D D O O D D O O D D G S D X 9 1 G S D X Detection ethods 9 3 Possible ways to detect extasola planets: Diect ethod:... diect imaging of planet xtasola Planets ndiect ethods: seach fo evidence fo...... gavitational inteaction with sta in adial velocity... gavitational inteaction with sta in motion of sta... influence of planet on light fom behind planet (gavitational lensing) o time easons: will look at diect imaging and adial velocity measuements only... Detection ethods 1 D D G S D X ntoduction 9 2 G S D X Diect maging 9 4 So fa: have looked at planets aound ou Sun Physics question: n ode to make an image of an extasola planet, need to sepaate images of sta and planet with telescope = equies two ingedients: s ou Sola System nomal? 1. contast (elative intensity of sta and planet) 2. esolving powe of telescope (angula distance between sta and planet) = e thee planets aound othe stas? can then compae sola system with othe systems. To answe these questions, we need to detect extasola planets. xtasola Planets 1 Detection ethods 2
D D O O D D O O D D G S D X Diect maging: ontast, 9 5 G S D X Diect maging: ontast, 9 6 stimate intensity contast between sta and planet: Sola system: uminosity of Sun = 3.9 1 26 W =: Sta uminosity This powe is emitted isotopically into all diections. = negy eceived pe second on whole aea of sphee of adius (aea = 4π 2 ) equals as well! = negy falling pe second on aea of 1 m 2 at distance ( flux ): = units: W m 2 o eg cm 2 s 1 4π 2 Detection ethods 5 Plugging in typical numbes: Jupite: distance: = 5.2 U = 7.8 1 8 km = P 51 W m 2 Total powe eceived by Jupite: pojected sola facing aea = π 2 = 1.6 116 m 2 = Total powe eceived: P total, = 8.2 117 W. Of this, about 3% is eflected, i.e., = 2.5 1 17 W 6 1 1. The luminosity of Jupite is 1 billion times weake than that of the Sun. = o typical planets aound sola type stas, we need to be able to detect intensity contasts of bette than 1:1 billion. = ot doable now, but not unealistic to achieve in you lifetime ( coonagaphs )... Detection ethods 7 D D G S D X Diect maging: ontast, 9 6 G S D X Diect maging: ngula Sepaation, 9 7 Plugging in typical numbes: ath: distance: = 1 U = 15 1 6 km = P 138 W m 2 ( sola constant ). ath θ d Sta Total powe eceived by ath: pojected sola facing aea = π 2 = 1.26 114 m 2 = Total powe eceived: P total, = 1.74 1 17 W. Of this, about 3% is eflected, i.e., = 5.2 1 16 W 1 1. The luminosity of the ath is 1 billion times weake than that of the Sun. How close on sky ae images of Sun and planet? tanθ = d = θ d (fo small θ: Taylo seies: tanθ θ + (1/3)θ 3 +...; small angle appoximation ) Typical distances to neaby stas: d 1 y = 9.5 1 17 m, typical distances in planetay system: 1 U = 1.5 1 11 m, = θ = d = 1.57 1 7 ad = 9 1 6 deg =.3 in infaed, luminosity contast is only 1 million, but still athe weak... (1 = 1 acsec = 1/36 deg). Detection ethods 6 Detection ethods 8
D O D G S D X Diect maging: ngula Sepaation, 9 8 Optics: esolving powe of telescope with diamete D: α = 12 D/1 cm = to esolve.3, need D = 4 m, so doable BUT ath atmosphee limits esolution to.5 ( seeing ) uently, diect detection of extasola planets aound sola-type stas is not doable fom gound, although it is technologically feasible fom space. (8.8) S: Space ntefeomety ission and Teestial Planet inde: 2 missions in the next decade(?): 4 6 m telescope (TP-); multiple 3 4 m telescopes (TP-, w/s) S: Dawin: 3 3 m telescopes, launch planned fo 215 Detection ethods 12 Using adaptive optics, it is possible to obtain diffaction limited esolution in the nea infaed. ontast is still a poblem, howeve, fo one vey dim sta (a bown dwafs ) a planetay companion was detected in ealy 25 with the T and confimed in 26 with HST. Distance between sta and planet: 2 eptune distance, distance to system 59 ± 7 pc. One possible configuation of S s Dawin mission: seveal fee-flying mio spacecaft plus one spacecaft seving as communications hub.... while planets aound nomal stas have yet to be found with imaging methods, diect imaging of the egion close to a sta is in pinciple doable with Hubble Space Telescope, but angula esolution not yet good enough.
