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Physics 55Friday, October 21, 2005
1. Doppler shift with application.2. Conservation of angular momentum.3. How star systems form, the nebular theory.
PRS Question I: Effect of Motion on Spectra?
If light source is moving toward prism with speed v:1. No change in absorption lines.2. Absorption lines are blueshifted.3. Absorption lines are redshifted4. Some lines are redshifted, some are blueshifted
PRS Question II
If thin cloud is moving away from prism with speed v:1. No change in absorption lines.2. Absorption lines are blueshifted.3. Absorption lines are redshifted4. Some lines are redshifted, some are blueshifted
PRS Question III
If thin cloud 1 is moving toward the prism with speed v and thin cloud 2 is moving away from the prism with speed v1. No change in absorption lines.2. Absorption lines are blueshifted.3. Absorption lines are redshifted4. Some lines are redshifted, some are blueshifted.
Doppler Shifts Give Rotational Information
Doppler Shift Can Identify Binary Stars
http://instruct1.cit.cornell.edu/courses/astro101/java/binary/binary.htm
Spectroscopic Binary Stars
Doppler Shift of Extrasolar Planets
MS = mass Sun ~2 x 1030 kgMJ = mass Jupiter ~ 2 x 1027 kg ~ 10-3 MS L = Sun-Jupiter distance ~ 800 x 106 kmCenter of mass of Sun-Jupiter system ~ (MJ /MS)L ~ dS ~ 742,000 km ~ 1.07 RS
Speed of Sun in its small orbit: v = 2dS / 12 y ~ 13 m/s, corresponds to incredibly small relative wavelength shifts = v/c ~ 4 10-8
Data from star 51 Pegasi (48 ly from Earth) implies presence of large planet with mass >~ 0.46 MJupiter.
Need Right Geometry For Extrasolar Planets
Transit Method to Detect Extrasolar PlanetsGives Size, Mass, Density so Kind
From Wien’s law, we can deduce surface temperature T of remote star. From apparent brightness (intensity) I measured on Earth and distance to star d, we can deduce luminosity L of star: I = L / (4 d2) .From L and Stefan-Boltzmann, we can deduce radius of star R from equation: L = (4 R2) ( T4)From radius of star and decrease in relative brightness f, we can deduce area and so radius r of occluding planet: f = ( r2) / ( R2) .
Extrasolar Planets
Overview of the Solar System
Other Parts of the Solar System: Asteroids, Kuiper Belt, Oort Cloud
Patterns of the Solar System
The Nebular Theory
Orion Nebula
Universalstarting
ingredients:75% H25% He
Gravity, Conservation of Energy, Momentum, Angular Momentum During Collapse of the Nebula
Relatively short time to produce star and planets: ~10,000,000 y
Predictions of Nebular Theory
1. Existence of disks of around stars, most stars should therefore have planets.
2. Infrared thermal emission.3. All objects rotate the same way (Doppler)4. Two kinds of planets, small rocky terrestrial
and large icy gaseous jovian planets.5. Small rocky asteroids in ecliptic plane.6. Small icy comets in ecliptic plane beyond
jovian planets.7. Small icy comets in all orientations far out into
space.8. Each solar system different in details because
of random events.
Angular Momentum With Demos1. Conservation of angular momentum holds for isolated
systems. sum of all M x V x R before = sum of all M x V x R after
1. Application to speeds at aphelion/perihelion, apogee/perigee.
2. Demos: spinning chair, collapsing model of star.