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Title - News
Astronomical Headlines
Jupiter Observers On Alert
An Early Universe Teeming With Stars
A Comet's Brush with the Sun

  Reports from the American
Astronomical Society
Chandra Views Milky Way Center
Giant Telescopes Snare Surprising Quadruple Star
Vega's Clumpy Dust May
Reveal Hidden Planet
Bush Science Policy:
The View from the Top
Gamma-Ray Bursts Next Door?
Chandra Snaps Superbubbles
in Galaxy Cluster
First Planet of a Giant Star
Astronomers Discover Unique
Brown-Dwarf System
Watching Dust in the Wind
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Tuesday, January 15
Jupiter Observers On Alert

This image by Maurizio Di Sciullo, taken January 12th at 03:45 UT with a 10-inch Excelsior Optics E-258 Newtonian reflector, reveals what John McAnally says "may be the beginning of the disruption of south temperate oval BA on Jupiter."



Jupiter is without doubt the most dynamic planet for amateur astronomers. From night to night, its appearance in backyard telescopes changes at an amazing rate, and as if to emphasize the point, Jupiter currently is undergoing a historic event.

John McAnally, assistant coordinator of the Association of Lunar and Planetary Observers Jupiter section (ALPO), issued an alert today to encourage amateurs to observe the activity taking place near the Great Red Spot (GRS), located in the south edge of Jupiter's South Equatorial Belt, one of the two conspicuous cloud bands girdling the planet.

For 60 years, three large ovals persisted in the South Temperate Belt. Now the last of the three, designated BA, appears to be on a collision course with the Great Red Spot. Observers favored with steady seeing conditions and clear skies will have a ringside seat for this rare event. But, more than this, amateur observations may also provide insight into the dynamics of Jupiter's cloud belts. Says McAnally, "Astronomers are asked to make special efforts to observe this GRS/BA interaction so that a complete sequence of events can be constructed to characterize the behavior of the winds, jet stream, and other atmospheric conditions surrounding this interaction — data that would be of great value."

To see the oval, you'll need our predictions of when Jupiter's Great Red Spot and surrounding areas transit the planet's meridian and are best for viewing. Amateurs are requested to visit the ALPO Jupiter section for instructions on how to submit their observations.

— Gary Seronik

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Report from the American Astronomical Society
Tuesday, January 15

Chandra Views Milky Way Center

This 400- by 900-light-year mosaic (click on image for full view) is the most detailed X-ray view of the Milky Way's center ever seen. Courtesy NASA/UMAS/D. Wang.



Scientists using the Chandra X-ray Observatory have peered deep into the heart of the Milky Way to create the sharpest-ever view of our galaxy's center. The image was presented last week at the American Astronomical Society meeting and also published in the January 10th Nature.

Q. Daniel Wang, Cornelia Lang (University of Massachusetts, Amherst), and Eric Gotthelf (Columbia University) took 30 Chandra images (totaling some 94 hours of exposure time) to create the 400- by 900-light-year (0.8-degree by 2-degree) mosaic of the Milky Way's middle. Inside they found thousands of discrete X-ray sources presumed to be white dwarfs, neutron stars, and black holes.

While most of our galaxy is easy to analyze in visible wavelengths, the core of the Milky Way is hidden by thousands of light-years of opaque dust. Previous studies had found much X-ray radiation eminating from behind the dusty curtain, but no instrument had the resolution to show how much of it was coming from diffuse clouds of hot gas and how much was due to point sources. Before Chandra, the state of the art could only discern vague blobs of X-rays. "Only a dozen sources had been previously identified before Chandra," says Wang.

Some of the radiation does come from thin gas (the hazy clouds in the image, and Chandra's observations will help astronomers understand its nature evolution. Previous to these observations, astronomers assumed the temperature of the gas must be some 100 million degrees Kelvin in the center. It now appears that it is only a balmy 10 million degrees.

The panorama has also helped astronomers gain "a new perspective of the interplay of the various components of our galaxy," says Wang. The hot gas in the core is seen escaping and cooling as it pours into the surrounding regions, even as far as the solar neighborhood, 27,000 light-years away. By tracing the history of the gas by its temperature profile, astronomers hope to better understand the inner workings our galaxy and countless others.

— David Tytell

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Report from the American Astronomical Society
Monday, January 14

Giant Telescopes Snare Surprising
Quadruple Star

An infrared ground-based view (1) of a wide binary system in the molecular cloud MBM 12. The same view using Gemini's adaptive optics system (2) reveals that the upper star is actually a close pair. In a longer exposure of the upper, close pair (3) another faint object is resolved, a close-up of which (4) reveals an edge-on protoplanetary disk. Courtesy of UC Berkeley, CfA, and NOAO.



