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STARE Search Method

STARE's method of detection relies on the edge-on alignment of the extrasolar system. If a planetary system is oriented so that Earth lies near the plane of the planet's orbit, then once per orbit the planet passes between its star and the Earth, causing a transit. This orientation is more likely for planets orbiting close to their parent star. During a transit, the planet blocks some of the light from the star, causing the star to appear dimmer (see figure below). For Jupiter-sized planets transiting Sun-sized stars, the expected dimming of the star's light will be about 1%, and the duration of the transit should be a few hours.

Move mouse over figure to view animated transit (884 K continuous loop GIF, requires JavaScript to be enabled); Click on figure to view or download MPEG animation (783 K). problem?


Figure based on one by Hans Deeg, from 'Transits of Extrasolar Planets'
To look for such a transit, the STARE telescope takes timed exposures of the same field-of-view all night for as many nights as the field is favorably positioned (usually around 3 months). When an observing campaign is completed for a particular field, the multitude of data are run through software which, after correcting for many sources of distortion and noise, produces light curves for thousands of stars in the field. Other software is run to analyze the processed data for variable stars and transit candidates. It takes two or more transits (or cycles in a variable star) to discern the period of the orbit (or the variability).

The STARE method therefore favors giant planets orbiting sun-like stars in close orbits. The results of successful radial-velocity planetary searches have shown that planetary systems of this type could be quite common.

STARE Instrument

The current STARE telescope, as of July, 1999, is a field-flattened Schmidt with a nominal focal length of 286 mm and a working aperture of 99 mm, giving a focal ratio of f/2.9. The telescope is coupled to a Pixelvision 2K x 2K CCD (Charge-Coupled Device) camera to obtain images with a scale of 10.8 arcseconds per pixel over a field of view 6.1 degrees square. Broad-band color filters (B, V, and R) that approximate the Johnson bands are slid between the telescope and camera. By taking exposures with different colored filters, the colors of stars in the field can be determined. This is necessary for accurate photometry.

Prior to the current telescope, the main instrument used in the STARE project was a 300mm focal length, f/2.5 telescope coupled to the same CCD camera, imaging an approximately 5.7 degree square patch of sky. The telescope's main optical element was a surplus aerial photographic lens. A planetary filter, P, was used instead of the current red, R, filter.

The telescope/camera system is mounted on a Meade LX200 equatorial fork mount which is motor-driven to track the apparent motion of the heavens. A separate small telescope coupled with a Santa Barbara Instruments Group CCD autoguider is also mounted to the main scope. It tracks a guide star and compensates for errors in the telescope drive and mounting.

	The STARE telescope. Click on image for a larger view and identification of the telescope's main parts.
	Dr. Tim Brown installing the current STARE telescope in its old location, behind the NCAR Foothills Lab in Boulder. Click on image for a larger view.
	Construction of the new home of the STARE telescope, an Ash dome located on the island of Tenerife in the Canaries. Click on the image for more information about the dome and location.
	The STARE telescope, sporting a new light/dew shield, within the dome. Click on image for a larger view.
	First STARE telescope in daylight. Note finder scope (in white) and autoguiding scope behind it at the top of the main scope. The main CCD camera is at the rear of the telescope. Click on image for a larger view.

STARE's Piece of Sky

The STARE telescope took the majority of its initial exposures pointed at a 5.7 degree square within the constellation Auriga, the Charioteer. This field-of-view was chosen because it lies within the star-rich band of the Milky Way and transits the zenith around midnight during the observing season.

Within this field-of-view, photometry has been done on over 24,000 stars (sample results). The image below shows (from left to right) the field superposed on a starmap of Auriga, the 5.7 degree square field as imaged by the telescope, and a 1.5 degree square blow-up of the field to show the multitude of stars detectable. Click on any to see a more detailed view.

Other fields of observation are chosen throughout the year as their positions in the sky become more favorable. Substantial data have also been collected in fields within the constellations of Cygnus, Boötes, Lynx, Andromeda, Cancer, Lyra, Corvus, Perseus, and Hercules.

STARE Current Status and Activities

Fall, 2004: The STARE telescope has now joined with the PSST project (at Lowell observatory in Arizona) and the Sleuth Project (at Mount Palomar in California) to form the TrES Network (Trans-Atlantic Exoplanet Survey). The time-series data from these three telescopes will be combined to improve data quality and time-coverage. A new project website is in the works as an eventual gateway to these data. A new planet has been discovered by the TrES Network!

As of the end of July, 2001, STARE has been operating from its new home on the island of Tenerife in the Canaries. A team of four industrious souls from HAO -- Dr. Tim Brown, Kim Streander, Greg Card, and Alice Lecinski -- flew out to construct the dome with the aid of STARE collaborator Roi Alonso.

A log containing info on current and past STARE observations can be found HERE. It is updated semi-regularly by R. Alonso (when emailing, change the '-at-' in the address to '@').

Also, some new data products are in the works. Don Kolinski is writing a web-based application to allow users to analyze time series (using power spectra and phase dispersion minima calculations), choose a frequency of interest, then plot folded light curves. This should aid in searching for both extra-solar planets and variable stars within our starlists. A rudimentary version of this application is already available within the Data Products page (shown as 'time series' option for relevant fields).

Look for new updates.
Last modified: Thu Mar 10 09:14:35 MST 2005