Wide‐Field Millimagnitude Photometry with the HAT: A Tool for Extrasolar Planet Detection

We discuss the system requirements for obtaining millimagnitude photometric precision over a wide field using small aperture short focal length telescope systems, such as are being developed by a number of research groups to search for transiting extra-solar planets. We describe the Hungarian-made Automated Telescope (HAT) system which attempts to meet these requirements. The attainable precision of HAT has been significantly improved by a technique in which the telescope is made to execute small pointing steps during each exposure so as to broaden the effective point spread function of the system to a value more compatible with the pixel size of our CCD detector. Experiments during a preliminary survey (Spring 2003) of two star fields with the HAT-5 instrument allowed us to optimize the HAT photometric precision using this method of PSF broadening; in this way have been able to achieve a precision as good as 2 millimagnitudes on brighter stars. We briefly describe development of a network of HAT telescopes (HATnet) spaced in longitude.