Blanketing effect

The blanketing effect (also referred to as line blanketing or the line-blanketing effect) is the enhancement of the red or infrared regions of a stellar spectrum at the expense of the other regions, with an overall diminishing effect on the whole spectrum. The term originates in a 1928 article by astrophysicist Edward Arthur Milne, where it was used to describe the effects that the astronomical metals in a star's outer regions had on that star's spectrum.{{cite journal|bibcode=1928Obs....51...88M|volume=51|pages=88–96|title=The total absorption in the Sun's reversing layer|journal=The Observatory|author=Milne, E. A.|year=1928}} The name arose because the absorption lines act as a "blanket", causing the continuum temperature of the spectrum to rise over what it would have been if these lines were not present.{{cite journal|journal=Monthly Notices of the Royal Astronomical Society|pages=278–296|title=On the existence of subdwarfs in the (M_bol, log T_e)-diagram|bibcode=1959MNRAS.119..278S|last1=Sandage |first1=Allan R.|last2=Eggen|first2=Olin J.|year=1959|volume=119|issue=3|doi=10.1093/mnras/119.3.278 |doi-access=free}}

Astronomical metals, which produce most of a star's spectral absorption lines, absorb a fraction of the star's radiant energy (a phenomenon known as the blocking effect) and then re-emit it at a lower frequency as part of the backwarming effect.{{cite book|publisher=Pachart Publishing House|title=Multicolor Stellar Photometry|year=1992|location=Tucson|author=Straižys, Vytautas}} The combination of both these effects results in the position of stars in a color-color diagram to shift towards redder areas as the proportion of metals in them increases. The blanketing effect is thus highly dependent on the metallicity index of a star, which indicates the fraction of elements other than hydrogen and helium that compose it.