A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 micron (MSX) fluxes indicative of highly evolved, intermediate- to high-mass stars with current or recent mass loss at large rates. We determine the chemistry of the circumstellar envelope from the mid-IR continuum and spectral features and classify the spectral types of the stars. In the sample of 60 sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch (AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find that the overwhelming majority of the sample AGB stars (with typical IR luminosities ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine mean bolometric corrections to the stellar K-band flux densities and find that for carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact HII regions with very red IRS spectra that include strong atomic recombination lines and PAH emission features. We demonstrate that the IRS spectral classes in our sample separate clearly in infrared color-color diagrams that use combinations of 2MASS data and synthetic IRAC/MIPS fluxes derived from the IRS spectra. On this basis, we suggest diagnostics to identify and classify, with high confidence levels, IR-luminous evolved stars and HII regions in nearby galaxies using Spitzer and near-infrared photometry.Comment: 46 pages, 9 figures; accepted for publication in AJ; abstract abridge

Astronomy Animations

This collection of animations introduces students to planetary motions, gravitational effects, and the scale of astronomical distances. Students can view visualizations of Earth's changing seasons, circumpolar motion, and the celestial equator and ecliptic plane. Animations on gravity explain how satellites orbit, the motions of comets and meteor storms, and gravitational 'warping'. Other animations explain how Earth's tides are produced, how astronomical distances are calculated, the use of spectra in astronomy, and the lifecycles of stars

A Virtual Museum of Fossils

This collection of fossils contains 300 fossils of vertebrates and invertebrates and casts of fossils from national museums, universities and private collections. For each geologic time period, the website provides ancient world configurations, important ancient world physiographic features, ancient world locations where the fossils were found, and a comprehensive table with thumbnails of all fossils in the collection. A separate page is devoted to each specimen where multiple high resolution photographs are displayed. Reference skeletal reconstructions are shown where available from the literature. Educational levels: High school, Intermediate elementary, Middle school, Undergraduate lower division, Undergraduate upper division