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

TelescopeInstrumentWavelength Reference 1-m MJUOHerculesTh-Ar / Iodine cell 1.2-m Euler TelescopeCORALIETh-Ar 1.8-m BOAOBOESIodine Cell 1.88-m Okayama Obs,HIDESIodine Cell 1.88-m OHPSOPHIETh-Ar 2-m TLSCoude EchelleIodine Cell 2.2m ESO/MPI La SillaFEROSTh-Ar 2.7m McDonald Obs.2dcoudeIodine cell 3-m Lick ObservatoryHamilton EchelleIodine cell 3.8-m TNGSARGIodine Cell 3.9-m AATUCLESIodine cell 3.6-m ESO La SillaHARPSTh-Ar 8.2-m Subaru TelescopeHDSIodine Cell 8.2-m VLTUVESIodine cell 9-m Hobby-EberlyHRSIodine cell 10-m KeckHiResIodine cell

Campbell & Walker: The Pioneers of RV Planet Searches 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. 1988:

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

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

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

51 Pegasi b: the 1 st 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

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 b: HD b: Beta Gem b: HD b:

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

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

Semi-Major Axis Distribution Semi-major Axis (AU) Number 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=0.4e=0.6e=0.8  =0  =90  =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!

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

Eccentricities Mass versus Orbital Distance 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

~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: 51 Peg Planets

Butler et al Santos et al M sin i = M Earth Classes of planets: Hot Neptunes

If there are „hot Jupiters“ and „hot Neptunes“ it makes sense that there are „hot Superearths“ Mass = 7.4 M E P = 0.85 d CoRoT-7b

Classes: The Massive Eccentrics Masses between 7–20 M Jupiter Eccentricities, e > 0.3 Prototype: HD discovered in 1989! m sini = 11 M Jup

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

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, 781L

Red: Planets with masses 4 M Jup

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? Why should we care about binary stars? Planets in Binary Systems

Some Planets in known Binary Systems: There are very few planets in close binaries. One exception is the  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)

2,13 AUa 0,2e 26,2 m/sK 1,76 M Jupiter Msini 2,47 YearsPeriod Planet 18.5 AUa 0,42 ± 0,04e 1,98 ± 0,08 km/sK ~ 0,4 ± 0,1 M Sun Msini 56.8 ± 5 YearsPeriod Binary  Cephei

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

The planet around  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  Cep this disk is truncated just at the ice line. No ice line, no solid core, no giant planet to migrate inward.  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 M Jup 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) M J sini a (AU) e HD GL UMa HD CnC Ups And HD HD HD Star P (d) M J sini a (AU) e HD HD HD HD HD HD HD HD HD

The 5-planet System around 55 CnC 5.77 M J Red lines: solar system plane orbits 0.11 M J 0.17M J 0.03M J 0.82M J

The Planetary System around GJ 581 (M dwarf!) 7.2 M E 5.5 M E 16 M E Inner planet M sin i = 1.9 M Earth

Resonant Systems Systems Star P (d) M J sini a (AU) e HD GL Cnc HD HD :1 → Inner planet makes two orbits for every one of the outer planet → → 2:1 →3:1 →4:1 →2:1

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

Eccentricities Mass versus Orbital Distance 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!