The Doppler Method or the Radial Velocity Detection

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

Telescope 1 -m MJUO 1. 2 -m Euler Telescope 1. 8 -m BOAO 1. 88 -m Okayama Obs, 1. 88 -m OHP 2 -m TLS 2. 2 m ESO/MPI La Silla 2. 7 m Mc. Donald Obs. 3 -m Lick Observatory 3. 8 -m TNG 3. 9 -m AAT 3. 6 -m ESO La Silla 8. 2 -m Subaru Telescope 8. 2 -m VLT 9 -m Hobby-Eberly 10 -m Keck Instrument Hercules CORALIE BOES HIDES SOPHIE Coude Echelle FEROS 2 dcoude Hamilton Echelle SARG UCLES HARPS HDS UVES HRS Hi. Res Wavelength Reference Th-Ar / Iodine cell Th-Ar Iodine Cell Th-Ar Iodine cell Iodine Cell Iodine cell Th-Ar Iodine Cell Iodine cell

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.

Campbell, Walker, & Yang 1988 „Probable third body variation of 25 m s– 1, 2. 7 year period, superposed on a large velocity gradient“

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 Mc. Donald 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

The Search For Extrasolar Planets At Mc. Donald Observatory Bill Cochran & Artie Hatzes Harlan J. Smith 2. 7 m Telescope 1988 - present Phillip Mac. Queen, Paul Robertson, Erik Brugamyer, Diane Paulson, Robert Wittenmyer, Stuart Barnes Michael Endl Hobby-Eberly 9 m Telescope 2001 - present

51 Pegasi b: the 1 st extrasolar planet: P = 4. 3 days!!! a = 0. 05 AU !!! M sin i = 0. 45 M Jupiter Michel Mayor & Didier Queloz 1995 A HOT JUPITER

1997: The first 2. 7 m Survey Planet: P = 2. 2 yrs a = 1. 67 AU M ~ 1. 7 M Jupiter

More Planets / Brown Dwarfs (co-)discovered with the 2. 7 m Telescope: Eps Eri b: Gam Cep: HD 137510 b: HD 13189 b: Beta Gem b: HD 91699 b:

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

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

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

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

Number Semi-Major Axis Distribution 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.

Updated:

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

e=0. 4 e=0. 6 e=0. 8 w=0 w=90 w=180 …high eccentricity orbits are hard to detect!

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!

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

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

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

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

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

If there are „hot Jupiters“ and „hot Neptunes“ it makes sense that there are „hot Superearths“ Co. Ro. T-7 b Mass = 7. 4 ME P = 0. 85 d

Classes: The Massive Eccentrics • Masses between 7– 20 MJupiter • Eccentricities, e > 0. 3 • Prototype: HD 114762 discovered in 1989! m sini = 11 MJup

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

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

Red: Planets with masses < 4 MJup Blue: Planets with masses > 4 MJup

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?

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

The first extra-solar Planet may have been found by Walker et al. in 1992 in a binary system: Ca II is a measure of stellar activity (spots)

g Cephei Planet Period Msini 2, 47 Years 1, 76 MJupiter e a K 0, 2 2, 13 AU 26, 2 m/s Binary Period Msini 56. 8 ± 5 Years ~ 0, 4 ± 0, 1 MSun e a 0, 42 ± 0, 04 18. 5 AU K 1, 98 ± 0, 08 km/s

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

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.

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?

Planetary Systems: ~50 Multiple Systems

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 47 UMa 30 61 1095 2594 0. 6 2. 0 2. 4 0. 8 HD 37124 153 0. 9 550 1. 0 55 Cn. C 2. 8 0. 04 14. 6 0. 8 44. 3 0. 2 260 0. 14 5300 4. 3 Ups And 4. 6 0. 7 241. 2 2. 1 1266 4. 6 HD 108874 395. 4 1. 36 1605. 8 1. 02 HD 128311 448. 6 2. 18 919 3. 21 HD 217107 7. 1 1. 37 3150 2. 1 0. 2 2. 1 3. 7 0. 27 0. 10 0. 06 0. 00 0. 5 2. 5 0. 04 0. 1 0. 2 0. 78 6. 0 0. 06 0. 8 2. 5 1. 05 2. 68 1. 1 1. 76 0. 07 4. 3 0. 20 0. 40 0. 17 0. 0 0. 34 0. 2 0. 16 0. 01 0. 28 0. 27 0. 07 0. 25 0. 17 0. 13 0. 55 Star P (d) MJsini a (AU) HD 74156 51. 6 1. 5 0. 3 2300 7. 5 3. 5 HD 169830 229 2. 9 0. 8 2102 4. 0 3. 6 HD 160691 9. 5 0. 04 0. 09 637 1. 5 2986 3. 1 0. 09 e 0. 65 0. 40 0. 31 0. 33 0 0. 31 0. 80 HD 12661 0. 35 0. 20 0. 53 0. 20 0. 28 0. 33 0. 01 0. 36 0. 44 0. 27 0. 15 0. 3 263 1444 HD 168443 58 1770 HD 38529 14. 31 2207 HD 190360 17. 1 2891 HD 202206 255. 9 1383. 4 HD 11964 37. 8 1940 2. 3 1. 6 7. 6 17. 0 0. 8 12. 8 0. 06 1. 5 17. 4 2. 4 0. 11 0. 7 0. 8 2. 6 0. 3 2. 9 0. 1 3. 7 0. 13 3. 92 0. 83 2. 55 0. 23 3. 17

The 5 -planet System around 55 Cn. C 0. 17 MJ 5. 77 MJ • 0. 11 M 0. 82 MJ J Red lines: solar system plane orbits • • 0. 03 M J

The Planetary System around GJ 581 (M dwarf!) 16 ME 7. 2 ME 5. 5 ME Inner planet M sin i = 1. 9 MEarth

Resonant 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 61 0. 6 2. 0 0. 1 0. 27 0. 10 → 2: 1 55 Cnc 14. 6 44. 3 0. 8 0. 2 0. 1 0. 2 0. 0 0. 34 → 3: 1 HD 108874 395. 4 1. 36 1605. 8 1. 02 1. 05 2. 68 0. 07 0. 25 → 4: 1 HD 128311 448. 6 2. 18 919 3. 21 1. 76 0. 25 0. 17 → 2: 1 → Inner planet makes two orbits for every one of the outer planet 2: 1

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

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.

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. )

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)

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 M סּ have 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!