Transcript High Resolution Spectroscopy of Stars with Planets

High Resolution Spectroscopy
of Stars with Planets
CHEMICAL ABUNDANCE OF PLANET-HOST STAR
Won-Seok Kang
Seoul National University
2010. 10. 6.
Sang-Gak Lee, Seoul National University
Kang-Min Kim, Korea Astronomy and Space science Institute
INTRODUCTION
• Why we study chemical abundances of host stars
– Conserve primordial abundances of planetary systems
• Related with planet formation process
– Find the relation between abundances and planets by observations
• Describe planet formation process in more detail
• Select proper candidates with interesting planets
– Super-Earths and habitable planets
• What we can to with GMT high-resolution spectroscopy
– Perform abundance analysis for more faint star
• Transiting planet-host star, M dwarf
– Obtain abundances and stellar parameters of more late-type stars
• Avoid strong molecular bands and pressure-broadened atomic lines
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PLANET AND METALLICITY
• Fischer and Valenti (2005) I
– Spectroscopic analysis of ~1000 stars
– For selecting planet-host stars
• Stars with planets were selected with period < 4 years and K > 30
m/s (gas giant planets)
• Stars without planets have
been verified by observations
P( planet )  0.03 102.0[Fe/H]
of over 10 times
for 4 or more years
– Calculate the planet-host ratio
for each [Fe/H] bin
• Planet-host ratios are exponentially
increasing with increasing metallicity
Fischer and Valenti 2005
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PLANET AND METALLICITY
• Fischer and Valenti (2005) II
– Suggest the relation between maximum of total planet mass and
metallicity
• Total planet mass is related with protoplanetary disk mass
⇒ upper limit of total planet mass is increasing with increasing [Fe/H]
• Planet mass from radial velocity
measurement is MJ sini, which
means that this planet mass is
lower limit of exact value
• So, need to know exact planet mass
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Fischer and Valenti 2005
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METHOD OF ABUNDANCE ANALYSIS
• Observations (166 FGK-type stars)
–
–
–
–
BOES at BOAO 1.8m telescope
R ~ 30,000 or 45,000 / SNR ~ 150 at 5500Å
Planet-host stars : 93 (74 dwarfs)
Comparisons : 73 (70 dwarfs) ← stars without known planets
• Abundance analysis
– Kurucz ATLAS9 model grids and MOOG code
– Measure EWs of Fe lines (TAME developed by IDL)
– Determine model parameters by fine analysis (MOOGFE)
• Iteratively run MOOG code and ATLAS9
– Estimate abundances of 13 elements
(Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, S)
• Measuring EWs of elemental lines (TAME)
• Comparing observational spectrum with synthetic spectrum
–
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METHOD OF ABUNDANCE ANALYSIS
• TAME and MOOGFE
Fe I
Fe II
Excitation potential
Equivalent-width
Result of MOOGFE for the Sun
Automatically find model parameters by iterations
By estimating the trend of iron abundance for
excitation potential or equivalent width, and the
abundance difference between Fe I and Fe II
Tools for Automatic Measurement
of Equivalent-widths
GMT Workshop 2010 at SNU
Model parameters
log eps(Fe) = 7.53 dex
Teff = 5765 K
log g = 4.46 dex
ξt = 0.82 km/s
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METALLICITY HISTOGRAM
74 PHSs
70 Comparions
• Metallicity distribution
– Mean value of PHS is 0.13 dex
higher than that of comparison
– Planet-Host Stars are more
concentrated at higher [Fe/H]
Only dwarfs
<[Fe/H>
-0.06
<[Fe/H]>
+0.07
• Comparisons are more widely
distributed overall
• In low-metallicity, comparisons are
more than PHSs
• In high-metallicity, PHSs are much
more than comparisons
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METALLICITY AND PLANET PROPERTIES
• [Fe/H] and Planet mass, MJsini
– Increase with increasing [Fe/H]
• Similar result to Fischer and
Valenti (2005)
– HD 114762
• Known as spectroscopic binary
• Companion is M6 dwarf at the
distance of 130 AU
• Exceptional case or new evidence?
