PRECISE ESTIMATES OF THE PHYSICAL PARAMETERS FOR THE EXOPLANET SYSTEM HD 17156 ENABLED BYHUBBLE SPACE TELESCOPEFINE GUIDANCE SENSOR TRANSIT AND ASTEROSEISMIC OBSERVATIONS

Abstract

We present observations of three distinct transits of HD 17156b obtained with the Fine Guidance Sensors (FGS) on board the Hubble Space Telescope (HST ) 5 . We analyzed both the transit photometry and previously published radial velocities to find the planet-star radius ratio R p /R ⋆ = 0.07454 ± 0.00035, inclination i = 86.49 +0.24 −0.20 deg, and scaled semi-major axis a/R ⋆ = 23.19 +0.32 −0.27 . This last value translates directly to a mean stellar density determination ρ ⋆ = 0.522 +0.021 −0.018 g cm −3 . Analysis of asteroseismology observations by the companion paper of Gilliland et al. (2009) provides a consistent but significantly refined measurement 6 of ρ ⋆ = 0.5308 ± 0.0040 g cm −3 . We compare stellar isochrones to this density estimate and find M ⋆ = 1.275 ± 0.018 M ⊙ and a stellar age of 3.37 +0.20 −0.47 Gyr. Using this estimate of M ⋆ and incorporating the density constraint from asteroseismology, we model both the photometry and published radial velocities to estimate the planet radius R p = 1.0870 ± 0.0066 R J and the stellar radius R ⋆ = 1.5007 ± 0.0076 R ⊙ . The planet radius is larger than While this work was in press, the companion work revised this measurement to ρ ⋆ = 0.5301 ± 0.0044 g cm −3 . We note that the change, which is less than 0.2 of the error, would translate to a stellar radius change of less than 0.001 R ⊙ and does not materially affect the results presented in this paper.that found in previous studies and consistent with theoretical models of a solarcomposition gas giant of the same mass and equilibrium temperature. For the three transits, we determine the times of mid-transit to a precision of 6.2 s, 7.6 s, and 6.9 s, and the transit times for HD 17156 do not show any significant departures from a constant period. The joint analysis of transit photometry and asteroseismology presages similar studies that will be enabled by the NASA Kepler Mission.

THE FLAT TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ1214b FROM WIDE FIELD CAMERA 3 ON THEHUBBLE SPACE TELESCOPE

“…The visit-long and orbit-long slopes are purely descriptive terms (as in Brown et al 2001;Carter et al 2009;Nutzman et al 2011), but relate to physical processes in the telescope and camera. The orbit-long slope probably arises from the combination of pointing/focus drifts (see Fig.…”

Homogeneous studies of transiting extrasolar planets - IV. Thirty systems with space-based light curves

“…The theoretical uncertainty of the former quantity is probably small, but is significant for the latter quantity. The HST/FGS data cover three transits, which were used by Nutzman et al (2011) to measure the physical properties of the system. Analyses including the asteroseismic ρ A as a constraint are in good agreement with standard analyses, but with smaller error bars (by a factor of 3 for R A and R b ).…”

“…I have solved the two light curves from Winn et al (2009c), which are in the (b + y)/2 and z passbands, each covering one transit. I also modelled the HST data from Nutzman et al (2011), which comprise partial coverage of each of three transits, using a light curve which has been corrected for instrumental effects. The FGS data were taken with the F583W filter which covers 440-710 nm, so I adopted for LDCs appropriate for a combined g+r filter.…”

How accurate are stellar ages based on stellar models?

“…One example is the star HD 17156, observed by the HST and modelled by Nutzman et al (2011 and Lebreton (2012). Like HD 52265, it is a metal rich star on the MS, in the same domain of mass.…”