Using the power of adaptive optics to achieve incredibly high resolution, a team of astronomers has peered deep into the heart of an emerging star cluster. The international team, led by Wolfgang Brandner of the University of Hawaii's Institute for Astronomy, believes the results may yield new insights into the origin of field stars and the recently discovered population of free-floating brown dwarfs in the vicinity of the sun.
 The area around the star MCW 1080 shows remarkable detail in this infrared image taken with adaptive optics. More than 30 faint, young low-mass objects can be seen. The faintest objects, possibly young brown dwarfs, are 65,000 times fainter than the bright central binary star (seen in detail in the inset). Wolfgang Brandner (University of Hawaii) |
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The observations targeted a region surrounding MWC 1080, a young star lying roughly 6,000 light-years from Earth in the constellation Cassiopeia. MWC 1080 weighs in with about eight times the mass of the sun and a luminosity some 10,000 times that of our star. With an age of less than a million years, it still lies embedded within the dark cloud from which it was born.
Previous studies reported just a handful of young, low-mass stars in the vicinity of MWC 1080. The new observations relied on adaptive optics to see far greater detail. Adaptive optics is a newly emerging technology in which a laser beam is shot into the sky and a sensor at the telescope collects the light that reflects off molecules in the atmosphere back to Earth. By analyzing this light, telescope operators can create a map of the atmospheric turbulence above the site and immediately tell the telescope how to correct for it. The technique works best at infrared wavelengths and has the capability of producing images from Earth's surface that rival the resolution of the Hubble Space Telescope.
The first set of adaptive-optics observations was made in October 1996 with an infrared camera on the 3.6-meter Canada-France-Hawaii Telescope located on Mauna Kea in Hawaii. The second set, also done in the infrared, was taken in September 1999 with the 5-meter Hale Telescope at Palomar Observatory in California.
The images reveal that up to 100 faint, young objects of low mass cluster around MWC 1080 -- 10 times as many as previously assumed. "It's amazing to discover so many faint cluster members, many of which appear still to have circumstellar disks, and some of which could possibly be young brown dwarfs," says Laird Close, a staff scientist at the European Southern Observatory and a member of the team. Brown dwarfs, objects intermediate in size between planets and stars, have been detected in increasing numbers during the past few years.
The young cluster has a diameter of only 3 light-years, giving it a stellar density several hundred times higher than that near the sun (where the nearest star, Proxima Centauri, lies a little more than 4 light-years away). Still, astronomers expect the cluster will dissolve gradually over the next 10 million to 20 million years. The cluster members -- including the presumed brown dwarfs -- will then become free-floating field objects, similar in many respects to the recently discovered population of unattached brown dwarfs in the sun's neighborhood.
3/6/00
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