Last week at the American Astronomical Society meeting, Ray Jayawardhana (University of California, Berkeley) and Kevin Luhman (Harvard-Smithsonian Center for Astrophysics) announced their discovery of a never before seen edge-on protoplanetary disk surrounding one member of a nearby, two-million-year-old quadruple star system. The observations were made with both the Gemini North and Keck telescopes atop Mauna Kea in Hawaii.

The unusual quartet is located 900 light-years away in Aries within a molecular cloud called MBM 12. Its young protoplanetary disk is about three times the size of Pluto's orbit, but when originally viewed with normal ground-based telescopes it was mistaken as a part of the close pair of stars in the system. According to Jayawardhana, there is evidence that the other stars in the system have dust disks as well.

The discovery was made possible by a technology called adaptive optics, which compensates for atmospheric aberrations and results in greatly improved resolution and contrast, allowing telescopes like Gemini and Keck to see farther and more clearly. If you've ever had difficulty seeing through heat-driven ripples to what was on the other side of a hot parking lot, you've seen a demonstration of the difficulty faced by astronomers gazing through our turbulent atmosphere.

"The new 8- to 10-meter telescopes really need adaptive optics to achieve the highest possible resolution," asserts Luhman. Jayawardhana agrees, saying that with adaptive optics it should now possible to see a Jupiter-mass planet orbiting a young star.

— Rhiannon Lewis

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Report from the American Astronomical Society
Monday, January 7

199th American Astronomical Society Meeting Begins



Astronomers from across the globe have gathered in Washington, D.C. this week for the 199th meeting of the American Astronomical Society. This year's event, the second largest gathering of professional astronomers ever, includes more than 2,200 scientists and participants, presenting the latest astronomical news and findings in 154 different oral and poster sessions. Sky & Telescope editors David Tytell and Joshua Roth will be on hand throughout the week to keep you up to date on the latest developments.

 

Report from the American Astronomical Society
Thursday, January 10

Vega's Clumpy Dust May Reveal Hidden Planet

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Millimeter-wavelength observations of Vega indicate that the cold dust orbiting it is gathered in two clumps, as suggested in this artist's concept. Dust would be herded into clumps such as these by a planet in an eccentric orbit. (Our actual view of Vega's dust disk is almost pole-on.) Courtesy David Wilner and David Aguilar.



Even casual skywatchers are familiar with Vega. The zero-magnitude star is the sky's fifth brightest, the jewel of the constellation Lyra, and a vertex of the Summer Triangle. Now it appears that Vega has another claim to fame: signs of a giant exoplanet orbiting it.

Vega looks bright because it is nearby, only 25 light-years away, and because it is hotter and larger than the Sun, putting out 50 times the Sun's light. Nearly two decades ago astronomers found far-infrared evidence of cold dust grains surrounded Vega. Observations in 1998 showed signs of structure in the dust. This week, at the American Astronomical Society meeting, two teams of astronomers announced that Vega's circumstellar dust is at least partly gathered into large clumps — in a characteristic shape that suggests the gravitational influence of a giant planet in an eccentric orbit.

Two separate teams made the observations using two telescopes half a world apart. The first group, led by David Koerner (University of Pennsylvania), used the Owens Valley Radio Observatory. The second, led by David Wilner (Harvard-Smithsonian Center for Astrophysics), used the Plateau de Bure Interferometer in the French Alps to resolve two knots in the circumstellar dust offset 60 and 75 astronomical units from Vega.

According to Wilner, the "features are naturally explained by a Jupiter-mass planet in an eccentric orbit around the star." The clumps, he says, are "trapped in resonances from a planet." Koerner adds that observations such as these are "starting to change the paradigm of what it means to be a disk."

While no planet has been seen, models by Wilner and his colleagues suggest that the semimajor axis of its orbit is most likely 30 a.u. (30 times the Earth's distance from the Sun). The simulations also place an upper limit to its mass. "If the planet is larger than 30 Jupiters, dust regions overlap and the resonances are destroyed," says Marc Kuchner, a theorist on Wilner's team.

— David Tytell

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Report from the American Astronomical Society
Wednesday, January 9

Bush Science Policy:
The View from the Top

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John H. Marburger III, director of the Bush Administration's Office of Science and Technology Policy, came to his new post from the Brookhaven National Laboratory. Courtesy U.S. Department of Energy.



