The STARE (STellar Astrophysics and Research on Exoplanets) telescope is a field-flattened Schmidt design, with an aperture of 102 mm and a effective focal length of 296 mm, giving an focal ratio of 2.9. The instrument has a system of three manually changeable filters. These were chosen to resemble the Johnson's standard filters B, V and R. Due to the poor sensitivity of the CCD detector to the blue wavelengths, the filter response of the B and V filters were shifted to the red. Our interest will reside in the relative magnitudes of the stars obtained in the R filter; thus, shortcomings in the absolute calibrations are of little importance.
The telescope was first developed in the United States in the late 1990s where it was installed for some time in the parking of the High Altitude Observatory (HAO) in Boulder (Colorado). At that stage, it was used to detect the transits of the planet orbiting the star HD209458, the first transiting planet ever observed. In July 2001, it was definitively installed at Observatorio del Teide where it has been operated almost permanently since then. Since summer 2003, it has been working as a part of the TrES network, involving two other similar instruments located in Arizona and California.
The most important scientific outcome has been the discovery in 2004 of the transiting extrasolar planet TrES-1, orbiting a K0V star in the constellation of Lyra. This is the first transiting planet of a relatively bright star discovered by this technique. Follow up observations have permitted to determine the mass, radius, temperature and eccentricity of the planet with high precision. STARE has been used also to discover low mass binary systems and new pulsating stars, including some in the stellar fields to be observed by the satellite COROT, devoted to astero-seismology and transiting planet detection, to be launched in June 2006. The quantity and quality of the data obtained in nine extended stellar fields has also permitted to establish a protocol to detect false alarms within transiting exoplanet research that will be very useful for similar projects and future space missions.
The CCD detector is a 2Kx2K front-illuminated Loral device installed in a camera fabricated by Pixel Vision, Inc. The square pixels are 15-microns wide. It is cooled down to 235 K with a 3-stage thermoelectric cooler. The readout time is 13s at a speed of 400kHz; at this rate, the read noise is 10 electrons. We operate the system with a gain of 6.4 analog-to-digital converter unit (ADU).
All the above components of the telescope are attached to a commercial Meade LX-200 fork mount. To maintain all the stars within the same 1 - 2 pixels all the night the telescope has a 90 mm Maksutov reflector piggy-backed, equipped with a Santa Barbara Instrument Group ST-4 autoguider. This system takes images of a bright star every 2 s, and corrects the mount drifts to guide on the star. To achieve this, every science image taken with the main CCD is compared to a sub-image of the field, and corrections to the position of the star in the ST-4 camera are done if necessary, every two minutes. The telescope and mount are inside a 3.2 m diameter Ash-Dome, and it is connected to the Cielo Nocturno building with optical fiber.
Computers and data storage devices are inside the Cielo Nocturno building. Two linked Pentium PC computers operate the whole system: Butch and Sundance. Butch is responsible for the dome and mount control, while Sundance controls the CCD acquisition and storage. Both computers operate under Windows 98, and the user interface consists of several programs written in Visual C++. These invoke scripts which are based on "Orchestrate Scripting Software" for the telescope control, and "AutomaDome" for the dome control; both are by Software Bisque.
STARE's operation depends on an operator that decides to start the system if observing conditions are acceptable. The operator has to remove the telescope covers, open the dome manually, and start a telescope control script. This script will begin the observations at a specified hour, once a sample field reached a prescribed altitude or when the sky is dark enough. The telescope will then perform the entire observing programme autonomously. At the end of a night, or once a sample field moves too low, the telescope parks itself in a safe position (no direct sunlight on the telescope), and waits for the return of the
operator. He will then close the dome and create copies of the acquired data. The operator is also required to monitor meteorological conditions and has to shut down the instrument in case of adverse conditions.
It is planned that the telescope will continue coordinated operation, within the TrES network, at OT for at least three more years, continuing with the regular observations on extended fields searching for new transiting extrasolar planets and other unexpected results.