Molecular Hydrogen Emission Lines in Far Ultraviolet Spectroscopic Explorer Observations of Mira B

Abstract

We present new Far Ultraviolet Spectroscopic Explorer (FUSE) observations of Mira A's wind-accreting companion star, Mira B. We find that the strongest lines in the FUSE spectrum are H2 lines fluoresced by H I Lyman-alpha. A previously analyzed Hubble Space Telescope (HST) spectrum also shows numerous Lyman-alpha fluoresced H2 lines. The HST lines are all Lyman band lines, while the FUSE H2 lines are mostly Werner band lines, many of them never before identified in an astrophysical spectrum. We combine the FUSE and HST data to refine estimates of the physical properties of the emitting H2 gas. We find that the emission can be reproduced by an H2 layer with a temperature and column density of T=3900 K and log N(H2)=17.1, respectively. Another similarity between the HST and FUSE data, besides the prevalence of H2 emission, is the surprising weakness of the continuum and high temperature emission lines, suggesting that accretion onto Mira B has weakened dramatically. The UV fluxes observed by HST on 1999 August 2 were previously reported to be over an order of magnitude lower than those observed by HST and the International Ultraviolet Explorer (IUE) from 1979--1995. Analysis of the FUSE data reveals that Mira B was still in a similarly low state on 2001 November 22.

23 pages, 6 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by ApJ

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• The High-Energy Radiation Environment Around a 10 Gyr M Dwarf: Habitable at Last?
• X-ray Outburst in Mira A
• High-resolution Ultraviolet Radiation Fields of Classical T Tauri Stars
• First Surface-resolved Results with the IOTA Imaging Interferometer: Detection of Asymmetries in AGB stars
• The wonderful complexity of the Mira AB system
• Lyman alpha dominance of the Classical T Tauri FUV Radiation Field
• Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse
• Outer jet X-ray and radio emission in R Aquarii: 1999.8 to 2004.0
• First Images of R Aquarii and its Asymmetric H${}_2$O Shell
• First Resolved Images of the Mira AB Symbiotic Binary at Centimeter Wavelengths
• A Low-Mass H2 Component to the AU Microscopii Circumstellar Disk
• CO and H2 Absorption in the AA Tauri Circumstellar Disk
• Mira B Rejuvenated
• X-rays from the Mira AB Binary System
• Detection of CI line emission towards the oxygen-rich AGB star omi Cet
• Molecular Hydrogen in Orion as Observed by the Far Ultraviolet Spectroscopic Explorer