42 Draconis

{{Short description|Star in the constellation Draco}} {{Starbox begin | name = 42 Draconis / Fafnir }} {{Starbox image | image = {{Location mark |image=Draco constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=42 Draconis |x=243|y=637 }} | caption = Location of 42 Draconis (circled in red) }} {{Starbox observe | epoch = J2000 | constell = [[Draco (constellation)|Draco]]<ref name=XHIP/> | ra = {{RA|18|25|59.13696}}<ref name=DR3/> | dec = {{DEC|+65|33|48.5313}}<ref name=DR3/> | appmag_v = 4.82<ref name=Ligi2016/> }} {{Starbox character | class = K1.5 III<ref name=Ligi2016/> | r-i = | v-r = | b-v = 1.18<ref name=XHIP/> | u-b = | variable = }} {{Starbox astrometry | radial_v = {{val|31.75|0.12}}<ref name=DR3/> | prop_mo_ra = +{{val|105.816}} | prop_mo_dec = {{val|-26.846}} | pm_footnote = <ref name=DR3/> | parallax = 11.056 | p_error = 0.0841 | parallax_footnote = <ref name=DR3/> | absmag_v = −0.10<ref name=XHIP/> }} {{Starbox detail | source = <ref name="Hatzes2025"/> | mass = {{val|1.07|0.01}} | radius = {{val|19.78|0.17}} | luminosity = {{val|129.26|1.77|1.05}} | gravity = {{val|1.9|0.02}} | temperature = {{val|4449|11|17|fmt=commas}} | metal_fe = {{val|-0.43|0.01}} | rotation = {{val|554|142|ul=d}}<br/>(~479 or ~690 d) | rotational_velocity = {{val|1.76|0.45}} | age_gyr = {{val|9.49|1.76}}<ref name="Döllinger2009"/> Gyr<br/>{{val|13.19|1.92}}<ref name=Ligi2016/> }} {{Starbox catalog | names = {{odlist | name=Fafnir | BD=+65°1271 | GC=25212 | GCRV=10941 | HD=170693 | HIP=90344 | HR=6945 | PPM=20916 | SAO=17888 }} }} {{Starbox reference | Simbad = 42+Dra | NSTED = 42Dra | EPE = 42+Dra }} {{Starbox end}}

'''42 Draconis''' (abbreviated '''42 Dra'''), formally named '''Fafnir''' ({{IPAc-en|ˈ|f|ɑː|v|n|ər}} or {{IPAc-en|ˈ|f|ɑː|f|n|ɪər}}),<ref>{{MW|Fafnir}}</ref><ref name="IAU-CSN">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}}</ref> is a 5th [[apparent magnitude|magnitude]] [[K-type star|K-type]] [[giant star|giant]] [[star]] located approximately 295 [[light-year]]s away in the [[constellation]] of [[Draco (constellation)|Draco]]. An [[exoplanet]] (designated 42 Draconis b, later named Orbitar) was once thought to be orbiting the star, but its existence has since been refuted.<ref name="Hatzes2025"/>

Of [[spectral classification|spectral type]] K1.5III, the star has a mass similar to the [[Sun]] but with a radius 22 times greater. It is a metal-poor star with metallicity as low as 35% that of the Sun and its age is 9.49 billion years. It is the southern [[pole star]] of [[Venus]].<ref>{{Cite web |title="Is Polaris the north star for all the other planets just like it is for Earth?" {{!}} Planetarium {{!}} University of Southern Maine |url=https://usm.maine.edu/planet/polaris-north-star-all-other-planets-just-it-earth |url-status=dead |archive-url=https://web.archive.org/web/20221103123242/https://usm.maine.edu/planet/polaris-north-star-all-other-planets-just-it-earth |archive-date=2022-11-03 |access-date=2022-07-12 |website=usm.maine.edu}}</ref>

A 2019 study using [[Gaia DR2]] data found a companion star to 42 Draconis, about half the Sun's mass, at a separation of 24 [[arcsecond]]s, corresponding to 2220 [[astronomical unit|AU]].<ref name="Mugrauer2019"/>

