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Haleakala Telescope Finds New Planet

XO camera
map for XO-1
Left: The XO telescope, on the summit of Haleakala, consists of two 200-millimeter telephoto camera lenses. The lenses are attached to electronic devices that measure slight dips in light output from stars when an object crosses in front of them. Credit: NASA, ESA, and J. Stys (STScI). Right: The location of the star XO-1.

An international team of astronomers has used a small, automated telescope located on Haleakala to discover a planet orbiting a Sun-like star 600 light-years from Earth.

The team, led by Peter McCullough of the Space Telescope Science Institute in Baltimore, includes IfA astronomer James Heasley. They used a relatively inexpensive telescope made from off-the-shelf components to scan the skies for extrasolar planets. Called the XO telescope, it consists of two 200-millimeter telephoto camera lenses and looks like a pair of binoculars.

The team found the planet, dubbed XO-1b, by detecting a two percent dip in the star's light output when the planet passed in front of the star. The observation also revealed that XO-1b is in a tight four-day orbit around its parent star, which is in the constellation Corona Borealis.

The team confirmed XO-1b's existence by using the Harlan J. Smith Telescope and the Hobby-Eberly Telescope at the University of Texas's McDonald Observatory to measure the slight wobble induced by the planet on its parent star. This technique, known as the radial-velocity method, allowed the team to calculate a precise mass for the planet, which is about nine-tenths the size of Jupiter.

Of the approximately 200 extrasolar planets found to date, only 10 have been found using the transit method employed by the XO telescope. All of the others were found using the radial-velocity method on large telescopes like the Keck on Mauna Kea. While very powerful for determining whether a star has a planetary companion, the radial-velocity method is limited to looking at one star at a time. The transit approach used by XO can be used to examine many thousands of stars every night.

Heasley stated, "In the future, we can use small telescopes such as XO to find out which stars might have planets orbiting around them, and then use larger telescopes such as those on Mauna Kea to confirm such discoveries. In searching for planets, the game is all about numbers. The more stars we can examine, the better our chances of actually finding an extrasolar planet."

Several IfA staff members on Maui—Bill Giebink, Les Hieda, Jake Kamibayashi, Daniel O'Gara, and Joey Perreira—have played important roles in the construction and maintenance of the telescope.