Heavy meteal rules
The star-planet connection

Vardan Adibekyan
Institute of Astrophysics and Space Sciences

1 June 2015
NAOJ, TokyoIntroduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

1

Introduction to exoplanets
Diversity of exoplanets
Planet formation theories

2

Planet formation and metallicity
Giant planets
Low-mass planets
Planets around evolved stars

3

Planet formation: Importance of other elements
Heavy elements in the metal-poor regime

4

Planet architecture and metallicity
Period, mass, eccentricity, and [Fe/H]: previous works
Period-mass diagram and [Fe/H] with SWEET-Cat

5Conclusion
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Outline1

Introduction to exoplanets
Diversity of exoplanets
Planet formation theories

2

Planet formation and metallicity
Giant planets
Low-mass planets
Planets around evolved stars

3

Planet formation: Importance of other elements
Heavy elements in the metal-poor regime

4

Planet architecture and metallicity
Period, mass, eccentricity, and [Fe/H]: previous works
Period-mass diagram and [Fe/H] with SWEET-Cat

5Conclusion
Vardan AdibekyanHeavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

1924 confirmed and 4600 planet candidates (Kepler )483 multiple planet systems

RV - 602 planets
Transit - 1206 planets
Other - 116 planets

Figure: MP vs. year of discovery (www.exoplanets.eu).
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

The spread in planetary properties

Figure: Period vs. mass (www.exoplanets.eu).
Vardan Adibekyan

Heavy meteal rules

Conclusion

IntroductionPlanet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

The spread in planetary properties

Hot Jupiters
Very eccentric planets (even e > 0.9)
Extremely short period planets (P < 1 day)
Evaporating planets...

New planet formation theories needed

Figure: Period vs. mass (www.exoplanets.eu).
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

The two main formation theories

Core-accretion
The formation of a giant planet begins with planetesimalcoagulation and cor formation (similar to terrestrial planets) whichthen attract gas, first slowly, and then in a runaway state.
Safronov & Svagina (1969), Pollack et al. (1996)
Gravitational instability
Giant planets form by the gravitational fragmentation in the
protoplanetary disk surrounding young stars
Boss (1997)

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Core-accretion

Formation in three phases:
I. Accretion of planetesimals within the gravitational reachII. Slow envelope accretion (formation time is defined by phase II)
III. Runaway (rapid) gas accretion (when Mgas = Mcore = 5-20 M⊕ )The model explains formation of giant (not very massive) and rocky planets at notvery large orbits (but see Kikuchi et al. 2014 and at not very low metallicities).
See e.g. Ida & Lin 2004; Mordasini 2009,2012; Hasegawa & Pudritz 2014
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Gravitational instability

Figure: 3D simulations by Mayer et al. 2002.
Giant planets form extremely rapidly, due to fragmentation of the disk under specificconditions (very cool and massive disks etc).
The model explains formation of gas giants (with and without cores) and possibly
rocky planets at large distances (but see Nayakshin 2015a,b,c).
See. e.g. Boss 1997, 2011, Mayer et al. 2007; Boley 2009; Vorobyov & Basu 2010
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

CA vs./and GI
The two processes can be complementary

Figure: Courtesy L. Close (2010).
Vardan Adibekyan

Heavy meteal rules

P-M and [Fe/H]

ConclusionIntroduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Outline1

Introduction to exoplanets
Diversity of exoplanets
Planet formation theories

2

Planet formation and metallicity
Giant planets
Low-mass planets
Planets around evolved stars

3

Planet formation: Importance of other elements
Heavy elements in the metal-poor regime

4

Planet architecture and metallicity
Period, mass, eccentricity, and [Fe/H]: previous works
Period-mass diagram and [Fe/H] with SWEET-Cat

5

Conclusion
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Different planet formation scenarios offerdifferent observationally testable signatures
However, mixed theories together with some physical processes (e.g. migration,scattering) and specific initial conditions can explain EVERYTHING

Core-accretion
Giant planet - metallicity correlation
Efficiency ∼ dust-to-gas ratio = M/H ' Fe/H

Gravitational instability
Giant planet - no (apparent) metallicity correlation

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Giant planetsApparent correlation between stellar metallicity and giant planet
frequency (e.g. Gonzalez et al. 1998, Santos et al. 2001,2004, Fischer & Valenti
2005, Sousa et al. 2011).

Figure: From Santos et al. 2004 (left) and from Sousa et al. 2011 (right).
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Giant planets - metallicity: the functional form
Is the planet formation mechanism the same at low and highmetallicities?

