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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.

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High Resolution Spectroscopy of Stars with Planets

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  1. High Resolution Spectroscopy of Stars with Planets CHEMICAL ABUNDANCEOF 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

  2. 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 GMT Workshop 2010 at SNU

  3. 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 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 GMT Workshop 2010 at SNU

  4. 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 Fischer and Valenti 2005 GMT Workshop 2010 at SNU

  5. 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 GMT Workshop 2010 at SNU

  6. 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 Model parameters log eps(Fe) = 7.53 dex Teff = 5765 K log g = 4.46 dex ξt = 0.82 km/s GMT Workshop 2010 at SNU For accurate estimation, we selected only weak lines of Fe I

  7. METALLICITY HISTOGRAM 74 PHSs 70 Comparions • Metallicity distribution • Mean value of PHS is0.13 dex higher than thatof 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 Only dwarfs <[Fe/H> -0.06 <[Fe/H]> +0.07 GMT Workshop 2010 at SNU

  8. 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? • For verifying, more samples in the range of low-metallicity will be required [Fe/H] vs. Planet Mass Only dwarfs HD 114762 b Only 4 samples In the case of multiple-planetary system, total planet mass is indicated These planetary masses represent MJsini, which is less than MJ GMT Workshop 2010 at SNU

  9. 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 & 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 Only dwarfs HD 114762 b GMT Workshop 2010 at SNU

  10. ABUNDANCE RESULTS Chemical Abundance Trend ; [Fe/H] vs. [X/Fe] • [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 • 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 Only dwarfs GMT Workshop 2010 at SNU

  11. 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 • 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 [Mn/H] vs. planet mass HD 114762 b GMT Workshop 2010 at SNU

  12. 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 • Transitobservation 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 GMT Workshop 2010 at SNU

  13. PRELIMINARY TEST • 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 Transiting planets Radial velocity method GMT Workshop 2010 at SNU

  14. 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 (37) 2009 (10) 2008 (17) 2007 (19) http://exoplanet.eu GMT Workshop 2010 at SNU

  15. WHAT WE CAN DO WITH GMT • Abundances of M dwarfs using GMTNIRS • Advantages • 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 • Life time in the stage of main-sequence • Enough time for life evolution • The large number of M dwarfs in the Galaxy • Disadvantages • Faint at visible wavelength ⇒ large telescope, GMTNIRS • Strongly pressure-broadened atomic lines, and strong molecular bands in visual wavelength range ⇒ GMTNIRS GMT Workshop 2010 at SNU

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