President Bush's science advisor, John H. Marburger III, warned members of the American Astronomical Society yesterday that researchers must change their approach to justifying requests for government funding. In his remarks at the society's winter meeting in Washington, D.C., Marburger outlined the administration's approach to science, fiscal management, and specifically, astronomy.

Marburger said that Bush's presidency marks the return of a "business-like administration" to the White House and that scientists, even those conducting basic research, should realize that "measures of performance are essential."

According to Marburger, federal support for science has historically been linked to national defense, specifically to Cold War technologies. After the breakup of the Soviet Union in 1991, the United States was left with an embarrassment of riches — lots of discoveries requiring additional research. "We've got too much," said Marburger. "We can't afford to follow it all up at once."

Marburger says, "This administration supports discovery-based science," but he adds, "[the president] insists on knowing why we are making an investment."

When addressing cost overruns at NASA, Marburger said, "I believe the rest of NASA should be isolated from the problems of the International Space Station." This comment brought thunderous applause from the audience of professional astronomers.

In a question-and-answer session with reporters after his talk, Sky & Telescope asked Marburger about the Bush administration's apparent trend toward consolidating astronomical projects and facilities. He specifically addressed a rumor that Smithsonian Institution funding for the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, would be reallocated to the National Science Foundation. Marburger said people "shouldn't conclude from recent [reports] what the [administration's] ultimate goal is. The intent is to get the best science for what we are doing. It is reasonable for Americans to expect a hard-nosed approach." Marburger stopped short of saying whether or not he believes the CfA's funding should be reassigned.

— David Tytell

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Wednesday, January 9
An Early Universe Teeming With Stars

Click here for larger view

A small piece of the Hubble Deep Field North, a 10-day-long time exposure of a little spot of sky in Ursa Major. Galaxies are recorded to nearly 30th magnitude in the image, made in December 1995. Since then the Hubble Space Telescope has taken two similarly deep exposures in the sky's southern hemisphere. The three have provided raw material for countless research projects. Courtesy Robert Williams (Space Telescope Science Institute) and NASA. Click on image for larger view.

Seven years after the first Hubble Deep Field (HDF) revealed the most distant galaxies ever seen, a team of astronomers has done a new analysis of those galaxies that could rewrite the history of the early universe. According to Kenneth M. Lanzetta (SUNY Stony Brook) and his colleagues, the rate of star formation peaked in just the first few hundred million years after the Big Bang and has been declining ever since. Older analyses had concluded that the rate of star formation peaked much later.

"Previous measurements have missed the dominant fraction of the light from the earliest galaxies," Lanzetta explained at a press conference Tuesday. All prior studies of the most ancient, highest-redshift galaxies in the Hubble Deep Fields saw only "the tip of the iceberg," the galaxies' very brightest portions. Most of a galaxy's starlight, however, comes from its intermediate-brightness regions, which are too faint to show at all in the HDF views of the farthest objects. As a result, said Lanzetta, "Even the deepest, most sensitive measurements have missed most of the light of the early universe." In other words, many more stars were shining back then than anyone realized.

The faintest galaxies in the HDF images are too dim for their spectra to be measured with any existing telescope. So instead, the SUNY team did multicolor photometry of 5,000 of the faintest galaxies through 9 to 12 broad-band color filters (using both Hubble images and large ground-based telescopes) to produce a sort of low-resolution spectrogram of each. This method proved good enough for redshift purposes after the astronomers calibrated it against the 150 brightest galaxies in the fields, for which actual spectra are available.

The new analysis, the team said, indicates that starbirth in the universe proceeded like a fireworks show in reverse. "The grand finale came first," summed up Bruce Margon (Space Telescope Science Institute). The rate of starbirth in the first few hundred million years, said Lanzetta, was 10 times what it is in each equivalent section of space today. If so, that initial dazzling display should become clearly visible with the launch later this decade of the Next Generation Space Telescope, Hubble's successor.

The result will appear in a future issue of the Astrophysical Journal.

— David L. Chandler

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Report from the American Astronomical Society
Wednesday, January 9

Gamma-Ray Bursts Next Door?

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Data collected by the Compton Gamma Ray Observatory (which reentered the Earth's atmosphere in June 2000) was used to determine that gamma-ray bursts occur closer than astronomers originally thought. Courtesy NASA. Click on image for larger view.



