Disentangling Metallicity and Age for Turnoff Stars |
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Authors: | RC Peterson |
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Institution: | (1) Astrophysical Advances, Palo Alto, CA 94301, USA |
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Abstract: | This is a progress report on calculations of near-ultraviolet spectrawith Ben Dorman at NASA/Goddard, for the ultimate purpose of extractingage and metallicity from extragalactic spectra. We are calculating fromfirst principles a grid of spectra covering 2200–3400 Å using theKurucz program SYNTHE, beginning with stars of metallicity less thanone-fifth solar (Fe/H] < ?0.7). For these stars, LTE calculationsusing known opacities and line lists including only transitions measuredin the laboratory, coupled with standard line-blanketed LTE models, providea satisfactory match to the spectra of turnoff stars of temperaturesT eff = 5750 K – 6250 K. For more metal-rich stars, two problemsarise: lines without a laboratory identification become increasinglyinfluential, and the cores of all strong lines become too strong. Theseproblems must be addressed to match near-UV spectra of turnoff stars ofsolar metallicity or higher. |
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