Radial Velocity Detection of Planets: II. Results To date 1783 exoplanets have been discovered ca 558 planets discovered with the RV method. The others are from transit searches 98 are in Multiple Systems (RV) → exoplanet.eu

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 SpectrographIodine 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 P = 84 d discovered by Latham et al. (1989)

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

51 Peg Rate of Radial Velocity Planet Discoveries

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

Mass Distribution at Low Masses

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

Another short period giant planet

~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

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

Mass = 1.31± 0.25 M Earth (Amplitude = 1.34 m/s) Period = 8.5 hours Earth-mass Planet: Kepler 78b Pepe et al. 2013, Howard et al. 2013

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

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? 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 1988 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/s K ~ 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 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: ~ 100 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 = 5.37 d, K = 12.7 m/s P2 = d, K = 3.2 m/s P3 = 66.7 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  =1.2 m/s Yes! 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?

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 Transiting surveys are finding more planets around M dwarfs

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 solar masses m sini = 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 M Jup 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 main sequence star from the Tautenburg program M * = 1.4 M

Long period planet Very young star Has a dusty ring Nearby (3.2 pcs) Astrometry (1-2 mas) Imaging (  m =20-22 mag) Other planets?  Eri: A „complete“ System Clumps in Ring can be modeled with a planet here (Liou & Zook 2000)

Radial Velocity Measurements of  Eri Large scatter is because this is an active star. It has been argued that this is not a planet at all, but rather the signal due to activity. Hatzes et al. 2000

Scargle Periodogram of  Eri Radial velocity measurements False alarm probability ~ 10 –8 Scargle Periodogram of Ca II measurements

Figure 10 from The HARPS-TERRA Project. I. Description of the Algorithms, Performance, and New Measurements on a Few Remarkable Stars Observed by HARPS Guillem Anglada-Escudé and R. Paul Butler 2012 ApJS doi: / /200/2/15

Period: 2501 ± days Eccentricity: 0.61 ± 04  : 49 ± 4degrees K: 19.0 ± 1.7 m/s msini : 0.86 M Jupiter Period: 2651 ± 36 days Eccentricity: 0.40 ± 0.1  : 141 ± 10 degrees K: 11.8 ± 1.1 m/s msini : 0.64 M Jupiter Hatzes et al Anglada-Escude & Butler 2011 Anglada-Escude & Butler argue that the variations are due to an activity cycle.

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 4. Noise Fake Planets

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

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

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:

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!

Figueira et al. 2010, Astronomy and Astrophysics, 511, 55 Points: IR measurements, Solid line is the orbital solution using optical radial velocity measurements, but with one-third the optical amplitude → No planet! A constant star The Non-Planet around TW Hya

Period = 3.24 d K = 0.5 m/s Msini = 1.13 M Earth FAP = 0.02% Is Alpha Cen Bb really there?

False alarm probability (FAP) ~ 0.02 % Dumusque et al Claimed detection:

False alarm probability = 0.4 False alarm probability = Data Fake Planet Maybe not!

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 Important for transit searches

Summary Radial Velocity Method Cons: Only effective for cool stars. Most effective for short (< 10 – 20 yrs) periods Only high mass planets, but getting closer to Earth mass planets Only get projected mass (msin i) Other phenomena (pulsations, spots, etc.) can mask as an RV signal. Must be careful in the interpretation

The Radial Velocity Method is successful, but highly biased – we only know about planets around solar- type stars!

Summary of Exoplanet Properties from RV Studies ~10 % of normal solar-type stars have giant planets < 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