lec23 - Lecture 23 Interstellar Gas Lecture 22 Purdue...

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Lecture 23 Interstellar Gas Purdue University, Astronomy 364 1 Lecture 22
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Reminder • HW05 will be ready for pick-up on March 16. • HW06 has been posted. Due: March 23. • Exam #2 on March 23 8-9 pm in Rm 203 (PHYS). Details can be found on the course web page. Lecture 22 Purdue University, Astronomy 364 2
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Dust vs Gas • Only about 1% (by mass) of the interstellar medium is in the form of dust grains. – Interstellar dust produces prominent observational effects at visible wavelengths. • About 99% of the interstellar medium is in the form of low density atomic or molecular gas. – Mostly hydrogen and helium – Heavy elements (metals) from stellar outflows (e.g., wind) and supernova explosions. – Interstellar gas may exist in different phases: cold molecular clouds, cold and warm atomic medium, or warm and hot plasma. Lecture 22 Purdue University, Astronomy 364 3
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• Absorption lines in the spectrum of stars – Narrow: little thermal or pressure broadening – Low temperature: molecular or low ionization – Different Doppler shift from stars
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lec23 - Lecture 23 Interstellar Gas Lecture 22 Purdue...

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