IMPROVING PHYSICAL PARAMETERS FOR TRANSITING PLANET HOSTS

GREAT Synergies on the HorizonGREAT Synergies on the Horizon Torino, 6 Nov 2012Torino, 6 Nov 2012

IMPROVING PHYSICAL IMPROVING PHYSICAL PARAMETERS FOR PARAMETERS FOR

TRANSITING PLANET TRANSITING PLANET HOSTSHOSTS

G. Torres, D. Fischer, A. Sozzetti, G. Torres, D. Fischer, A. Sozzetti,

L. Buchhave, J. Winn,L. Buchhave, J. Winn,

M. Holman, and J.CarterM. Holman, and J.Carter


Resolving an Old Paradox Resolving an Old Paradox of Astrophysicsof Astrophysics

• Why is it that with improvements of spectroscopic data, stellar Why is it that with improvements of spectroscopic data, stellar atmospheres and atomic/molecular data, the accuracy of the derived atmospheres and atomic/molecular data, the accuracy of the derived stellar parameters does not improve (much)?stellar parameters does not improve (much)?

• An attempt to solve the conundrum from an observer's perspective, An attempt to solve the conundrum from an observer's perspective, with an honest and exhaustive description of the steps and with an honest and exhaustive description of the steps and uncertainties involved, setting a benchmark for practical stellar uncertainties involved, setting a benchmark for practical stellar spectroscopy, highlighting the strong and weak aspects of different spectroscopy, highlighting the strong and weak aspects of different techniques and proposing a path for improvement.techniques and proposing a path for improvement.

• A much-needed analysis in many fields of modern astrophysics A much-needed analysis in many fields of modern astrophysics from galactic chemical evolution to exoplanets, of significance for from galactic chemical evolution to exoplanets, of significance for on-going and coming surveys (e.g. Gaia etc.) on-going and coming surveys (e.g. Gaia etc.)


Deriving reliable stellar parameters Deriving reliable stellar parameters

based on stellar spectra analysisbased on stellar spectra analysis

• A comparison of three popular approaches

• SME:SME: spectral fitting by adjusting stellar parameters • SPC:SPC: searching for the best fit in a library of pre-

computed synthetic spectra• MOOG:MOOG: a classic curve-of-growth approach

• A homogeneous spectroscopic determinations of Teff, [Fe/H], Vsin(i) for 56 transiting planet hosts


U: unconstrained analysis(logg free)

C: constrained analysis(logg fixed to the best valuefrom photometry, see e.g.Sozzetti et al. 2007)


Unconstrained Unconstrained AnalysisAnalysis


On average, MOOG gives slightly hotter temperatures and higher On average, MOOG gives slightly hotter temperatures and higher surface gravities than both SPC and SME, but lower iron abundances. surface gravities than both SPC and SME, but lower iron abundances. The SPC results are intermediate between the other two.The SPC results are intermediate between the other two.


For V sin(i) >10 km/s, the SPC values tend to be systematically larger than those from SME (continuum-fitting algorithms?).


Constrained vs. Unconstrained AnalysisConstrained vs. Unconstrained Analysis


HATNet and WASP have HATNet and WASP have the same mean V mag the same mean V mag and indistiguishable and indistiguishable Brightness distribution.Brightness distribution.

Observed mean difference Observed mean difference in [Fe/H] is 0.17 dex. in [Fe/H] is 0.17 dex.

It goes in the direction expected, It goes in the direction expected, as the constrained Logas the constrained Logg g values values adopted by HATNet are more adopted by HATNet are more often larger than the often larger than the unconstrained values, which unconstrained values, which should lead to higher metallicities should lead to higher metallicities in that survey, just as observedin that survey, just as observed


By constraining logg, By constraining logg, hotter, mildly evolved hotter, mildly evolved stars move back to stars move back to the main sequence.the main sequence.

Their radii get smaller!Their radii get smaller!


SMESME


ConclusionsConclusions

• Accurate knowledge of the properties of the Accurate knowledge of the properties of the host stars in transiting exoplanet systems is host stars in transiting exoplanet systems is essential to derive accurate characteristics for essential to derive accurate characteristics for the planets.the planets.

• Strong correlations arise between Strong correlations arise between TTeffeff, [Fe, [Fe//H], H], and logand logg g when solving for all three quantities when solving for all three quantities simultaneouslysimultaneously

• Systematic errors in the stellar masses and Systematic errors in the stellar masses and radii of up to 20% and 10%, respectively, radii of up to 20% and 10%, respectively, which can be larger than other observational which can be larger than other observational uncertainties, and whichalso cause systematic uncertainties, and whichalso cause systematic errors in the planetary mass and radius.errors in the planetary mass and radius.

IMPROVING PHYSICAL PARAMETERS FOR TRANSITING PLANET HOSTS

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