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Giant planets - metallicity: the functional form
Bayesian analysis with different functional forms
Flat or exponential - no statistical difference. Mortier et al. 2013a

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Low-mass planets
No correlation found for Super-Earth/Neptune-like planets ?
e.g. Sousa et al. 2011, Mayor et al. 2011, Buchhave et al. 2012

Figure: From Sousa et al. 2011 (left) and from Buchhave et al. 2012 (right).

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Small-size planets: Boundary at ∼2R⊕ ?
The sample – Kepler multi-planet candidates
Parameters – KIC

Figure: Wang & Fischer 2013, submitted
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Small-size planets: Boundary at ∼2R⊕ ?
Planet-metallicity correlation for all but planets with RP < 2R⊕

Figure: Wang & Fischer 2013, submitted
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Small-size planets: Boundary at ∼2R⊕ ?
The sample – Planet candidates from Buchhave et al. 2014 - B14
Parameters – B14 and KIC corrected according B14

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Small-size planets: Boundary at ∼2R⊕ ?
A universal planet-metallicity correlation for all planets

Figure: Wang & Fischer 2015, accepted
Vardan Adibekyan

Heavy meteal rules

Conclusion

IntroductionPlanet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Small-size planets: Boundary at ∼2R⊕ ?
Three size regimes of exoplanets: Boundaries at 1.7R⊕ and 3.9R⊕
Metallicity controls the structure of planetary systems.

Three distinct populations of planetswith different metallicities.
RP < 1.7RE - terrestrial-like planets
1.7RE < RP < 3.9RE - gas dwarf
planets with rocky cores
RP > 3.9RE - ice or gas giant planets

Figure: Buchhave et al. 2014
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Small-size planets: Boundary at ∼2R⊕ ?
No evidence for the proposed radius boundary at 1.7 R⊕
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10p − value

10−2
10−3

10−6

Terrestrial?

10−5

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−1

10−4Gas dwarfs?

100

0

Ice/gas giants

24

6
8
10
Planet radius [REarth]Figure: Schlaufman 2015
Vardan Adibekyan

Heavy meteal rules

1214Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Small-size planets: Important but difficult
Planet frequency vs. metallicity is very important to constrain the formation theories,
but it is difficult from the observational point of view. Difficult to create a“comparison” sample (especially in the transit surveys).

Figure: Hasegawa & Pudritz 2014 (left) and Nayakshin 2015 (right)

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Evolved stars with giant planets

Relative frequency

0.25

Red giant hosts - TS13
Red comparison stars

0.20

No metallicity correlation?

0.15
0.10

Evidence for planet engulfment?
(Pasquini et al. 2007)

0.05
0.00

1.0

0.80.60.40.2[Fe/H] - TS130.00.20.4

A mass effect? (Ghezzi et al. 2010)
A spectroscopic analysis issue? (Hekker& Meléndez 2007; Santos et al. 2009)

There is a correlation after all? (Quirrenbachet al. 2011; Reffert et al. 2015)
Figure: Mortier et al. 2013b.
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]Conclusion

Evolved stars with giant planets
A selection bias? (Mortier et al. 2013b).
Missing metal-rich stars in the giant star sample from (giant) planet search
programs due to B-V cuts.

Takeda et al. 2008 + da Silva et al. 2006 +Zielinski et al. 2012

Vardan Adibekyan

Giant planet hosts

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Planet - metallicity

A lot has been done in this field but there are still many open
questions and conflicting observations and theories.

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Outline1

Introduction to exoplanets
Diversity of exoplanets
Planet formation theories

2

Planet formation and metallicity
Giant planets
Low-mass planets
Planets around evolved stars

3

Planet formation: Importance of other elements
Heavy elements in the metal-poor regime

4

Planet architecture and metallicity
Period, mass, eccentricity, and [Fe/H]: previous works
Period-mass diagram and [Fe/H] with SWEET-Cat

5Conclusion
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Are stars with planets chemically different?

Previous studies yielded contradictory results
Most studies found no systematic difference in abundances(Takeda 2007; Bond et al. 2008; Neves et al. 2009; Delgado Mena et al. 2010)
Possible enrichment in some species(Bodaghee et al. 2003; Robinson et al. 2006; Brugamyer et al. 2011; Kang et al. 2011)

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Refractory elements

Figure: [X/Fe] vs. [Fe/H] for HARPS sample. Adibekyan et al. 2012a.

