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

II. Results

Telescope Instrument Wavelength Reference

1-m MJUO Hercules Th-Ar / Iodine cell

1.2-m Euler Telescope CORALIE Th-Ar

1.8-m BOAO BOES Iodine Cell

1.88-m Okayama Obs, HIDES Iodine Cell

1.88-m OHP SOPHIE Th-Ar

2-m TLS Coude Echelle Iodine Cell

2.2m ESO/MPI La Silla FEROS Th-Ar

2.7m McDonald Obs. 2dcoude Iodine cell

3-m Lick Observatory Hamilton Echelle Iodine cell

3.8-m TNG SARG Iodine Cell

3.9-m AAT UCLES Iodine cell

3.6-m ESO La Silla HARPS Th-Ar

8.2-m Subaru Telescope HDS Iodine Cell

8.2-m VLT UVES Iodine cell

9-m Hobby-Eberly HRS Iodine cell

10-m Keck HiRes Iodine cell

Campbell & Walker: The Pioneers of RV Planet Searches

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.

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 114762 with M sin i = 11 MJ 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 Telescope1988 - present

Hobby-Eberly 9 m Telescope2001 - present

51 Pegasi b: the 1st extrasolar planet:

P = 4.3 days!!!a = 0.05 AU !!!M sin i = 0.45 M Jupiter

A HOT JUPITERMichel 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:Eps Eri b:

Gam Cep:Gam Cep:

HD 137510 b:

HD 13189 b:

Beta Gem b:

HD 91699 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 TimesApril 19, 1996

The Brown Dwarf Desert

Mass Distribution

Global Properties of Exoplanets:

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

Semi-Major Axis Distribution

Semi-major Axis (AU)

Num

ber

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

=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

EccentricitiesMass 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. 2004

Santos et al. 2004

M sin i = 14-20 MEarth

Classes of planets: Hot Neptunes

If there are „hot Jupiters“ and „hot Neptunes“ it makes sense that there are „hot Superearths“

Mass = 7.4 ME P = 0.85 d

CoRoT-7b

Classes: The Massive Eccentrics

• Masses between 7–20 MJupiter

• Eccentricities, e > 0.3

• Prototype: HD 114762 discovered in 1989!

m sini = 11 MJup

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 MJup

Blue: Planets with masses > 4 MJup

• 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

Star a (AU)16 Cyg B 80055 CnC 540

HD 46375 300Boo 155 And 1540

HD 222582 4740HD 195019 3300

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 MJupiterMsini

2,47 YearsPeriod

Planet

18.5 AUa

0,42 ± 0,04e

1,98 ± 0,08 km/sK

~ 0,4 ± 0,1 MSunMsini

56.8 ± 5 YearsPeriod

Binary Cephei

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 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 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 0.4055 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 0.16Ups And 4.6 0.7 0.06 0.01 241.2 2.1 0.8 0.28 1266 4.6 2.5 0.27HD 108874 395.4 1.36 1.05 0.07

1605.8 1.02 2.68 0.25HD 128311 448.6 2.18 1.1 0.25 919 3.21 1.76 0.17HD 217107 7.1 1.37 0.07 0.13 3150 2.1 4.3 0.55

Star P (d) MJsini a (AU) eHD 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 0.20HD 38529 14.31 0.8 0.1 0.28 2207 12.8 3.7 0.33HD 190360 17.1 0.06 0.13 0.01 2891 1.5 3.92 0.36HD 202206 255.9 17.4 0.83 0.44 1383.4 2.4 2.55 0.27HD 11964 37.8 0.11 0.23 0.15

1940 0.7 3.17 0.3

The 5-planet System around 55 CnC

5.77 MJ

Red lines: solar system plane orbits

•0.11 MJ ••

0.17MJ

0.03MJ

0.82MJ

The Planetary System around GJ 581 (M dwarf!)

7.2 ME

5.5 ME

16 ME

Inner planet M sin i = 1.9 MEarth

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 → Inner planet makes two orbits for every one of the outer planet

→

→

2:1

2:1

→ 3:1

→ 4:1

→ 2:1

•

Eccentricities

Period (days)Red points: SystemsBlue points: single planets

Eccentricities

Mass versus Orbital Distance

Red points: SystemsBlue 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 Mּס 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!