== Nomenclature == [[File:42 Draconis.jpg|thumb|left|280px|42 Draconis in optical light]] 42 Draconis is the star's [[Flamsteed designation]]. Following its discovery the planet was designated 42 Draconis b. In July 2014 the [[International Astronomical Union]] launched [[NameExoWorlds]], a process for giving proper names to certain exoplanets and their host stars.<ref>[http://www.iau.org/news/pressreleases/detail/iau1404/ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars]. IAU.org. 9 July 2014</ref> The process involved public nomination and voting for the new names.<ref>{{Cite web |url=http://nameexoworlds.iau.org/process |title=NameExoWorlds The Process |access-date=2015-09-05 |archive-date=2015-08-15 |archive-url=https://web.archive.org/web/20150815025117/http://www.nameexoworlds.iau.org/process |url-status=dead }}</ref> In December 2015, the IAU announced the winning names were Fafnir for this star and Orbitar for its planet.<ref>[http://www.iau.org/news/pressreleases/detail/iau1514/ Final Results of NameExoWorlds Public Vote Released], International Astronomical Union, 15 December 2015.</ref>

The winning names were submitted by the Brevard Astronomical Society of [[Brevard County, Florida]], [[United States]].<ref>[http://www.brevardastro.org/ Website]</ref> [[Fafnir]] was a [[Norse mythology|Norse mythological]] [[Dwarf (folklore)|dwarf]] who turned into a [[Germanic dragon]]. It is also the name of a fictional planet in [[Larry Niven]]'s [[Known Space]] universe of similar description, ('Draco' is [[Latin]] for 'dragon'); Orbitar is a contrived word paying homage to the space launch and orbital operations of [[NASA]].<ref>{{Cite web |url=http://nameexoworlds.iau.org/names |title=NameExoWorlds The Approved Names |access-date=2015-12-18 |archive-date=2018-02-01 |archive-url=https://web.archive.org/web/20180201043609/http://nameexoworlds.iau.org/names |url-status=dead }}</ref>

In 2016, the IAU organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|access-date=22 May 2016}}</ref> to catalog and standardize proper names for stars. In its first bulletin of July 2016,<ref name="WGSN1">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |access-date=28 July 2016}}</ref> the WGSN explicitly recognized the names of exoplanets and their host stars approved by the Executive Committee Working Group Public Naming of Planets and Planetary Satellites, including the names of stars adopted during the 2015 NameExoWorlds campaign. This star is now so entered in the IAU Catalog of Star Names.<ref name="IAU-CSN"/>

== Disproven planet == {{redirect|Orbitar|the video game weapon|Kid Icarus: Uprising}} The discovery of 42 Draconis b (later named Orbitar) by the [[radial velocity method]] was announced in 2009. It was thought to be a [[super-Jupiter]], with a [[minimum mass]] 4 times that of Jupiter, an orbital period of 479 days, and an [[orbital eccentricity|eccentricity]] of 0.38.<ref name="Döllinger2009"/> However, the existence of this planet was questioned in a 2021 study by the same authors, which found that more recent radial velocity measurements were inconsistent with the proposed planetary orbit.<ref name="DöllingerHartmann2021"/> With further observations, by 2025 the planet hypothesis could be conclusively ruled out.<ref name="Hatzes2025"/> The star appears to have intrinsic radial velocity variations that mimic a planetary companion, as observed in other giant stars such as [[Gamma Draconis]] and [[Aldebaran]].<ref name="Hatzes2025"/>

In a 2024 study, 42 Draconis b was listed as one of several doubtful planets around giant stars, along with other named planets around [[14 Andromedae]] and [[41 Lyncis]].<ref name="Spaeth2024"/> With the 2025 refutation, it is now the second named exoplanet to be conclusively disproven, after [[Fomalhaut b]] (Dagon) in 2020.<ref name="Gaspar2020"/>

== See also == * [[HD 139357]] * [[Iota Draconis]] * [[Lists of exoplanets]]

== References == {{Reflist|refs=

<ref name="Döllinger2009">{{cite journal | title=Planetary companion candidates around the K giant stars 42 Draconis and HD 139 357 | url=http://www.aanda.org/articles/aa/full_html/2009/21/aa10837-08/aa10837-08.html | last1=Döllinger | first1=M. P. | last2=Hatzes | first2=A. P. | last3=Pasquini | first3=L. | last4=Guenther | first4=E. W. | last5=Hartmann | first5=M. | last6=Girardi | first6=L. | display-authors=1 | journal=Astronomy and Astrophysics | volume=499 | issue=3 | pages=935–942 | year=2009 | arxiv=0903.3593 | bibcode=2009A&A...499..935D | doi=10.1051/0004-6361/200810837 | s2cid=15677079 }}</ref>

