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.