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May 2001

The Laboratory
in the News

Commentary by
Jeff Wadsworth

Uncovering
Hidden Defects
with Neutrons

The Human in the Mouse Mirror

The NIF Target Chamber—Ready
for the Challenge

Indoor Testing Begins Soon at
Site 300

Patents

Awards


The Laboratory
in the News

Hubble data support MACHOs
At the January meeting of the American Astronomical Society in San Diego, California, Livermore's Kem Cook and Cailin Nelson—reporting on behalf of the 14-organization collaboration to detect and study Massive Compact Halo Objects (MACHOs)—presented evidence of microlensing events caused by MACHOs in the halo of the Milky Way. Microlensing is a physical phenomenon that causes a star to appear to shift or brighten when it lies on the same line of sight as another star. The phenomenon is a way to detect MACHOs, which emit light below current detection thresholds and must therefore be discovered by other means. In MACHO microlensing, the MACHO passes through an observer's line of sight to an ordinary, luminous star. The MACHO's gravitational presence causes the light from the ordinary star to bend and also temporarily increase in brightness. That brightened star is called a source star.
The MACHO project has been monitoring the sky with the 1.27-meter telescope at Mount Stromlo Observatory in Australia to detect microlensing events in a line of sight toward our neighboring Large Magellanic Cloud galaxy, which provides a convenient backdrop of source stars. When the microlensing events were detected, some astronomers speculated that it was not MACHOs, but the faint stars in the Large Magellanic Cloud that were lensing other stars. If MACHOs are the cause of the microlensing, the source stars would be randomly distributed in the Large Magellanic Cloud, but if the source stars were found toward the far side of that galaxy, then the Large Magellanic Cloud would likely be the cause of microlensing.
To determine the cause of microlensing, the project collaborators turned to Hubble Space Telescope data on the area surrounding each microlensing event. Using the technique of difference image analysis, they were able to identify the source star of each microlensing event and therefore determine the arrangement of the source stars. The team found no evidence that the source stars are not randomly distributed in the Large Magellanic Cloud.
Contact: Kem Cook (925) 423-4634 (cook12@llnl.gov).

Over 150 high-proper-motion stars discovered
Also at the January meeting of the American Astronomical Association, astronomer Andrew Drake presented results from studying fifty thousand astronomical images of fifty-five million stars made by the Great Melbourne Telescope in Canberra, Australia, over a 7-year period. The telescope had been used during the 1990s to detect the gravitational microlensing of stars.
Drake reported finding 154 rapidly moving stars—called high-proper-motion (HPM) stars—toward the center of our galaxy and that of our brightest neighbor, the Large Magellanic Cloud. This finding is of special interest because it is the first time that scientists have been able to discover HPMs in front of the stars seen at our galactic center, which is packed so densely with stars that images of the stars seem merged, or in the Large Magellanic Cloud, which appears as a faint nebulous patch in the sky.
To find the HPMs, Drake identified the stars that appear to move and measured their motions. The yearly motions of these objects are estimated to be accurate to 6 milliarcseconds, which is equivalent to the width of a human hair seen from the distance of a mile. Drake's measurements led to the discovery of the HPMs.
Using astrometry, a branch of astronomy that deals with the measurement of positions and movements and has produced a picture of the motions of stars within our galaxy, Drake was able to predict that most of his discovered HPM stars are between 100 and 1,000 light years away. These measurements, however, are preliminary, and more studies are needed to gather details about the HPM stars.
Contact: Andrew Drake (925) 424-6781 (drake7@llnl.gov).

Lab enlisted in war against chemical weapons
At the behest of the U.S. State Department, Lawrence Livermore, home to the Forensic Science Center, has begun the procedure to become certified by the Organization for the Prohibition of Chemical Weapons (OPCW). The organization implements the Chemical Weapons Convention ratified by over 135 countries to outlaw chemical weapons and the transfer of chemical-weapon-related technologies. As an accredited laboratory, Livermore would participate in testing chemical samples from around the world to determine whether samples contain chemical weapons agents, their precursor chemicals, or their decomposition products.
Under the terms of the Convention, all chemical samples must be tested at two OPCW-designated laboratories. Congress mandates that all U.S. samples must be tested in the U.S. Currently, the nation has one designated laboratory, the Edgewood Chemical and Biological Forensic Analytical Center in Maryland. Livermore would become the second laboratory required for this testing.
Jeff Richardson, deputy program leader for the Proliferation Prevention and Arms Control Program, says that this work is "one more way the Laboratory can contribute to national and international security." Richardsons stresses that the samples for testing will "be extremely dilute (that is, on the part-per-million level). So dilute that they can be shipped commercially or sent through the mail." One of the reasons the Laboratory was selected for this work is its ability to characterize chemicals at ultratrace levels.
Contact: Jeff Richardson (925) 423-5187 (richardson6@llnl.gov).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



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UCRL-52000-01-5 | May 25, 2001