SLAC Today is available online at:
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In this issue:
Astronomically Large Lenses Measure the Age and Size of the Universe
Cooling Tower 101 Replacement Update
Colloquium Today: The Large Synoptic Survey Telescope—Technical Progress and Selections from the "Science Book"

SLAC Today

Monday - March 1, 2010

Astronomically Large Lenses Measure the Age and Size of the Universe

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Phil Marshall demonstrates lensing using a wine glass. (Video by Brad Plummer and Julie Karceski.)

Using entire galaxies as lenses to look at other galaxies, researchers have a newly precise way to measure the size and age of the universe and how rapidly it is expanding, on par with other techniques. The measurement determines a value for the Hubble constant, which indicates the size of the universe, and confirms the age of the universe as 13.75 billion years old, within 170 million years. The results also confirm the strength of dark energy, responsible for accelerating the expansion of the universe.

These results, by researchers at the Kavli Institute for Particle Astrophysics and Cosmology at the US Department of Energy's SLAC National Accelerator Laboratory and Stanford University, the University of Bonn, and other institutions in the United States and Germany, will be published in The Astrophysical Journal in March. The researchers used data collected by the NASA/ESA Hubble Space Telescope, and showed the improved precision they provide in combination with the Wilkinson Microwave Anisotropy Probe.  Read more...

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(Photo courtesy Javier Sevilla.)

Cooling Tower 101 Replacement Update

The project to replace Cooling Tower 101 is progressing. Last week, the subcontractor with the support of SLAC mechanics, electricians, technicians, Environment, Safety and Health staff and project team has transferred all of the planned cooling loads to a temporary cooling tower. The permanent cooling tower CT101 is "offline." Today, Facilities Division staff will start draining the water from the existing tower. The subcontractor will continue with activities to disassemble the existing tower.

The use of a temporary cooling tower will limit cooling tower water to Buildings 23, 24, 25, 34, and 44. Low conductivity water system 102, which serves the main SLAC campus area (Buildings 25, 26, 33, 40, 44 and 84), will be out of service today, for one day.

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(Photo courtesy Javier Sevilla.)

Buildings 31, 40, 41, 42, 43, 44, 45, 48, 51, 84, 137E and 137W, which have been isolated from the chilled water piping loop, will bring in cold air through outside air dampers to minimize any rise in temperature while the chilled water is not functioning. Assuming the cool weather holds, this should not prove troublesome for building comfort and operations. Building managers and users have been notified by e-mail.

During the winter and spring seasons, predicted outside air temperatures below 60 degrees F will help to maintain comfortable room temperatures inside the buildings, except where there are many computers or other heavy heat loads.

Chilled water cooling for air conditioning systems will remain fully operational for Building 50 (the computer building), Building 84 and the Fermi Large Area Telescope data facilities.

Demolition of the existing cooling tower is scheduled to begin next Monday, March 8. During the demolition, it may be necessary to close one lane of Loop Road near Building 267. Notice of any closures will be posted in SLAC Today.

See "Work on Cooling Tower 101 Begins Today" for additional information about the project. Please direct any questions to Javier Sevilla.

Colloquium Today: The Large Synoptic Survey Telescope—Technical Progress and Selections from the "Science Book"

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The Large Synoptic Survey Telescope, or LSST, is proposed to be a large aperture, wide-field ground-based optical telescope designed to survey the entire visible sky (20,000 square degrees) in six colors every few nights. As such, it will produce an enormous database suitable for a wide variety of scientific investigations ranging from studies of small bodies in the solar system to constraints on the nature of dark energy and dark matter on cosmic scales. A large project team has been assembled at many institutions distributed across the country to design and build this facility.

In today's colloquium, Deputy Project Director and Lead Scientist for the Camera on LSST Steve Kahn will report on recent technical progress on the telescope, the 3.2 Gigapixel camera, and the data management system, all of which present novel technical challenges. Over the past year, the project has convened a set of science collaborations which have collectively generated a 600-page "LSST Science Book" that details the expected performance characteristics of LSST in addressing a wide range of astrophysical and cosmological problems. More than 250 scientists contributed text to that volume. Kahn will review some of the highlights from the Science Book in the latter half of his talk.

For most of his career, Kahn was an X-ray astrophysicist, specializing in high resolution X-ray spectroscopy of cosmic sources. He was the U.S. principal investigator for the development of the Reflection Grating Spectrometer experiment, launched in December 1999 and still flying on the European Space Agency's XMM-Newton Observatory. This experiment provided the first high resolution X-ray spectra for many classes of astrophysical sources. He switched to experimental cosmology when he moved to Stanford in 2003, and led SLAC and the Department of Energy into LSST. His intellectual interests in LSST mainly involve using weak lensing to constrain the nature of dark energy.

Kahn is currently the Cassius Lamb Kirk Professor in the Natural Sciences at Stanford, and served as deputy director of the Kavli Institute for Particle Astrophysics and Cosmology from 2003 to 2007, as well as associate lab director and director of SLAC's Particle Physics and Astrophysics Division from 2007 to 2009. In August 2010, he will Become Chair of Physics at Stanford.

Kahn's talk will begin at 4:15 p.m. today in Panofsky Auditorium. The colloquium is free and open to all.

Next Monday, SLAC accelerator scientist Eric Colby will present "A New Generation of Particle Accelerators."

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