high resolution spectroscopy of stars with planets

High Resolution High Resolution Spectroscopy of Stars Spectroscopy of Stars

with Planetswith Planets

Won-Seok Kang Seoul National University

2010. 10. 6.

Sang-Gak Lee, Seoul National UniversityKang-Min Kim, Korea Astronomy and Space science Institute

CHEMICAL ABUNDANCE OF PLANET-HOST STAR

INTRODUCTIONINTRODUCTION

• 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

2GMT Workshop 2010 at SNU

PLANET AND METALLICITYPLANET 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 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

[Fe/H]0.21003.0)( planetP

PLANET AND METALLICITYPLANET 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

4GMT Workshop 2010 at SNUFischer and Valenti 2005

METHOD OF ABUNDANCE METHOD OF ABUNDANCE ANALYSISANALYSIS

• 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

–


METHOD OF ABUNDANCE METHOD OF ABUNDANCE ANALYSISANALYSIS

• TAME and MOOGFE


Tools for Automatic Measurement of Equivalent-widths

Result of MOOGFE for the Sun

Excitation potential

Equivalent-width

Fe I Fe II

Model parameterslog eps(Fe) = 7.53 dex Teff = 5765 K

log g = 4.46 dex ξt = 0.82 km/s

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

METALLICITY HISTOGRAMMETALLICITY HISTOGRAM

• 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]

• Comparisons are more widely distributed overall

• In low-metallicity, comparisons are more than PHSs

• In high-metallicity, PHSs are much more than comparisons


<[Fe/H>-0.06

<[Fe/H]> +0.07

Only dwarfs

74 PHSs70 Comparions

METALLICITY AND PLANET METALLICITY AND PLANET PROPERTIESPROPERTIES

• [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?

– For verifying, more samples in the range of low-metallicity will be required


In the case of multiple-planetary system, total planet mass is indicated

These planetary masses represent MJsini , which is less than MJ

HD 114762 b

Only dwarfs

[Fe/H] vs. Planet Mass

Only 4 samples

METALLICITY AND PLANET METALLICITY AND PLANET PROPERTIESPROPERTIES


Only dwarfs

• 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 & 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 low-mass multiple planets

X : semi-major axisY : [Fe/H] Size of circle : planet mass

HD 114762 b

ABUNDANCE RESULTSABUNDANCE RESULTS

• [X/Fe] vs. [Fe/H] – Averaged for each [Fe/H]

bin– For most elements,

statistical difference between two groups ~ 0.03 dex

• [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


Chemical Abundance Trend ; [Fe/H] vs. [X/Fe]

Only dwarfs

Red : Planet-Host StarsBlue : Comparisons

• Bin size : 0.2 dex• Center of each [Fe/H] bin : -0.5, -0.3, -0.1, +0.1, +0.3, +0.5

ABUNDANCE RESULTSABUNDANCE RESULTS


HD 114762 b

[Mn/H] vs. planet mass• [Mn/H] and Planet mass– Maximum of planet mass are

increasing in low [Mn/H] range and decreasing in high [Mn/H] range

– 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

DIFFICULTIESDIFFICULTIES


• 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

PRELIMINARY TESTPRELIMINARY TEST


JM

iM J sin

Transiting planets

Radial velocity method

• Homogeneous studies of 30 transiting extrasolar planets (Southworth, 2010)– Provide the properties of planets and host

stars

• 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

– Solutions • More low-metallicity stars with transiting planets• Perform abundance analysis in uniform method and

with the same instrument

WHAT WE CAN DO WITH GMTWHAT 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

14GMT Workshop 2010 at SNUhttp://exoplanet.eu

Number of planets by year of discovery

2010 (37)2009 (10) 2008 (17)2007 (19)

WHAT WE CAN DO WITH GMTWHAT WE CAN DO WITH GMT

• Abundances of M dwarfs using GMTNIRS– Advantages

1. Easy to detect new exoplanets or extraterrestrial lives– 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

2. Life time in the stage of main-sequence – Enough time for life evolution

3. The large number of M dwarfs in the Galaxy

– Disadvantages 1. Faint at visible wavelength ⇒ large telescope, GMTNIRS2. Strongly pressure-broadened atomic lines, and strong

molecular bands in visual wavelength range ⇒ GMTNIRS


high resolution spectroscopy of stars with planets

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