Gamma-ray bursts, or GRBs — fleeting flashes of high-energy photons that appear anywhere on the sky — emanate from galaxies halfway across the visible universe and their origination predates the solar system. At least that's the picture astronomers deduced from the mysterious explosions' stupendously distant redshifts. So more than a few eyebrows went up in a Washington, D.C., lecture hall Monday when Jay Norris (NASA/Goddard Space Flight Center) told an audience of astrophysicists that many GRBs may have actually popped off in our intergalactic neighborhood: the pancake-shaped Local Supercluster of galaxies, which extends some 300 million light-years from the Milky Way.

"There's this myth that gamma-ray bursts are chaotic and unpredictable, said Norris, "but that's not true." In fact GRBs might even be used as "standard candles" with which to measure cosmic distances. Astronomers monitoring GRBs have found they emit their highest-energy gamma rays first, with somewhat "cooler" gamma rays following milliseconds or seconds later. In one study of nine GRBs with known redshifts, the time delay appeared to be correlated with the GRB's luminosity as seen from Earth: the longer a GRB takes to "cool," the less luminous it is.

Using data from the recently destroyed Compton Gamma Ray Observatory, Norris identified roughly 100 GRBs that cooled especially slowly, taking a second or more. Intriguingly, he finds that these presumably feeble GRBs are clustered along the plane of the Local Supercluster. Since GRBs as a whole are distributed randomly about the sky without any preferred direction, this suggests that Norris's sample originated "locally." It also bolsters the notion that the "lag-luminosity" relationship can provide at least a crude indication of a GRB's distance.

"I wouldn't consider it fact at this point," says GRB expert Robert Nemiroff (Michigan Technological University) of Norris's yet-unpublished analysis, "but it's a very interesting conjecture." The Swift spacecraft, slated for a September 2003 launch, should settle the issue, says Nemiroff, by obtaining redshifts for dozens if not hundreds of gamma-ray bursts.

— Joshua Roth

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Report from the American Astronomical Society
Wednesday, January 9

Chandra Snaps Superbubbles
in Galaxy Cluster

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This false-color image from the Chandra observatory depicts X-rays emanating from multimillion-degree gas within Abell 2597. The central hot spot marks the heart of the cluster's dominant galaxy, which contains a supermassive black hole. New research suggests that the dark void near the cluster's edge is a long-lived bubble that formed when the black hole briefly spouted jets of high-speed particles. Courtesy NASA, the Chandra Science Center, and Brian McNamara (Ohio University). The event can also be viewed as an MPEG animation (QuickTime version 5.0 or higher required).

Scientists using the Chandra X-ray Observatory have documented the existence and longevity of buoyant magnetic bubbles in a distant galaxy cluster. And in doing so, they may have discovered how magnetic fields came to permeate galaxy clusters — the largest gravitationally bound structures in the universe.

Brian McNamara (Ohio University, Athens) and his colleagues used Chandra to image the multimillion-degree gas permeating Abell 2597, a galaxy cluster more than 1 billion light-years from Earth. Chandra observed several vast cavities in the cluster's otherwise ubiquitous plasma. Similar holes had been seen in another galaxy cluster, Hydra A, McNamara notes. In Hydra A's case, radio telescopes revealed those cavities were filled with magnetized jets of gas streaming from the cluster's central galaxy — just what one would expect if those jets had blown bubbles in the plasma flooding that cluster.

But radio telescopes have not revealed any jets within Abell 2597's expansive cavities, which span tens of millions of light-years. The implication? According to McNamara, the cavities in Abell 2597's gas shroud "were probably created . . . about 100 million years ago and rose like bubbles in a Coke bottle." Powered by a still-mysterious process involving accretion onto a supermassive black hole, the bubbles' birth event probably only lasted about 1 million years. The gases that briefly jetted out from Abell 2597's central galaxy were threaded with relatively strong magnetic fields, McNamara adds. Those fields presumably rose along with the long-lived bubbles and keep the surrounding X-ray-luminous gas at bay.

"It's always been a mystery why we see dynamically important magnetic fields . . . in this type of cluster," McNamara says. Now, thanks to the new Chandra study, "it's plausible to explain all of these magnetic fields as being burped out of the black hole." The finding has broader implications for galaxy evolution. "These [central] black holes are depositing an enormous amount of energy into the centers of these clusters," with each bubble containing the energy equivalent of 1 million supernovae, "and [they] may have played an important role . . . in the shaping of the galaxies themselves."

— Joshua Roth

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Report from the American Astronomical Society
Tuesday, January 8

First Planet of a Giant Star

An artist's concept of a Jupiter-like planet eclipsing the giant star Iota Draconis, which is 13 times larger than the Sun. Courtesy JPL/NASA.



