UV Spectral Dating of Stars and Galaxies
S. R. Heap, T. M. Brown, I. Hubeny, W. Landsman, S. Yi, M. Fanelli, J. P. Gardner, T. Lanz, S. P. Maran, A. Sweigart, M. E. Kaiser, J. Linsky, J. G. Timothy, D. Lindler, T. Beck, R. C. Bohlin, M. Clampin, J. Grady, J. Loiacono, C. Krebs
Abstract
An echelle spectrogram (R = 30,000) of the 2300-3100 A region in the ultraviolet spectrum of the F8V star 9 Comae is presented. The observation is used to calibrate features in the mid-ultraviolet spectra of similar stars according to age and metal content. In particular, the spectral break at 2640 A is interpreted using the spectral synthesis code SYNSPEC. We use this feature to estimate the time since the last major star formation episode in the z=1.55 early-type galaxy LBDS 53W091, whose rest frame mid-ultraviolet spectrum, observed with the Keck Telescope, is dominated by the flux from similar stars that are at or near the main-sequence turnoff in that system (Spinrad et al. 1997). Our result, 1 Gyr if the flux-dominating stellar population has a metallicity twice solar, or 2 Gyr for a more plausible solar metallicity, is significantly lower than the previous estimate and thereby relaxes constraints on cosmological parameters that were implied by the earlier work.
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