An HST Search for Planets in the Globular Cluster 47 Tucanae

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

HST was used for 8.3 days in July '99 to monitor over 30,000 stars on the main sequence of 47 Tuc photometrically with a goal of detecting planets via transit signals. Expected transit depths for 1.3 Jupiter radii planets increase from 1% near main sequence turnoff to 6% at 4 magnitudes fainter due to decreasing stellar radii. Over this domain realized time series rms, obtained with PSF fitting in difference images, smoothly increases from 0.3% to 2.5%. With ~645 data points in each of WFPC2 F555W and F814W filters any planet with P < 4.2 days should provide securely detectable transits lasting 2-4 hours twice in each of V and I. Based on the frequency of inner-orbit, gas-giant planets from solar neighborhood radial velocity surveys we expect to detect 15 to 20 candidate planets, but see none (with 75% search completion) in this low metalicity, crowded stellar system; see also T.M. Brown poster. Many eclipsing binaries and variable stars are detected; see also E.F. Milone poster. We provide a project overview and details on: (1) reduction steps and resulting deep (> 100,000s in V, I; 14,360s U) co-added, over-sampled images, (2) key analysis steps that provide near-Poisson limited photometric time-series precisions for dithered, under-sampled, crowded-field images with significant focus variations in time, (3) global summaries of time series precisions and sensitivity to detecting planets, and (4) a few time series of particular interest. Funding has been provided via a NASA/STScI grant for GO-8267.

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