HOW TO DETECT HOW TO DETECT EXOPLANETSEXOPLANETSEAAE General AssemblyEAAE General Assembly

ESO HQ, Garching bei München, GermanyESO HQ, Garching bei München, Germany

March 4, 2005March 4, 2005

Anders VästerbergAnders Västerberg

European Association for Astronomy Education (EAAE)European Association for Astronomy Education (EAAE)

Saltsjöbadens Samskola, SwedenSaltsjöbadens Samskola, Sweden

ExoplanetsExoplanets(Extrasolar planets)(Extrasolar planets)

Planets in orbits around other stars than our sunPlanets in orbits around other stars than our sun

144 known (Michel Mayor et al., The Geneva 144 known (Michel Mayor et al., The Geneva Extrasolar Planet Search Programmes) Extrasolar Planet Search Programmes) (obswww.unige.ch/~udry/planet/planet.html February (obswww.unige.ch/~udry/planet/planet.html February 8, 2005)8, 2005)

First found in 1995 by Michel Mayor & Didier Queloz First found in 1995 by Michel Mayor & Didier Queloz of the Geneva Observatory. Orbiting 51 Pegasi. of the Geneva Observatory. Orbiting 51 Pegasi.

Observations indicate at least about 7% of all stars Observations indicate at least about 7% of all stars have at least one planet.have at least one planet.

Roughly 0.05 - 13 Jupiter masses (15 - 4000 Earth Roughly 0.05 - 13 Jupiter masses (15 - 4000 Earth masses). Lower limit due to sensitivity of instruments, masses). Lower limit due to sensitivity of instruments, upper limit set by the definition of a planet. (Brown upper limit set by the definition of a planet. (Brown dwarfs: about 13 - 75 Jupiter masses, above this are dwarfs: about 13 - 75 Jupiter masses, above this are the stars)the stars)

Properties of known ExoplanetsProperties of known Exoplanets

Average distance from star: 0,02 - 5 AUAverage distance from star: 0,02 - 5 AU Most have fairly excentric orbits. (In the Solar Most have fairly excentric orbits. (In the Solar

system all planets except Mercury and Pluto system all planets except Mercury and Pluto have quasi-circular orbits)have quasi-circular orbits)

Period: 30 hours – 13 years (Jupiter: 5.20 AE, Period: 30 hours – 13 years (Jupiter: 5.20 AE, 318 earth masses, 12 years)318 earth masses, 12 years)

Detection of exoplanetsDetection of exoplanetsIndirect methodsIndirect methods Measurements of variations in stellar radial velocitiesMeasurements of variations in stellar radial velocities Detection of transits (Planet dims the light from a star Detection of transits (Planet dims the light from a star

when it passes in front of it)when it passes in front of it)

Direct methodsDirect methods Detecting planets on images (Possibly sucessful in one Detecting planets on images (Possibly sucessful in one

case, but needs confirmation) Hard because the stars case, but needs confirmation) Hard because the stars are often more than one billion times as luminous as are often more than one billion times as luminous as their planets and very close to them in the sky. (The Sun their planets and very close to them in the sky. (The Sun is 10is 109 9 times brighter than Jupiter and 10times brighter than Jupiter and 1010 10 times brighter times brighter than Earth at visible wavelengths). Instruments with the than Earth at visible wavelengths). Instruments with the required sensitivity are under construction and planned required sensitivity are under construction and planned to be operative around 2007.to be operative around 2007.

Measurements of Measurements of stellar radial velocitiesstellar radial velocities

Planets and stars move around their common Planets and stars move around their common center of gravity. center of gravity.

The amplitude of the radial velocity for the Sun due The amplitude of the radial velocity for the Sun due to Jupiter is 13 m/s, for the Earth it is 1 dm/s.to Jupiter is 13 m/s, for the Earth it is 1 dm/s.

