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This Week at Physics

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Event Number 3534

  Thursday, November 20th, 2014

Astronomy Colloquium
"The First Results From CHAOS: The Chemical Abundances Of Spirals Project"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Danielle Berg, Center for Gravitation, Cosmology and Astrophysics, UW Milwaukee
Abstract: "The CHemical Abundances of Spirals (CHAOS) project seeks to establish a broader understanding of the chemical evolution of spiral galaxies in general. CHAOS harnesses the combined power of the Large Binocular Telescope (LBT) with the large spectral range and sensitivity of the Multi Object Double Spectrographs (MODS) to observe “direct” abundances in a large sample of spiral galaxy H II regions. In this manner, we measure the largest sample of the highest quality spectra to date in NGC 628, with one or more temperature sensitive auroral lines ([O III] λ4363, [N II] λ5755, and [S III]λ6312) being observed at a strength of 3σ or greater in 45 H II regions. This high quality, homogeneous dataset allow us to examine trends in physical conditions and abundances with an unprecedented statistical significance. This analysis provided some atypical results. The comparison of derived temperatures where more than one auroral line is observed in an H II region demonstrates, unexpectedly, that temperatures based on [S III] λ6312 and [N II] λ5755 are consistent, while those based on [O II] λλ7320,7330 and [O III] λ4363 can often show large discrepancies. Understanding these temperature discrepancies will be a major goal for the CHAOS project. We examine the relative alpha-element abundances, as well as measure the O/H and N/O gradients in NGC 628. We find a large dispersion in O/H and posit that this dispersion represents an upper limit to the true dispersion in O/H at a given radius and that some of that dispersion is due to systematic uncertainties arising from temperature measurements.”
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