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ps08 - Astronomy 10 Fall 2008 Homework 8 40 points total...

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Astronomy 10, Fall 2008 Homework 8 - 40 points total Due in the boxes in the basement of Campbell Hall by 5pm Tuesday, November 4 . Be sure to include your name, SID, Section Number, and GSI name on your homework, and staple it together. 1. The Life of Red Giants (9 points) After the Sun fuses hydrogen into helium, it will become a red giant star and at least for a while, fuse helium into carbon in its core. Three helium nuclei can be fused into one carbon nucleus through the so-called “triple alpha process” (because helium nuclei are also known as alpha particles and it takes three of them). (a) During its main sequence lifetime, about 10% of the Sun’s hydrogen is in the core and able to fuse into helium. How many helium atoms are thus created in the core during its main sequence life? (2 points) (b) When three helium atoms are fused into a single carbon nucleus, 1 . 2 × 10 5 erg of energy is created. How much total energy would the red giant Sun be able to produce if it fused all of its helium core into carbon? (2 points) (c) Red giants fusing helium in their cores have luminosities of about 50 L . How long could the red-giant Sun sustain that luminosity with its helium fusion? Compare your answer to the Sun’s 10 billion year main sequence lifetime. (3 points) (d) When the Sun is a red giant, it’s surface temperature will only be about 3500 K. Using the same luminosity as in part (c), what would the Sun’s radius be when it is a red giant (in solar units)? (2 points) 2. Dating the Ring (4 points) If you have attended star parties, you might have seen the Ring Nebula. This planetary nebula looks
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