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Session 40 - Supernova Remnants & SN 1987A.
Display session, Thursday, January 08
Exhibit Hall,
We present and discuss HST WFPC2 images and FOS spectra of the remnant of SN 1885 (S And) in M31. This supernova remnant (SNR) is seen as a small, dark absorption spot silhouetted against M31's central bulge. Although initially attributed to resonance Fe I 3860 A line absorption in keeping with S And's suspected Type Ia SN classification, the new HST data show that the major absorber making the SNR visible is Ca II 3933, 3968 A. WFPC2 images taken using the FQUVN-3 filter centered on 3916 A (FWHM = 60 A) show a circular absorption disk 0.35 +/- 0.03'' exactly at SN 1885's historically reported position. In contrast, the remnant is only faintly visible using a Fe I 3860 sensitive filter (FQUVN-4; 3839 +/- 30 A). Low-disperson FOS spectra using a 0.4'' diameter aperture confirm the presence of strong and broad Ca II absorption, as well as revealing strong Ca I 4227 absorption and a weak feature on the blue wing of Ca II 3933 line profile, possibly due to Fe I 3860. The remnant's blended Ca II 3933,3968 absorption has an equivalent width of 130 A, an expansion velocity around 10,000 km/s, and a 500 km/s blueshifted line center. The feature's line depth suggests S And is located in the outskirts of the bulge, near the front of the facing hemisphere. The SNR's Ca I 4227 line absorption has a EQW = 55 A, appears redshifted by 1400 km/s, and also exhibits an expansion velocity of 10,000 km/s.
