Radial Velocity Detection of Planets:II. Results

1. Mutiple Planets

2. The Planet-Metallicity connection

3. Fake Planets

Planetary Systems: 41 Multiple Systems

41 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: solar system planets

•0.11 MJ ••

0.17MJ

0.03MJ

0.82MJ

The Planetary System around GJ 581

7.2 ME

5.5 ME

16 ME

Inner planet 1.9 ME

Can we find 4 planets in the RV data for GL 581?

1 = 0.317 cycles/d

2 = 0.186

3 = 0.077

4 = 0.015

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 = 12.99 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 = 12.93 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 frequency

Published solution:

Measurements from two telescopes: AAT (red) and Keck (blue)

= 2.17 m/s

Published solution:

P1 55.5 d, K = 1.2 m/s

P2 = 3.8 d, K = 1.2 m/s

P3 = 39 d, K = 1.14 m/s

P1 = 4.214 d, K = 2.09 m/s

P2 = 38.01 d, K = 3.58 m/s

P3 = 124 d, K = 3.18 m/s

The Planetary System around 61 Vir?

The Period04 solution:

Note: a 0.895 m/s offset was applied to the AAT data

= 2.17 m/s = 2.02 m/s

With different periods and amplitudes (and the same number of sine functions) we have come up with a better solution.

Problem #1

Largest peak is at 55 d, second peak is at 3.8 d, not 4.2 d. The False Alarm Probability of the 3.8 d peak is 0.004. I only believe planets with FAP << 0.001

Problem #2

Removing first two signals gives a peak at 39 d, but I do not believe it!

AAT Data only

Peak at 55 d (0.018 c/d), but nothing signficant at 4.2 d (0.24 c/d)

Remove the strongest peak and get two signals at 0.033 c/d (30 d, moon contamination?) and another at 0.26 c/d (3.8 d), but smaller peak at 4.44 d

Peak at 10.3 d (0.097c/d)

Remove the dominant peak and residuals show a peak at 4.26 d (0.24 c/d)

Keck Data only

?

AAT Keck

AAT

Keck

Conclusions about the „Planetary System“ around 61 Vir

1. Combined data shows a 3.8 d period, not 4.26 d

2. AAT data shows 3.8 d peak

3. Individual data sets do not show either 39 d, or 124 d signal

There might be a signal at ~4 d, but the fact that different data sets give different answers makes me doubt this

The other two „planets“ are noise

→ This is not a robust or confirmed planetary system because a different approach gives an entirely different answer!

„The first principle is that you must not fool yourself – and you are the easiest person to fool.“

- Richard Feynman

44

RV

(m

/s)

JD

Radial Velocity Measurements of CoRoT-7b with HARPS. CoRoT-7b is a transiting planet discovered by CoRoT. The additional planets were found from the radial velocity follow up.

The CoRoT-7 Planetary System

Mass = 6.9 ME

P = 0.85 Days

CoRoT-7bP = 3.7 DaysMass = 12.4 ME

CoRoT-7c

P = 9 Days

Mass = 16.7 ME

CoRoT-7d

The RV variations are dominated by the stellar activity. This must be removed in order to find the planet(s) signal(s).

CoRoT-7b

CoRoT-7c

CoRoT-7d

47

0.017 AU

0.045 AU

0.082 AU

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

EccentricitiesMass versus Orbital Distance

Red points: SystemsBlue points: single planets

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

The Dependence of Planet Formation on Stellar Mass

A0 A5 F0 F5

RV

Err

or (

m/s

)

G0 G5 K0 K5 M0

Spectral Type

Main Sequence Stars

Ideal for 3m class tel. Too faint (8m class tel.). Poor precision

~10000 K ~3500 K

2 Msun 0.2 Msun

Exoplanets around low mass stars

Ongoing 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:

• Giant planets (2) around GJ 876. Giant planets around low mass M dwarfs seem rare

• Hot neptunes around several.

Currently too few planets around M dwarfs to make any real conclusions

GL 876 System

1.9 MJ

0.6 MJ

Inner planet 0.02 MJ

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 off the Main Sequence“

Result: few planets around early-type, more massive stars, and these are mostly around F-type stars (~ 1.4 solar masses)

Galland et al. 2005

HD 33564

M* = 1.25

msini = 9.1 MJupiter

P = 388 days

e = 0.34

F6 V star

HD 8673

A Planet around an F star from the Tautenburg Program

Frequency (c/d)

Sca

rgle

Pow

erP = 328 days

Msini = 8.5 Mjupiter

e = 0.24

An F4 V star from the Tautenburg Program

M* = 1.4 Mּס

Parameter 30 Ari B HD 8673

Period (days) 338 1628

e 0.21 0.711

K (m/s) 278 290

a (AU) 1.06 2.91

M sin i (MJup) 10.1 12.7

Sp. T F4 V F7 V

Stellar Mass (Mּס) 1.4 1.2

The Tautenburg F-star Planets

As we will see later, more massive stars tend to have more massive planets.

M ~ 1.4 Msun M ~ 1 Msun

M ~ 0.2 Msun

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.

Jovian Analogs: Giant Planets at ≈ 5 AU

Definition: A Jupiter mass planet in a 11 year orbit (5.2 AU)

One of the better candidates:

Why care about Jupiter analogs?

