Poster Abstracts

Name/Affiliation:  Christopher M. Johns-Krull (Rice University)

Title:  The HST-FGS Parallax of XO-3 and Implications for its Hot Jupiter

We use HST+FGS to measure the parallax of the transiting planet host star XO-3. Our parallax measurement, 5.674 +/- 0.139 mas, gives a distance to this planet hosting star of 176.2 +/- 4.3 pc. This distance implies a radius for the star XO-3 of 1.40 +/- 0.04 Rsun and a radius for its planet XO-3b of 1.26 +/- 0.04 Rjup. The predicted radius for XO-3b is 1.15 Rjup taking into account insolation from the central star. The measured radius is then marginally larger than model predictions, but at less than the 3 sigma level. XO-3b is somewhat unique among hot Jupiters in that it has a substantial eccentricity (e ~ 0.22) at a short orbital period (p = 3.2 d) and thus may be subject to tidal heating, a proposed mechanism for explaining the inflated radii of some giant exoplanets. However, the agreement of the measured and predicted radius does not suggest a major role for tidal heating, at least in the case of this exoplanet.