We present photometry of the G0 star HAT-P-1 during six transits of its close-in giant planet, and we refine the estimates of the system parameters. Relative to Jupiters properties, HAT-P-1b is 1.20 +/- 0.05 times larger and its surface gravity is 2.7 +/- 0.2 times weaker. Although it remains the case that HAT-P-1b is among the least dense of the known sample of transiting exoplanets, its properties are in accord with previously published models of strongly irradiated, coreless, solar-composition giant planets. The times of the transits have a typical accuracy of 1 min and do not depart significantly from a constant period.
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