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From the 1200 galactic PNe listed in Acker et al (1992), only 10 objects have been identified to belong to the halo. Therefore we are trying to measure and understand their characteristics in more detail. Towards this goal we have been approved time with the Hubble Space Telescope during Cycle 3 for WFC imagery and FOS spectroscopy of two halo PN: M2-29 and DDDM-1.
M2-29 is located toward the galactic center and has been oconsidered as a bulge PN (Ratag 1991; Dopita et al 1991) although its distance is about 4 kpc. It is the PN with lowest derived O and Ne, and therefore it has been classified as a halo object (Pe\~na et al 1991). Its O/H is 1/40 solar; while the proportion of Ne/S/Ar/O is solar. We have obtained direct imagery of M2-29 in H$\alpha$ (F656N) with the WFC on HST in 1993 September which shows structure previously not apparent from ground-based images. It appears to be a double-shell PN with an inner circular ring 3.0 arc sec in diameter with the central star centered. An outer more diffuse ``halo'' of diameter 7.4 arc sec is seen. The most interesting feature seen is a ``knot'' at PA$\approx$11 $^{\circ}$ located 1.2 arc sec from the star. Isophotal maps and its elongated structure towards the star suggests that this knot might be a jet structure propagating into the mass-loaded inner shell boundary. A fainter elongated knot is seen outside the inner shell in almost the same PA. Physical and structural parameters of the PN from the imagery and spectroscopy are being derived and will be presented.
DDDM-1 has been studied by Clegg et al (1987); it is well above the Galactic plane with z=13 kpc. Its O/H ratio is 1/6 solar with very low C abundance, and C/O $<$ 0.12. WFC imagery of DDDM-1 is scheduled for mid-November and we will present the results and analysis for this object as well, if it is successful.
RJD's acknowledges support from Conacyt (Mexico) and AURA grant GO-4383.01-92A.
