Extra Solar Planets ASTR 1420 Lecture 17 Sections 11.2

Searching for Extra Solar Planets Extra Solar Planets  Exo-planets (Exoplanets) Extra Solar Planets  Exo-planets (Exoplanets) 0 th order expectation: 0 th order expectation: o exoplanets should be moderately common  theoretical : planet formation theory… Disk forming is inevitable followed by temperature dependent condensation.  observation : flat disks… and actual discovery of them since mid 90s. Main difficulty Main difficulty o Planets are much fainter than the star : even the brightest (largest and youngest) planets are 1 million times fainter than a typical star. o Planet—star separation is very small  Solar system at ~10 light years = 1 second of arc (the extent of a penny seen ~2.5 miles away).

History 1 st discovery of exo-planet : “Pulsar Planet” 1992, Aleksander Wolszczan and Dale Frail discovered two planets orbiting around a pulsar, PSR , Aleksander Wolszczan and Dale Frail discovered two planets orbiting around a pulsar, PSR , Mayor and Queloz, 51 Peg b  first radial velocity planet 1995, Mayor and Queloz, 51 Peg b  first radial velocity planet To date, 429 exo-planets were discovered as of today. To date, 429 exo-planets were discovered as of today.

Definition of Exoplanet Objects with masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they were formed). Objects with masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they were formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System. The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System. o Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed. o Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate). Planetary mass objects orbiting around other stars!

Search Methods Not a planet 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing

Search Methods 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing 7.Orbital phase

Search Methods 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing 7.Orbital phase

Search Methods 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing 7.Orbital phase

Search Methods 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing 7.Orbital phase

Search Methods 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing 7.Orbital phase

Search Methods 1.Direct Imaging 2.Astrometry 3.Doppler shift 4.Pulsar Timing 5.Transit 6.Microlensing 7.Orbital phase (?)

Naming exoplanets Name is given relative to the central star… Naming stars:: Naming stars:: o Relative to constellation name (in Latin adjective) o In a constellation, the brightest star is “alpha”, then, beta, …, omega, 1, 2, 3,… o Stars in multiple system are named relative to the brightest star with prefix capital alphabets Examples: brightest star in Orion = α Orioni (α Ori) brightest star in Cygnus = α Cygni 2 nd companion of the 3 rd brightest star in Pegasus = γ Peg C planets around a star is given a prefix in small alphabet… planets around a star is given a prefix in small alphabet… o 1 st detected planet around 51 Peg = 51 Peg b o planetary system HR 8799 : HR HR8799 b + HR8799 c + HR8799 d

Doppler Effect stationary sourcemoving source

Doppler effect and sonic boom

Doppler Effect

Light = Wave Light = wave : blue light (high frequency), red light (low frequency) Light = wave : blue light (high frequency), red light (low frequency)

Solar Spectrum Each of the 50 slices covers 60 angstroms, for a complete spectrum across the visual range from 4000 to 7000 angstroms

Doppler shift of Stellar spectrum due to unseen planet(s) blue shift : getting closer red shift : getting farther away

Effect of Planets on the Stellar Motion Magnitude of reflex motion ≈ mass of the planet + orbital distance

For non-circular motion

First Discovery : 51 Pegasi b

Line of sight motion only… Doppler shifts reveal only the part of a star’s motion directed toward or away from us (i.e., line of sight motion)! Therefore, face-on orbits do not cause any shift in the spectrum…

Real Data

Currently known RV Exoplanets 413 RV planets as of today!

Hot Jupiters… Doppler technique is best suited for identifying massive planets close to their stars Doppler technique is best suited for identifying massive planets close to their stars Hot Jupiters  many gas planets close to the central stars were discovered! Hot Jupiters  many gas planets close to the central stars were discovered! 143/696 are hot Jupiters

Astrometry Had been used many decades to discover binary stars Had been used many decades to discover binary stars Similar to the Doppler technique  looking for reflex motions. Similar to the Doppler technique  looking for reflex motions. o astrometry : tangential motions o Doppler : line of sight motions Therefore, more massive planets, planets at wide orbits are easier to be detected! Therefore, more massive planets, planets at wide orbits are easier to be detected! For a given planet mass and orbit, lower mass central stars showing larger reflex motions. For a given planet mass and orbit, lower mass central stars showing larger reflex motions. However, planets take longer time to make one orbit However, planets take longer time to make one orbit at wide orbits (Period 2 = Distance 3 ) at wide orbits (Period 2 = Distance 3 ) Current limit : ~10 milli arc second (1/100 arc second) Current limit : ~10 milli arc second (1/100 arc second) Not many discoveries (a handful)… Not many discoveries (a handful)…

Sun’s Reflex Motion seen at 33 light-years away Similar to measure the width of human hair about 10 miles away!

European Mission GAIA Launch 2012 Launch Million Euros 320 Million Euros 1.45m telescope 1.45m telescope catalog 1 billion stars catalog 1 billion stars  3D map of Milky Way ~10,000 planets ~10,000 planets

Mercury Transits (2006, Nov 8) Transit of Venus Transit of Venus o 2012 June 6 Transit of Mercury Transit of Mercury o 2016 May 9 o 2019 Nov 11

HST Observation of HD b Could detect 0.01% variation Could detect 0.01% variation

Transit Power! with inclination + RV Orbital period Orbital period Planet Radius Planet Radius Planet mass Planet mass Planet’s density Planet’s density Planet temperature Planet temperature Stellar radius Stellar radius Limb darkening… Limb darkening…

Can even detect the effect of Planetary Atmosphere!

Exoplanetary atmosphere H 2 O, CH 4 … H 2 O, CH 4 …

Currently 258 transiting exoplanets were discovered!

Kepler Mission Successfully launched on 03/06/2009 Successfully launched on 03/06/2009 o 1.4m telescope o 95 mega pixels o 3.5 years search for Earth-sized habitable planets search for Earth-sized habitable planets

Kepler FoV Will look at 100,000 stars for 3.5 years… Will look at 100,000 stars for 3.5 years… 20ppm for 12 th mag star 20ppm for 12 th mag star  ~50 Earths to be found!

Kepler discoveries to date : 114 confirmed

Great sensitivity from Kepler!!

One example : Kepler 68c (4.8 Earth-mass planet)

Gravitational Lensing

Microlensing ~6 exoplanets were found as of 2009 In 2006, a 5 Earth mass planet was discovered. Lensing by the same planet can never(?) be observed again! But, can detect planets furthest from Earth and sensitive to discover planet on wide orbits. Optical Gravitational Lensing Experiment (OGLE) toward the Galactic center (~100 million stars)

In summary… Important Concepts Exoplanet detection methods o direct & indirect Nomenclature of exoplanets Definition of exoplanets Doppler shift Doppler shift planet search o line of sight motion only! Pros and cons of different exoplanet detection methods Important Terms Hot Jupiters Transit Astrometry Microlensing Chapter/sections covered in this lecture : 11.2 Direct Imaging Detection of Exoplanets : next class