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Radial Velocity Detection of Planets: II. Results

Radial Velocity Detection of Planets: II. Results. To date 701 planets have been detected with the RV method ca 500 planets discovered with the RV method. The others are from transit searches 94 are in Multiple Systems. → exoplanets.org.

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Radial Velocity Detection of Planets: II. Results

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  1. Radial Velocity Detection of Planets:II. Results • To date 701 planets have been detected with the RV method • ca 500 planets discovered with the RV method. The others are from transit searches • 94 are in Multiple Systems → exoplanets.org

  2. Campbell & Walker: The Pioneers of RV Planet Searches 1988: 1980-1992 searched for planets around 26 solar-type stars. Even though they found evidence for planets, they were not 100% convinced. If they had looked at 100 stars they certainly would have found convincing evidence for exoplanets.

  3. Campbell, Walker, & Yang 1988 „Probable third body variation of 25 m s–1, 2.7 year period, superposed on a large velocity gradient“

  4. e Eri was a „probable variable“

  5. The first extrasolar planet around a normal star: HD 114762 with Msini = 11 MJ discovered by Latham et al. (1989) Filled circles are data taken at McDonald Observatory using the telluric lines at 6300 Ang as a wavelength reference

  6. Rate of Radial Velocity Planet Discoveries 51 Peg

  7. 51 Pegasi b: The Discovery that Shook up the Field Discovered by Michel Mayor & Didier Queloz, 1995 Period = 4,3 Days Semi-major axis = 0,05 AU (10 Stellar Radii!) Mass ~ 0,45 MJupiter

  8. i decreasing probability decreasing Global Properties of Exoplanets: Mass Distribution Because we only measure msini one could argue that all of these companions are not planets but low mass stars viewed near i = 0 degrees.

  9. Argument against stars #1 Probability an orbit has an inclination less than q P(i < q) = 1– cos q e.g. for m sin i = 0.5 MJup for this to have a true mass of 0.5 Msun sin i would have to be 0.01. This implies q = 0.6 deg or P =0.00005: highly unlikely! This argument was probably valid when you had 10 exoplanets, but with 700 it is highly unlikely that all of them are stellar companions viewed at a low inclination

  10. Argument against stars #2 We have detected approximately 200 transiting planets where we know the inclination. All of these have masses in the planetary regime.

  11. Planet: M < 13 MJup→ no nuclear burning Brown Dwarf: 13 MJup < M < ~80 MJup→ deuterium burning Star: M > ~80 MJup→ Hydrogen burning Global Properties of Exoplanets: Mass Distribution The Brown Dwarf Desert

  12. Brown Dwarf Desert: Although there are ~100-200 Brown dwarfs as isolated objects, and several in long period orbits, there is a paucity of brown dwarfs (M= 13–50 MJup) in short (P < few years) as companion to stars

  13. An Oasis in the Brown Dwarf Desert: HD 137510 = HR 5740

  14. Brown Dwarfs versus Planets Bump due to deuterium burning The distinction between brown dwarfs and planets is vague. Until now the boundary was taken as ~ 13 MJup where deuterium burning is possible. But this is arbitrary as deuterium burning has little influence on the evolution of the brown dwarf compared to the planet

  15. A better boundary is to use the different distributions between stars and planets: By this definition the boundary between planets and non-planets is 20 MJup

  16. A note on the naming convention: Name of the star: 16 Cyg If it is a binary star add capital letter B, C, D If it is a planet add small letter: b, c, d 55 CnC b : first planet to 55 CnC 55 CnC c: second planet to 55 CnC 16 Cyg B: fainter component to 16 Cyg binary system 16 Cyg Bb: Planet to 16 Cyg B The IAU has yet to agree on a rule for the naming of extrasolar planets

  17. Semi-Major Axis Distribution The lack of long period planets is a selection effect since these take a long time to detect The short period planets are also a selection effect: they are the easiest to find and now transiting surveys are geared to finding these.

