The Doppler Method, or the Radial Velocity Detection of Planets: II. Results

1. The Doppler Method, or the Radial Velocity Detection of Planets:II. Results

3. 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.

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

5. The first (?) extrasolar planet around a normal star: HD 114762 with M sin i = 11 MJ discovered by Latham et al. (1989) Filled circles are data taken at McDonald Observatory using the telluric lines at 6300 Ang. The mass was uncomfortably high (remember sin i effect) to regard it unambiguously as an extrasolar planet

6. The Search For Extrasolar PlanetsAt McDonald Observatory Bill Cochran & Artie Hatzes Phillip MacQueen, Paul Robertson, Erik Brugamyer, Diane Paulson, Robert Wittenmyer, Stuart Barnes Michael Endl Hobby-Eberly 9 m Telescope 2001 - present Harlan J. Smith 2.7 m Telescope 1988 - present

7. 51 Pegasi b: the 1st extrasolar planet: P = 4.3 days!!! a = 0.05 AU !!! M sin i = 0.45 M Jupiter A HOT JUPITER Michel Mayor & Didier Queloz 1995

8. 1997: The first 2.7 m Survey Planet: P = 2.2 yrs a = 1.67 AU M ~ 1.7 M Jupiter

9. Gam Cep: HD 13189 b: HD 137510 b: Eps Eri b: Beta Gem b: HD 91699 b: More Planets / Brown Dwarfs (co-)discovered with the 2.7 m Telescope:

10. And then the discoveries started rolling in: “New Planet Seen Outside Solar System” New York Times April 19, 1996 “10 More Planets Discovered” Washington Post August 6, 2000 “First new solar system discovered” USA TODAY April 16, 1999

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

12. Up-to-date Histograms with all ~ 500 exoplanets:

13. One argument: Because of unknown sin i these are just low mass stars seen with i near 0 i decreasing probability decreasing

15. Semi-Major Axis Distribution Number Semi-major Axis (AU) 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.

16. Updated:

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

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

19. 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!

20. At opposition with Earth would be 1/5 diameter of full moon, 12x brighter than Venus e Eri 2 ´´ Comparison of some eccentric orbit planets to our solar system

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

22. Classes of planets: 51 Peg Planets: Jupiter mass planets in short period orbits Discovered by Mayor & Queloz 1995

23. Classes of planets: 51 Peg Planets • ~35% of known extrasolar planets are 51 Peg planets (selection effect) • 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) • Somehow these giant planets ended • up very close to the star! • => orbital migration

24. Classes of planets: Hot Neptunes Santos et al. 2004 Butler et al. 2004 M sin i = 14-20 MEarth

25. 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

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

27. There are no massive planets in circular orbits Classes: The Massive Eccentrics

28. 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

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

30. 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? • For what range of binary periods are planets found? • What conditions make it conducive to form planets?(Nurture versus Nature?) • Are there circumbinary planets?

31. Some Planets in known Binary Systems: There are very few planets in close binaries. One exception is the g Cep system.

32. 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)

33. 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

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

35. 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.

36. The interesting Case of 16 Cyg B These stars are identical and are „solar twins“. 16 Cyg B has a giant planet with 1.7 MJup in a 800 d period, but star A shows no evidence for any planet. Why?

37. Planetary Systems: ~50 Multiple Systems

38. Extrasolar Planetary Systems (18 shown) 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

39. 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

40. The Planetary System around GJ 581 (M dwarf!) 16 ME 7.2 ME 5.5 ME Inner planet M sin i = 1.9 MEarth

41. Resonant Systems 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 55 Cnc 14.6 0.8 0.1 0.0 44.3 0.2 0.2 0.34 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 → 2:1 → 2:1 → 3:1 → 4:1 → 2:1 2:1 → Inner planet makes two orbits for every one of the outer planet

42. Eccentricities • Period (days) Red points: Systems Blue points: single planets

43. Mass versus Orbital Distance Eccentricities Red points: Systems Blue points: single planets On average, giant planets in planetary sytems tend to be lighter than single planets. Either 1) Forming several planets in a protoplanetary disks „divides“ the mass so you have smaller planets, or 2) if you form several massive planets they are more likely to interact and most get ejected.

44. Summary • Radial Velocity Method • Pros: • Most successful detection method • Gives you a dynamical mass and orbital • parameters • Distance independent • Will provide the bulk (~1000) discoveries in the next 10+ years • Important for transit technique (mass determ.)

45. Summary • Radial Velocity Method • Cons: • Only effective for late-type stars • Most effective for short (< 10 – 20 yrs) periods • Only high mass planets (no Earths! maybe) • Projected mass (m sin i) • Other phenomena (pulsations, spots) can mimic RV signal. Must be careful in the interpretation (check all diagnostics)

46. Summary of Exoplanet Properties from RV Studies • ~5% of normal solar-type stars have giant planets • ~10% or more of stars with masses ~1.5 Mסּhave giant planets that tend to be more massive (more on this later in the course) • < 1% of the M dwarfs stars (low mass) have giant planets, but may have a large population of neptune-mass planets • → low mass stars have low mass planets, high mass stars have more planets of higher mass → planet formation may be a steep function of stellar mass • 0.5–1% of solar type stars have short period giant plants • Exoplanets have a wide range of orbital eccentricities (most are not in circular orbits). This indicates a much more dynamical past than for our Solar System! • Massive planets tend to be in eccentric orbits and large orbital radii • Many multiple systems, some in orbital resonances • Close-in Jupiters must have migrated inwards!