About 80 planets are known to orbit main-sequence stars that are more or less like the Sun — ranging from spectral type F (a little hotter and larger than the Sun) to M (quite a bit cooler and smaller). Now astronomers have extended the range of star types that have planets. At today's AAS meeting in Washington D.C., Sabine Frink (University of California, San Diego) and several colleagues announced finding a planet-mass body orbiting an orange giant — an old star that has used up most of its hydrogen fuel and swollen to huge proportions, as our Sun will do in about 7 billion years.

The star is Iota Draconis, shining brightly at 3rd magnitude from 100 light-years away in the constellation Draco. It's a run-of-the-mill giant (spectral type K2 III) with 13 times the Sun's diameter, though it probably has only 1.05 times the Sun's mass. Its newfound companion has at least 8.6 Jupiter masses and probably somewhat more. The object swoops around the star every 1.5 years in a highly elongated orbit (eccentricity 0.7).

"Until now, it was not known if planets existed around giant stars," said Frink in a press statement. "This provides the first evidence that planets at Earthlike distances can survive the evolution of their host star into a giant." If the star keeps expanding, however, it could still engulf and vaporize the planet in the distant future.

The planet of Iota Draconis has a very elongated orbit that is a little larger than Earth's. Courtesy Sabine Frink. Click on image for larger view.



The discovery came by accident. The astronomers were making Doppler-shift measurements of Iota Draconis as part of a project to reconnoiter reference stars for NASA's Space Interferometry Mission (SIM), scheduled to launch in 2009. The star showed noticeable changes in its radial (line-of-sight) velocity. That isn't surprising for a giant — they often pulse at least slightly, mimicking planet-induced wobbles, which is why extrasolar planet hunters have generally avoided them. But in this case the "pulses" in radial velocity traced out a telltale pattern indicating an object following Newton's laws of gravity in a strongly elongated orbit.

— Alan M. MacRobert

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Tuesday, January 8
A Comet's Brush with the Sun

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Comet Machholz 1 (96P) sweeps past the Sun on January 7th, just one day before its perihelion. This image, recorded by the Solar and Heliospheric Observatory, shows the comet's bright nucleus and tail. The white circle represents the Sun's hidden disk, and Venus is to the Sun's lower right. Click on the image to see an animation of the comet's motion (456K). Courtesy SOHO/LASCO Consortium; Sky & Telescope animation by Sean Walker.



Right now the periodic comet known as Machholz 1 is its closest to the Sun, just 19 million kilometers away. Human eyes cannot see the rendezvous, because the comet is positioned just a few degrees from our star in the sky. But if we could, we'd be dazzled — the comet's near-solar experience has turned its icy nucleus into a fizzing factory of gas and dust that has spawned a tail several degrees long.

Fortunately, the NASA/ESA Solar and Heliospheric Observatory has captured the comet's arrival. The spacecraft's Large Angle and Spectrometric Coronagraph, which continuously monitors conditions in the solar corona, picked up the comet in its wide field of view yesterday and has recorded its passage in a remarkable series of images.

When amateur skygazer Don Machholz discovered this comet in May 1986, astronomers initially thought it would make one quick pass through the inner solar system and then disappear forever. But they soon realized that Machholz's find was a periodic comet that orbits the Sun every 5.3 years, traveling in a looping trajectory that extends beyond the orbit of Jupiter. "This is really a remarkable orbit," observes Daniel W. E. Green (Harvard-Smithsonian Center for Astrophysics), in that the comet spirals a little nearer to the Sun at each perihelion then evolves outward over a 4,000-year-long cycle. By the year 2450, should Machholz 1 survive that long, it will pass only 5 million km (0.03 astronomical unit) from the Sun.

— J. Kelly Beatty

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Report from the American Astronomical Society
Tuesday, January 8

Astronomers Discover Unique
Brown-Dwarf System

The very faint brown-dwarf companion orbiting HD 7672 is seen at about 7 o'clock in this false-color, 2.2-micron adaptive-optics image from the Gemini North telescope. The dwarf orbits closer to its partner star than any other brown dwarf that has yet been directly imaged. Courtesy Gemini Observatory/University of Hawaii Institute for Astronomy/Michael Liu/NSF. Click on image for larger view.

