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Surface gravity
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Orbital speed
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Escape speed
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Virial theorum for bound orbits
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Clicker question
A. 4.4B. 5.4C. 3.9D. 3.4E. Not enough information to answer.
In cgs units, the log of sun’s gravity is log gsun=4.4. What is log g for a star with with mass M=10 Msun and radius R=10 Rsun?
Clicker question
A. 62 km/sB. 620 km/sC. 6200 km/sD. 200 km/sE. 2000 km/s
The sun has an escape speed Ve,s=620 km/s. What is the escape speed from a star with mass M=10 Msun and radius R=10 Rsun?
Clicker question
A. 3 km/sB. 30 km/sC. 300 km/sD. 90 km/sE. 900 km/s
The earth at 1 au from the sun has an orbital speed Ve=30 km/s. What is the orbital speed of a planet orbiting a star of mass M=10 Msun at a distance of d=0.1 au?
Inferring stellar motion
• Across the sky– “Proper motion”
• Toward/away from us– “Radial velocity”– Doppler shift
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Proper Motion & Tranverse Speed
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Doppler shift and Radial velocity
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observer
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