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

TelescopeInstrumentWavelength Reference 1-m MJUOHerculesTh-Ar 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.Tull SpectroraphIodine 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

 Eri was a „probable variable“

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

51 Peg Rate of Radial Velocity Planet Discoveries

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 M Jupiter

Mass Distribution Global Properties of Exoplanets: i decreasing probability decreasing 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.

P(i <  ) = 1 – cos  Probability an orbit has an inclination less than  e.g. for m sin i = 0.5 M Jup for this to have a true mass of 0.5 M sun sin i would have to be This implies  = 0.6 deg or P = : highly unlikely! Argument against stars #1 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

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.

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 → deuterium burning Star: M > ~80 M Jup → Hydrogen burning

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

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

The distinction between brown dwarfs and planets is vague. Until now the boundary was taken as ~ 13 M Jup 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 Brown Dwarfs versus Planets Bump due to deuterium burning

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 M Jup

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

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.

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.

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 16 Cyg Bb was one of the first highly eccentric planets discovered

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

~40% of known extrasolar planets are 51 Peg planets with orbital periods of less than 20 d. This is a selection effect due to: 1.These are easier to find. 2. 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) Classes of planets: 51 Peg Planets

Another short period giant planet

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

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 Hot Superearths were discovered by space-based transit searches

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

As of 2011 there were no massive planets in circular orbits 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 M Jup with e 0.2 Classes: The Massive Eccentrics

Red: Planets with masses 4 M Jup

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

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!) Why should we care about binary stars? Classes: Planets in Binary Systems

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

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

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)  Cep Ab: A planet that challenges formation theories

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)

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 M Jup.

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 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 ± 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 M Jup in a 800 d period

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

Kozai Mechanism: changes the inclination and eccentricity

Planetary Systems: 94 Multiple Systems The first:

Some Extrasolar Planetary Systems 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 M E 5.5 M E 16 M E Inner planet 1.9 M E

Can we find 4 planets in the RV data for GL 581? 1 = cycles/d 2 = = = Note: for Fourier analysis we deal with frequencies (1/P) and not periods

The Period04 solution: P1 = 5.38 d, K = 12.7 m/s P2 = d, K = 3.2 m/s P3 = 83.3 d, K = 2.7 m/s P4 = 3.15, K = 1.05 m/s P1 = 5.37 d, K = 12.5 m/s P2 = d, K = 2.63 m/s P3 = 66.8 d, K = 2.7 m/s P4 = 3.15, K = 1.85 m/s  =1.53 m/s  =1.17 m/s Almost: Conclusions: 5.4 d and 12.9 d probably real, 66.8 d period is suspect, 3.15 d may be due to noise and needs confirmation. A better solution is obtained with 1.4 d instead of 3.15 d, but this is above the Nyquist sampling frequency Published solution:

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 Idea: If you divide the disk mass among several planets, they each have a smaller mass?

The Dependence of Planet Formation on Stellar Mass

RV Error (m/s) Stellar Mass (solar masses) Main Sequence Stars Ideal for 3m class tel. Too faint (8m class tel.). Poor precision The shape of the previous histogram merely reflects the detection bias of the radial velocity method

Exoplanets around low mass stars (M star < 0.4 M sun ) Programs: ESO UVES program (Kürster et al.): 40 stars HET Program (Endl & Cochran) : 100 stars Keck Program (Marcy et al.): 200 stars HARPS Program (Mayor et al.):~200 stars Results: ~15 planets around low mass (M = M sun ) Giant planets (2) around GJ 876. Giant planets around low mass M dwarfs seem rare Hot neptunes around several → low mass start tend to have low mass planets Currently too few planets around M dwarfs to make any real conclusions

GL 876 System 1.9 M J 0.6 M J Inner planet 0.02 M J

Exoplanets around massive stars Difficult with the Doppler method because more massive stars have higher effective temperatures and thus few spectral lines. Plus they have high rotation rates. A way around this is to look for planets around giant stars. This will be covered in „Planets around evolved stars“ Result: Only a few planets around early-type, more massive stars, and these are mostly around F-type stars (~ 1.4 solar masses)

Galland et al HD M * = 1.25 msini = 9.1 M Jupiter P = 388 days e = 0.34 F6 V star

HD 8673 A Planet around an F star from the Tautenburg Program Mplanet = 14.6 MJup Period = 4.47 Years ecc = 0.72

Frequency (c/d) Scargle Power P = 328 days Msini = 8.5 M jupiter e = 0.24 An F4 V star from the Tautenburg Program M * = 1.4 M סּ

M star ~ 1.4 M sun M star ~ 1 M sun M star = M sun

Preliminary conclusions: more massive stars have more massive planets with higher frequency. Less massive stars have less massive planets → planet formation is a sensitive function of the planet mass.