Element enhancement of planet hosts
Mg,Ti, Si, Sc, and Al at [Fe/H] . -0.2 dex
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

α-elements

Figure: HARPS + Kepler samples. Adibekyan et al. 2012b.
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

α-elements

Planet frequency 12.3 ± 4.1%

Planet frequency 2.2 ± 1.3%

Figure: HARPS + Kepler samples. Adibekyan et al. 2012b.
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements[Fe/H] 6= [M/H] at low metallicities

Vardan Adibekyan

Heavy meteal rules

P-M and [Fe/H]

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Planet frequency and [Ref] index[Ref] - the mass abundances of Mg, Si and Fe relative to the Sun

Figure: Gonzalez 2014.
Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Planet frequency and [Ref] index

Figure: Adibekyan et al. 2012. Super-Earths (blue), giants (red)Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Interior structure of planets and chemical elements

Figure: Dorn et al. 2015.
Observations of mass and radius are sufficient to constrain core size
Stellar elemental abundances (Fe, Si, Mg) are principal constraints to reducedegeneracy in interior structure models and to constrain mantle composition

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Outline1

Introduction to exoplanets
Diversity of exoplanets
Planet formation theories

2Planet formation and metallicity
Giant planets
Low-mass planets
Planets around evolved stars

3

Planet formation: Importance of other elements
Heavy elements in the metal-poor regime

4

Planet architecture and metallicity
Period, mass, eccentricity, and [Fe/H]: previous works
Period-mass diagram and [Fe/H] with SWEET-Cat

5

Conclusion
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Dawson & Murray-Clay (2013)

Close-in giant planets orbiting metal-poor stars have lower
eccentricities than those orbiting metal-rich stars.

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Dawson & Murray-Clay (2013)
Metal-poor

Smooth disk migration

Metal-richRebekah Dawson CfA

Dynamical interactions

Close-in giant
planets
orbiting
metal-poorstars stars
have lower
Giant
planets
orbiting
metal-richshoweccentricitiessignatures
than those oforbiting
metal-richstars.
planet-planet interactions
R. Dawson & R. Murray-Clay 2013, ApJ, 767, L24

Vardan Adibekyan

Heavy meteal rules

Conclusion

IntroductionPlanet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Tsang, Turner, & Cumming 2014
In the shadowed region (0.1 - 1 AU),lack of gap insolation allows diskinteractions to damp eccentricity.
Outside such shadowed regions
stellar illumination can heat theplanetary gaps and drive eccentricity
growth for giant planets.

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Beaugé & Nesvorniý (2013)

A lack of R . 4R⊕ planets with periods P < 5 days around metal-poor stars
A paucity of sub-Jovian planets around metal-poor stars with P < 100 days

Small planets around metal-poor stars do not migrate far
Disk migration?

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]SWEET-Cat:a catalog of stellar parameters for stars with planets

Homogeneous stellar parameters. Santos et al. 2013
Over 65% of all planet host stars known
More than 90% of all stars with RV-detected planets

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicityOther elements

P-M and [Fe/H]

Conclusion

P-MP diagram and [Fe/H] with SWEET-Cat[Fe/H] >= -0.1

Planets around metal-poor stars[Fe/H] < -0.1

Have longer periods than planets aroundmetal-rich stars (≈10M⊕ < MP < ≈4MJup ).
Form farther out
Form later and do not have time tomigrate far
Giant planets show long periods (>100 days)
Migration is less rapid than assumed

Figure: P-MP from Adibekyan et al. 2013.

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]Conclusion

P-MP diagram and [Fe/H] with SWEET-Cat:
Earth-like planets
No metal-rich planet with long period
Detection bias?
If not, then
Metal-rich systems ordinarily migrate
Always form close to their parent stars(Is there enough material?)

Habitable planets should be morecommon around metal-poor stars?

Figure: P-MP from Adibekyan et al. 2013, modified.

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Conclusion

Different Formation Mechanisms for Hot versus Warm Super-Earths?

Figure: Zhu 2015.

Short- and long-period super-Earths show different dependence on
the host metallicity: transition at 70-100 days.

Vardan Adibekyan

Heavy meteal rules

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]

Outline1

Introduction to exoplanets
Diversity of exoplanets
Planet formation theories

2

Planet formation and metallicity
Giant planets
Low-mass planets
Planets around evolved stars

3

Planet formation: Importance of other elements
Heavy elements in the metal-poor regime

4

Planet architecture and metallicity
Period, mass, eccentricity, and [Fe/H]: previous worksPeriod-mass diagram and [Fe/H] with SWEET-Cat

5Conclusion
Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Other elements

P-M and [Fe/H]Conclusion

Metallicity and planet formation and evolution
Metallicity is an important factor for planet formation andevolution
Elements other than iron are also important for planet formation
Are all the elements equally important?
Even low-mass/small-size planets need metals to form
Which metals do they need?
Orbital parameters may depend on the metallicity (directly orindirectly)
Imposes new constraints in the models

Vardan Adibekyan

Heavy meteal rules

Conclusion

Introduction

Planet formation and metallicity

Vardan Adibekyan

Other elements

Heavy meteal rules

P-M and [Fe/H]

Conclusion