Exoplanet Detection Techniques II GUASA 12/10/2013 Prof. Sara Seager MIT

1. Exoplanet Detection Techniques II GUASA 12/10/2013 Prof. Sara Seager MIT

2. Exoplanet Detection Techniques II • Planet Detection Techniques in More Detail • Direct Imaging • Microlensing • Astrometry

3. Direct Imaging Lecture Contents • Direct Imaging • Planet and Star Spatial Separation • Adaptive Optics • Direct Imaged Candidates • What is Being Measured? • Planet-Star Flux Ratios

4.  National Geographic used with permission

5. Direct Imaging • Number 1 requirement is to spatially separate planet and star

6. Direct Imaging • Number 2 requirement is to literally block out the glare of the star

7. Diffraction • Light from a point source passes through a small circular aperture, it does not produce a bright dot as an image, but rather a diffuse circular disc known as Airy's disc • The disk is surrounded by much fainter concentric circular rings.

8. Diffraction • Light from a point source passes through a small circular aperture, it does not produce a bright dot as an image, but rather a diffuse circular disc known as Airy's disc • The disk is surrounded by much fainter concentric circular rings.

9. Spatial Resolution • Rayleigh criterion: the minimum resolvable angular separation of the two objects • Single slit • Circular aperture •  is the wavelength of light, D is the aperture diameter

10. Ground-Based Limitations • Turbulence in the atmosphere blurs mixes up photon paths through the atmosphere and blurs images

11. Ground-Based Limitations • Turbulence in the atmosphere blurs mixes up photon paths through the atmosphere and blurs images • Adaptive optics can correct for this! • http://planetquest.jpl.nasa.gov/Planet_Quest-movies/AO_quickTime.html

12. Direct Imaging Lecture Contents • Direct Imaging • Planet and Star Spatial Separation • Adaptive Optics • Direct Imaged Planet Candidates • What is Being Measured? • Planet-Star Flux Ratios • Direct Imaging Techniques for Earths

13. Direct Imaged Planet Candidates Note this plot is somewhat out of date Based on data compiled by J. Schneider

14. TMR-1 NASA/Terebey

15. This is a discovery image of planet HD 106906 b in thermal infrared light from MagAO/Clio2, processed to remove the bright light from its host star, HD 106906 A. The planet is more than 20 times farther away from its star than Neptune is from our Sun. AU stands for Astronomical Unit, the average distance of the Earth and the Sun. (Image: Vanessa Bailey)

16. HR 8799 See also: http://www.space.com/20231-giant-exoplanets-hr-8799-atmosphere-infographic.html

17. 2M1207

18. Gl 229 a NASA/Kulkarni, Golimowsk)

19. 55 Cnc Oppenheimer

20. GQ Lup

21. AB Pic

22. SCR 1845-6357 Biller et al. 2006

23. SCR 1845-6357 9 - 65 MJup (likely T-dwarf) Very close to Earth: 3.85 pc ~4.5 AU from primary Biller et al. 2006

24. CT Cha Schmidt et al. 2008

25. CT Cha 17±6 MJup 2.2±0.8 RJup 165±30 pc ~440 AU T=2600±250 K Background star Star: classical T Tauri (0.9-3 Myr) Schmidt et al. 2008

26. 1RXS J160929.1-210524 Lafreniere et al. 2008

27. 1RXS J160929.1-210524 330 AU 150 pc T=1800±200 K M=8 (+4 -1) MJup Young solar mass star (5 Myr) Lafreniere et al. 2008

28. Direct Imaged Planet Candidates This table is incomplete. Let’s look at a table online …

29. Direct Imaging Lecture Contents • Direct Imaging • Planet and Star Spatial Separation • Adaptive Optics • Direct Imaged Candidates • What is Being Measured? • Planet-Star Flux Ratios

30. What is Being Measured?

31. What is Being Measured? • Do we know the mass and radius of the planet? • Mass and radius are inferred from planet evolution models

32. What is Being Measured? • Astronomers are measuring the planet flux at the detector • Flux = energy/(m2 s Hz)

33. Flux from a Planet • Stars become fainter with increasing distance • Inverse square law • F ~ 1/D2 • Energy radiates outward • Think of concentric spheres centered on the star • The surface of each sphere has the same amount of energy per s passing through it • Energy = flux * surface area

34. The History of Pluto’s Mass http://hoku.as.utexas.edu/~gebhardt/a309f06/plutomass.gif

35. Planets • A flux measurement at visible wavelengths gives albedo*area • A flux measurement at thermal infrared wavelengths gives temperature*area • Same brightness from • A big, reflective and hence cold planet • A small, dark, and therefore hot planet • A combination gives of the two measurements gives: • Albedo, temperature, and area!

36. Direct Imaging Lecture Contents • Direct Imaging • Planet and Star Spatial Separation • Adaptive Optics • Direct Imaged Candidates • What is Being Measured? • Planet-Star Flux Ratios

37. In the interests of time I will skip the planet-star flux ratio derivation and leave it for you if you are interested

38. Flux from a Planet • Stars become fainter with increasing distance • Inverse square law • F ~ 1/D2 • Energy radiates outward • Think of concentric spheres centered on the star • The surface of each sphere has the same amount of energy per s passing through it • Energy = flux * surface area • Flux at Earth

39. Thermal Flux at Earth • Fp() is the flux at the planet surface • Fp () is the planet flux at Earth

40. Visible-Wavelength Flux at Earth • Fp() is the flux at the planet surface • Fp () is the planet flux at Earth

41. Planets at 10 pc Sun hot Jupiters J V E M Solar System at 10 pc (Seager 2003)

42. Planet-Star Flux Ratio at Earth • Fp() is the flux at the planet surface • Fp () is the planet flux at Earth

43. Thermal Emission Flux Ratio • Planet-to-star flux ratio • Black body flux • Take the ratio • Approximation for long wavelengths • Final flux ratio • Thermal emission is typically at infrared wavelengths

44. Scattered-Light Flux Ratio • Planet-to-star flux ratio • Black body flux • Scattered stellar flux • Take the planet-to-star flux ratio • Scattered flux is usually at visible-wavelengths for planets

45. Direct Imaging Lecture Summary • Direct Imaging • Diffraction limits detection • Spatial resolution • Diffracted light is brighter than planets • Direct Imaged Candidates • Four direct imaged planet candidates • Mass and radiusi are inferred from models • No way to confirm mass • What is Being Measured? • Flux at detector. • Other parameters are inferred • Planet-Star Flux Ratios • Approximations are useful for estimates

46. Exoplanet Detection Techniques II • Planet Detection Techniques in More Detail • Direct Imaging • Microlensing • Astrometry

47. Microlensing Lecture Contents • Gravitational Microlensing Overview • Planet-Finding Microlensing Concept • Tour of Planet Microlensing Light Curves

48. Gravitational Lensing • Light from a very distant, bright source is "bent" around a massive object between the source object and the observer • A product of general relativity

49. Gravitational Lensing • According to general relativity, mass "warps" space-time to create gravitational fields • When light travels through these fields it bends as a result • This theory was confirmed in 1919 during a solar eclipse when Arthur Eddington observed the light from stars passing close to the sun was slightly bent, so that stars appeared slightly out of position

50. Strong Gravitational Lensing Image is distorted into a ring if the lens and source are perfecty aligned (and the lens is a “point” or spherical compact mass)