Feature: MSU Plays a Key Role in a New Survey of the Cosmos

            Just as Lewis and Clark once set out to map the West, MSU scientists are engaged in a massive effort to digitize and spectroscopically analyze over half of the entire Northern Sky.

            For much of the past two centuries, our knowledge of the nature of the night sky was limited to either hand drawings made by an astronomer looking through the eyepiece of a telescope, or images that could be recorded on photographic plates at the focal planes of their telescopes. 

            Times have changed. 

            Over the past 5 years, a consortium of more than 300 scientists and engineers at institutions around the world have implemented modern digital approaches to obtain imaging for large swaths of the night sky over well-calibrated ranges of wavelengths.  This survey, known as the Sloan Digital Sky Survey (SDSS), has used a dedicated 2.5-m telescope at Apache Point Observatory near Sunspot, NM to measure precise brightness and positions for hundreds of millions of galaxies, stars, and quasars located in the Northern sky.  Because the data are in digital form, they can be quickly analyzed to harvest the wealth of information they contain.  Members of the SDSS consortium – and hundreds of other scientists working in collaboration – are using these data to address fascinating and fundamental questions about the Universe.

            Yet, this is only the beginning of the new era of survey astronomy.   And MSU is now a partner in this continuing adventure of exploration.

            The Joint Institute for Nuclear Astrophysics (JINA), an NSF Physics Frontier Center involving Michigan State University, The University of Notre Dame, and The University of Chicago, has joined forces with over 25 international participants in a newly funded extension of the SDSS, known as SDSS-II. SDSS-II will complete observations of a huge contiguous region of the Northern skies and will study the structure and origins of the Milky Way Galaxy and the nature of  the mysterious “dark energy” that may be responsible for the recently detected acceleration in the expansion of the Universe. 

            SDSS-II began observations in July, 2005.  Because of the efficiency with which data can be gathered using this approach, SDSS-II will finish in only 3 years, by July 2008.  The data will initially be studied exclusively by members of the SDSS-II consortium, and then will be released to the public for further investigations.

            SDSS-II has three components. The first, called LEGACY, will complete the SDSS survey of the extragalactic Universe, obtaining images and distances for nearly a million galaxies and quasars over a continuous swath of sky in the Northern Hemisphere, comprising some 8500 square degrees.

            The new funding also inaugurates the second part of SDSS-II, the Sloan Extension for Galactic Understanding and Exploration (SEGUE), which will map the structure and stellar makeup of the Milky Way Galaxy, and gather fundamental data on how the Milky Way formed and evolved.  The SEGUE project will allow astronomers, for the first time, to obtain a “big picture” of the structure of our own Milky Way. 

            The mapping of the Milky Way is more than an exercise in cartography. Ages, chemical compositions, and the space distribution of stars provide major clues to understanding how our own Galaxy formed, and, by example, how other large spiral galaxies like the Milky Way were formed.

            SEGUE will obtain imaging for another 3500 square degrees, or about 20 percent, of the Northern sky in the five SDSS filters, covering lower Galactic latitudes than the original SDSS, so that detailed studies of the disk population of the Milky Way can be carried out.  In the past decade, astronomers have found convincing evidence that many large galaxies, including ours, have continued to be “built up” over the history of the Universe by the incorporation of the shredded remains of smaller galaxies that have been torn apart by gravitational interactions with their “parent” galaxy.  The measurements made by SEGUE will be able to quantify the numbers of such interactions that have occurred in the past, as well as place strong constraints on the fraction of  stars in the Milky Way that have been “donated” by other galaxies.

            Of greatest significance to JINA scientists, SEGUE will obtain medium-resolution spectroscopy of 250,000 individual stars that have been selected to sample all of the stellar populations of the Galaxy.  Spectroscopy is a technique employed by astronomers to spread the light coming from a star into its constituent wavelengths, from which very detailed knowledge of its elemental makeup can be obtained.  In the future, additional spectroscopy observations of SEGUE stars will be made with the SOAR 4.1m telescope on Cerro Pachon, Chile, in which MSU is a partner.

            JINA scientists are particularly interested in the chemical compositions of the most metal-deficient (and by inference, oldest) stars that will be found by SEGUE. Identifying the oldest stars will help us understand how the elements of the periodic table were formed long ago inside of stars, and distributed throughout the early Universe by their explosions.  The huge number of stellar spectra that will be gathered by SEGUE will enable the detection of some 20,000 stars with abundances of heavy metals less than 1 percent than found in our Sun, more than a factor of 10 larger than the samples known today.   It is expected that studies of these stars will reveal direct evidence of the nature of the very first generations of stars that formed in the early Universe.