<ref name=Ligi2016>{{citation | title=Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters | last1=Ligi | first1=R. | last2=Creevey | first2=O. | last3=Mourard | first3=D. | last4=Crida | first4=A. | last5=Lagrange | first5=A.-M. | last6=Nardetto | first6=N. | last7=Perraut | first7=K. | last8=Schultheis | first8=M. | last9=Tallon-Bosc | first9=I. | last10=ten Brummelaar | first10=T. | journal=Astronomy & Astrophysics | display-authors=1 | volume=586 | id=A94 | pages=23 | date=February 2016 | postscript=. | doi=10.1051/0004-6361/201527054 | bibcode=2016A&A...586A..94L |arxiv = 1511.03197 | s2cid=15941645 }}</ref>

<ref name="Mugrauer2019">{{cite journal |last1=Mugrauer |first1=M. |date=December 2019 |title=Search for stellar companions of exoplanet host stars by exploring the second ESA-Gaia data release |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=490 |issue=4 |pages=5088–5102 |doi=10.1093/mnras/stz2673 |doi-access=free |bibcode=2019MNRAS.490.5088M}}</ref>

<ref name="Gaspar2020">{{cite journal |last1=Gáspár |first1=András |last2=Rieke |first2=George H. |title=New HST data and modeling reveal a massive planetesimal collision around Fomalhaut |date=April 20, 2020 |journal=[[PNAS]] |volume=117 |issue=18 |pages=9712–9722 |doi=10.1073/pnas.1912506117 |pmid=32312810 |pmc=7211925 |arxiv=2004.08736 |bibcode=2020PNAS..117.9712G |doi-access=free }}</ref>

<ref name="DöllingerHartmann2021">{{cite journal |last1=Döllinger |first1=M. P. |last2=Hartmann |first2=M. |date=September 2021 |title=A Sanity Check for Planets around Evolved Stars |journal=[[The Astrophysical Journal Supplement Series]] |volume=256 |issue=1 |page=10 |doi=10.3847/1538-4365/ac081a |doi-access=free |bibcode=2021ApJS..256...10D |s2cid=237369556}}</ref>

<ref name="Spaeth2024">{{cite journal |last1=Spaeth |first1=Dane |last2=Reffert |first2=Sabine |display-authors=etal |date=September 2024 |title=Non-radial oscillations mimicking a brown dwarf orbiting the cluster giant NGC 4349 No. 127 |journal=[[Astronomy & Astrophysics]] |volume=689 |issue= |pages=A91 |doi=10.1051/0004-6361/202450163 |arxiv=2407.21583 |bibcode=2024A&A...689A..91S}}</ref>

<ref name="Hatzes2025">{{cite journal |last1=Hatzes |first1=Artie P. |last2=Perdelwitz |first2=Volker |display-authors=etal |date=May 2025 |title=No Planet around the K Giant Star 42 Draconis |journal=[[Astronomy & Astrophysics]] |volume= 699|issue= |pages= A260|doi= 10.1051/0004-6361/202554197|arxiv=2505.05260 |bibcode=2025A&A...699A.260H }}</ref>

}}

==External links== * {{cite encyclopedia |url=http://exoplanet.eu/star.php?st=42+Dra |archive-url=https://web.archive.org/web/20090819031259/http://exoplanet.eu/star.php?st=42+Dra |url-status=dead |archive-date=August 19, 2009 |title=Notes for star 42 Dra |author=Jean Schneider |year=2011 |encyclopedia=[[Extrasolar Planets Encyclopaedia]] |access-date=3 October 2011}}

[[Category:K-type giants]] [[Category:Flamsteed objects|Draconis, 42]] [[Category:Henry Draper Catalogue objects|170693]] [[Category:Hipparcos objects|090344]] [[Category:Bright Star Catalogue objects|6945]] [[Category:Draco (constellation)]] [[Category:Hypothetical planetary systems]] [[Category:Durchmusterung objects|BD+65 1271]] [[Category:Stars with proper names|Fafnir]] [[Category:Fáfnir]] [[Category:Southern pole stars]]