Wiley, Monthly Notice- Royal Astronomical Society -Letters-, 1(477), p. L21-L24
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Abstract We recover transits of WASP-18b and WASP-33b from Hipparcos (1989–1993) photometry. Marginal detections of HAT-P-56b and HAT-P-2b may be also present in the data. New ephemerides are fitted to WASP-18b and WASP-33b. A tentative (∼1.3σ) orbital decay is measured for WASP-18b, but the implied tidal quality factor (Q΄ ∼ 5 × 105) is small and survival time (<106 yr) is too short to be likely. No orbital decay is measured for WASP-33b, and a limit of Q΄ > 2 × 105 is placed. For both planets, the uncertainties in published ephemerides appear underestimated: the uncertainty in the period derivative of WASP-18b would be greatly reduced if its current ephemeris could be better determined.