Astronomy 1021 Chapter Notes - Chapter 10: Doppler Spectroscopy, Semi-Major And Semi-Minor Axes, Methods Of Detecting Exoplanets
29 May 2018
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Astronomy 1021
Chapter 10: Other Planetary Systems
The Nature of Planets Around Other Stars
•Orbital Period and Distance
-Astrometric method- star’s orbital motion same as planet’s orbital period; Doppler method- orbital
period is time b/w peaks in the star’s velocity curve; Transit method- orbital period is time b/w
repeated transits
-Orbital period gives orbital distance (semimajor axis)
•Orbital Eccentricity
-Eccentricity- how stretched out ellipses are; planets in Solar System have low eccentricity (Circular
orbits) meaning actual distance from Sun is average distance; high eccentricity planets are close to
the star on one side of orbit and away from it on the other side
-Astrometric and Doppler give measure of eccentricity; doppler- symmetrical velocity curve means
low eccentricity, asymmetrical velocity curve means higher eccentric orbit
•Planetary Mass
-Measured by astrometric and Doppler methods; b/c for a given orbital distance, massive planet
makes star move at higher velocity around the center of mass
-Doppler shift only tells us star’s full orbital velocity when its orbit is seen edge-on; otherwise mass
calculated will be the minimum possible mass
•Planetary Size
-Measured by transits- more of the light the planet blocks, larger the star must be; Ex. Kepler 11
planetary system
•Planetary Density (mass/volume)
-Can be calculated from planet’s size (transit method) and planet’s mass (Doppler method)
•Atmospheric Composition and Temperature
-Eclipses give info on temp; planets emit infrared light, system’s infrared brightness drops when
planet goes behind it, the extend of the drop tell us how much infrared the planet emits; this plus
planet’s radius (measured by transits) gives temperature
-Find atmospheric composition by comparing spectra of system with planet in front or behind star,
and other times, this gives spectra lines, can infer atmospheric gases
Document Summary
The nature of planets around other stars: orbital period and distance. Astrometric method- star"s orbital motion same as planet"s orbital period; doppler method- orbital period is time b/w peaks in the star"s velocity curve; transit method- orbital period is time b/w repeated transits. Orbital period gives orbital distance (semimajor axis: orbital eccentricity. Astrometric and doppler give measure of eccentricity; doppler- symmetrical velocity curve means low eccentricity, asymmetrical velocity curve means higher eccentric orbit. Measured by astrometric and doppler methods; b/c for a given orbital distance, massive planet makes star move at higher velocity around the center of mass. Doppler shift only tells us star"s full orbital velocity when its orbit is seen edge-on; otherwise mass calculated will be the minimum possible mass. Measured by transits- more of the light the planet blocks, larger the star must be; ex. Can be calculated from planet"s size (transit method) and planet"s mass (doppler method: atmospheric composition and temperature.
