Editing Sirius (section)

=== Sirius A ===
[[File:Relative sizes of the Alpha Centauri components and other objects (artist’s impression).tif|thumb|Relative sizes of [[List of nearest stars and brown dwarfs|local stars]], incl. Sirius, the Sun and Jupiter (artist’s impression)]]
[[File:Sirius A-Sun comparison2.png|thumb|Comparison of Sirius&nbsp;A and the Sun, to scale and relative surface brightness]]

Sirius&nbsp;A, also known as the Dog Star, has a mass of {{Solar mass|2.063}}.<ref name=bond/><ref name="Liebert2005"/><ref name="Braganca2003"/> The radius of this star has been measured by an [[astronomical interferometer]], giving an estimated angular diameter of 5.936±0.016&nbsp;[[milliarcsecond|mas]]. The [[stellar rotation|projected rotational velocity]] is a relatively low 16&nbsp;km/s,<ref name="Royer2002"/> which does not produce any significant flattening of its disk.<ref name="Kervella2003"/> This is at marked variance with the similar-sized [[Vega]], which rotates at a much faster 274&nbsp;km/s and bulges prominently around its equator.<ref name="Aufdenberg2006"/> A weak [[magnetic field]] has been detected on the surface of Sirius&nbsp;A.<ref name=petit2011/>

Stellar models suggest that the star formed during the collapsing of a [[molecular cloud]] and that, after 10&nbsp;million years, its internal energy generation was derived entirely from nuclear reactions. The core became [[convection zone|convective]] and used the [[CNO cycle]] for energy generation.<ref name="Kervella2003"/> It is calculated that Sirius&nbsp;A will have completely exhausted the store of hydrogen at its core within a billion ({{10^|9}})&nbsp;years of its formation, and will then evolve away from the main sequence.<ref>{{cite AV media |title=Stellar mass and lifetime on the main sequence |medium=diagram |website=NASA's cosmos |url=https://ase.tufts.edu/cosmos/view_picture.asp?id=1406 |access-date=8 February 2021 }}</ref> It will pass through a [[red giant]] stage and eventually become a white dwarf.{{sfn|Brosch|2008|p=198}}

Sirius&nbsp;A is classed as a type {{nobr|[[Am star]],}} because the spectrum shows deep metallic [[absorption line]]s,<ref name=auriere2010/> indicating an enhancement of its surface layers in elements heavier than helium, such as iron.<ref name="SolStation"/><ref name="Kervella2003"/> The spectral type has been reported as {{nobr|A0mA1 Va,}} which indicates that it would be classified as A1 from hydrogen and helium lines, but A0 from the metallic lines that cause it to be grouped with the Am&nbsp;stars.<ref name=nstars/> When compared to the Sun, the proportion of iron in the atmosphere of Sirius&nbsp;A relative to hydrogen is given by <math chem>\textstyle\ \left[\frac{\ce{Fe}}{\ce{H}}\right] = 0.5\ ,</math><ref name="Qiu2001"/> meaning iron is 316% as abundant as in the Sun's atmosphere. The high surface content of metallic elements is unlikely to be true of the entire star; rather the iron-peak and heavy metals are radiatively levitated towards the surface.<ref name="Kervella2003"/>