Editing Proxima Centauri (section)

==General characteristics==
[[File:Relative sizes of the Alpha Centauri components and other objects (artist’s impression).tif|thumb|Relative sizes and colour of the Alpha Centauri A, B and C (Proxima) and other [[List of nearest stars and brown dwarfs|local stars]], incl. the Sun and [[Jupiter]] for comparison (artist’s impression)]][[File:ProxCenLightCurve.png|thumb|left|Three [[Photometric_system#Photometric_letters|visual band]] [[light curves]] for Proxima Centauri are shown, illustrating the variability of Proxima. Plot A shows a superflare which dramatically increased the star's brightness for a few minutes. Plot B shows the relative brightness variation over the course of the star's 83 day rotation period. Plot C shows variation over a 6.8 year period, which may be the length of the star's magnetic activity period. Adapted from Howard ''et al.'' (2018)<ref name=howard/> and Mascareño ''et al.'' (2016)<ref name="Masc2016"/>]]
Proxima Centauri is a [[red dwarf]], because it belongs to the [[main sequence]] on the [[Hertzsprung–Russell diagram]] and is of [[Stellar classification|spectral class M5.5]]. The M5.5 class means that it falls in the low-mass end of M-type [[dwarf star]]s,<ref name="ESO2003">{{cite news | last1=Kervella | first1=Pierre | last2=Thevenin | first2=Frederic |title=A family portrait of the Alpha Centauri system: VLT interferometer studies the nearest stars |publisher=European Southern Observatory |date=March 15, 2003 |url=https://www.eso.org/public/news/eso0307/ |access-date=May 10, 2016}}</ref> with its hue shifted toward red-yellow<ref>{{cite book | title=Future Spacecraft Propulsion Systems: Enabling Technologies for Space Exploration | first1=Paul A. | last1=Czysz | first2=Claudio | last2=Bruno | date=2009 | page=36 | publisher=Springer Berlin Heidelberg | isbn=9783540888147 | url=https://books.google.com/books?id=aI9QhDA4AVwC&pg=PA376 }}</ref> by an [[effective temperature]] of {{val|3000|u=K|fmt=commas|p=~}}.<ref name="aaa397" /> Its [[absolute visual magnitude]], or its visual magnitude as viewed from a distance of {{convert|10|pc|ly|0|abbr=out}}, is 15.5.<ref name="abs_mag">{{cite journal |last1=Kamper |first1=K. W. | last2=Wesselink | first2=A. J. |title=Alpha and Proxima Centauri |journal=Astronomical Journal |date=1978 |volume=83 |pages=1653–1659 |doi=10.1086/112378 |bibcode=1978AJ.....83.1653K|doi-access=free }}</ref> Its total luminosity over all [[wavelength]]s is only 0.16% that of the Sun,<ref name="Pineda2021">{{cite journal
 | title=The M-dwarf Ultraviolet Spectroscopic Sample. I. Determining Stellar Parameters for Field Stars
 | last1=Pineda | first1=J. Sebastian | last2=Youngblood | first2=Allison
 | last3=France | first3=Kevin 
 | journal=The Astrophysical Journal
 | volume=918 | issue=1 | id=40 | pages=23 | date=September 2021
 | doi=10.3847/1538-4357/ac0aea | arxiv=2106.07656
 | bibcode=2021ApJ...918...40P  | s2cid=235435757 | doi-access=free }}</ref> although when observed in the wavelengths of [[visible light]] to which the eye is most sensitive, it is only 0.0056% as luminous as the Sun.<ref>{{cite book | last1=Binney | first1=James | first2=Scott | last2=Tremaine |title=Galactic dynamics |publisher=Princeton University Press |location=Princeton, New Jersey |date=1987 |isbn=978-0-691-08445-9 |page=8}}</ref> More than 85% of its radiated power is at [[infrared]] wavelengths.<ref>{{cite journal |last=Leggett |first=S. K. |title=Infrared colors of low-mass stars |journal=Astrophysical Journal Supplement Series |date=1992 |volume=82 |issue=1 |pages=351–394, 357 |doi=10.1086/191720 |bibcode=1992ApJS...82..351L}}</ref>

In 2002, [[optical interferometry]] with the [[Very Large Telescope]] (VLTI) found that the [[angular diameter]] of Proxima Centauri is {{val|1.02|0.08|ul=mas}}. Because its distance is known, the actual diameter of Proxima Centauri can be calculated to be about 1/7 that of the Sun, or 1.5 times that of [[Jupiter]]. The star's mass, estimated from stellar theory, is {{Solar mass|12.2%|link=y}}, or 129 [[Jupiter mass]]es ({{Jupiter mass}}).<ref>{{cite web |title=How Small are Small Stars Really? |first=Didier |last=Queloz |date=November 29, 2002 |publisher=European Southern Observatory |url=https://www.eso.org/public/news/eso0232/ |access-date=September 5, 2016}}</ref> The mass has been calculated directly, although with less precision, from observations of [[microlensing]] events to be {{val|0.150|0.062|0.051|u=solar mass}}.<ref name=zurlo>{{cite journal |doi=10.1093/mnras/sty1805 |bibcode=2018MNRAS.480..236Z |title=The gravitational mass of Proxima Centauri measured with SPHERE from a microlensing event |journal=Monthly Notices of the Royal Astronomical Society |volume=480 |issue=1 |pages=236 |last1=Zurlo |first1=A. |last2=Gratton |first2=R. |last3=Mesa |first3=D. |last4=Desidera |first4=S. |last5=Enia |first5=A. |last6=Sahu |first6=K. |last7=Almenara |first7=J. -M. |last8=Kervella |first8=P. |last9=Avenhaus |first9=H.|last10=Girard|first10=J. |last11=Janson |first11=M. |last12=Lagadec |first12=E. |last13=Langlois |first13=M. |last14=Milli |first14=J. |last15=Perrot |first15=C. |last16=Schlieder |first16=J. -E. |last17=Thalmann |first17=C. |last18=Vigan |first18=A. |last19=Giro |first19=E.|last20=Gluck|first20=L. |last21=Ramos |first21=J. |last22=Roux |first22=A. |year=2018 |doi-access=free |arxiv=1807.01318|s2cid=118971274 }}</ref>

