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click:vHQTA(QwLHlb);"><a class="aJHbb hDrhEe HlqNPb" jsname="QwLHlb" role="link" tabindex="0" data-navtype="1" href="/a/uis.edu/john-c-martin-s-homepage/research/eta-carinae/problems-with-the-stis-ccd-err-array" data-url="/a/uis.edu/john-c-martin-s-homepage/research/eta-carinae/problems-with-the-stis-ccd-err-array" data-type="1" data-level="3">Problems with the STIS CCD ERR Array</a></div></div></li><li jsname="ibnC6b" data-nav-level="3"><div class="PsKE7e r8s4j-c5RTEf IKA38e baH5ib oNsfjf"><div class="I35ICb" jsaction="keydown:mPuKz(QwLHlb); click:vHQTA(QwLHlb);"><a class="aJHbb hDrhEe HlqNPb" jsname="QwLHlb" role="link" tabindex="0" data-navtype="1" href="/a/uis.edu/john-c-martin-s-homepage/research/eta-carinae/revision-history-for-eta-car-database" data-url="/a/uis.edu/john-c-martin-s-homepage/research/eta-carinae/revision-history-for-eta-car-database" data-type="1" data-level="3">Revision History For Eta Car Database</a></div></div></li><li jsname="ibnC6b" data-nav-level="3"><div class="PsKE7e r8s4j-c5RTEf IKA38e baH5ib oNsfjf"><div class="I35ICb" jsaction="keydown:mPuKz(QwLHlb); click:vHQTA(QwLHlb);"><a class="aJHbb hDrhEe HlqNPb" jsname="QwLHlb" role="link" tabindex="0" data-navtype="1" href="/a/uis.edu/john-c-martin-s-homepage/research/eta-carinae/sequencing-of-stis-observations" data-url="/a/uis.edu/john-c-martin-s-homepage/research/eta-carinae/sequencing-of-stis-observations" data-type="1" data-level="3">Sequencing of STIS Observations</a></div></div></li></ul></div></li><li jsname="ibnC6b" data-nav-level="2"><div class="PsKE7e r8s4j-ibL1re IKA38e baH5ib oNsfjf"><div class="I35ICb" jsaction="keydown:mPuKz(QwLHlb); click:vHQTA(QwLHlb);"><a class="aJHbb hDrhEe HlqNPb" jsname="QwLHlb" role="link" tabindex="0" data-navtype="1" href="/a/uis.edu/john-c-martin-s-homepage/research/abundance-analysis-and-kinematics-of-high-galactic-latitude-b-stars" data-url="/a/uis.edu/john-c-martin-s-homepage/research/abundance-analysis-and-kinematics-of-high-galactic-latitude-b-stars" data-type="1" data-level="2">High Galactic Latitude B Stars</a></div></div></li><li jsname="ibnC6b" data-nav-level="2"><div class="PsKE7e r8s4j-ibL1re IKA38e baH5ib oNsfjf"><div class="I35ICb" jsaction="keydown:mPuKz(QwLHlb); 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click:vHQTA(QwLHlb);"><a class="aJHbb hDrhEe HlqNPb" jsname="QwLHlb" role="link" tabindex="0" data-navtype="1" aria-selected="true" href="/a/uis.edu/john-c-martin-s-homepage/research/rr-lyrae-kinematics/what-we-learn-from-a-star-s-metal-content" data-url="/a/uis.edu/john-c-martin-s-homepage/research/rr-lyrae-kinematics/what-we-learn-from-a-star-s-metal-content" data-type="1" data-level="3">What we learn from a star's metal content</a></div></div></li></ul></div></li><li jsname="ibnC6b" data-nav-level="2"><div class="PsKE7e r8s4j-ibL1re IKA38e baH5ib oNsfjf"><div class="I35ICb" jsaction="keydown:mPuKz(QwLHlb); click:vHQTA(QwLHlb);"><a class="aJHbb hDrhEe HlqNPb" jsname="QwLHlb" role="link" tabindex="0" data-navtype="1" href="/a/uis.edu/john-c-martin-s-homepage/research/supernova-impostors" data-url="/a/uis.edu/john-c-martin-s-homepage/research/supernova-impostors" data-type="1" data-level="2">Supernova Impostors</a></div></div></li><li jsname="ibnC6b" data-nav-level="2"><div class="PsKE7e r8s4j-ibL1re IKA38e baH5ib oNsfjf"><div class="I35ICb" jsaction="keydown:mPuKz(QwLHlb); 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This is because when the Universe began in the Big Bang the only elements produced in large abundances where hydrogen and helium (the two lightest elements). Stars produce all elements heavier than hydrogen in their cores as a result of the process of fusion by which they produce energy to shine. So all the chemical elements produced in stars are considered metals.</p><p dir="ltr" class="CDt4Ke zfr3Q">What is metallicity?