Lecture 11: The Discovery of the World of Exoplanets What are exoplanets & where are they? Indirect methods for planet detection
Planets Orbiting Other Stars Number of planets discovered around other stars: 540 planets 58 multiple planet systems Reminder: gives minimum mass F to G etc. Compute this more exactly by updating excel spreadsheet on plane
Star-to-planet inequalities: In light: 1010 (optical) to 107 (infrared) In mass: 105 to 103 In size: 102 to 10.
Four main methods of discovery: Direct Radial velocity or Doppler ‘wobble’ Transits Gravitational microlensing
51 Peg b & HD 209458b: “Hot Jupiters”
Method of discovery: Radial velocity ‘wobble’ of the star Radial velocities seen in star HD 209458 - the variation is due to a planet that is less massive than Jupiter. (Mazeh et al. 1999; Marcy et al. 2000)
Ups And System vs. Solar System
Kepler-11 System vs. Solar System
HD 209458b: a Hot Jupiter
Transits: A Method for Planet Discovery
Venus in Front of the Sun
Transit Measurements
Kepler discoveries
Evidence for Planet OGLE-TR-56b Doppler Shift Light Dimming Konacki, Torres, Sasselov, Jha, 2003, Nature
Method of discovery: Radial velocity ‘wobble’ of the star Radial velocities seen in star HD 209458 - the variation is due to a planet that is less massive than Jupiter. (Mazeh et al. 1999; Marcy et al. 2000)
Mass: For HD 209458b: Mp sin(i) = Ms vs P / 2 ap = const. x (Ms /1.1MSun) Mjup + 0.018 + 0.1 Transit light curve helps derive the orbit inclination: i = 86o.7 + 0.2 Both Mp and Rp determined to better than 5%!
What can we learn from transiting extrasolar planets HD 209458b: Dimming of light due to transit, observed with HST. Tells us DIRECTLY: Planet radius, INDIRECTLY: Planet density Planet composition Just to remind you, that this transiting planet was first discovered by the standard spectroscopic “wobble” technique, and only afterwards were transits detected. Brown, Charbonneau, Gilliland, Noyes, Burrows (2001)
Radius Mass Kepler: New Planets on the Mass-Radius Diagram after Latham et al.’10
Transiting Planets - the search is on! Transits occur due to chance alignments, therefore one has to observe millions of stars in order to ‘catch’ a few transiting planets; Here at Harvard we have 2 automated networks of small telescopes searching: HAT & MEarth.
The HAT Network: FLWO Mt.Hopkins AZ (Bakos et al. 2004)
… and at Mauna Kea Obs., Hawaii
Main points to take home: Four main methods of discovery: direct, Doppler wobble, transits, microlensing. Doppler effect: deriving planet mass. Transits: (1) detection probability; (2) deriving the radius. NASA Kepler Mission