AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 67. Stellar Spectra
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southwest Exhibit Hall

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[67.02] Detailed non-LTE Analysis of the High-S/N STIS Spectrum of the Hot Subdwarf, BD+28{{}\circ}4211

I. Hubeny, T. Lanz, S. Haas, S.R. Heap, D.J. Lindler, M.E. Kaiser (NASA/GSFC)

During the course of commissioning the Space Telescope Imaging Spectrograph (STIS), observations were obtained to demonstrate the feasibility of achieving very high S/N spectra in the ultraviolet with the MAMA detectors. The hot subdwarf, BD+28{{}\circ}4211, was selected as the test case. The two series of FP-SPLIT observations (E140M and E230M) have been shown to provide spectra with S/N=370 per resolution element in both the far-UV and near-UV. The observations were reduced by an iterative procedure that uses models of all relevant scatter sources including echelle scatter, MAMA detector halo and OTA scatter.

We have performed a detailed analysis of the spectrum, using sophisticated non-LTE model atmospheres including several million metal lines in non-LTE. First, we derive basic parameters of this star (effective temperature, surface gravity, chemical composition) and compare to earlier results. We present a detailed comparison of predicted and observed spectra in order to provide a benchmark for future detailed spectroscopic studies of hot compact objects. Finally, we present a preliminary analysis of the effects of elemental abundance stratification on the selected line profiles with the aim of studying the detectability of non-homogeneous abundance patterns.

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