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

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6. Conclusions

In this paper the consequences of the Hipparcos parallax measurements have been explored. It is suggested that the surface gravities derived from the measured distances for 3 objects are at least a factor of 3 higher than found from the Balmer line profile fitting method (Mendez et al., 1988b). Two other objects whose distances are known from the VLA expansion method (Hajian et al., 1995) show the same effect: the surface gravity derived from the distances is an order of magnitude higher than found from the line profile fitting. It is possible that the difficulty is related to the uncertain theoretical basis for the Balmer line fitting method. Napiwotzki and Rauch (1994) have shown that in about half of the cases where the method has been applied to different Balmer lines in the same object, different values of T [FORMULA] and log g are obtained for each line. Presumably this occurs because the temperature variation in the atmosphere is not determined well enough in the models, but it is not clear why this is so.

The 5 difficult cases discussed in this paper should be further investigated. They should not be generalized since for the PN in M 15 the distance obtained from the profile fitting method is in good agreement with the cluster distance.

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© European Southern Observatory (ESO) 1998

Online publication: November 24, 1997