  18. Eccentricity versus Orbital Distance Note that there are few highly eccentric orbits close into the star. This is due to tidal forces which circularizes the orbits quickly.

  19. Eccentricity distribution Fall off at high eccentricity may be partially due to an observing bias…

  20. e=0.4 e=0.6 e=0.8 w=0 w=90 w=180 …high eccentricity orbits are hard to detect!

  21. For very eccentric orbits the value of the eccentricity is is often defined by one data point. If you miss the peak you can get the wrong mass!

  22. At opposition with Earth would be 1/5 diameter of full moon, 12x brighter than Venus e Eri 16 Cyg Bb was one of the first highly eccentric planets discovered 2 ´´ Comparison of some eccentric orbit planets to our solar system

  23. Mass versus Orbital Distance There is a relative lack of massive close-in planets

  24. Classes of planets: 51 Peg Planets: Jupiter mass planets in short period orbits

  25. Classes of planets: 51 Peg Planets • ~40% of known extrasolar planets are 51 Peg planets with orbital periods of less than 20 d. This is a selection effect due to: • These are easier to find. • RV work has concentrated on transiting planets • 0.5–1% of solar type stars have giant planets in short period orbits • 5–10% of solar type stars have a giant planet (longer periods)

  26. Another short period giant planet

  27. Classes of planets: Hot Neptunes Santos et al. 2004 McArthur et al. 2004 Butler et al. 2004 Note that the scale on the y-axes is a factor of 100 smaller than the previous orbit showing a hot Jupiter Msini = 14-20 MEarth

  28. If there are „hot Jupiters“ and „hot Neptunes“ it makes sense that there are „hot Superearths“ CoRoT-7b P = 0.85 d Mass = 7.4 ME Hot Superearths were discovered by space-based transit searches

  29. Classes of Planets: The Massive Eccentrics • Masses between 7–20 MJupiter • Eccentricities, e > 0.3 • Prototype: HD 114762 discovered in 1989! m sini = 11 MJup

  30. As of 2011 there were no massive planets in circular orbits Classes: The Massive Eccentrics

  31. Classes: The Massive Eccentrics Now there is more, but still relatively few. Ignoring the blue points (close in planets) there are ~ 10 planets with masses > 10 MJup with e < 0.2 and ~20 with e > 0.2

  32. Red: Planets with masses < 4 MJupBlue: Planets with masses > 4 MJup

  33. Initially you have two giant planets in circular orbits These interact gravitationally. One is ejected and the remaining planet is in an eccentric orbit Planet-Planet Interactions Lin & Ida,  1997, Astrophysical Journal, 477, 781L

  34. Classes: Planets in Binary Systems Why should we care about binary stars? • Most stars are found in binary systems • Does binary star formation prevent planet formation? • Do planets in binaries have different characteristics? • What role does the environment play? • Are there circumbinary planets? (see Kepler Lecture!)

  35. Some Planets in known Binary Systems: For more examples see Mugrauer & Neuhäuser 2009, Astronomy & Astrophysics, vol 494, 373 and references therein There are very few planets in close binaries. The exception is g Cep.

  36. If you look hard enough, many exoplanet host stars in fact have stelar companions A new stellar companion to the planet hosting star HD 125612 Mugrauer & Neuhäuser 2009 Approximately 17% of the exoplanet hosting stars have stellar companions (Mugrauer & Neuhäuser 2009). Most of these are in wide systems.

  37. g Cep Ab: A planet that challenges formation theories The first extra-solar Planet may have been found by Walker et al. in 1992 in abinary system: Ca II is a measure of stellar activity (spots)

  38. g Cephei Period 2.47 Years Msini 1.76 MJupiter e 0.2 a 2,13 AU K 26.2 m/s Planet Period 56.8 ± 5 Years Msini ~ 0,4 ± 0,1 MSun e 0,42 ± 0,04 a 18.5 AU K 1.98 ± 0,08 km/s Binary

  39. Primary star (A) g Cephei Secondary Star (B) Planet (b)

  40. Neuhäuser et al. Derive an orbital inclination of AB of 119 degrees. If the binary and planet orbit are in the same plane then the true mass of the planet is 1.8 MJup.

