Editing Procyon (section)

==Stellar system==
Procyon is a [[binary star]] system with a bright primary component, Procyon A, having an apparent magnitude of 0.34,<ref name=aaa413/> and a faint companion, Procyon B, at magnitude 10.7.<ref name="ApJ119_2"/> The pair orbit each other with a [[orbital period|period]] of 40.84&nbsp;years along an elliptical orbit with an [[Orbital eccentricity|eccentricity]] of 0.4,<ref name=Bond/> more eccentric than [[Mercury (planet)|Mercury]]'s. The [[orbital plane|plane]] of their orbit is inclined at an angle of 31.1° to the line of sight with the Earth.<ref name=aj119_5/> The average separation of the two components is {{val|15.0|ul=AU}}, a little less than the distance between [[Uranus]] and the [[Sun]], though the eccentric orbit carries them as close as 8.9&nbsp;AU and as far as 21.0&nbsp;AU.<ref name=Kaler2011/>

===Procyon A===
The primary has a [[stellar classification]] of F5IV–V, indicating that it is a late-stage [[F-type main-sequence star]]. Procyon A is bright for its spectral class, suggesting that it is evolving into a [[subgiant]] that has nearly [[nuclear fusion|fused]] its [[hydrogen]] core into [[helium]], after which it will expand as the nuclear reactions move outside the core.<ref name=aaa413/> As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and become a red or orange color. This will probably happen within 10 to 100 million years.{{sfn|Schaaf|2008|p=168}}

The [[effective temperature]] of the [[stellar atmosphere]] is an estimated {{val|6582|ul=K|fmt=commas}}, giving Procyon A a white hue. It is 1.5 times the [[solar mass]] ({{Solar mass|link=y}}), twice the [[solar radius]] ({{Solar radius|link=y}}), and has seven times the [[Sun's luminosity]] ({{Solar luminosity|link=y}}).<ref name=Bond/><ref name=Soubiran2024/> Both the core and the envelope of this star are [[Convection zone|convective]]; the two regions being separated by a wide [[radiation zone]].<ref name=Liebert2013/>

