Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2

By A. Sozzetti, G. Torres, D. Charbonneau, D. Latham, M. Holman, J. Winn, J. B. Laird, Francis T. O'Donovan. 2007

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We report on a spectroscopic determination of the atmospheric parameters and chemical abundance of the parent star of the recently discovered transiting planet TrES-2. A detailed LTE analysis of a set of Fe I and Fe II lines from our Keck spectra yields Teff = 5850 ± 50 K, log g = 4.4 ± 0.1, and [Fe/H] = -0.15 ± 0.10. Several independent checks (e.g., additional spectroscopy, line-depth ratios) confirm the reliability of our spectroscopic Teff estimate. The mass and radius of the star, needed to determine the properties of the planet, are traditionally inferred by comparison with stellar evolution models using Teff and some measure of the stellar luminosity, such as the spectroscopic surface gravity. We apply here a new method in which we use instead of log g the normalized separation a/R⋆ (related to the stellar density), directly measurabele from the light curves of transiting planets with much greater precision. With the a/R⋆ value from the light-curve analysis of Holman and coworkers and our Teff estimate, we obtain M⋆ = 0.980 ± 0.062 M☉ and R⋆ = 1.000 R☉, and an evolutionary age of 5.1 Gyr, in good agreement with other constraints (Ca II H and K line cores, lithium abundance, and rotation). The new stellar parameters yield improved values for the planetary mass and radius of Mp = 1.198 ± 0.053 MJ and Rp = 1.220 RJ, confirming that TrES-2 is the most massive among the currently known nearby (d ≲ 300 pc) transiting hot Jupiters. The surface gravity of the planet, log gp = 3.299 ± 0.016, can be derived independently of the knowledge of the stellar parameters (i.e., directly from observations), and with a very high precision rivaling that of the best known double-lined eclipsing binaries.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/60b6c99e180573e5592cf39a9608942cb48fc90f

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Citations in the corpus

HAT-P-7b: An Extremely Hot Massive Planet Transiting a Bright Star in the Kepler Field (2008, background): “As described by Sozzetti et al. (2007), a/R⋆ is a better luminosity indicator than the spectroscopic value of log g⋆ since the variation of stellar surface gravity has a subtle effect on the line profiles.”
Spectroscopy Made Easy: Evolution (2016, background): “For example, Sozzetti et al. (2007) forced log g to be consistent with stellar structure models, constrained by the ratio of semi-major axis to stellar radius inferred from the light curve of a transiting planet.”
Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first Super-Earth with measured radius (2009, unknown): “On the other hand, the NaiD and Mgi line wings in the spectra yield good constraints on the measured logg value,± 0.10, an accuracy already obtained by other authors, e.g. Sozzetti et al. (2007), so we used our spectroscopic estimate of the surface gravity (logg= 4.50) as a proxy for the luminosity.”
DISCOVERY OF A TRANSITING PLANET AND EIGHT ECLIPSING BINARIES IN HATNet FIELD G205 (2009, background): “As described by Sozzetti et al. (2007) and Torres et al. (2008), a/R is a better luminosity indicator than the spectroscopic value of log g , because the variation of stellar surface gravity has only a subtle effect on the line profiles.”
SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs - I. New atmospheric parameters and masses for 48 stars with planets (2013, methodology): “As such, the temperatures and metallicities derived with our adopted spectroscopic method can be used as reference values even if the derived spectroscopic surface gravitiesdiffer from those derived using the transit light curve (and the stellar density – Sozzetti et al. 2007).”
THE KEPLER-10 PLANETARY SYSTEM REVISITED BY HARPS-N: A HOT ROCKY WORLD AND A SOLID NEPTUNE-MASS PLANET (2014, methodology): “…the asteroseismic stellar density ρ as measured by Fogtmann-Schulz et al. (2014), the Teff , and [Fe/H] with the Yonsei-Yale evolutionary tracks (Torres et al. 2012; Sozzetti et al. 2007; Demarque et al. 2004) and by performing the same chi-square minimization as in Santerne et al. (2011).”
HD 147506b: A Supermassive Planet in an Eccentric Orbit Transiting a Bright Star (2007, background): “It has been pointed out by Sozzetti et al. (2007) that the normalized separation a/R⋆ can provide a much better constraint for stellar parameter determination than log g.”
CHARACTERIZING THE COOL KOIs. II. THE M DWARF KOI-254 AND ITS HOT JUPITER (2011, methodology): “Relationship Between a/R⋆ and M⋆ The mass can also be estimated using the scaled semimajor axis from the fit to the transit light curve (e.g. Seager & Mallén-Ornelas 2003; Sozzetti et al. 2007; Winn 2008).”
Mass-Radius Relationships for Solid Exoplanets (2007, methodology): “Sozzetti et al. (2007) show that a more precise stellar radius (and hence planet radius) can be derived using stellar evolution models in in the a/R∗ vs. Teff parameter space instead of in the usual log g vs. Teff parameter space.”
IMPROVED SPECTROSCOPIC PARAMETERS FOR TRANSITING PLANET HOSTS (2012, methodology): “It has been advocated (see Sozzetti et al. 2007; Holman et al. 2007; Torres et al. Torres et al. Fig.”
HAT-P-11b: A SUPER-NEPTUNE PLANET TRANSITING A BRIGHT K STAR IN THE KEPLER FIELD (2009, background): “However, it has been shown (Sozzetti et al. 2007) that log g⋆ has a subtle effect on the spectral line shapes, and is usually not the best luminosity indicator.”
The GAPS Programme with HARPS-N at TNG - XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets (2017, unknown): “System ages are usually derived via stellar evolutionary tracks by using constraints on the stellar density from the transit ﬁt-ting and on the metallicity and the e ﬀ ective temperature of the host stars from spectral analysis (e.g. Sozzetti et al. 2007).”
Homogeneous studies of transiting extrasolar planets – I. Light-curve analyses (2008, methodology): “Excellent z-band light curves of three transits were presented and analysed by the TLC project (Holman et al. 2007b), who worked in close collaboration with Sozzetti et al. (2007) to obtain a highly accurate and consistent set of properties for the system.”
Tidal Heating of Extrasolar Planets (2008, methodology): “The following planets have larger radii than predicted by models: TrES-2 (Sozzetti et al. 2007), WASP-2b (Sozzetti et al. 2007), OGLE-TR-56b (Pont et al. 2007), and XO-1b (Holman et al. 2006).”
HAT-P-16b: A 4 MJ PLANET TRANSITING A BRIGHT STAR ON AN ECCENTRIC ORBIT, (2010, methodology): “Instead, we used the a/R⋆, the normalized semimajor axis (related to ρ⋆, the mean stellar density), which can be derived directly from the light curves (Sozzetti et al. 2007).”
Homogeneous studies of transiting extrasolar planets - III. Additional planets and stellar models (2010, methodology): “Excellent ground-based light curvesof three transits were obtained and studied by Holman et al. (2007), in close collaboration with Sozzetti et al. (2007).”
FUNDAMENTAL PROPERTIES OF KEPLER PLANET-CANDIDATE HOST STARS USING ASTEROSEISMOLOGY (2013, unknown): “Equation (5) can be used to infer host-star properties in systems with transiting exoplanets, for example, to reduce degeneracies between spectroscopic parameters (see, e.g., Sozzetti et al. 2007; Torres et al. 2012).”