            The astrophysical origin of the elements is one of the primary research interests of many scientists at MSU, in particular nuclear physicists working at MSU’s National Superconducting Cyclotron Laboratory (NSCL). 

            “The metal-poor stars found by SEGUE will provide the elemental abundance data which, with the help of astrophysical models, can be compared to the nuclear data obtained in experiments at radioactive beam accelerators such as the NSCL, and in the future, the Rare Isotope Accelerator (RIA),” says NSCL scientist Hendrik Schatz.  “Because these metal-poor stars formed so early in the history of the Universe, they provide us with a unique glimpse of how individual supernova explosions began to enrich the newborn Galaxy with light and heavy elements.

            ”With the astronomical observations from SEGUE and the experimental nuclear data from the NSCL and RIA there is now a real chance to finally solve one of the big mysteries in science—the origin of the heavy elements from iron to uranium—within the coming decades.”

            The final piece of SDSS-II includes an intensive study of supernovae, sweeping the sky to find these remnants of gigantic explosions from dying stars. Astronomers can precisely measure the distances of distant supernovae, using them to map the rate of expansion of the universe, as well as to learn about the nature of the explosion phenomenon itself, which bears directly on the formation of the elements.

            JINA provides financial support for MSU Post-doctoral fellow Sivarani Thirupathi, as well as for MSU graduate student Young Sun Lee, who are working with myself to construct and refine the SDSS-II spectroscopic pipeline, which will be used to automatically assign estimates of atmospheric parameters (temperatures, surface gravities, and metallicities) for the SEGUE stars with available spectroscopy.  Already, four MSU graduate students are planning to work with data from SDSS-II in their PhD thesis work.  Additional undergraduate students are participating in SDSS-II related research projects.

            At MSU's NSCL, JINA Post-doctoral fellows Jorge Pereira, Daniel Galaviz, and Milan Matos, as well as JINA graduate students Alfredo Estrade, Paul Hosmer and Fernando Montes, together with MSU professors Hendrik Schatz and Paul Mantica, JINA visitors, and other collaborators from the NSCL, the University of Mainz in Germany, the University of Maryland, and the University of Notre Dame have begun to carry out first experiments with the unstable nuclei that participate in the nuclear processes in supernovae.  In order to understand the supernova explosion mechanism itself, JINA/NSCL groups led by MSU professors Remco Zegers and Sam Austin investigate experimentally the nuclear processes that lead to and trigger supernovae. SEGUE and JINA will be instrumental in bringing together the various observational, experimental, and theoretical results to address the open question of the origin of the elements.

            Funding for SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the Japanese Monbukagakusho, and the Max Planck Society. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The institutions that enabled SDSS-I and SDSS-II are: the American Museum of Natural History, the University of Basel, Cambridge University, Case Western Reserve University, the University of Chicago, Fermilab, The Institute for Advanced Study, the Japan Participation Group, the Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, Los Alamos National Laboratory, the Ohio State University, the

            Max-Planck-Institute for Astronomy, the Max-Planck-Institute for Astrophysics, New Mexico State University, University of Pittsburgh, University of Portsmouth, Astrophysical Institute Potsdam, Princeton University, the United States Naval Observatory and the University of Washington.

            The next few years promise to be quite exciting times for MSU astronomers and physicists alike.

            Timothy Beers is Professor of Astronomy in  MSU's Dept. of Physics and Astronomy.  He was recently awarded the University Distinguished Faculty Award, as well as the College of Natural Science Distinguished Faculty Award.  In 2003 he was named “Michigan Scientist of the Year” by the Impressions 5 Museum in Lansing.  Professort Beers earned two B.S. degrees from Purdue University (Physics and Metallurgical Engineering, '79) and two graduate degrees in astronomy from Harvard University (M.A. '80, and Ph.D. '83). After a three-year postdoctoral research fellowship at the California Institute of Technology, Beers joined MSU’s faculty in 1986. When not teaching students and travelling to conduct observations with telescopes in Arizona, Hawaii, Australia and Chile, Beers enjoys playing his guitar and talking with groups interested in the SOAR telescope.

