Timothy C. Beers
Notre Dame Chair in Astrophysics
Notre Dame Chair in Astrophysics
B.S. in Physics, Purdue University, June 1979
B.S. in Metallurgical Engineering, Purdue University, June 1979
Ph.D. in Astronomy, Harvard University, November 1983
Office address: 339 Nieuwland Science Hall
Office phone: 574-631-4088
Timothy Beers is interested in the origin and evolution of the elements in the Universe, and the assembly of large spiral galaxies such as the Milky Way. For decades, Professor Beers has designed and executed large-scale surveys of stars in the Milky Way, efficiently sifting through literally millions of individual stars in order to find those objects that have recorded the chemical history of the Universe in their atmospheres. Beers’ efforts have been responsible for the identification (and subsequent analysis) of the great majority of stars known with overall abundances of heavy metals (such as Ca, Mg, and Fe) less than 1/1000th that of our Sun.
Among the discoveries that have been made to date:
- The discovery of moderate to highly r-process-element enhanced stars (now known as r-I and r-II stars), including the first metal-poor stars with measured abundances of the radioactive chronometers Th and U, which have enabled a cosmo-chronometric estimate of a lower limit on the age of the Universe.
- Exploration of the nature of the so-called Spite Lithium Plateau, including the demonstration that it exhibits extremely small scatter, and a “downturn” at low metallicity, with clear implications for the evolution of cosmological Li, possibly associated with the mixing of Li astrated by the first generations of massive stars.
- Demonstration that the subset of the so-called carbon-enhanced metal-poor (CEMP) stars without neutron-capture element overabundances (CEMP-no stars) exhibit a characteristic light-element signature (enhanced C, N, O, Na, Mg, Al, Si) that is now associated with the nucleosynthesis of the very first stars born in the Universe.
Beers played a major role in the execution of the next great survey of the Milky Way, which obtained medium-resolution spectroscopy of over 240,000 stars through an extension of the Sloan Digital Sky Survey (SDSS-II) known as SEGUE: The Sloan Extension for Galactic Understanding and Exploration. Beers led the group responsible for the development, testing, and validation of the software pipeline that obtains estimates of atmospheric parameters for these stars, including their metallicities. This effort produced (and made available to the public) abundance estimates for over 200,000 stars, the first time this had been accomplished for such large samples. Beers served as Survey Scientist for the SEGUE-2 effort, which obtained an additional 200,000 medium-resolution spectra during the second extension of SDSS, known as SDSS-III. As the result of these efforts (which continue to the present), Beers and his colleagues now have measured abundances for over 400,000 stars in the Galaxy, including over 30,000 stars with metallicities below 1% Solar, an order of magnitude increase in the numbers of very metal-poor stars that were previously known.
Among the important results that have come from analysis of stars from SDSS/SEGUE to date:
- Identification of the inner/outer halo structure of the Milky Way, including the important recognition that the most metal-deficient stars in the Galaxy are associated with the outer-halo component, thought to be formed from the debris of low-mass sub-Galactic fragments.
- Photometric metallicity estimates for over one million stars, including the first “fair” determination of the metallicity distribution function of halo stars, based on refined photometric estimates of metallicity for several thousand stars in the Solar Neighborhood (and with kinematic properties that are incompatible with a single halo population).
- Identification of many thousands of CEMP stars, which are now being used to constrain the distribution of masses for early generation stars in the Galaxy.
Beers now leads the involvement of Notre Dame astronomers in SDSS-IV, the third extension of the Sloan Digital Sky Survey. Beers’ particular interest in SDSS-IV is the APOGEE-II project, which is obtaining high-resolution near-infrared spectroscopy of several hundred thousand stars in the Milky Way. These stars with help constrain the chemical evolution of all of the stellar populations in our Galaxy, including the thin disk, thick disk, the bulge, and the inner our outer halo.
Beers is a co-PI and an Associate Director of the highly successful NSF Physics Frontier Center, JINA: Joint Institute for Nuclear Astrophysics, which brings together the work of nuclear physicists and astronomers at numerous institutions worldwide to make transformational progress on understanding of the formation of the elements, and the astrophysics of the sites in which they were produced (e.g., supernovae, neutron stars, AGB stars, etc.). This center, which has been in existence for the past decade, was recently awarded a new six-year funding cycle by the NSF, with particular emphasis on the origin and evolution of elements.
Selected Recent Publications
2016 JR-384 “The Role of Binaries in Enriching the Early Galactic Halo. II. The CEMP-no Stars,” Hansen, T., Andersen, J., Nordstrom, B., Beers, T.C., Placco, V.M., Yoon, J., & Buchhave, L., Astronomy & Astrophysics, 586, 160
2015 JR-380 “Chonography of the Milky Way’s Halo System with Field Blue Horizontal-Branch Stars,” Santucci, R.M., Beers, T.C., Placco, V.M., Carollo, D., Rossi, S., Lee, Y.S., Denissenkov, P., Tumlinson, J., & Tissera, P.B., Astrophysical Journal (Letters), 813, L16
2015 JR-377 “Hubble Space Telescope Near-Ultraviolet Spectroscopy of Bright CEMP-s Stars,” Placco, V.M., Beers, T.C., Ivans, I.I., Filler, D., Imig, J.A., Roederer, I.U., Abate, C., Hansen, T., Cowan, J.J., Frebel, A., Lawler, J.E., Schatz, H., Sneden, C., Sobeck, J.S., Aoki, W., Smith, V.V., & Bolte, M., Astrophysical Journal, 812, 190
2015 JR-375 “Metal-Poor Stars Observed with the Magellan Telescope. III. New Extremely and Ultra Metal-Poor Stars from SDSS/SEGUE and Insights on the Formation of Ultra Metal-Poor Stars,” Placco, V.M., Frebel, A., Lee, Y.S., Jacobsen, H.R., Beers, T.C., Pena, J.M., Chan, C., & Heger, A., Astrophysical Journal, 809, 136
2015 JR-362 “High-Resolution Spectroscopy of Extremely Metal-Poor Stars from SDSS/SEGUE. II. Binary Fraction,” Aoki, W., Suda, T., Beers, T.C., & Honda, S., Astronomical Journal, 139, 39