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As a step towards clarifying the ionization mechanism of LINERs, we have usedthe Hubble Space Telescope Faint Object Spectrograph to obtain an ultravioletspectrum of the nucleus of NGC 6500. Compared with more luminous Seyfertnuclei, the emission-line spectrum of NGC 6500 is remarkable for itslow-excitation character: C III], C II], and Mg II are the strongestcollisionally excited lines in the UV, and C IV is not detected. The fast shockmodels of Dopita & Sutherland (1995, 1996) are a poor match to the observedspectrum, as they predict much stronger emission than is observed forhigh-excitation lines such as C IV. Photoionization by an obscured nonstellarcontinuum source, or possibly ionization by slower (100 km/s) shocks, are morelikely explanations for the emission-line ratios. The origin of the UVcontinuum is unclear; its overall spectral shape is reasonably well matched byspectral evolution models for single-burst populations with ages in the range70-100 Myr, but no definite absorption features from young stars are present.Alternately, the UV continuum (or some fraction of it) may be scatteredradiation from a hidden active nucleus. We tentatively detect a broad He II4686 emission feature, which may be due to Wolf-Rayet stars, although the UVspectrum does not show any clear Wolf-Rayet signatures. We also find that NGC6500 is weakly detected in an archival ROSAT HRI image with a luminosity of 5 x10^40 erg/s in the 0.1-2.4 keV band, within the normal range for LINERs.Comment: 21 pages, 4 figures, LaTeX with AASTeX v4.0 style file, accepted for  publication in The Astronomical Journa

Ultraviolet Emission from the Liner Nucleus of NGC 6500