StarTrek 2004: The Quest for Planets has Begun

1. StarTrek 2004:The Quest for Planets has Begun By Benjamin Simmons Tennessee State University S.T.A.R. program Center of Excellence In Information Systems

2. Overview • Planets rotate around stars • We use indirect and direct methods • 51 Pegasi b was the first planet to be found in 1995 • Since we have been able to find 116 planets out of 93 planetary systems. • Planets can not be directly seen • We use telescopes that makes images using conceptualization and deceptualization. • The new design of interferometers is revolutionizing planet finding.

3. Interferometer • An Interferometer consists of multiple mirrors that collect reflective images. The light from the mirror travels through a tube to one central base where all the images are combined to make one image. • History a. Newton was one of the first to study interferometers b. Electron interferometers were used introduced the 1950’s c. Neutron interferometers were created in the 1960’s d. Then Astronomers and scientist revolutionized the idea of planet finding by using interferometers about a decade ago. • Astronomers use interferometers to get a better picture of a parent star. • Once the technology for the new missions to find planets are complete, the usage of interferometers will play a major role in seeing a planet. • Interferometers can use three different light sources to search for a planet: x-ray light, visible light, and infrared light.

4. Indirect methods of Searching for Planets • Radial velocity search • Astrometric search • Photometric search • Microlensing

5. Radial Velocity • aka Doppler system • Main indirect planetary search system • Found the first planet outside our Solar System, 51 Pegasi b • Uses a spectroscope to find the velocity • Distance doesn’t play a role • Works from faintness of a star • Measures in meters per second • A spectroscope with a sensitivity of 2 m/s will easily detect a Jupiter size planet • Using the radial velocity method will not allow you to detect a Earth-like planet x

6. How Radial Velocity works Astronomers know that the planets rotating around parent stars cause the star to wobble. So radial velocity looks at a star through a spectroscope that is suspected to contain a planet, takes the spectral lines produced in the chromospheres, and calculate the velocity from the different positions of multiple observations with respect to time. x

7. How Radial Velocity Works • Calculation for radial velocity is • V = 30Mpsin i sqrt(M*ap) • Mp is the mass of the planet in Jupiter’s mass • M* is the mass of the central star in multiples of the Sun’s mass • ap is the semi-major axis of the planet’s orbit in astronomical units • sin i is the factor where i is the planet’s orbital inclination from the sky x

8. Astrometric Search • Also looks at the wobble of a parent star • Needs superb resolving power • To get good resolution, an interferometer is used. • Looks at the stars wobble to see if there is a planet pulling on the parent star • The formula for the wobble movement is r = 1000 Mpa M*D • Wobble movement is measured in microarcseconds

9. Photometric Searches • aka the Planetary Transit Method • Relies on planets crossing in front of a star, otherwise known as a transit • This prevents a small amount of light from reaching the Earth • Using this method, you can calculate the mass of the planet, the mass of the star, the velocity, and the diameter. Planetary transits in HD 209458 observed with the APTs. The planet blocks 1.58% of the light that comes from the star.

10. Microlensing • Relies on the star becoming brighter • The gravitational field bends the light and acts like a lens. • Microlensing occurs when the lensing object does not possess the gravitational field to split the source into separate images. • Instead it refocuses some of the stray light and thus makes the source brighter. • Not a popular method.

11. Direct Methods • Actually sees the planets orbiting around stars • Useful methods: *Adaptive Optics and Coronagraphs *Optical Interferometers *Thermal Imaging of Extrasolar planets

12. Adaptive Optics and Coronagraphs • Adaptive Optics increases the sharpness of images. • Senses and corrects the distortion in the wavefront. • Problem: The halo of parent star will distort the image of the planet. • Coronagraphs gets rid of the surrounding halo produced by the parent star. • Suspected to detect older, cold planets.

13. How Adaptive Optics and Coronagraphs Works Adaptive Optics Coronagraphs • Enables the adaptive optics to study around possible parent star by allowing the fainter corona to be studied.

14. Optical Interferometers • The future of planet finding • The Keck interferometer • Nulling Interferometers is a new method used for finding planets.

15. Nulling Interferometers • One telescope feds light straight to focus and the other telescope delays the focus of light. • One focuses on a wave crest and the other will focus a trough. If object is on-axis this process works perfectly. If object is off-axis, the telescope configuration can be adjusted so that cancellation will not take place.

16. Thermal Imaging of Extrasolar Planets • Use mid infrared wavelengths to locate planets radiating their energy • Between the wavelengths of 10 and 20 um, the star-planet contrast may drop to a million to one. • Hope to find an Earth-like planet this way.

17. Different Missions • OASES- has four telescope interferometer • Darwin- has five spacecrafts with daughter crafts rotating around the big spacecrafts. • COBE removes the zodiacal dust cloud. • Hubble Space Craft. • SIM • TPF