1. Extra-Solar Planets Astronomy 311 Professor Lee Carkner Lecture 24

2. End of Semester  Observing project due Friday  Should be neat, legible and organized  Answer questions on a separate sheet of paper  Final exam Monday, 3 pm

3. Finding Exoplanets  How do you find a planet around another star?  Planets are much too faint to be seen with a telescope   As the planet orbits the star, the star also orbits the planet   The motion of the star is quite small, but can be detected as a slight shift in the spectral lines of the star

4. Finding Exoplanets

5. The Doppler Effect  When you observe a moving object, the wavelengths of light you observe change  Moving away --  Moving towards --  Example: the change in a car’s sound as it moves past you   By measuring the shift of lines in a spectrum, you can determine how fast the object is moving

6. Doppler Effect

7. Searching For Exoplanets   Measurements are made over a long period of time and plotted   As the planet moves around in its orbit the velocity of the star should go from positive to zero to negative and back to positive again   We find exoplanets by noticing changes in the spectral lines that indicate a planet tugging on the star

8. Orbits of a Star+Planet System Star Planet Center of Mass V star V planet

9. Light Curve of 51 Peg

10. Planetary Properties  From the period you can get the radius of the orbit   From the velocity you can get the mass   It is easiest to find large planets in small orbits  Large velocities and short periods are easier to measure

11. What is a Planet?  Star -- large enough to have hydrogen fusion  Mass >  Brown Dwarf -- a star not large enough to have fusion reactions  Mass >  Planet -- object formed by accretion of planetesimals  Mass <  Planets and brown dwarfs can be hard to tell apart

12. Known Exoplanets  About 300 exoplanets are known   Masses range from ~  Orbits range from ~  Searches are biased towards large planets in tight orbits

13. Sample Exoplanets Data

14. Exoplanet Orbits   Most systems have only one known planet but we are starting to find more   Long term observations are needed to see the longer periods   Are the nearly circular orbits of our solar system atypical?

15. Velocity Plots for Upsilon And System

16. Orbits in Upsilon And System

17. A Multiple Exoplanet System

18. Orbit Evolution   It should be too hot close to the star to form giant planets (no icy planetesimals)   The best theory holds that large planets form in the outer protoplanetary disk and then move inward due to friction in the disk  The magnetic field of the star may produce a “hole” in the inner disk, stopping the motion before the planet hits the star

19. Exoplanets and Habitability  Are any of the new planets habitable?  No,   They are almost all gas giants with no surface  However,   Example: 47 UMa, R orbit =2.1 AU   The velocities they produce are too small to measured via Doppler shift

20. Transits   For orbits seen edge on, the planet passes in front of the star once per orbit   We can measure and time this slight dimming with CCD cameras  By measuring the degree and length of the dimming the size and orbit of the planet can be found

21. Transit Light Curve

22. Planetary Spectra

23. Space Interferometry  One idea to find low mass planets is with an interferometer   A two telescope, Space Interferometry mission (SIM) may be launched in 2015 (?)   Would be able to detect the movement of a star in the sky as it is being pulled by its planets (astrometry)   Very large interferometers could take spectra of planets to look for signs of life

24. Next Time  Read Chapter 28

25. Summary  Recently many planets around other stars have been found  The planets are detected by measuring the motions they induce in the central star  The period and velocity of the motions allows the determination of the mass and orbit of the planet  New missions in the next 20 years will allow for the detection of many new planets, including Earth-like, habitable ones

26. Summary: Exoplanet Properties  Most known exoplanets are large (~M Jupiter ) and in close orbits  They may form further out and then move in  A few are near the habitable zone  We are starting to find additional planets in the systems