1. Extrasolar planets

2. Detection methods 1.Pulsar Timing Pulsars are rapidly rotating neutron stars, with extremely regular periods Anomalies in these periods indicate the gravitational influence of a companion.

3. Detection methods 2. Astrometry the oldest method used in the search for extrasolar planets, used as early as 1943. Involves measuring the proper motion of a star in the search for an influence caused by its planets changes in proper motion are so small that the best current equipment cannot produce reliable enough measurements. This method requires that the planets' orbits be nearly perpendicular to our line of sight, and so planets detected by it could not be confirmed by other methods.

4. 3. Radial motions: the Doppler shift Recall the Doppler shift of the wavelength of light due to the velocity of the source:

5. Spectroscopic binaries Single-line spectroscopic binary: the absorption lines are redshifted or blueshifted as the star moves in its orbit Double-line spectroscopic binary: two sets of lines are visible Java applet: http://instruct1.cit.cornell.edu/courses/astro101/java/binary/binary.htmhttp://instruct1.cit.cornell.edu/courses/astro101/java/binary/binary.htm

6. Spectroscopic binaries: circular orbits If the orbit is in the plane of the sky (i=0) we observe no radial velocity. Otherwise (if the orbit is inclined at an angle i relative to the plane of the sky) the radial velocities are a sinusoidal function of time. The minimum and maximum velocities (about the centre of mass velocity) are given by

7. Spectroscopic binaries: circular orbits If both velocity curves are observed, we can solve for both masses, depending only on the inclination angle i This gives lower limits to the masses. If i<90 degrees, the masses will be larger.

8. Extrasolar Planet searches A planet orbiting a distant star will behave like a single-lined binary system. In principle we can determine the mass from the Doppler shift of the star. If the star can be accurately classified (i.e. with a good spectral classification and a parallax distance) we can determine its mass independently of the orbit. Since the mass of the planet is generally much less than that of the star Assuming circular orbits,

9. Extrasolar Planet searches E.g. the star HD73256: From Hipparcos data (and detailed stellar modelling) we know M star ~1.05 M sun From the light curve we measure P=2.54858 days and v max =269.8 m/s. Sinusoidal shape means e~0 So the planet is very massive (1.86 M J ) and very close to the star (0.037 AU: a tenth as big as Mercury’s semimajor axis of 0.3871 A.U.) Why?

10. Extrasolar Planet searches The maximum velocity shift is only ~270 m/s. The Doppler shift is therefore: which is very small. For example the H  line is redshifted by only 0.00059 nm! The spectral resolution must therefore be very high. Detecting smaller planets, farther away from the star, is an even more difficult task.

11. Break

12. Detection methods 4. Gravitational microlensing  This effect occurs when the gravitational field of a planet and its parent star act to magnify the light of a distant background star.  The key advantage of gravitational microlensing is that it allows low mass (i.e. Earth-mass) planets to be detected using available technology.  A notable disadvantage is that the lensing cannot be repeated because the chance alignment never occurs again.

13. 5. Transit methods Detects a planet's shadow when it transits in front of its host star. Can be used to measure the radius of a planet.

14. Transits Imagine viewing the Earth-Sun system from a distant star. By how much will the Sun fade during a transit of the Earth? How about during a transit of Jupiter?

15. 6. Circumstellar disks Young main sequence stars often still have disks, even after the molecular cloud has been dispersed. Infrared-emitting dust disk around  -Pic. The central star has been subtracted. The dust disk around Vega. At least one large planet is known to exist within this disk.

16. Circumstellar Disks

17. 7. Direct detection Infrared image of the star GQ Lupi orbited by a massive, young (therefore warm) planet at a distance of approximately 20 times the distance between Jupiter and our Sun. 2005 image of 2M1207 (blue) and its planetary companion, one of the first exoplanets to be directly imaged

18. 7. Direct Detection The albedo of the Earth is about A V =0.4. How bright is it in visible (reflected) light, relative to the Sun? How do they compare at infrared wavelengths, where Earth emits thermal radiation? A picture of Earth, from the surface of Mars, just before sunrise.

19. HD 209458b was the first transiting planet discovered, the first extrasolar planet known to have an atmosphere, the first extrasolar planet observed to have an evaporating hydrogen atmosphere, and the first extrasolar planet found to have an atmosphere containing oxygen and carbon.

20. Extrasolar planet searches As of December 2005, 170 planets have been detected outside our solar system (in 146 systems). See http://exoplanets.org/http://exoplanets.org/ Most of these have a M Jupiter

21. 19 Future missions Keck Interferometer Spitzer Space Telescope SIM PlanetQuest Kepler Large Binocular Telescope Interferometer Terrestrial Planet Finders

22. Space Interferometry mission http://planetquest.jpl.nasa.gov/SIM/sim_index.cfm Interferometer with 9m baseline 5 year mission; estimated launch in 2010 will determine the positions of stars several hundred times more accurately than anything previously possible Will search for terrestrial planets around the nearest ~250 stars, with astrometry accurate to 1  as.

23. Kepler http://www.kepler.arc.nasa.gov/ NASA mission to hunt for planets using a one-meter diameter telescope photometer to measure the small changes in brightness caused by transiting planets. Transits by terrestrial planets produce a periodic change in a star's brightness of about 1/10,000, lasting for 2 to 16 hours. Scheduled to launch 2008, 4 year mission

24. sensitivity limits of radial velocity surveys, astrometric surveys, microlensing surveys, and space- based transit techniques. The shaded areas show the expected progress towards the detection of Earth-like planets by 2006 and 2010. The filled circles indicate the planets found by radial velocity surveys (blue), transit surveys (red), and microlensing surveys (yellow). The discovered extrasolar planets shown in this plot represent the reported findings up until 31 August 2004.

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