Chemical Composition of Planet-Host Stars

2013. 2. 22.

Wonseok Kang Kyung Hee University

Sang-Gak Lee Seoul National University

2Workshop on Stars, Planets, and Life 2013

Why? : Abundances of Planet Host Stars

Proto-planetary Disk

Disk PropertiesMass

Temperature……

Chemical Abundances

Extrasolar Planets

Planet Occurrence

Planet PropertiesMass

Semi-major Axis…………

Planet Formation

Process

Chemical Abundances of Planet Host atmosphere

Planet OccurrencePlanet PropertiesObservations

Theories

Planet Formation TheoryCandidates of Planet Search

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1. Planet-Host Star (PHS) is metal-rich?– Core-accretion model – Gravitational instability in disk

Issues on PHS Abundances

Core-accretion Model Amount of planetesimals depends on metallicity

Gravitational instability Gravitational instability is less sensitive to metallicity

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• Planet-metallicity correlation ( observationally )– The planet detectability is exponentially increasing with increasing metallicity (Fischer & Valenti 2005) using ~ 1000 stars of SPOCS catalog– Planet occurrence is correlated with stellar mass and metallicity (Johnson et al. 2010) using the data of SPOCS (+ M dwarfs and A dwarfs)

Previous Studies – Metallicity

P(planet) = 0.03 × 10 2 [Fe/H]

Fischer & Valenti 2005

Johnson et al. 2010

f (M,F)=0.07 × (M/M⊙)1.0 × 101.2 [Fe/H]

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1. Why metal-rich?– Primordial metal-rich nebula make more planets in stars – Stars with planets rocky matrial engulfed into the atmosphere

Issues on PHS Abundances

Enhancement of Both

Volatiles & RefractoriesLess Volatiles,

More Refractories

Self-enrichment (Pollution) HypothesisPrimordial Hypothesis

Metal-richPlanet Host Stars

More Planetesimals

Primordial High-metallicity Composition

Accretion of Metal-rich Material

Normal Composition

Core-accretion Model → More Planets

Migration of Planets and Planetesimals

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• Chemical abundance of PHSs– Bondaghee et al. (2003), Gilli et al. (2006), Neves et al. (2009)

• Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni , Na, Mg, Al ; refractories – Ecuvillon et al. (2004, 2006)

• C, N, O, S, Zn ; volatiles

• Difference between volatile and refractory (pollution?)– Abundance difference between volatiles and refractories for planet host stars

(Ecuvillon et al. 2006) • CNO, S, Zn / Cu, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, / Na, Mg, Al (from 6 references)• 88 planet host stars and 33 comparison stars• No difference more than the error of abundance analysis and the star-to-star scatter

– Volatiles and refractories in solar analog (Gonzalez et al. 2010) • 14 solar analogs with super-Earths and 14 “single” solar analogs • Considering the galactic chemical evolution, difference in mean abundance disappears

Previous Studies – Chemical Abundance

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• Samples – Planet-Host Stars (PHSs)

• Butler et al. (2006) and http://exoplanet.eu (Jean Schneider , 2010)• F, G, K type stars with planet

– Comparison stars • Tycho-2 spectral type catalog (Wright et al. 2003) • F, G, K type stars within 20 pc from the Sun, without known planets

• Observations (2007 ~ 2010)– BOES with BOAO 1.8-m telescope, in uniform way

• High-resolution echelle spectrograph – 166 stars : 93 PHSs (67 dwarfs) / 73 Comparison stars (68 dwarfs)– S/N ratio > 100 at 6070 Å– R = 30,000 or 45,000

STARS for Abundance Analysis

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• 26 elements by EW measurement– CNO, α-elements, iron-peak elements, and neutron-capture elements– Line list

• Fe lines (VALD) verified with BOES solar spectrum • C, N, O, K, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, Eu (Reddy et al. 2003) • Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni (Neves et al. 2009)

• Sulfur by synthetic spectrum– Three multiplet lines near 6757 Å in optical (Caffau et al. 2005)

• located in the narrow range of 0.05 Å

ELEMENTS for Abundance Analysis

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How? : Abundance Analysis

• Using Equivalent-Widths (EWs)

• Using Synthetic Spectrum

Model Atmosphere

EWs (elemental lines)

MOOG code(Sneden, 2010)

Model atmosphere

Abundance

MOOG code(Sneden, 2010)

Synthetic Spectrum

Observed spectrum

Abundance

Line Data (log gf, E.P.)

