Get in Line to Find Extrasolar Planet
|Artist concept of star system outside our own nine planet neighborhood. Banner image shows HET Telescope.
Credit:John Rowe animation
More than 100 planetary systems have already been discovered around distant stars.
McDonald Observatory astronomers Bill Cochran, Michael Endl, and Barbara McArthur have exploited the Hobby-Eberly Telescope’s (HET’s) capabilities to find and confirm, with great precision, the giant telescope’s first planet outside our solar system. The event serves as proof-of-concept that HET, combined with its High Resolution Spectrograph instrument, is on track to become a major player in the hunt for other worlds. The research has been accepted for publication in an upcoming edition of Astrophysical Journal Letters.
With a mass 2.84 times that of Jupiter, the newly discovered planet orbits the star HD 37605 every 54.23 days. HD 37605 is a little smaller and little cooler than the Sun. The star, which is of a type called "K0" or "K-zero," is rich in heavy chemical elements compared to the Sun.
Of the approximately 120 extrasolar planets found to date, this new planet has the third most eccentric orbit, bringing it in close in to its parent star like a "hot Jupiter," and swinging it back out. The planet’s average distance from its star is 0.26 Astronomical Units (AU). One AU is the Earth-Sun distance.
The team used the "radial velocity" technique, a common planet-search method, to find the planet. By measuring changes in the star’s velocity toward and away from Earth –its wobble– they deduced that HD 37605 is orbiting the center of mass of a star-planet system.
|Scene from a moon orbiting the extra-solar planet in orbit around a distant star.
Credit:David A. Hardy, astroart.org (c) pparc.ac.uk
"In 100 days of observations –less than two full orbits– we were able to get a very good solution for this planet’s orbit," Cochran said. The quick results were due to HET’s "queue scheduling" system. Astronomers do not travel to the observatory to operate the telescope themselves. Rather, a telescope operator at McDonald Observatory has a list of all HET research projects and selects the ones best suited to any given night’s weather conditions and Moon phase. This way, many targets for different research projects can be observed each night, and any particular target can be observed dozens of nights in a row. According to Cochran, "queue scheduling is the ideal way to do planet searching. If the HET had a normal scheduling system, it would have taken us a year or two to confirm this planet."
Endl added that "with the queue scheduling mode, we can put every candidate star back into the queue at a high priority to secure follow-up telescope observations immediately."
Cochran added that the high precision of the team’s radial velocity measurements "proves that the HET and the High Resolution Spectrograph have met their design specs." He explained that the total error (called "root-mean-square deviation") in the team’s velocity measurements was 3 meters per second — state of the art for planet searching. Many of the team’s measurements had even lower errors.
The HET contains the world’s largest primary mirror, measuring 11 meters (433 inches) from edge to edge. Due to its innovative design, the HET was built and commissioned for $15 million, a fraction of the cost of other comparable telescopes. Because of the way the Hobby-Eberly Telescope is used, 9.2 meters (362 inches) of its surface are accessible at any given time. Thus, the Hobby-Eberly Telescope is effectively the third-largest telescope in the world, after the twin 10-meter (393-inch) Keck I and Keck II telescopes in Hawaii. The HET attained "first light" in December 1996 and "first spectrum" in September 1997. HET stands on Mount Fowlkes at McDonald Observatory in far West Texas, which has the darkest skies of any major observatory in the continental United States.
The High Resolution Spectrograph that made this research possible was built by Phillip MacQueen, Robert Tull, and John Good of The University of Texas at Austin. The 9.2 meter Hobby-Eberly Telescope is a joint project of The University of Texas at Austin, The Pennsylvania State University (Penn State), Stanford University, Ludwig-Maximilians-Universitat Muenchen, and Georg-August- Universitat Goettingen. This planet detection research is supported by the National Aeronautics and Space Administration.