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Astron. Astrophys. 329, L5-L8 (1998)

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4. Discussion

Taken together, the 3 observations discussed above suggest that the gravities determined from the spectroscopic analysis of the H [FORMULA] profile may be too low by at least 0.5 in the log. There are two other central stars where this also appears to be true. The central stars of NGC 3242 and NGC 6210 have been determined by the reasonably reliable method of measuring the expansion at two (or more) epochs (Hajian et al., 1995). The surface gravities determined from these distances (Pottasch, 1997) are shown in the second column of Table 4 and are compared to the spectroscopic gravities in the third column. Again the differences are large, at least 0.5 in the log.


[TABLE]

Table 4. Comparison of expansion and spectral data


The conclusion that the analysis of the H [FORMULA] profiles always gives too low a value of gravity for PN central stars is too extreme. The central star of the PN in M 15 has a spectroscopically determined gravity which leads to a distance which is in good agreement with the distance to the cluster. However the 5 cases presented here are evidence that sometimes the spectroscopic gravity is too low.

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© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997
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