Using the Gemini North and Keck telescopes atop Mauna Kea, Hawaii, astronomers have directly observed a brown dwarf that appears to be orbiting as little as 14 a.u. from its partner star. (If orbiting our Sun, the dwarf would reside between Saturn and Uranus.) The separation is the smallest for a brown dwarf that has ever been directly imaged. (Extrasolar-planet hunters have found several brown dwarfs orbiting even closer to Sun-like stars.)"

Michael Liu (University of Hawaii) and his colleagues explained Monday at the American Astronomical Society meeting that the cool companion — weighing in at between 55 and 78 times the mass of Jupiter — orbits the G-type star HR 7672 in the constellation Sagitta. Spectroscopy confirmed its brown-dwarf nature, yielding a temperature from 1,500 to 1,800 Kelvin.

The result implies that despite the apparent lack of brown dwarfs at distances less than 4 a.u. from Sun-like stars (known as the brown-dwarf desert), "brown dwarfs do exist at separations comparable to the outer planets," says Liu.

Theories abound as to the formation of brown-dwarf systems. Recently Bo Reipurth (University of Colorado) and Cathie Clarke (Cambridge University, England) proposed that brown dwarfs began their lives as protostellar "embryos" exactly like ordinary stars — but were gravitationally ejected before they grew. Liu's contends that his dwarf is far too massive to have formed within a circumstellar disk the way planets do. This result contradicts Reipurth and Clark's viewpoint. According to Liu, the brown dwarf's presence is at variance with scenarios where brown dwarfs form as ejected stellar embryos.

The discovery also highlights the power of the new adaptive-optics systems employed on both the Keck and Gemini North telescopes. These advanced instruments almost completely eliminate the blurring caused by atmospheric turbulence. In this case, adaptive optics allowed Liu and his team to distinguish a 14.4-magnitude brown dwarf from a 5.8-magnitude companion 0.79 arcsecond distant. "The result is tantalizing evidence of things to come," says exoplanet theorist Alan Boss (Carnegie Institution of Washington).

— David Tytell

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Report from the American Astronomical Society
Tuesday, January 8

Watching Dust in the Wind

This artist's conception shows a brilliant red arc where winds from a blue-hot, supermassive Wolf-Rayet star and its O-type companion collide. Courtesy David Aguilar (Harvard-Smithsonian Center for Astrophysics).



The latest steps in an 8-year-long stellar tango have been tracked by one of the world's largest telescopes, astronomers reported yesterday at the American Astronomical Society meeting in Washington, D.C.

Wolf-Rayet (WR) stars are ultra-hot stellar heavyweights in their final presupernova stage of life. They tip the scales at some 25 solar masses (or more) and shine so brightly that their outermost atmospheres fly off into surrounding space. But WR104 is superlative even among Wolf-Rayets. It's a binary system in which an O-type star orbits an even larger Wolf-Rayet companion. Given such energetic dance partners, the last thing astronomers would expect to see in the system is dust — any grains in the environs should be blasted apart in the strong radiation field.

But astronomers do see dust around WR104, and they see it in a spectacular fashion. During the O-type star's 8-year-long orbit, it approaches within 2.5 astronomical units (375 million kilometers) of the WR star. At this close approach, called periastron, the two star's energetic winds smash into each other, creating a shock front that, oddly enough, provides a dense, shielded environment where dust grains can form.

John Monnier (Harvard-Smithsonian Center for Astrophysics), Peter Tuthill (University of Sydney, Australia) and William Danchi (NASA/Goddard Space Flight Center) have been monitoring the WR104 system for the past few years using the Keck I telescope. Their technique is of particular note — with special optics they essentially cover the 10-meter primary mirror with an aperture mask containing 36 small holes. By mixing the signals from each of these microtelescopes, they turn Keck's mirror into a "multi-element interferometer." In doing so, Monnier and his colleagues attain an incredible imaging resolution of some 20 milliarcseconds — 50 times better than typical obtained from ground-based instruments.

Click on this image to see an animation (266K GIF) showing how the energetic Wolf-Rayet binary star system WR140 spews out an arc of dust when the smaller star passes 2.5 astronomical units from its companion. Courtesy John Monnier (Harvard-Smithsonian Center for Astrophysics).



By watching the system before and after its February 2001 periastron event, Monnier and his team found that "a bow shock arc of dust is seen within one month of periastron," says Monnier. Danchi adds that the system spews dust, "like a nozzle shooting material from a sprinkler." The result is an enormous spiral of gas cast out into space. Monnier's team is the first to ever see such a transient dust shield and to track its very high-speed motion (up to one milliarcsecond per day).

— David Tytell

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