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Alpha Centauri
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===== Alpha Centauri B ===== {{hatnote group| {{about-distinguish|Ξ± Centauri B, also known as Toliman|Beta Centauri{{!}}Ξ² Centauri|HD 102964{{!}}B Centauri|HD 129116{{!}}b Centauri|section=yes}}{{other uses|Toliman (disambiguation)}} }} '''Alpha Centauri B''', also known as '''Toliman''', is the secondary star of the binary system. It is a main-sequence star of spectral type K1-V, making it more an orange colour than Alpha Centauri A;<ref name="csiro"/> it has around 90% of the mass of the Sun and a 14% smaller diameter. Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the [[X-ray]] band.<ref name="Xrays"/> Its [[light curve]] varies on a short time scale, and there has been at least one observed [[Flare star|flare]].<ref name="Xrays">{{cite journal|last1=Robrade|first1=J.|last2=Schmitt|first2=J. H. M. M.|last3=Favata|first3=F. |year=2005|title=X-rays from Ξ± Centauri β The darkening of the solar twin|journal=Astronomy and Astrophysics|volume=442|issue=1|pages=315β321|bibcode=2005A&A...442..315R|doi=10.1051/0004-6361:20053314 |arxiv=astro-ph/0508260|s2cid=119120}}</ref> It is more magnetically active than Alpha Centauri A, showing a cycle of {{Val|8.2|0.2|u=yr}} compared to 11 years for the Sun, and has about half the minimum-to-peak variation in coronal luminosity of the Sun.<ref name="Ayres2014"/> This cycle was recently re-estimated based on more than 20 years of high-resolution spectroscopic observations of the CaIIH&K lines showing a cycle of {{Val|7.8|0.2|u=yr}}.<ref name="Cretignier2024">{{cite journal|last1=Cretignier|first1=M.|last2=Hara|first2=N.|last3=Pietrow|first3=A.G.M.|year=2024|title=Stellar surface information from the Ca II H&K lines - II. Defining better activity proxies|journal=Monthly Notices of the Royal Astronomical Society|volume=535|issue=1|pages=2562β2584|bibcode=2024MNRAS.535.2562C|doi= 10.1093/mnras/stae2508 |doi-access=free |arxiv=astro-ph/0508260|s2cid=119120}}</ref> Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than [[Mimosa (star)|Mimosa]].<ref name="IAU-LSN"/>
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