Astronomer‘s Metals More Metals ! Even more Metals !! Planets and the Properties of the Host Stars: The Star- Metallicity Connection

The „Bracket“ [Fe/H] Take the abundance of heavy elements (Fe for instance) Ratio it to the solar value Take the logarithm e.g. [Fe/H] = –1 → 1/10 the iron abundance of the sun

These are stars with metallicity [Fe/H] ~ +0.3 – +0.5 There is believed to be a connection between metallicity and planet formation. Stars with higher metalicity tend to have a higher frequency of planets. This is often used as evidence in favor of the core accretion theory Valenti & Fischer The Planet-Metallicity Connection? There are several problems with this hypothesis

Endl et al. 2007: HD two planets and.. …[Fe/H] = –0.68. This certainly muddles the metallicity-planet connection

The Hyades

Hyades stars have [Fe/H] = 0.2 According to V&F relationship 10% of the stars should have giant planets, The Hyades Paulson, Cochran & Hatzes surveyed 100 stars in the Hyades According to V&H relationship we should have found 10 planets We found zero planets! Something is funny about the Hyades.

False Planets or How can you be sure that you have actually discovered a planet?

HD In 1996 Michel Mayor announced at a conference in Victoria, Canada, the discovery of a new „51 Peg“ planet in a 3.97 d. One problem…

HD shows the same period in in photometry, color, and activity indicators. This is not a planet!

What can mimic a planet in Radial Velocity Variations? 1. Spots or stellar surface structure 2. Stellar Oscillations 3. Convection pattern on the surface of the star

Starspots can produce Radial Velocity Variations Spectral Line distortions in an active star that is rotating rapidly Radial Velocity (m/s) Rotation Phase

Tools for confirming planets: Photometry Starspots are much cooler than the photosphere Light Variations Color Variations Relatively easy to measure

Ca II H & K core emission is a measure of magnetic activity: Active star Inactive star Tools for confirming planets: Ca II H&K

HD Ca II emission measurements

Bisectors can measure the line shapes and tell you about the nature of the RV variations: What can change bisectors: Spots Pulsations Convection pattern on star Span Curvature Tools for confirming planets: Bisectors

Correlation of bisector span with radial velocity for HD Spots produce an „anti-correlation“ of Bisector Span versus RV variations:

Activity Effects: Convection Hot rising cell Cool sinking lane The integrated line profile is distorted. The ratio of dark lane to hot cell areas changes with the solar cycle RV changes can be as large as 10 m/s with an 11 year period This is a Jupiter! One has to worry even about the nature long period RV variations

The Planet around TW Hya?

Figueira et al. 2010, Astronomy and Astrophysics, 511, 55 A constant star In the IR the radial velocity variations have 1/3 the amplitude in the optical. This is what expected from spots that have a smaller contrast in the IR

How do you know you have a planet? 1. Is the period of the radial velocity reasonable? Is it the expected rotation period? Can it arise from pulsations? E.g. 51 Peg had an expected rotation period of ~30 days. Stellar pulsations at 4 d for a solar type star was never found 2.Do you have Ca II data? Look for correlations with RV period. 3. Get photometry of your object 4. Measure line bisectors 5. And to be double sure, measure the RV in the infrared!

Radial Velocity Planets Period in years → Red line: Current detection limits Green line detection limit for a precision of 1 m/s

Summary Radial Velocity Method Pros: Most successful detection method Gives you a dynamical mass Distance independent Will provide the bulk (~1000) discoveries in the next 10+ years

Summary Radial Velocity Method Cons: Only effective for cool stars. Most effective for short (< 10 – 20 yrs) periods Only high mass planets (no Earths…yet!) Only get projected mass (msin i) Other phenomena (pulsations, spots, etc.) can mask as an RV signal. Must be careful in the interpretation

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) Massive planets tend to be in eccentric orbits and have large orbital radii Stars with higher metallicity tend to have a higher frequency of planets, but this needs confirmation