TransitsTransits

HD209458HD209458

(HD = Henry Draper (a star catalogue)(HD = Henry Draper (a star catalogue)

The planet HD209458b was detected through The planet HD209458b was detected through variations in the radial velocities of the star.variations in the radial velocities of the star.

The star: F8 The star: F8 (Sun: G2)(Sun: G2) Distance: about 154 light-years (in Pegasus) Distance: about 154 light-years (in Pegasus) 7.65 mag7.65 mag

HD209458bHD209458b

Period 3.5 daysPeriod 3.5 days Average distance from star 0.045 AUAverage distance from star 0.045 AU About 0.7 Jupiter massesAbout 0.7 Jupiter masses About 1.4 Jupiter radiiAbout 1.4 Jupiter radiievaporating extended hydrogen atmosphere evaporating extended hydrogen atmosphere

around the planetaround the planet

Tabel showing coming transits:Tabel showing coming transits:

www.astro.caltech.edu/~dc/upcoming_transits.ascwww.astro.caltech.edu/~dc/upcoming_transits.asc

HD209458b transitHD209458b transit

Copyright: ESACopyright: ESA

Transits from extrasolar planets can Transits from extrasolar planets can be observed by amateurs…be observed by amateurs…

eg.eg.Group in Jyväskylän Sirius Group in Jyväskylän Sirius Marko Moilanen et al.Marko Moilanen et al.Nyrölä observatory Nyrölä observatory

41 cm telescope 41 cm telescope CCDCCD V-filterV-filter Computer program for data reductionComputer program for data reduction

… … and by students!and by students!

Anders Nyholm (Bronze medal winner in the IAO Anders Nyholm (Bronze medal winner in the IAO 2002), Rymdgymnasiet in Kiruna, (an upper 2002), Rymdgymnasiet in Kiruna, (an upper secondary school) observed transits of secondary school) observed transits of HD209458bHD209458b

Project work (compulsory in Swedish Schools –Project work (compulsory in Swedish Schools –1+ month of full time studies)1+ month of full time studies)

Tycho Brahe observatory in Oxie outside MalmöTycho Brahe observatory in Oxie outside Malmö 36 cm teleskope36 cm teleskope CCDCCD

OGLE-TR-56BOGLE-TR-56B

Was detected by the transit methodWas detected by the transit method Existence confirmed by radial velocity Existence confirmed by radial velocity

measurements of the starmeasurements of the star Average distance from star: 5 solar radii, period Average distance from star: 5 solar radii, period

of revolution 30 hours.of revolution 30 hours.

The dimming of the light of a The dimming of the light of a

sun-like star at a transitsun-like star at a transit 1% (0.01 mag) for a planet of the size of Jupiter1% (0.01 mag) for a planet of the size of Jupiter 0.01% (0.0001 mag) for an earth-sized planet0.01% (0.0001 mag) for an earth-sized planet

The probability that transits will occur if a star has The probability that transits will occur if a star has planets:planets:

0.5% if the star has a planet at a distance of 1 AE.0.5% if the star has a planet at a distance of 1 AE. If 10% of the stars have a planet at a distance of 1 If 10% of the stars have a planet at a distance of 1

AE, the light from about 2000 stars need to be AE, the light from about 2000 stars need to be monitored continuoiusly during one year if the stars monitored continuoiusly during one year if the stars are of the same size as the Sun – to find one single are of the same size as the Sun – to find one single exoplanet using this method!exoplanet using this method!

LinksLinks

ExoplanetsExoplanets California & Carnegie Planet SearchCalifornia & Carnegie Planet Search

exoplanets.orgexoplanets.org

Search for transitsSearch for transits TransitsearchTransitsearch

www.transitsearch.orgwww.transitsearch.orgAmateur network for observing stars with known Amateur network for observing stars with known planets in order to find transitsplanets in order to find transits

skolor.nacka.se/samskolan/anders/skolor.nacka.se/samskolan/anders/