  The nucleus of M87 displays a LINER spectrum at optical wavelengths, with a
nuclear disk of nebulosity that is resolved by the Hubble Space Telescope. We
present new results from optical and ultraviolet spectra of the central ~40pc
as measured by HST. In contrast with previous results for the extended disk,
the emission-line spectrum of the central region is best reproduced by a
multi-component photoionization scenario, rather than shock heating. The
nebular properties as well as energetic considerations suggest a transition on
scales of several tens of parsecs, from predominantly photoionization by a
central accretion source, to shock ionization within the disk. If this source
is at all representative, it suggests that many LINERs may be composite in
terms of the energetic processes that give rise to the emission spectrum. We
also report measurements of resonance-line absorption for the nucleus. The
absorption spectrum, like the emission lines, is characterized by low
ionization. The absorption line measurements coupled with independent
constraints suggests a total hydrogen column density of 10^19 - 10^20 cm^-2,
outflowing from the galaxy center with a velocity of ~126 km/s. The kinematic
signature of an outflow, along with evidence that the absorber covers the
power-law continuum source but not the emission-line clouds, suggests that the
absorbing matter is related to accretion phenomena in the nucleus. The presence
of such an outflow resembles similar behaviour in luminous AGN, although the
low ionization that characterizes LINERs is probably indicative of a different
mode of accretion in these sources.
