SFSU Public Affairs Press Release
Published by the Public Affairs Office at San Francisco State University, Diag Center.
SAN FRANCISCO, CA-- January 9, 1999 -- A search of 88 sun-like stars by the most prolific discoverers of planets beyond our solar system has detected two new planetary companions orbiting Sun-like stars, bringing to 17 the total of known extrasolar planets.
The results show that giant planets far from Earth can be found rapidly and provide strong support for the idea that up to two percent of stars in the solar neighborhood may harbor closely orbiting gaseous giants, sometimes called "51 Peg-like" planets for their similarity to the planet orbiting the star 51 Pegasi.
"I think we're smarter than we were about how to find planets," said Debra Fischer, a post-doctoral researcher in the Physics and Astronomy Department at San Francisco State University, who announced the discovery today during a press conference at a meeting of the American Astronomical Society in Austin, Texas. "With a sample of suitable stars and enough telescope time, we expect to find planets around about two percent of sun-like stars within a few months," Fischer said.
The new candidate planets orbit the stars HD195019 and HD217107, located in the constellations of Delphinus and Pisces, respectively. The planet around HD195019 resides 0.14 Astronomical Units (one A.U. equals the mean distance from the Earth to the Sun) from its host star and circuits the star once every 18.3 days. It has an estimated mass equal to 3.5 Jupiters. The planet around HD217107 is only 0.072 A.U. from its star, makes a nearly circular orbit every 7.1 days and has an estimated mass of 1.3 Jupiters. These planets join six others in the "51 Peg" class that all orbit their star within three weeks.
The fact that both stars are quiet or relatively inactive like the Sun, Fischer said, helped her team to obtain the necessary high-quality data and increases the reliability of the planet dectection.
Fischer conducted her search from the three-meter telescope at Lick Observatory near San Jose, CA, where a team of San Francisco State astronomers has been hunting extrasolar planets since 1987. The team uses the now-famous technique of detecting the wobble in the motion of stars as they react to the gravitational pull of their planets. The team can measure the precise speed of stars to within three meters per second, about as fast as an average person rides a bicycle.
Last summer, Fischer launched a new planet search from Lick Observatory and began a survey of 200 stars. To optimize the efficiency of the search, five observations of each star were made. The team then honed in on those stars with any hint of a wobble for more intensive scrutiny from Lick Observatory and from the W.M. Keck Observatory in Hawaii. The two new planets turned up among the first 88 stars to be sampled. Follow-up analysis at Lick determined each planet's orbit.
"We quickly look for the plums easily pluckable from low on the tree, and Debra's found two planetary plums right off the bat," says team member Geoffrey Marcy, Fischer's advisor and University Distinguished Professor of Science at San Francisco State.
Other members of the planet-finding team include R. Paul Butler of the Anglo-Australian Observatory, Steven Vogt of the University of California at Santa Cruz, and Kevin Apps of the University of Sussex, England. Marcy and Butler observed from the Keck Observatory. Vogt developed the spectrometers used at both Lick and Keck for planet detection, and Apps selected which stars to target from a vast database of possibilities. A paper announcing their discovery appears in the January 1999 issue of Publi cations of the Astronomical Society of the Pacific.
Fischer's search focused on catching giant planets close to their host stars. The survey from Lick Observatory will continue to seek Jupiter-like planets with short orbital periods as well as planets that are farther out (and thus elicit a less noticable wobble) from their stars.
"We really want to find solar system analogues," said Fischer. "We want smaller planets that are farther away from their host stars, because we want to probe the habitable zone of stars--the place where life may form."
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