</p><p dir="ltr" class="CDt4Ke zfr3Q">Metallicity is a measure of the amount of metals (as astronomers define metals) in an object of study. Most often astronomers use measurements of absorption lines in a stellar spectrum to measure the amount of iron present. Absorption lines due to hydrogen are analyzed in a similar manner to obtain the amount of hydrogen. The ratio of the amount of iron to the amount of hydrogen in the object is divided by the ratio of the amount of iron to the amount of hydrogen in our Sun to obtain a metallicity relative to the Sun. This value, denoted as [Fe/H] for that object, is plotted on a logarithmic scale. Therefore [Fe/H] = -1 denotes that the object of interest has 1/10th the amount of metals in it that the Sun has and [Fe/H] = +1 would denote 10 times the metal content of the Sun.</p><p dir="ltr" class="CDt4Ke zfr3Q">What do we learn from a star's metallicity?</p><p dir="ltr" class="CDt4Ke zfr3Q">Since all only hydrogen and helium (with very small trace amounts of Lithium and Beryllium) were produced at the beginning of the universe in the Big Bang, all of the iron and other metals in the universe have been produced in stars. At the end of a star's life, it recycles some or all of the elements it has produced in it's core over it's lifetime back into the interstellar medium. This processed material becomes mixed into clouds where the next generation of stars are born. So each subsequent generation of stars is enriched with the metals produced in previous generations. Because of this we can infer in a closed system, like our galaxy, that stars with a lower metal content (smaller [Fe/H]) are older than stars with a higher metal content (larger [Fe/H])</p><p dir="ltr" class="CDt4Ke zfr3Q">How is this useful when studying the structure of our galaxy?</p><p dir="ltr" class="CDt4Ke zfr3Q">Different parts of our galaxy have different metal contents so we can infer their relative ages, as well as use the [Fe/H] of a star to identify which population that star belongs to. For example, the halo is the part of the galaxy with the smallest amount of metals (the stars have an average [Fe/H] of -1.6 or about 30 times less iron than the sun). For this reason we believe that the halo may be the oldest part of the galaxy. Since the distribution of metallicities in the halo has a long tail towards more negative [Fe/H] values, we believe that the halo could have been the first part of the galaxy to form. The lack of stars with small metallicities in the disk of the galaxy lead us to believe that the disk was one of the last parts of the galaxy to form.</p></div></div></div></div></div></div></div></div></div></section></div><div class="Xpil1b xgQ6eb"></div><div jscontroller="j1RDQb" jsaction="rcuQ6b:rcuQ6b;MxH79b:JdcaS;FaOgy:XuHpsb;" class="dZA9kd ynRLnc" data-last-updated-at-time="1622217903965" data-is-preview="false"><div role="button" class="U26fgb JRtysb WzwrXb I12f0b K2mXPb zXBiaf ynRLnc" jscontroller="iSvg6e" jsaction="click:cOuCgd; mousedown:UX7yZ; mouseup:lbsD7e; mouseenter:tfO1Yc; mouseleave:JywGue; focus:AHmuwe; blur:O22p3e; contextmenu:mg9Pef;touchstart:p6p2H; touchmove:FwuNnf; touchend:yfqBxc(preventDefault=true); touchcancel:JMtRjd;;keydown:I481le;" jsshadow jsname="Bg3gkf" aria-label="Site actions" aria-disabled="false" tabindex="0" aria-haspopup="true" aria-expanded="false" data-menu-corner="bottom-start" data-anchor-corner="top-start"><div class="NWlf3e MbhUzd" jsname="ksKsZd"></div><span jsslot class="MhXXcc oJeWuf"><span class="Lw7GHd snByac"><svg width="24" height="24" viewBox="0 0 24 24" focusable="false" class=" NMm5M"><path d="M11 17h2v-6h-2v6zm1-15C6.48 2 2 6.48 2 12s4.48 10 10 10 10-4.48 10-10S17.52 2 12 2zm0 18c-4.41 0-8-3.59-8-8s3.59-8 8-8 8 3.59 8 8-3.59 8-8 8zM11 9h2V7h-2v2z"/></svg></span></span><div jsname="xl07Ob" style="display:none" aria-hidden="true"><div class="JPdR6b hVNH5c" jscontroller="uY3Nvd" jsaction="IpSVtb:TvD9Pc;fEN2Ze:xzS4ub;frq95c:LNeFm;cFpp9e:J9oOtd; 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