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IMPROVING PHYSICAL PARAMETERS FOR TRANSITING PLANET HOSTS

IMPROVING PHYSICAL PARAMETERS FOR TRANSITING PLANET HOSTS. G. Torres, D. Fischer, A. Sozzetti, L. Buchhave, J. Winn, M. Holman, and J.Carter. Resolving an Old Paradox of Astrophysics.

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IMPROVING PHYSICAL PARAMETERS FOR TRANSITING PLANET HOSTS

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  1. IMPROVING PHYSICAL PARAMETERS FOR TRANSITING PLANET HOSTS G. Torres, D. Fischer, A. Sozzetti, L. Buchhave, J. Winn, M. Holman, and J.Carter Torino, 6 Nov 2012

  2. Resolving an Old Paradox of Astrophysics • Why is it that with improvements of spectroscopic data, stellar atmospheres and atomic/molecular data, the accuracy of the derived stellar parameters does not improve (much)? • An attempt to solve the conundrum from an observer's perspective, with an honest and exhaustive description of the steps and uncertainties involved, setting a benchmark for practical stellar spectroscopy, highlighting the strong and weak aspects of different techniques and proposing a path for improvement. • A much-needed analysis in many fields of modern astrophysics from galactic chemical evolution to exoplanets, of significance for on-going and coming surveys (e.g. Gaia etc.) Torino, 6 Nov 2012

  3. Deriving reliable stellar parameters based on stellar spectra analysis • A comparison of three popular approaches • SME:spectral fitting by adjusting stellar parameters • SPC:searching for the best fit in a library of pre-computed synthetic spectra • MOOG: a classic curve-of-growth approach • A homogeneous spectroscopic determinations of Teff, [Fe/H], Vsin(i) for 56 transiting planet hosts Torino, 6 Nov 2012

  4. C: constrained analysis (logg fixed to the best value from photometry, see e.g. Sozzetti et al. 2007) U: unconstrained analysis (logg free) Torino, 6 Nov 2012

  5. Unconstrained Analysis Torino, 6 Nov 2012

  6. On average, MOOG gives slightly hotter temperatures and higher surface gravities than both SPC and SME, but lower iron abundances. The SPC results are intermediate between the other two. Torino, 6 Nov 2012

  7. For V sin(i) >10 km/s, the SPC values tend to be systematically larger than those from SME (continuum-fitting algorithms?). Torino, 6 Nov 2012

  8. Constrained vs. Unconstrained Analysis Torino, 6 Nov 2012

  9. HATNet and WASP have the same mean V mag and indistiguishable Brightness distribution. Observed mean difference in [Fe/H] is 0.17 dex. It goes in the direction expected, as the constrained Logg values adopted by HATNet are more often larger than the unconstrained values, which should lead to higher metallicities in that survey, just as observed Torino, 6 Nov 2012

  10. Torino, 6 Nov 2012

  11. By constraining logg, hotter, mildly evolved stars move back to the main sequence. Their radii get smaller! Torino, 6 Nov 2012

  12. SME Torino, 6 Nov 2012

  13. SME Torino, 6 Nov 2012

  14. Conclusions • Accurate knowledge of the properties of the host stars in transiting exoplanet systems is essential to derive accurate characteristics for the planets. • Strong correlations arise between Teff, [Fe/H], and logg when solving for all three quantities simultaneously • Systematic errors in the stellar masses and radii of up to 20% and 10%, respectively, which can be larger than other observational uncertainties, and whichalso cause systematic errors in the planetary mass and radius. Torino, 6 Nov 2012

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