Download Detailed Abundance Analysis for Planet Host Stars

Chemical Composition of
Planet-Host Stars
2013. 2. 22.
Wonseok Kang Kyung Hee University
Sang-Gak Lee Seoul National University
Why? : Abundances of Planet Host Stars
Theories
Proto-planetary Disk
Disk Properties
Mass
Temperature
……
Extrasolar Planets
Planet Occurrence
Planet
Formation
Process
Chemical Abundances
Planet Properties
Mass
Semi-major Axis
……
……
Chemical Abundances of
Planet Host atmosphere
Observations
Planet Occurrence
Planet Properties
Planet Formation Theory
Candidates of Planet Search
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Issues on PHS Abundances
1. Planet-Host Star (PHS) is metal-rich?
–
–
Core-accretion model
Gravitational instability in disk
Core-accretion Model
Amount of planetesimals
depends on metallicity
Gravitational instability
Gravitational instability is
less sensitive to metallicity
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Previous Studies – Metallicity
• 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)
P(planet) = 0.03 × 10 2 [Fe/H]
f (M,F)=0.07 × (M/M⊙)1.0 × 101.2 [Fe/H]
Fischer & Valenti 2005
Johnson et al. 2010
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Issues on PHS Abundances
1. Why metal-rich?
–
–
Primordial metal-rich nebula  make more planets in stars
Stars with planets  rocky matrial engulfed into the atmosphere
Primordial Hypothesis
Self-enrichment (Pollution) Hypothesis
Primordial High-metallicity Composition
Normal Composition
More Planetesimals
Migration of Planets and Planetesimals
Core-accretion Model → More Planets
Accretion of Metal-rich Material
Enhancement of
Both
Metal-rich
Planet Host Stars
Volatiles & Refractories
Less Volatiles,
More Refractories
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Previous Studies – Chemical Abundance
• 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
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STARS for Abundance Analysis
• 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
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ELEMENTS for Abundance Analysis
• 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
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How? : Abundance Analysis
• Using Equivalent-Widths (EWs)
Model Atmosphere
Fine Analysis
EWs
(Fe lines)
Line Data (log gf, E.P.)
MOOG code
(Sneden, 2010)
Abundance
EWs (elemental lines)
• Using Synthetic Spectrum
Model atmosphere
Fine Analysis
EWs
(Fe lines)
Line Data (log gf, E.P.)
MOOG code
(Sneden, 2010)
Synthetic
Spectrum
Abundance
Observed spectrum
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EW Measurement / Synthetic Spectrum
Ni I (MOOGEL)
HD 222368
S I (MOOGSY)
HD 222368
Color lines
Blue : - 0.15 dex
Red : best-fit
Green : +0.15 dex
Black circles
Observed
Spectrum
Wavelength
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WHICH ELEMENT IS
MOST ABUNDANT IN
“PLANET”-HOST STARS?
• Mean abundance in planet-host stars
Abundance Difference on TC
<[X/H]>PHS - <[X/H]>Comparison
•
•
•
Refractory
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]
N
Zn
Na Cu
Mg
Co
Ni
Mn
Al
Sc
Δ<[Fe/H]>
C
O
S
Fe
K
Ba
Nd Zr
Volatile
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Manganese
⊙
= 5.50 dex
[X/H]
[X/Fe]
Mn I (4) log ε
All stars follow the Galactic chemical evolution
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Barium
Ba II (2) log ε
= 2.40 dex
[X/H]
[X/Fe]
⊙
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The Origin of [X/H] Difference
• 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
Metal-rich PHS
Galactic chemical evolution
Difference
71 % of PHS
in [Fe/H] > 0
Increasing at [Fe/H] > 0
More <[X/H]>
Decreasing at [Fe/H] > 0
Less <[X/H]>
• There is no evidence for pollution!
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WHICH ELEMENT IS
SENSITIVE TO
“PLANET” OCCURRENCE?
• Kolmogorov-Smirnov Test
• Proportion of PHS
Our Sample is …
• 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
Kolmogorov-Smirnov Test
The probability,
that [X/H] distributions of two groups
belong to the same population for each element
Low probability from K-S test
(< 0.02%) :
C, O, Na, Mg, Ca, Al, Si, Zn
Fe : 0.02%
50% Condensation temperature (Lodders 2003)
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Our Sample is …
• 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
Proportion of PHS for [X/H]
• Histogram of [X/H]
– In each bin of [X/H] ( bin size = 0.1 dex)
– For each bin,
æ the number of planet host stars ö
%planet host stars =100 ´ ç
÷
total number of samples
è
ø
• Probability function of planet occurrence
• 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]
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Histogram
- Planet host star
- Comparison star
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Proportion of PHS for [X/H]
• β coefficient for each element
C
•
•
O
Mg Si
Ca
Ti
Cr
Zn
β[X/H] > β[Fe/H]
Dotted line :  [Fe/H] = 0.77
Error bar : fitting error of 
Probability more steeply increase with increasing abundances of
C, O, Mg, Si, Ca, Ti, Cr, Zn , relative to [Fe/H]
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Summary
• No significant difference between volatiles and refractories
– Considering the galactic chemical evolution
No evidence for
“pollution hypothesis”
• 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
C, O, Mg, Si, Ca, Zn
Sensitive to Planet occurrence
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THANK YOU
감사합니다
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