William P. Blair
Department of Physics and Astronomy, Johns Hopkins University
Charles and 34th Streets, Baltimore, MD 21218
wpb@pha.jhu.edu
Knox S. Long
Space Telescope Science Institute, 3700 San Martin Dr.
Baltimore, MD 21218
long@stsci.edu
and
John C. Raymond
Harvard-Smithsonian Center for Astrophysics,
60 Garden St.,
Cambridge, MA 02138
jraymond@cfa.harvard.edu
of iron should be present in the expanding remnant. The X-ray spectrum
shows no evidence for this quantity of iron in the hot gas, indicating
that this material may still be interior to the reverse shock.
Broad absorption lines of Fe II have been seen in the spectrum of the
Schweizer-Middleditch star previously,
but can only account for a small fraction of the expected iron. Our
spectrum covers the region of the strongest expected Fe III resonance
line at 1123 Å. We use stellar model fits to the spectra to
constrain the strength of Fe III and Fe II lines in the spectral region
below Ly
. Absorption from Fe III is inferred in our
spectrum of the SM star, but at a nominal level of only 1.0 Å
equivalent width, below the value of 
2.3 Å predicted with the
current best model (Hamilton & Fesen 1988). However, the Hamilton
& Fesen model is not precluded by the statistics in our data, which
provide a 3-
upper limit of 3.4 Å for the equivalent width of
Fe III 
1123. Converting into mass, our
best-fit corresponds to only 0.016 
of 
, and the
3-
limit corresponds to 
of 
.
This indicates that if the expected iron is present in the ejecta, it must
be largely in ionization states higher than 
.
No other absorption lines attributable to the supernova
remnant are detected in the spectrum below Ly
. A faint excess
in the spectrum near 1170 Å is unexplained, but might be due to
Ly
emission from the nonradiative shock on the near side of the SNR
shell. This possibility is testable with improved optical data for SN 1006.
Subject headings: ISM: Individual (SN1006) --- ISM: Supernova Remnants --- Stars: Post--AGB --- Ultraviolet: ISM