Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...468..871b&link_type=abstract
Astrophysical Journal v.468, p.871
Astronomy and Astrophysics
Astronomy
10
Shock Waves, Stars: Supernovae: Individual Alphanumeric: Sn 1006, Ism: Supernova Remnants, Ultraviolet: Ism
Scientific paper
We have observed the 912-1840 Å spectrum of the sdOB star known as the Schweizer-Middleditch star, which lies behind the remnant of SN 1006, to search for absorption lines due to the unshocked ejecta. We have also observed the sdB star PG 0839+399 for comparison. The spectra were obtained using the Hopkins Ultraviolet Telescope on the Astro-2 Space Shuttle mission in 1995 March. Assuming SN 1006 was a Type Ia supernova, 0.3-0.5 Msun 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 (SM) 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 A. We use stellar model fits to the spectra to constrain the strength of Fe III and Fe II lines in the spectral region below Lyα. Absorption from Fe Hi 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 provided by Hamilton & Fesen. However, the Hamilton & Fesen model is not precluded by the statistics in our data, which provide a 3 σ upper limit of 3.4 Å for the equivalent width of Fe III λ1123. Converting into mass, our best fit corresponds to only 0.016 Msun of Fe++, and the 3 σ limit corresponds to ≤0.054 Msun of Fe++. This indicates that if the expected iron is present in the ejecta, it must be largely in ionization states higher than Fe ++. No other absorption lines attributable to the supernova remnant are detected in the spectrum below Lyα. A faint excess in the spectrum near 1170 is unexplained but might be due to Lyα emission from the nonradiative shock on the near side of the supernova remnant shell. This possibility is testable with improved optical data for SN 1006.
Blair William Patrick
Long Knox S.
Raymond John C.
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