thesis - IRS, The Infrared Spectrograph

5.3. Accurate abundances of ISO-observed PNe 75Figure 5.2–. Observational abundances with respect to Solar. In the upper-left corner a typical errorbar for all elements except helium is plotted. The solid line represents abundances equal to solarabundancesare related to the core mass rather than the initial mass. Stars with different initial mass anddifferent mass loss functions can lead to the same core mass.The majority of PNe are within the range of temperature and luminosity of the theoreticalevolutionary tracks. Most are in the last stage of the PNe phase. NGC 6537 lies outsideand it must be noticed that using T Z (H) makes this object closer to NGC 6302. While thisfigure may provide some insight in core mass and time evolution of these objects, the manyuncertainties (especially in distance) should be born in mind.5.3 Accurate abundances of ISO-observed PNe5.3.1 AbundancesAccurate abundances are needed in order to make a reliable comparison with theoreticalmodels. For this purpose a sample of ten PNe was selected in which precise abundances usingISO data have been derived. The references for the abundances are as follows: NGC 2440 →Bernard Salas et al. (2002, chapter 3); NGC 5315 → Pottasch et al. (2002); NGC 6302 →Pottasch & Beintema (1999); NGC 6445 → van Hoof et al. (2000); NGC 6537 and He 2-111→ Pottasch et al. (2000); NGC 6543 → Bernard-Salas et al. (2003, chapter 4); NGC 6741and NGC 7662 → Pottasch et al. (2001); NGC 7027 → Bernard Salas et al. (2001, chapter 2).It should be noticed that NGC 6302, NGC 6537 and He 2-111 are among those PNe with ahot central star, a strong bipolar morphology, and in which high velocity shocks are present.