Asteroseismology of the Transiting Exoplanet Host HD 17156 with Hubble Space Telescope Fine Guidance Sensor

Observations conducted with the Fine Guidance Sensor on the Hubble Space Telescope (HST) providing high cadence and precision time-series photometry were obtained over 10 consecutive days in 2008 December on the host star of the transiting exoplanet HD 17156b. During this time, 1.0 X 1012 photons (corrected for detector dead time) were collected in which a noise level of 163 parts per million per 30 s sum resulted, thus providing excellent sensitivity to the detection of the analog of the solar 5-minute p-mode oscillations. For HD 17156, robust detection of p modes supports the determination of the stellar mean density of Delta *r* = 0.5301 ? 0.0044 g cm--3 from a detailed fit to the observed frequencies of modes of degree l = 0, 1, and 2. This is the first star for which the direct determination of Delta *r* has been possible using both asteroseismology and detailed analysis of a transiting planet light curve. Using the density constraint from asteroseismology, and stellar evolution modeling results in M * = 1.285 ? 0.026 M , R * = 1.507 ? 0.012 R , and a stellar age of 3.2 ? 0.3 Gyr.