Appendix A: Notes on individual PNe
Here, we provide detailed information on the physical properties of the PNe of our sample. Unless otherwise noted, B and V magnitudes are from the Acker et al. (1992) catalogue. Fluxes, extinction constants, and diameters are from Cahn et al. (1992, hereafter CKS).
NGC 7027 : The Zanstra analysis yields and . We have used the expansion distance from the radio image of Masson (1989). The derived mass of the central star is .
NGC 2346 : The distance, kpc, is derived from the average extinction distance (Pottasch 1996). We obtain and . The mass of the central star results .
NGC 7293 : Many distance measurements are available for this nebula. Pottasch (1996) quotes a very uncertain (error up to 100%) parallax distance of kpc. A more reliable value of kpc comes from averaging several individual distances (Pottasch 1996). We obtain and or , using the parallax and average distances, respectively. The corresponding central star masses are and 0.60 . The progenitor masses are 2.6 and 2.0 . Given the large error on the parallax, we prefer the latter value for the initial mass of NGC 7293.
NGC 6781 : We obtain . By using the statistical (CKS) and the average of individual (Acker et al. 1992) distances, we obtain respectively and . In both cases, the mass of the central star coincides with the evolutionary track for .
M 1-16 : By using kpc (CKS method with a newly measured diameter), we find and . The inferred mass of the central star is .
M 1-17 : With a distance of kpc (from CKS method), we obtain and . The location on the HR diagram is just below the 0.55 .
M 2-9 : We calculate the distance with the method of CKS, but we evaluate the effective diameter from the image ( arcsec). The new distance to this nebula is kpc. No HeII flux has been detected. Thus, the Zanstra analysis gives lower limits to the temperature and luminosity. We obtain and from the hydrogen recombination lines. To date, nothing has been published on this nebula to set better constraints on the mass of the central star.
M 2-51 : The Zanstra analysis gives and . The luminosity is estimated using a distance kpc, derived with the CKS method and a new estimate of the diameter. The resulting final mass is .
M 4-9 : The distance evaluated with the newly measured angular size based on the H image by Schwarz et al. (1992) is kpc. For the central star, only a photographic magnitude exists. Thus, the resulting Zanstra analysis is quite uncertain. The flux is from Acker et al. . The HeII flux has never been measured. We obtain and . A value of the mass of the central star cannot be derived.
CRL 2688 : Catalogued as a "possible planetary nebula", the famous Egg nebula is actually a proto-PN. The standard analysis via Zanstra method is not feasible, as the nebula is still very thick to optical radiation. There are two mass estimates in the literature, or 2.7 respectively, which depend on the assumed mass loss rate (Sahai et al. 1998).
CRL 618 : The HeII flux is not available. Therefore, we cannot derive a Zanstra temperature. Hydrogen recombination lines give and a luminosity of , if kpc is used. This distance has been derived with the CKS method and diameter measured by Manchado et al. (1996). No mass determination is possible.
OH 09+1.3 : Another proto-PN, with no published mass to date.
IC 5117 : The distance is the average of the extinction distances quoted in Acker et al. (1992). We calculate and . The derived mass of the central star is .
M 1-59 : Since no stellar magnitudes are available for this object, we calculate the effective temperature with the "crossover" method (Kaler 1983). We use the statistical distance kpc from CKS, based on a new diameter measured by Manchado et al. (1996) and obtain and . The mass of the central star mass is .
NGC 6853 : The parallax distance quoted in Pottasch (1996) is of the best quality, so we can confidently use this value to evaluate the luminosity. From the Zanstra analysis we derive and , and a central mass
BD+30o3639 : The HeII flux is not detected. Thus, we obtain lower limits to the luminosity and temperature: and , using the hydrogen recombination lines and the average of extinction distances from Acker et al. (1992). No mass determination is possible.
NGC 7008 : We calculate and . The distance used is the average of the extinction distances quoted in Acker et al. (1992). The derived central mass is .
M 1-13 : Since no stellar magnitudes are available for this object, we calculate the effective temperature with the "crossover" method (Kaler 1983). We use the statistical distance kpc from CKS to obtain and . The central star mass is .
© European Southern Observatory (ESO) 2000
Online publication: March 17, 2000