Line Data (log gf, E.P.)

Fine Analysis

EWs (Fe lines)

Fine Analysis

EWs (Fe lines)

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EW Measurement / Synthetic Spectrum

Color lines Blue : - 0.15 dexRed : best-fitGreen : +0.15 dex

Black circles Observed Spectrum

Wavelength

S I (MOOGSY)Ni I (MOOGEL)

HD 222368HD 222368

WHICH ELEMENT ISMOST ABUNDANT IN “PLANET”-HOST STARS?

• Mean abundance in planet-host stars

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<[X/H]>PHS - <[X/H]>Comparison

Abundance Difference on TC

Na CuMn

MgCoNi

AlSc

Δ<[Fe/H]>

Ba NdK

• Solid line : Δ<[X/H]> between PHSs and comparisons • Dotted line : Δ<[Fe/H]> = 0.13 ± 0.23 dex • Shaded region : the standard deviation of [X/H]

Volatile

Zr

Refractory

C

N

O S

Zn

Fe

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Manganese

Mn I (4) log ε⊙ = 5.50 dex[X

/Fe]

[X/H

]

All stars follow the Galactic chemical evolution

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Barium

Ba II (2) log ε⊙ = 2.40 dex[X

/Fe]

[X/H

]

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• PHSs are metal-rich • Chemical evolution trend in high-[Fe/H]

– If an element is more abundant in metal-rich stars, [X/H] of PHS is higher than [X/H] of normal star

• This is nothing more than a reflection of metal-rich PHS

• There is no evidence for pollution!

The Origin of [X/H] Difference

Difference Galactic chemical evolu-tion

Metal-rich PHS

Less <[X/H]>

More <[X/H]>

Decreasing at [Fe/H] > 0

Increasing at [Fe/H] > 071 % of PHS in [Fe/H] > 0

WHICH ELEMENT IS SENSITIVE TO “PLANET” OCCURRENCE?

• Kolmogorov-Smirnov Test• Proportion of PHS

• Not volume-limited • Not covering all nearby stars • Not homogeneous

• Therefore, we performed K-S test– Shows only the degree of difference between two distributions

Our Sample is …

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Kolmogorov-Smirnov Test

Low probability from K-S test(< 0.02%) : C, O, Na, Mg, Ca, Al, Si, Zn

The probability,that [X/H] distributions of two groups belong to the same population for each element

Fe : 0.02%

50% Condensation temperature (Lodders 2003)

• Not volume-limited • Not covering all nearby stars • Not homogeneous

• Therefore, we performed K-S test– Shows only the degree of difference between two distributions

• Nevertheless, we tried to find the relation between planet occurrence and chemical abundances, [X/H]

– Shows the direction

Our Sample is …

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• Histogram of [X/H]– In each bin of [X/H] ( bin size = 0.1 dex)– For each bin,

• Probability function of planet occurrence

Proportion of PHS for [X/H]

• α : the proportion at the solar abundance, at [X/H] = 0 • β : increasing trend coefficient

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Proportion of PHS for [X/H] Histogram- Planet host star- Comparison star

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SiC

Proportion of PHS for [X/H]

O Mg ZnCa Ti Cr β[X/H] > β[Fe/H]

• Dotted line : [Fe/H] = 0.77

• Error bar : fitting error of

• β coefficient for each element

Probability more steeply increase with increasing abundances of C, O, Mg, Si, Ca, Ti, Cr, Zn , relative to [Fe/H]

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• No significant difference between volatiles and refractories – Considering the galactic chemical evolution

• The elements from K-S test– Low probability that the distributions of two groups belong to the same population >> C, O, Na, Mg, Al, Ca, Si, Zn ( < 0.02 %, Fe)

• The elements from the proportion of PHS– β [X/H] > β [Fe/H]

>> C, O, Mg, Si, Ca, Ti, Cr, Zn

Summary

C, O, Mg, Si, Ca, ZnSensitive to Planet occurrence

No evidence for “pollution hypothesis”

THANK YOU감사합니다

24Workshop on Stars, Planets, and Life 2013