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K648 is one of the few Planetary Nebulae (PN) known in the galactic halo. It belongs to the globular cluster M15, therefore it is particularly interesting, both from the point of view of the evolution, and because its distance is known better than is usually possible for PNe.
We present a UV spectrum of the central star, obtained with the Faint Object Spectrograph (FOS) of the \it Hubble Space Telescope \rm. This spectrum represents a substantial improvement over the previously existing IUE observations, not only for the better S/N and resolution, but because the flux through the large IUE aperture was contaminated by several field objects.
From the FOS spectrum, the continuum flux can be used to derive Temperature, and Luminosity. The stellar lines can be analysed, including a strong wind line of CIV.
Images in H$_{\alpha}$ and [OIII] obtained with HST (PC and FOC) were analysed in a previous paper (Bianchi et al 1994, preprint). These images allowed for the first time to resolve the nebula, measure its extension, and therefore to quantify nebular parameters, and to interpret its morphology: a bipolar structure of 2.5arcsec diameter, and an approximately spherical fainter shell extending out to 5 arcsec.
Finally, we obtained a high resolution spectrum of the H$_{\alpha}$ emission, at the Observatory of La Palma. With the measurement of the expansion velocity, we can compare evolutionary age with expansion age.
