chemical composition of planet-host stars 2013. 2. 22. wonseok kang kyung hee university sang-gak...
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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
3Workshop on Stars, Planets, and Life 2013
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
4Workshop on Stars, Planets, and Life 2013
• 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]
5Workshop on Stars, Planets, and Life 2013
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
8Workshop on Stars, Planets, and Life 2013
• 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)
10Workshop on Stars, Planets, and Life 2013
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
12Workshop on Stars, Planets, and Life 2013
<[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 …
18Workshop on Stars, Planets, and Life 2013
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
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