USING THE SOAR TELESCOPE  FROM THE MSU CAMPUS

By Jack Baldwin

            Located at a superb astronomical site high in the Andes Mountains of South America, the brand new SOAR Telescope produces some of the sharpest images ever taken from the Earth’s surface.  MSU has a 1/6 share of this 4m diameter “Window on the Universe.”  After a nine-year gestation period, SOAR is now coming to life scientifically, and MSU astronomers are right there on the scene—at least, we are electronically on the scene. Actually, for our share of its usage we control the telescope from a new Remote Observing Room open to public view from the atrium of the Biomedical Physical Sciences Building on the MSU campus.

            Our first remote use of the telescope was on the evening of December 26 of 2005, and that has been followed by seven more very successful nights so far. This is “instant access” observing.  Instead of enduring that 15-hour plane ride to Chile, we just stroll down the hall and start to work!  One result of this is that MSU astronomers—professors and students alike—can easily share nights and even switch between different instruments on the telescope to work on a wide variety of projects. This has clearly paid off in this inaugural series of observing nights, during which 12 different astronomers carried out 7 different science programs, including several midnight switches between the optical camera and the infrared spectrograph on SOAR. This is the start of 18 years of payback for our investment in SOAR.

            The ambitious goal of MSU’s Center for the Study of Cosmic Evolution is to use SOAR as an observational astronomy laboratory to study how our universe came to have its present physical structure of stars and galaxies, and how its chemical makeup came to include the heavy chemical elements that we humans are made of.

            Here is a sampling of what we are up to:

• The Chemical Evolution of our Galaxy. University Distinguished Professor Tim Beers, in collaboration with research associate Sivarani Thirupathi and graduate students Brian Marsteller and Young Sun Lee, is using SOAR to study the way in which all of the elements except hydrogen and helium were formed through nuclear reactions in generation after generation of stars. The Beers team is among the world leaders in the study of the very earliest stages of this process here within the Milky Way. And they were first off the mark in MSU’s remote use of SOAR, taking infrared spectra of the oldest known stars in our Galaxy. Their results show how the abundances of different carbon isotopes can be measured in these stars, which tells us important details about the exact nature of that very early stellar generation.
• Variable Stars in the Milky Way’s Satellite Galaxies.The Magellanic Clouds are smaller satellite galaxies of the Milky Way.  Like our own Milky Way, they contain old star clusters harboring pulsating giant stars.  These star clusters and their pulsating stars help tell us whether the Magellanic Clouds formed at the same time and in the same way as the old halo of our own Galaxy.  Series of observations with SOAR reveal the presence of pulsating stars and let us characterize their properties. MSU astronomer Horace Smith and graduate student Nathan DeLee have launched a long-term campaign, using SOAR’s optical imager, to study these ancient stellar systems.
• Giant Star-Forming Regions in the Southern Sky.The Magellanic Clouds can only be seen from southern-hemisphere sites such as SOAR’s location, and the central regions of our own Milky Way Galaxy are also much better studied from the South. I and graduate student Eric Pellegrini have started a program with SOAR to study in detail some of the most important star-forming regions in our own corner of the universe, in order to obtain better insight into what similar systems would look like at very great distances. The light from those much more distant star-forming regions has taken most of the age of the universe to reach us and, if we can learn to decipher its message, carries the record of the earliest steps in 13 billion years of repeated cycling of interstellar gas through stars. Calibrating these distant systems through careful study of nearby examples is the key to understanding them.
• Dark Matter in Distant Galaxy Clusters.Giant galaxy clusters contain thousands of massive galaxies, but most of their mass is actually in the form of a mysterious substance called Dark Matter. MSU astronomy professor Megan Donahue leads a team that is using SOAR to carefully weigh this Dark Matter, using an effect called gravitational lensing. About 85 percent of all matter in the universe is in the form of Dark Matter, but we don’t know what it is, so anything we can find out about it is very important in the big scheme of things.
• Black Holes at the Edge of the Universe.  Professors Megan Donahue and Mark Voit are also using SOAR to study the way in which gas falls onto central galaxies from the outer parts of giant galaxy clusters. They are finding evidence that gas accretion onto massive black holes at the centers of these galaxies ionizes and heats the infalling gas, with strong effects on the overall evolution of the galaxy cluster

            Jack Baldwin is MSU associate chair for astronomy in the Dept. of Physics and Astronomy, and co-director of MSU's Center for the Study of Cosmic Evolution. He received his Ph.D. in astrophysics from the University of California at Santa Cruz in 1974. He has been at MSU for six years.