An Ultraviolet Fe II Image of SN 1885 in M31

Abstract

Ultraviolet imaging of the remnant of supernova (SN) 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, ~0.5", is consistent with the 0.70"+/-0.05" diameter measured in the higher quality WFPC2 Ca II absorption image previously reported by us. The flux in the spot is 0.76+/-0.21 lower than that in adjacent regions; that is, three-quarters of the bulge starlight is being absorbed by supernova remnant (SNR) 1885. The depth of absorption is consistent with the amount 0.67+/-0.04 expected on the basis of a model fit to the previously obtained near-UV Faint Object Spectrograph (FOS) spectrum. The observed depth of Fe II absorption suggests that Fe II is fully saturated, with an iron mass consistent with the range M_Fe=0.1-1.0 M_solar previously inferred from the near-UV spectrum. 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.