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Millimagnitude‐Precision Photometry of Bright Stars with a 1 m Telescope and a Standard CCD

This paper summarizes a three‐night observing campaign aimed at achieving millimagnitude‐precision photometry of bright stars (V < 9.0 mag) with the 1 m Swope Telescope at Las Campanas Observatory. The test targets were the main‐sequence stars HD 205739 and HD 135446. The results show that by placing a concentric diaphragm in front of the aperture of the telescope, it is possible to avoid saturation and achieve a photometric precision of 0.0008–0.0010 mag per data point, with a cadence of less than 4 minutes. It is also possible to reach an overall precision of less that 0.0015 mag for time series of 6 hr or more. The photometric precision of this setup is only limited by scintillation. Scintillation could be reduced, and therefore the photometric precision further improved, by using a neutral‐density filter instead of the aperture stop. Given the expected median depth of about 0.01 mag for extrasolar‐planet transits, plus their typical duration of several hours, the results of this paper show that 1 m telescopes equipped with standard CCDs can be used to detect planet transits as shallow as 0.002 mag around bright stars.