Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.8105p&link_type=abstract
American Astronomical Society Meeting 210, #81.05; Bulletin of the American Astronomical Society, Vol. 39, p.190
Astronomy and Astrophysics
Astronomy
Scientific paper
For our Hubble Treasury program GO-9455, we are modeling the mid- and near-ultraviolet regions of old stars across the color-magnitude diagram. After revising the list of input atomic and molecular line parameters from 2200A to 9000A, we are calculating spectra of individual stars from first principles, and combining their weighted fluxes to form composite spectra representing single-age, single-metallicity populations older than 1Gyr. We are doing this for metallicities from one-hundredth to three times solar, and for three different ratios of the abundances of light versus iron-peak elements. We show plots comparing the calculated spectra with observations of stars, M31 globular clusters, and more distant galaxies. We find that the light-element ratio affects not only the strengths of individual lines and bands, but also the blue continuum in cool stars of near-solar metallicity and higher, as the continuous opacity is increased by high magnesium abundance. We also note that at such metallicities, the mid-ultraviolet spectrum of composite systems is suppressed below 2500A, and the near-ultraviolet becomes the spectral region providing the strongest observable constraints on age, metallicity, and abundance ratio.
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