Period = 14.5 yrs

Mass = 4.3 MJupiter

e = 0.16

There is a lot of junk in the solar system and in the past there was more.

Eri: A young stars with a planet(s)

Pic: A young star with planets

And sometimes this junk hits something.

On Jupiter you get big holes.

On the Earth it can destroy most of life.

What would the Solar System Look Like without Jupiter?

Conclusion: Jupiters at 5 AU may be important for the development of intelligent life!

G. Wetherill asked this question and through numerical simulations establised:

• The gravitational influence of Jupiter quickly removes most of the junk from the solar system.

• Without Jupiter the frequency of a cataclysmic collision like the one that killed off the dynosaurs would occur every 100.000 years instead of every 150.000.000 Years

• 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

Clumps in Ring can be modeled with a planet here

(Liou & Zook 2000)

A good Jovian analog but with a lot of junk, and in an eccentric orbit

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

3.39 AUa

0.7e

19 m/sK

1.55 MJupiterMsini

6.85 YearsPeriod

Planet Mass (MJup)

Period (years)

a

(AU)

e

HD 187123c 1.99 10.4 4.89 0.25

HD 13931b 1.88 11.3 5.15 0.02

HD 160691e 1.81 11.5 5.2 0.1

HD 217107c 2.49 11.5 5.27 0.51

55 Cnc c 3.83 14.3 5.77 0.02

HD 134987 c 0.82 13.7 5.8 0.12

Jupiter 1 11.9 5.2 0.05

The Best Candidates

Note: These are the best candidates for direct imaging

Wittenmyer et al. Combined data from 2 programs (McDonald and CFHT) to get a time base of over 23 years (probes to 8 AU). Could exclude M sin i > 2.0 ± 1.1 MJup for 17 objects (frequency < 6%)

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 155358 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.

Something else is funny about the Hyades:

Spitzer observations of the Hyades suggest that the fraction of stars in the Hyades with debris disks is comparable to old field stars and significantly less than for stars with planets.

→ In the cluster environment of the Hyades, whatever something removed the disks so planets could not form.

False Planets

or

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

HD 166435

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 166435 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

P = 4.8 days

Oscillations can produce Radial Velocity 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

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

Dl (Å)

Where does this emission core come from?

Keep in mind:

1. Strong spectral lines are formed higher up in the atmosphere

2. The core of a line is formed higher up than the wings.

The core of the line is formed in the chromosphere where the temperature is higher

HD 166435

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 166435

Spots produce an „anti-correlation“ of Bisector Span versus RV variations:

Setiawan et al. 2007

The Planet around TW Hya?

And my doubts…

Maximum RV variations in the velocity span is ~500 m/s

The claim is no bisector variations in this star

Doppler image of V 410 Tau: A Weak T Tauri Star

The spot distribution on V410 Tau has been present for 15 years!

In a Galaxy (The Milky Way) a long time ago (1990) I did some simulations. I new that active stars had polar spots and I asked the question: „What would the RV and bisector variations look like for a star with a polar spot viewed nearly pole on. My results (from memory):

1. The RV curve is nearly sinusoidal

2. There are virtually no bisector span variations detectable at resolving power R =100,000

3. The largest effect is in the bisector curvature, but high resolution is needed to detect this. R ´= 50,000 (resolving power of TW Hya measurements) is too low.

• TW Hya is a T Tauri star (that will become a weak T Tauri star) viewed pole-on

• It most likely has a decentered polar spot (Doppler images of another TW Hya association star indeed shows a polar spot)

From my lecture of 2009: What is needed to confirm this:

1. Contemporaneous photometry (but this star has a disk and complicated light variations)

2. RV measurements in the infrared where the spot contrast is smaller.

I = 1

(exp(hc/kT) – 1)

2hc2

5

Ispot/Iphotosphere = (exp(hc/kTp) – 1)

(exp(hc/kTs) – 1)

Tspot ≈ 3000 K

Tspot ≈ 5000 K

At 5500 Å contrast ratio = 0.03

At 1.5 m contrast ratio = 0.25 → weaker distortions in line profile

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

Confirming Extrasolar Planet Discoveries made with Radial Velocity Measurements

The commandments of planet confirmation:

• Must have long-lived coherent periodic variations

• RV amplitude must be constant with wavelength

• Must not have photometric variations with the same period as the planet

• Must not have Ca II H&K emission variations with the planet period

• Most not have line shape (bisector) variations with the same period as the planet

Why I think CoRoT-7b is a 3 planet System

Another source of „Fake Planets“

Secular changes in proper motion:

Small proper motion

Large proper motion

Perspective effect

The Secular Acceleration of Barnard‘s Star (Kürster et al. 2003).

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!

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 late-type stars

• Most effective for short (< 10 – 20 yrs) periods

• Only high mass planets (no Earths!)

• Projected mass (msin i)

• Other phenomena (pulsations, spots) can mask as an RV signal. Must be careful in the interpretation

Summary of Exoplanet Properties from RV Studies

• ~6% 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)

• Massive planets tend to be in eccentric orbits

• Massive planets tend to have large orbital radii

• Stars with higher metallicity tend to have a higher frequency of planets, but this needs confirmation