====Oscillations====
In late June 2004, Canada's orbital [[MOST satellite telescope]] carried out a 32-day survey of Procyon&nbsp;A. The continuous optical monitoring was intended to confirm [[solar-like oscillations]] in its brightness observed from Earth and to permit [[asteroseismology]]. No [[oscillation]]s were detected and the authors concluded that the theory of stellar oscillations may need to be reconsidered.<ref name=nature430_921/> However, others argued that the non-detection was consistent with published ground-based [[radial velocity]] observations of solar-like oscillations.<ref name=nature432_7015/><ref name=aaa432/> Subsequent observations in radial velocity have confirmed that Procyon is indeed oscillating.<ref>{{cite journal |display-authors=1 |bibcode=2008ApJ...687.1180A | doi=10.1086/592040 | volume=687 | title=A Multisite Campaign to Measure Solar-like Oscillations in Procyon. I. Observations, Data Reduction, and Slow Variations | year=2008 | journal=The Astrophysical Journal | pages=1180–1190 | last1 = Arentoft | first1 = Torben | last2 = Kjeldsen | first2 = Hans | last3 = Bedding | first3 = Timothy R. | last4 = Bazot | first4 = Michaël | last5 = Christensen-Dalsgaard | first5 = Jørgen | last6 = Dall | first6 = Thomas H. | last7 = Karoff | first7 = Christoffer | last8 = Carrier | first8 = Fabien | last9 = Eggenberger | first9 = Patrick | last10 = Sosnowska | first10 = Danuta | last11 = Wittenmyer | first11 = Robert A. | last12 = Endl | first12 = Michael | last13 = Metcalfe | first13 = Travis S. | last14 = Hekker | first14 = Saskia | last15 = Reffert | first15 = Sabine | last16 = Butler | first16 = R. Paul | last17 = Bruntt | first17 = Hans | last18 = Kiss | first18 = László L. | last19 = O'Toole | first19 = Simon J. | last20 = Kambe | first20 = Eiji | last21 = Ando | first21 = Hiroyasu | last22 = Izumiura | first22 = Hideyuki | last23 = Sato | first23 = Bun'Ei | last24 = Hartmann | first24 = Michael | last25 = Hatzes | first25 = Artie | last26 = Bouchy | first26 = Francois | last27 = Mosser | first27 = Benoit | last28 = Appourchaux | first28 = Thierry | last29 = Barban | first29 = Caroline | last30 = Berthomieu | first30 = Gabrielle | last31 = Garcia | first31 = Rafael A. | last32 = Michel | first32 = Eric | last33 = Provost | first33 = Janine | last34 = Turck-Chièze | first34 = Sylvaine | last35 = Martić | first35 = Milena | last36 = Lebrun | first36 = Jean-Claude | last37 = Schmitt | first37 = Jerome | last38 = Bertaux | first38 = Jean-Loup | last39 = Bonanno | first39 = Alfio | last40 = Benatti | first40 = Serena | last41 = Claudi | first41 = Riccardo U. | last42 = Cosentino | first42 = Rosario | last43 = Leccia | first43 = Silvio | last44 = Frandsen | first44 = Søren | last45 = Brogaard | first45 = Karsten | last46 = Glowienka | first46 = Lars | last47 = Grundahl | first47 = Frank | last48 = Stempels | first48 = Eric| issue=2 | arxiv=0807.3794 | hdl = 2152/34819 | s2cid=15693672 | hdl-access = free }}</ref><ref>{{cite journal | display-authors=1 |bibcode=2010ApJ...713..935B | doi=10.1088/0004-637X/713/2/935 | volume=713 | year=2010 | journal=The Astrophysical Journal | pages=935–949 | last1 = Bedding | first1 = Timothy R. | last2 = Kjeldsen | first2 = Hans | last3 = Campante | first3 = Tiago L. | last4 = Appourchaux | first4 = Thierry | last5 = Bonanno | first5 = Alfio | last6 = Chaplin | first6 = William J. | last7 = Garcia | first7 = Rafael A. | last8 = Martić | first8 = Milena | last9 = Mosser | first9 = Benoit | last10 = Butler | first10 = R. Paul | last11 = Bruntt | first11 = Hans | last12 = Kiss | first12 = László L. | last13 = O'Toole | first13 = Simon J. | last14 = Kambe | first14 = Eiji | last15 = Ando | first15 = Hiroyasu | last16 = Izumiura | first16 = Hideyuki | last17 = Sato | first17 = Bun'Ei | last18 = Hartmann | first18 = Michael | last19 = Hatzes | first19 = Artie | last20 = Barban | first20 = Caroline | last21 = Berthomieu | first21 = Gabrielle | last22 = Michel | first22 = Eric | last23 = Provost | first23 = Janine | last24 = Turck-Chièze | first24 = Sylvaine | last25 = Lebrun | first25 = Jean-Claude | last26 = Schmitt | first26 = Jerome | last27 = Bertaux | first27 = Jean-Loup | last28 = Benatti | first28 = Serena | last29 = Claudi | first29 = Riccardo U. | last30 = Cosentino | first30 = Rosario | last31 = Leccia | first31 = Silvio | last32 = Frandsen | first32 = Søren | last33 = Brogaard | first33 = Karsten | last34 = Glowienka | first34 = Lars | last35 = Grundahl | first35 = Frank | last36 = Stempels | first36 = Eric | last37 = Arentoft | first37 = Torben | last38 = Bazot | first38 = Michaël | last39 = Christensen-Dalsgaard | first39 = Jørgen | last40 = Dall | first40 = Thomas H. | last41 = Karoff | first41 = Christoffer | last42 = Lundgreen-Nielsen | first42 = Jens | last43 = Carrier | first43 = Fabien | last44 = Eggenberger | first44 = Patrick | last45 = Sosnowska | first45 = Danuta | last46 = Wittenmyer | first46 = Robert A. | last47 = Endl | first47 = Michael | last48 = Metcalfe | first48 = Travis S. | last49 = Hekker | first49 = Saskia | last50 = Reffert | first50 = Sabine| title=A Multi-Site Campaign to Measure Solar-Like Oscillations in Procyon. Ii. Mode Frequencies | issue=2 | arxiv=1003.0052 | hdl = 2152/34818 | s2cid=118470468 | hdl-access = free }}</ref>

