 |issue=3 |pages=4557–4574 |arxiv=2206.05258 |bibcode=2022MNRAS.517.4557E |doi=10.1093/mnras/stac2908 |doi-access=free |issn=0035-8711}}</ref>
<ref name="Gaia EDR3wd">{{Cite journal |last1=Gentile Fusillo |first1=N. P. |last2=Tremblay |first2=P. -E. |last3=Cukanovaite |first3=E. |last4=Vorontseva |first4=A. |last5=Lallement |first5=R. |last6=Hollands |first6=M. |last7=Gänsicke |first7=B. T. |last8=Burdge |first8=K. B. |last9=McCleery |first9=J. |last10=Jordan |first10=S. |date=2021-12-01 |title=A catalogue of white dwarfs in Gaia EDR3 |journal=Monthly Notices of the Royal Astronomical Society |volume=508 |issue=3 |pages=3877–3896 |arxiv=2106.07669 |bibcode=2021MNRAS.508.3877G |doi=10.1093/mnras/stab2672 |doi-access=free |issn=0035-8711}}</ref>
<ref name="blr01">{{cite journal |last1=Bergeron |first1=P. |last2=Leggett |first2=S. K. |last3=Ruiz |first3=María Teresa |date=April 2001|title=Photometric and Spectroscopic Analysis of Cool White Dwarfs with Trigonometric Parallax Measurements |journal=Astrophysical Journal Supplement Series |volume=133 |issue=2 |pages=413–449 |doi=10.1086/320356 | arxiv=astro-ph/0011286 |bibcode=2001ApJS..133..413B |s2cid=15511301 |doi-access=free }}</ref>
</references>
{{whitedwarf-star-stub}} [[Category:White dwarfs]] [[Category:Hydra (constellation)]]