Chemical Abundances of Planetary Nebulae in the Sagittarius Dwarf Elliptical Galaxy

Spectrophotometry and imaging of the two planetary nebulae He2-436 andWray16-423, recently discovered to be in the Sagittarius dwarf ellipticalgalaxy, are presented. Wray16-423 is a high excitation planetary nebula (PN)with a hot central star. In contrast He2-436 is a high density PN with a coolercentral star and evidence of local dust, the extinction exceeding that forWray16-423 by E(B-V)=0.28. The extinction to Wray16-423, (E(B-V)=0.14), isconsistent with the extinction to the Sagittarius (Sgr) Dwarf. Both PN showWolf-Rayet features in their spectra, although the lines are weak inWray16-423. Images in [O III] and H-alpha+[N II], although affected by poorseeing, yield a diameter of 1.2'' for Wray16-423 after deconvolution; He~2-436was unresolved. He2-436 has a luminosity about twice that of Wray16-423 and itssize and high density suggest a younger PN. In order to reconcile the differingluminosity and nebular properties of the two PN with similar age progenitorstars, it is suggested that they are on He burning tracks The abundance pattern is very similar in both nebulae and shows an oxygendepletion of -0.4 dex with respect to the mean O abundance of Galactic PN and[O/H] = -0.6. The Sgr PN progenitor stars are representative of the highermetallicity tail of the Sgr population. The pattern of abundance depletion issimilar to that in the only other PN in a dwarf galaxy companion of the MilkyWay, that in Fornax, for which new spectra are presented. However theabundances are larger than for Galactic halo PN suggesting a later formationage. The O abundance of the Sgr galaxy deduced from its PN, shows similaritieswith that of dwarf ellipticals around M31, suggesting that this galaxy was adwarf elliptical before its interaction with the Milky Way.Comment: 24 pages, Latex (aas2pp4.sty) including 5 postscript figures. To appear in Ap