Lower mass main-sequence stars have higher mean [[density]] than higher mass ones,<ref>{{cite book |first=Martin V. |last=Zombeck |date=2007 |title=Handbook of space astronomy and astrophysics |url=https://archive.org/details/handbookspaceast00zomb_781 |url-access=limited |publisher=Cambridge University Press |edition=Third |pages=[https://archive.org/details/handbookspaceast00zomb_781/page/n122 109] |location=Cambridge, UK |isbn=978-0-521-78242-5}}</ref> and Proxima Centauri is no exception: it has a mean density of {{convert|47.1e3|kg/m3|g/cm3|abbr=on}}, compared with the Sun's mean density of {{convert|1.411e3|kg/m3|g/cm3|abbr=on}}.<ref group="nb" name="density">The density (''ρ'') is given by the mass divided by the volume. Relative to the Sun, therefore, the density is <math>\rho = \frac{M}{M_\odot} \cdot \left( \frac{R}{R_\odot} \right)^{-3} \cdot \rho_\odot</math> = {{nobr|0.122 · 0.154<sup>−3</sup> · (1.41{{E-sp|3}}&nbsp;kg/m<sup>3</sup>)}} = {{nobr|33.4 · (1.41{{E-sp|3}}&nbsp;kg/m<sup>3</sup>)}} = 4.71{{E-sp|4}}&nbsp;kg/m<sup>3</sup>, where <math>\rho_\odot</math> is the average solar density. See:
* {{cite web | last1=Munsell | first1=Kirk | last2=Smith | first2=Harman | last3=Davis | first3=Phil | last4=Harvey | first4=Samantha |date=June 11, 2008 |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |title=Sun: facts & figures |work=Solar system exploration |publisher=NASA |access-date=July 12, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080102034758/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |archive-date=January 2, 2008}}
* {{cite book |last1=Bergman |first1=Marcel W. |last2=Clark |first2=T. Alan |last3=Wilson |first3=William J. F. |date=2007 |pages=220–221 |title=Observing projects using Starry Night Enthusiast |edition=8th |publisher=Macmillan |isbn=978-1-4292-0074-5}}</ref> The measured [[surface gravity]] of Proxima Centauri, given as the [[Base 10 logarithm|base-10 logarithm]] of the [[Gravitational acceleration|acceleration]] in [[cgs unit|units of cgs]], is 5.20.<ref name="aaa397" /> This is 162 times the [[Standard gravity|surface gravity]] on Earth.<ref group="nb" name="gravity">The standard surface gravity on the Earth is {{val|980.665|u=cm/s<sup>2</sup>}}, for a "log&nbsp;''g''" value of 2.992. The difference in logarithms is 5.20 − 2.99 = 2.21, yielding a multiplier of 10<sup>2.21</sup> = 162. For the Earth's gravity, see: {{cite book | page=29 | url=https://physics.nist.gov/cuu/pdf/sp330.pdf | title=The International System of Units (SI) | editor1-first=Barry N. | editor1-last=Taylor | year=2001 | publisher=United States Department of Commerce: National Institute of Standards and Technology | access-date=2012-03-08 }}</ref>

A 1998 study of [[photometry (astronomy)|photometric]] variations indicates that Proxima Centauri completes a full rotation once every 83.5 days.<ref name=McArthur1998>{{cite journal | last1=Benedict | first1=G. F. |title=Photometry of Proxima Centauri and Barnard's Star using Hubble Space Telescope fine guidance sensor 3: a search for periodic variations |journal=The Astronomical Journal |date=1998 |volume=116 |issue=1 |pages=429–439 |doi=10.1086/300420 |bibcode=1998AJ....116..429B |arxiv=astro-ph/9806276 | last2=McArthur | first2=B. |last3=Nelan |first3=E. |last4=Story |first4=D. |last5=Whipple |first5=A. L. |last6=Shelus |first6=P. J. |last7=Jefferys |first7=W. H. |last8=Hemenway |first8=P. D. |last9=Franz |first9=Otto G.|s2cid=15880053 }}</ref> A subsequent [[time series]] analysis of [[Chromosphere|chromospheric]] indicators in 2002 suggests a longer rotation period of {{val|116.6|0.7}}&nbsp;days.<ref>{{cite journal |title=Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators |last1=Suárez Mascareño |first1=A. |last2=Rebolo |first2=R. |last3=González Hernández |first3=J. I. |last4=Esposito |first4=M. |journal=Monthly Notices of the Royal Astronomical Society |volume=452 |issue=3 |pages=2745–2756 |date=September 2015 |doi=10.1093/mnras/stv1441 |doi-access=free |bibcode=2015MNRAS.452.2745S |arxiv=1506.08039|s2cid=119181646 }}</ref> Later observations of the star's magnetic field subsequently revealed that the star rotates with a period of {{val|89.8|4}}&nbsp;days, consistent with a measurement of {{val|92.1|4.2|3.5}}&nbsp;days from radial velocity observations.<ref name="Klein2020"/><ref name="ArtigauCadieux2022"/>