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Planetary News: Extrasolar Planets (2007)Giant Planet Found Transiting Star 800 Light Years AwayMay 31, 2007
Astronomers with the Trans-atlantic Exoplanet Survey (TrES) have announced the discovery of their third exoplanet, designated TrES-3. According to the team the planet is a gas giant, twice as massive as Jupiter and completing each orbit around its star in a mere 31 hours. Being so close to its star it is extremely hot, with an average temperature of around 1500 degrees Kelvin according to the discoverers. It is located 800 light-years away in the constellation Hercules. Unlike the vast majority of known exoplanets, which were detected using the radial velocity method, the TrES planets were detected using the transit technique. In radial velocity detections scientists measure the slight shifts in a star’s spectrum as it wobbles back and forth to the tug of an orbiting planet. In contrast, in transit searches astronomers look for the slight dimming of the light from a star as an orbiting planet transits in front of it – i.e. passes directly between it and the Earth. Each method has bith advantages and limitations: radial velocity searches are very effective for stars that are relatively close to us, but lose their effectiveness at longer ranges; transit searches are effective at much longer distances (TrES 3 is a full 800 light-years away!) but they can only detect planets that happen to pass cross the line of site between their star and the Earth. To look for transits, the small telescopes of the TrES network are automated to take wide-field timed exposures of the clear skies on as many nights as possible. When an observing run is completed for a particular field — usually over an approximate two-month period — astronomers measure very precisely the light from every star in the field in order to detect the possible signature of a transiting planet. "TrES-3 blocks off about 2.5 percent of the light of the star as it passes in front of it," said team member Georgi Mandushev of the Lowell Observatory's Planet Search Survey Telescope (PSST). "With our telescopes, we can measure this tiny drop in the star's brightness and deduce the presence of a planet there." The new planet TrES-3 was first noticed by Lowell Observatory's PSST telescope, set up and operated by Edward Dunham and Mandushev. The transits were then also observed by the Sleuth telescope, maintained by David Charbonneau of the Hrvard-Smithsonian Center for Astrophysics (CfA) and Francis O'Donovan of Caltech at the Palomar Observatory, and by the Hungarian Automated Telescope Network (HATNet), led by Gaspar Bakos. All these additional detections confirmed the original discovery. "The search for extrasolar planets is an exciting and competitive field” said O'Donovan. “I was happy to see that cooperation between separate teams led to a rapid confirmation of this planet."
In order to help confirm they had found a planet, HATNet's Gaspar Bakos and CfA's Guillermo Torres switched from the 10-centimeter TrES telescopes to one of the 10-meter telescopes at the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii. Using this giant telescope, they confirmed that they had found a new planet. In order to measure accurately the size and other properties of TrES-3, astronomers also made follow up observations of it with bigger telescopes at Lowell Observatory and Fred L. Whipple Observatory in Arizona, and with the Las Cumbres Observatory Global Telescope in Hawaii. "TrES-3 will be an intriguing object to study more deeply, said Edward Dunham, Lowell Observatory instrument scientist. "For example, its tight orbit causes it to be illuminated very strongly. This may make it possible to measure the variation in reflected light as it goes through its phases. This will tell us how reflective its atmosphere is." Did you like this article? Send
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