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Pulsar Timing. How it works Pulsar sends out very regular signal Pulsar is slightly nearer/farther from us Pulses come slightly late/early. Advantages Very sensitive Cheap See low mass planets. Disadvantages Works only on pulsars (weird stars). Score = 33. Other Timing.
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Pulsar Timing How it works • Pulsar sends out very regular signal • Pulsar is slightly nearer/farther from us • Pulses come slightly late/early Advantages • Very sensitive • Cheap • See low mass planets Disadvantages • Works only on pulsars (weird stars) Score = 33
Other Timing How it works • There are other very regular signals from stars • Orbiting eclipsing binary stars • Pulsating subdwarf stars • Signals come slightly late/early Disadvantages • Works only in very special circumstances (rare) Advantages • Can see planets with large orbits Score = 25?
Radial Velocity / Doppler Method How it works • Star moves towards and away from us • Alternating red-shift / blue shift Disadvantages • Massive planets • Small fast orbits • No observation of planet Advantages • Sensitive method Q. 60: Radial Velocity Method Score = 814
Transit Method How it works • Planet blocks light from star, making it dim • Star blocks light from planet Disadvantages • Requires Luck • False Positives (requires confirmation) Advantages • Works well from space • Measure spectrum of planet • Measure atmosphere of planet Score = 2911
Spacecraft for the Transit Method TESS • Operating ’18–’30? • Expect 20,000+ planets COROT • Operated from ’08–’13 Kepler • Operated ’09–’18 • Has seen sub-Earth sized planets
What Have We Learned? • Many large planets – Jupiter size and greater • Planets as small as Earth and smaller • Observational bias favors finding large planets • Often find planets very close to star • Observational bias • Gas giants can live very near their stars • Orbits often highly eccentric
Lessons from Extrasolar Planets? • We probably need to rethink our understanding of how stellar systems form • Planetary migration is often an important factor? • Giant planets form far away • Later move inwards • Eccentric and even retrograde planets are not rare • Planets are not uncommon • Including Earth-sized planets • Stay tuned
End of Material for Test 2 Questions?
The Sun Magnetic Fields and Charged Particles • Charged particles are affected by magnetic fields • They are forced to follow magnetic field lines Magnetic fields
Plasmas • At ordinary temperatures, atomic nuclei attract electrons to make them neutral • At extreme temperatures, the electrons pop loose, and the electrons can run off freely • This is a plasma • Plasmas are excellent conductors • They can generate magnetic fields
Atomic Spectra • Suppose you take an atom and bump the electrons up (by heating it, for example). What type of light comes out? • Spectrum consists of emission lines • Exactly which lines tells you the kind of atom, like a fingerprint
Atomic Spectra • Suppose you take an atom and shine a bright white light on it. What does the spectrum of the light look like when it comes out? • Initial spectrum is continuous • Atom absorbs certain very specific frequencies • The same frequencies you saw before.
Kirchoff’s Laws • Hot thick solid, liquid, or gas – Continuous spectrum • Thin gas – bright line spectrum • Thin gas with hotter thick gas behind it – dark line spectrum
Kirchoff’s Laws Continuous Spectrum: Hot, thick solid, liquid, or gas Bright Line Spectrum: Hot, thin gas Dark Line Spectrum: Cooler gas in front of hot, thick solid, liquid, or gas
Stellar Spectra Q. 61 Simple Stellar Spectrum Q. 62: Complicated Stellar Spectrum
The Sun’s Spectrum • Hundreds of lines • Scores of Elements
Composition of a Typical Star (Sun) Know These! • Hydrogen • Helium • Oxygen • Carbon • Iron • Neon • Sulfur • Nitrogen • Silicon • Etc.
The Sun: Basic Facts March 1, 2019 from SDO • 109 Earth diameter • 333,000 Earth mass • Density: a bit higher than water • Rotates once every 25 days • Differential rotation
The Sun: How We Know What We Know Exterior • Spectra • Temperature • Motion • Chemical Composition • Magnetic Fields • Ground-based telescopes • Eclipses • Space telescopes • Solar Wind Interior • Gravity • Magnetic Fields • Neutrinos • Helioseismology
Solar Dedicated Spacecraft Solar Dynamics Observatory STEREO SOHO IRIS
More Solar Dedicated Spacecraft Advanced Composition Explorer Hinode Parker Solar Probe DSCOVR