D D O O D O D G S D X adial elocity easuements 9 12 f we cannot see planet diectly = use indiect methods. Two-body poblem: Sta and planet move aound common cente of mass: 1 m 2 m 1 2 m 1 1 = m 2 2 o cicula obits and obital peiod P, velocity of sta due to action of planet is v 1 = 2π 1 P = 2π P m2 m 1 2 xample: Sun vs. Jupite: m 1 = 2 1 3 kg, m 2 = 2 1 27 kg, 2 = 5.2 U = 7.8 1 11 m, P J = 11.9 y = 3.76 1 8 s = v 1 = 13.1 m s 1 5 km h 1 xample: Sun vs. ath gives v 1 = 1 cm s 1.8 km h 1 Detection ethods 16.. Shap, OO/SO/Kitt Peak TS/U/S bsoption line spectum of the Sun: aunhofe ines D D G S D X adial elocity easuements 9 13 G S D X adial elocity easuements 9 15 To detect planets, need to be able to measue sta velocities with pecision to much bette than 13 m s 1. easue motion of stas using spectoscopic methods. ntensity (abitay units) 1 Sola tlas (afte Delbouille et al.,1972, 1981) 1111111111111111111 1111111111111111111 8 6 4 2 655. 655.4 655.8 656.2 656.6 657. Wavelength (nm) Using moden spectogaphs, position of absoption lines can be measued with vey high pecision. xample: Hα line fom hydogen in sola spectum. but: ight, such as all waves, suffes fom Dopple-effect: ines emitted fom moving sta ae Dopple shifted: λ obseved λ emitted λ emitted = v c = an use line shifts to detect extasola planets!... but need good spectogaph: v = 13 m s 1 = λ/λ = 4 1 8, which is only doable by using many ticks. Detection ethods 17 Detection ethods 19
D D O O D D O O D D G S D X esults, 9 16 G S D X esults, 9 18 How to hunt extasola planets using the Dopple Detection ethod: unseen planet 1. get access to lots of telescope time 2. get access to vey good spectogaph G. acy 3. measue fo yeas, to detemine changes in velocity of stas due to motion of sta aound G. acy/u ick s of 26 ovembe 28, 195 extasola planets wee known, cicling 172 stas. elocity signatue and obits of the thee planets aound υ ndomedae. esults 1 esults 3 D D G S D X esults, 9 17 G S D X esults: ass, 9 19 xample: hanging adial velocity of HD 13322 esults in discovey of Jupite-mass planet (Udy et al., 2). Hee: velocity amplitude: 115 m s 1. umbe of Planets 5 4 3 2 1 umbe of Planets 6 4 2 1 2 3 4 ass [ ath ] 5 1 15 2 ass [ Jupite ] any (most!) Planets found have > = 318 adial velocity = velocity along ou line of sight. esults 2 Selection effect: lage = lage velocity amplitude = easie to detect! So, the fact that we have not seen any ath-like planets does not mean that they do not exist, just that we cannot detect them yet. Smallest mass found so fa: 7.5 aound Gliese 876 esults 4
D O D D O O D D G S D X esults: Semimajo xis, 9 21 G S D X esults: Peiod 9 23 umbe of Planets 4 3 2 1 umbe of Planets 15 1 5..5 1. 1.5 2. Semimajo xis [U] umbe of Planets 4 3 2 1 umbe of Planets 15 1 5 2 4 6 8 1 Obital peiod [days] 2 4 6 Semimajo xis [U] ost planets found ae close to companion sta! 2 4 6 8 1 Obital peiod [days] ost planets found in shot obits! Selection effect: small a = shot peiod = detectable in small amount of time (yeas, not decades) Statistics is diect consequence of the selection effect of the pevious slide: shot peiod planets ae detectable duing typical duations of obseving uns... esults 6 esults 8 D G S D X esults: ccenticity 9 24 25 2 Jupite-scale planets close to stas: hot Jupites e.g., HD 29458b, only 7 illion km fom sta: planet is evapoating (HST spectoscopy: mass loss is 1 7 kg s 1 )! S umbe of Planets 15 1 5..2.4.6.8 1. ccenticity any planets ae in eccentic obits! diffeent fom sola system! ight be selection effect due to ou existence: Jupite in eccentic obit in ou sola system = stong distubances of ath s obit = no life! So, in some sense openican pinciple does not always seem to hold! esults 9
D..Hady / PP But not all is bleak HD 7642 (d = 9 ly): discoveed by Hugh Jones (ivepool John ooes Univesity): Jupite mass planet at 3 U fom sola-like sta in cicula obit = stable aths ae possible.