Molecular Hydrogen Emission Lines inFar Ultraviolet Spectroscopic ExplorerObservations of Mira B

We present new Far Ultraviolet Spectroscopic Explorer (FUSE) observations ofMira A's wind-accreting companion star, Mira B. We find that the strongestlines in the FUSE spectrum are H2 lines fluoresced by H I Lyman-alpha. Apreviously analyzed Hubble Space Telescope (HST) spectrum also shows numerousLyman-alpha fluoresced H2 lines. The HST lines are all Lyman band lines, whilethe FUSE H2 lines are mostly Werner band lines, many of them never beforeidentified in an astrophysical spectrum. We combine the FUSE and HST data torefine estimates of the physical properties of the emitting H2 gas. We findthat the emission can be reproduced by an H2 layer with a temperature andcolumn density of T=3900 K and log N(H2)=17.1, respectively. Another similaritybetween the HST and FUSE data, besides the prevalence of H2 emission, is thesurprising weakness of the continuum and high temperature emission lines,suggesting that accretion onto Mira B has weakened dramatically. The UV fluxesobserved by HST on 1999 August 2 were previously reported to be over an orderof magnitude lower than those observed by HST and the International UltravioletExplorer (IUE) from 1979--1995. Analysis of the FUSE data reveals that Mira Bwas still in a similarly low state on 2001 November 22.Comment: 23 pages, 6 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by Ap