Ast 105 1st Edition Lecture 11 Outline of Last LectureI. Star Birtha. Composition of Interstellar Medium II. Interstellar ReddeningIII. 2.6 mm Radiation IV. Jean’s Instability a. Protostarsb. PMS stars c. Main sequence star V. Brown DwarfVI. Upper LimitVII. Main sequence lifetimesVIII. Red DwarfsOutline of Current LectureI. Giantsa. 6 steps to form II. Helium Fusiona. Helium flashIII. Variable Starsa. Instability strip b. Low-mass starsc. High-mass starsd. CeiphadsGiants- Main sequence stars with masses greater than 40% the mass of our sun became giants when core hydrogen has been converted to helium - 6 steps1. core is completely helium2. core fusion stops 3. gravity compresses the stara. no photon pressure to counter the gravity forces 4. hydrogen in shell begins to fuse into helium 5. photon pressure dominates gravity and pushes the outer regions of the star away 6. outer regions, due to expansion, coolThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. surface temp. drops to 3000K ~ 6000KRed Giant is formed- in about 5 billion years, our sun will become a red giant Helium Fusion - as the temp. in the core rises, it will eventually reach about 100 million Kelvin, now the helium can fuse some of the carbon is fused- fusion of helium appears suddenly this event is called a helium flash- helium fusion will occur for a few billion years during this time, we have both helium core fusion and hydrogen shell fusion Variable Stars- once the helium fusion in the core begins, the star is now post-main sequence- stars leave the main sequence line and track, toward the upper right - during this, a star can become unstable and pulsate- this region is called the instability strip when stars are in this region they will pulsate (brightness will vary) Low Mass Stars- post helium flash - called RR Lyrae variables- have pulsation periods less than one day High Mass Stars- called Cepheid variables or just Cepheid’s- Cepheid’s pulsate by a rapid brightening followed by a gradual dimming During this change in brightness the stars surface expands and contracts- Used to compute distances “standard candle” we clock the pulsation period- two Cepheid types Type 1: metal rich Type 2: metal poor- Look at spectral analysis of light- Stable pulsation period we can determine the distance to the
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