  41. The planet around g Cep is difficult to form and on the borderline of being impossible. Standard planet formation theory: Giant planets form beyond the snowline where the solid core can form. Once the core is formed the protoplanet accretes gas. It then migrates inwards. In binary systems the companion truncates the disk. In the case of g Cep this disk is truncated just at the ice line. No ice line, no solid core, no giant planet to migrate inward. g Cep can just be formed, a giant planet in a shorter period orbit would be problems for planet formation theory.

  42. The interesting Case of 16 Cyg B Effective Temperature: A=5760 K, B=5760 K Surface gravity (log g): 4.28, 4.35 Log [Fe/H]: A= 0.06 ± 0.05, B=0.02 ± 0.04 16 Cyg B has 6 times less Lithium These stars are identical and are „solar twins“. 16 Cyg B has a giant planet with 1.7 MJup in a 800 d period

  43. Kozai Mechanism: One Explanation for the high eccentricty of 16 Cyg B Two stars are in long period orbits around each other. A planet is in a shorter period orbit around one star. If the orbit of the planet is inclined, the outer planet can „pump up“ the eccentricity of the planet. Planets can go from circular to eccentric orbits. This was first investigated by Kozai who showed that satellites in orbit around the Earth can have their orbital eccentricity changed by the gravitational influence of the Moon

  44. Kozai Mechanism: changes the inclination and eccentricity

  45. Planetary Systems: 94 Multiple Systems The first:

  46. Some Extrasolar Planetary Systems Star P (d) MJsini a (AU) e HD 82943 221 0.9 0.7 0.54 444 1.6 1.2 0.41 GL 876 30 0.6 0.1 0.27 61 2.0 0.2 0.10 47 UMa 1095 2.4 2.1 0.06 2594 0.8 3.7 0.00 HD 37124 153 0.9 0.5 0.20 550 1.0 2.5 0.40 55 CnC 2.8 0.04 0.04 0.17 14.6 0.8 0.1 0.0 44.3 0.2 0.2 0.34 260 0.14 0.78 0.2 5300 4.3 6.0 0.16 Ups And 4.6 0.7 0.06 0.01 241.2 2.1 0.8 0.28 1266 4.6 2.5 0.27 HD 108874 395.4 1.36 1.05 0.07 1605.8 1.02 2.68 0.25 HD 128311 448.6 2.18 1.1 0.25 919 3.21 1.76 0.17 HD 217107 7.1 1.37 0.07 0.13 3150 2.1 4.3 0.55 Star P (d) MJsini a (AU) e HD 74156 51.6 1.5 0.3 0.65 2300 7.5 3.5 0.40 HD 169830 229 2.9 0.8 0.31 2102 4.0 3.6 0.33 HD 160691 9.5 0.04 0.09 0 637 1.7 1.5 0.31 2986 3.1 0.09 0.80 HD 12661 263 2.3 0.8 0.35 1444 1.6 2.6 0.20 HD 168443 58 7.6 0.3 0.53 1770 17.0 2.9 0.20 HD 38529 14.31 0.8 0.1 0.28 2207 12.8 3.7 0.33 HD 190360 17.1 0.06 0.13 0.01 2891 1.5 3.92 0.36 HD 202206 255.9 17.4 0.83 0.44 1383.4 2.4 2.55 0.27 HD 11964 37.8 0.11 0.23 0.15 1940 0.7 3.17 0.3

  47. The 5-planet System around 55 CnC 0.17MJ • 5.77 MJ • • 0.82MJ 0.11 MJ 0.03MJ Red lines: solar system plane orbits

  48. The Planetary System around GJ 581 16 ME 7.2 ME 5.5 ME Inner planet 1.9 ME

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