Hubble Space Telescope Images and Spectra of the Remnant of SN 1885 in M31

Near UV HST images of the remnant of SN 1885 (S And) in M31 show a 0"70 +-0"05 diameter absorption disk silhouetted against M31's central bulge, at SN1885's historically reported position. The disk's size corresponds to a lineardiameter of 2.5 +- 0.4 pc at a distance of 725 +- 70 kpc, implying an averageexpansion velocity of 11000 +- 2000 km/s over 110 years. Low-dispersion FOSspectra over 3200-4800 A; reveal that the absorption arises principally from CaII H & K (equivalent width ~215 A;) with weaker absorption features of Ca I4227 A; and Fe I 3720 A;. The flux at Ca II line center indicates a foregroundstarlight fraction of 0.21, which places SNR 1885 some 64 pc to the near sideof the midpoint of the M31 bulge, comparable to its projected 55 pc distancefrom the nucleus. The absorption line profiles suggest an approximatelyspherically symmetric, bell-shaped density distribution of supernova ejectafreely expanding at up to 13100 +- 1500 km/s. We estimate Ca I, Ca II, and Fe Imasses of 2.9(+2.4,-0.6) x 10^-4 M_o, 0.005(+0.016,-0.002) M_o, and0.013(+0.010,-0.005) M_o respectively. If the ionization state of iron issimilar to the observed ionization state of calcium, M_CaII/M_CaI = 16(+42,-5),then the mass of Fe II is 0.21(+0.74,-0.08) M_o, consistent with that expectedfor either normal or subluminous SN Ia.