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Session 40 - Supernova Remnants & SN 1987A.
Display session, Thursday, January 08
Exhibit Hall,

[40.09] HST Images and Spectra of the Remnant of SN 1885 (S And) in M31.

R. Fesen, C. Gerardy (Dartmouth), K. McLin, A. Hamilton (JILA/Colorado)

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.

Program listing for Thursday