Lecture16

Lecture16 - Previous Lecture We live in the Milky Way...

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Previous Lecture We live in the Milky Way galaxy Herschel: first attempt to measure using star counts assumed a uniform stellar luminosity Kapteyn: added stellar luminosity function to analysis did not know about dust absorption MW structure thin disk, ~50 Kpc diameter, ~200 pc thick spheroidal bulge, ~6 Kpc diameter spherical halo ~60 Kpc diameter Cepheid and RR Lyrae variable stars period – luminosity relation
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The Interstellar Medium Two components: gas and dust About 10% of Galaxy’s total mass Gas comes in several forms Clouds HII Regions HI Clouds Giant Molecular Clouds Intercloud Medium Warm Hot
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H II regions aka “emission nebulae” glowing clouds of ionized hydrogen surrounding & heated by hot O or B star T ~ 10,000 K density: 10 – 100 ions/cm 3 size: ~ 10 pc mass: ~ 10 4 M sun very conspicuous, but less than 1% of ISM
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H I Clouds neutral hydrogen temperature: ~ 100 K density: 1–10 atoms/cm 3 size: ~ 5 pc mass: ~ 50 M sun more than half the ISM mass is in H I clouds emit 21 cm radio waves from hydrogen spin flip
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This note was uploaded on 01/31/2012 for the course 750 110 taught by Professor Ericgawaiser during the Fall '10 term at Rutgers.

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Lecture16 - Previous Lecture We live in the Milky Way...

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