[[Photometry (astronomy)|Photometric]] measurements from the [[NASA]] [[Wide Field Infrared Explorer]] (WIRE) satellite from 1999 and 2000 showed evidence of granulation ([[convection]] near the surface of the [[star]]) and [[solar-like oscillations]].<ref name=apj633/> Unlike the MOST result, the variation seen in the WIRE photometry was in agreement with [[radial velocity]] measurements from the ground. Additional observations with MOST taken in 2007 were able to detect oscillations.<ref>{{Cite journal |display-authors=1 |bibcode=2011ApJ...731...94H |title=Solar-like Oscillations and Activity in Procyon: A Comparison of the 2007 MOST and Ground-based Radial Velocity Campaigns |last1= Huber |first1= Daniel |last2= Bedding |first2= Timothy R. |last3= Arentoft |first3= Torben |last4= Gruberbauer |first4= Michael |last5= Guenther |first5= David B. |last6= Houdek |first6= Günter |last7= Kallinger |first7= Thomas |last8= Kjeldsen |first8= Hans |last9= Matthews |first9= Jaymie M. |last10= Stello |first10= Dennis |last11= Weiss |first11= Werner W. |journal=The Astrophysical Journal |year=2011 |volume=731 |issue=2 |page=94 |doi=10.1088/0004-637X/731/2/94 |arxiv=1102.2894 |s2cid=56123076}}</ref>

===Procyon B===
[[File:Procyonorbitillustration.jpg|thumb|left|Orbit of Procyon B seen from above its plane]]
Like Sirius B, Procyon B is a [[white dwarf]] that was inferred from [[astrometry|astrometric]] data long before it was observed. Its existence had been postulated by German astronomer [[Friedrich Bessel]] as early as 1844, and, although its orbital elements had been calculated by his countryman [[Arthur Auwers]] in 1862 as part of his thesis,<ref name=auwers/> Procyon&nbsp;B was not visually confirmed until 1896 when [[John Martin Schaeberle]] observed it at the predicted position using the 36-inch refractor at [[Lick Observatory]].<ref name=burnham78/> It is more difficult to observe from Earth than Sirius&nbsp;B, due to a greater [[apparent magnitude]] difference and smaller angular separation from its primary.<ref name=Kaler2011/>

At {{Solar mass|0.6|link=y}}, Procyon&nbsp;B is considerably less massive than Sirius&nbsp;B; however, the peculiarities of [[degenerate matter]] ensure that it is larger than its more famous neighbor, with an estimated radius of 8,600&nbsp;km, versus 5,800&nbsp;km for Sirius&nbsp;B.<ref name="Provencal2002"/><ref name=apj497/> The radius agrees with white dwarf models that assume a carbon core.<ref name="Provencal2002"/> It has a [[stellar classification]] of DQZ,<ref name=Provencal2002/> having a helium-dominated atmosphere with traces of heavy elements. For reasons that remain unclear, the mass of Procyon&nbsp;B is unusually low for a white dwarf star of its type.<ref name=Liebert2013/> With a surface temperature of {{val|fmt=commas|7740|ul=K}}, it is also much cooler than Sirius&nbsp;B; this is a testament to its lesser mass and greater age. The mass of the progenitor star for Procyon B was about {{val|2.59|+0.22|-0.18|u=solar mass}} and it came to the end of its life some {{val|1.19|0.11}}&nbsp;billion years ago, after a main-sequence lifetime of {{val|680|170}}&nbsp;million years.<ref name=Liebert2013/>

===X-ray emission===
Attempts to detect X-ray emission from Procyon with nonimaging, [[soft X-ray]]-sensitive detectors prior to 1975 failed.<ref name=apj202/> Extensive observations of Procyon were carried out with the [[Orbiting Astronomical Observatory#OAO-3 (Copernicus)|''Copernicus'']] and [[TD-1A]] satellites in the late 1970s.<ref name=apj228_1/> The X-ray source associated with Procyon AB was observed on 1&nbsp;April 1979, with the [[Einstein Observatory]] high-resolution imager (HRI).<ref name=apj540/> The HRI X-ray pointlike source location is ~4″ south of Procyon A, on the edge of the 90% confidence error circle, indicating identification with Procyon A rather than Procyon B which was located about 5″ north of Procyon&nbsp;A (about 9″ from the X-ray source location).<ref name=apj228_1/>
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===Possibility of life===
Life is unlikely around Procyon, because the habitable zone around 2.7&nbsp;AU from the primary may not contain stable orbits, due to the white dwarf companion with a [[periastron]] of 8.9 AU.{{or|date=July 2015}} Also the white dwarf companion to Procyon would have stressed life severely during its [[red-giant]] phase. Procyon emits more of its light in the [[ultraviolet]] spectrum, which may be damaging to life. Still, life cannot be ruled out for other stars of the spectral type of Procyon, but such life would have a relatively short time to evolve and would face heavy bombardment from [[comet]]s and [[meteorite]]s as happened in the first few million years of the Earth's existence. Shortly after the phase of heavy bombardment has ended for a planet orbiting a star like Procyon the star is likely to leave the [[main sequence]] preventing further development of life.<ref name=exoplaneten/>
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