[Fe/H] vs. Planet Mass
Only dwarfs
HD 114762 b
Only 4
samples
– For verifying, more samples in the
range of low-metallicity will be
In the case of multiple-planetary system,
total planet mass is indicated
required
These planetary masses represent MJsini ,
which is less than MJ
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METALLICITY AND PLANET PROPERTIES
X : semi-major axis
Y : [Fe/H]
Size of circle : planet mass
• Metallicities and Planet properties
– Hot jupiters are concentrated in the
region of [Fe/H] > 0
• It can support the relation between
migration and metallicity (Livio &
Only dwarfs
Pringle, 2003)
• A Few stars in low-metallicity region
– In the region of low-metallicity,
about half of host stars have
relatively low-mass multiple planets.
• 2 of 5 planet-host stars have lowmass multiple planets
HD 114762 b
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ABUNDANCE RESULTS
• [X/Fe] vs. [Fe/H]
– Averaged for each [Fe/H] bin
– For most elements, statistical
difference between two
groups ~ 0.03 dex
Chemical Abundance Trend ; [Fe/H] vs. [X/Fe]
• Bin size : 0.2 dex
• Center of each [Fe/H] bin :
-0.5, -0.3, -0.1, +0.1, +0.3, +0.5
Red : Planet-Host Stars
Blue : Comparisons
• [Mn/Fe] ratio
– Difference between two
groups ~ 0.10 dex
– Hyperfine structure
• It is necessary to confirm
this difference by synthetic
spectra and high S/N
observational spectra
Only dwarfs
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ABUNDANCE RESULTS
• [Mn/H] and Planet mass
– Maximum of planet mass are
increasing in low [Mn/H] range
and decreasing in high [Mn/H]
range
[Mn/H] vs. planet mass
HD 114762 b
– Turn-off point of trend is located
at solar Mn abundance
– It seems that the high [Mn/H]
ratio has suppressed the
massive planet formation
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DIFFICULTIES
• Most of planets were detected by radial velocity method
– Don’t know exact mass of planet
– Samples are limited to almost nearby stars
– Solution ; transiting planet
• Transit observation gives us more accurate mass of planet
• Transit observation is available for faint and distant stars
• Lack of low-metallicity star
– More low-metallicity stars are required to verify the relation between
planet properties and abundances
– It seems to be easier to find Neptune-mass planets in low-metallicity stars
(Sousa et al. 2009)
• They have only three Neptune-mass samples
• Expect that more low-metallicity stars will be detected, in the near future
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PRELIMINARY TEST
• Homogeneous studies of 30 transiting
extrasolar planets (Southworth, 2010)
– Provide the properties of planets and host
stars
MJ
Transiting planets
• Test the relation for only transiting planets
– Maximum of planet mass is decreasing with
increasing [Fe/H]
– Inverse trend for the previous result of
samples detected by radial velocity method
– Problems
• No stars of metallicity less than -0.2 dex
• It seems that there are two groups of planet mass
• Metallicities were adopted from several references
M J sin i
Radial velocity method
– Solutions
• More low-metallicity stars with transiting planets
• Perform abundance analysis in uniform method
and with the same instrument
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WHAT WE CAN DO WITH GMT
• Detailed abundances of host stars with transiting planets
– Potential to detect new transiting planets in the near future
• HATNet, Kepler, CoRoT, SuperWASP, SWEEPS
– There are already 37 planets detected by transit in this year
– Host stars are relatively faint, V ~ 10-15
– Magnitude limit of transit observations will be fainter ⇒ GMT
Number of planets by year of discovery
2010
2009
2008
2007
GMT Workshop 2010 at SNU
http://exoplanet.eu
(37)
(10)
(17)
(19)
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WHAT WE CAN DO WITH GMT
• Abundances of M dwarfs using GMTNIRS
– Advantages
1.
Easy to detect new exoplanets or extraterrestrial lives
–
–
2.
Life time in the stage of main-sequence
–
3.
Host star is less massive (radial velocity method)
»
Less massive exoplanets (super-earths)
Habitable zone is closer to host star (extraterrestrial life)
»
Short period and probability of transits
Enough time for life evolution
The large number of M dwarfs in the Galaxy
– Disadvantages
1.
2.
Faint at visible wavelength ⇒ large telescope, GMTNIRS
Strongly pressure-broadened atomic lines, and strong molecular
bands in visual wavelength range ⇒ GMTNIRS
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