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HST WFPC2 images of M87 have revealed a small nuclear disk of ionized gas with apparent spiral structure (Ford et al. 1994, Ap.J., in press). Post-COSTAR FOS spectra taken at the nucleus, and at 0.\arcsec25 along the approximate major axis on either side of the nucleus, show that the gas is in rapid rotation about the nucleus (Harms et al. 1994, Ap.J., in press). For the inclination angle and major axis position angle deduced from the emission line image, the central mass is $\sim$2.4x$10^{9} M_{\sun}$. M/L within 0.\arcsec25 is $\sim$170 $M_{\sun}/L_{\sun}$, implying that most of the mass is in a black hole. Two other FOS observations were made well off the major axis, at radii of 0.\arcsec34 and 0.\arcsec55. Central mass estimates made from the velocities of all five FOS observations are consistent for inclination angle and position angle pairs which include the pair deduced independently from the image. A disk in Keplerian rotation about a point mass is thus consistent with all of the imaging and spectroscopic data. I am now using kinematic models of the disk in combination with the observed surface brightness in H$\alpha$+[NII] to generate line profiles as a function of central mass, inclination angle, and position angle for comparison with the line profiles in the five observed spectra. These model spectra will be used to further constrain the angles and the mass of the point source, to determine how much additional distributed mass could be present, and to show how much gas with non-rotational motion is present.
This work is supported by NASA grant NAS5-1630.
