An Ultraviolet Fe Ii Image of Sn 1885 in M31

Ultraviolet imaging of the remnant of Supernova 1885 in M31 with the Hubble Space Telescope using the F255W filter on the WFPC2 reveals a dark spot of Fe II absorption at the remnant’s known position in the bulge of M31. The diameter of the absorbing spot is 0. 55 ± 0. 15, slightly smaller than, but consistent with, the 0. 70 ± 0. 05 diameter measured in the higher quality WFPC2 Ca II absorption image previously reported by us. The measured ratio of flux inside to outside SNR 1885 in the Fe II image is 0.24 ± 0.17, consistent with the ratio 0.33 ± 0.04 expected on the basis of a model fit to the previously obtained near-UV FOS spectrum. The observed depth of Fe II absorption suggests that Fe II is fully saturated, with an iron mass in the range MFe = 0.1–1.0M⊙. Besides Fe, ion species Mg I, Mg II, and Mn I probably make some contribution to the absorption from the SN 1885 remnant in the F255W image. Subject headings: galaxies: individual (M31) — ISM: supernova remnants — stars: supernovae: individual (SN 1885) — ultraviolet: galaxies — ultraviolet: ISM