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Astron. Astrophys. 337, 253-260 (1998)

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1. Introduction

Despite recent improvements of distance determinations (parallax and expansion methods, see Pottasch, 1997) of planetary nebulae (PN), many questions remain open. We showed in a preceding paper (Pottasch & Acker, 1998) that HIPPARCOS distances appear smaller than "gravity-distances". We will check whether such a conclusion is valid in the case of other methods. On the other hand, the theoretical ages of bright nuclei still appear different from the kinematic ages of the nebulæ. We try to bring some contribution to these points, through HIPPARCOS observations. We determine first more accurate values of the stellar apparent magnitudes (Sect. 2). Trigonometric parallaxes are compared to other distances scales, individual and statistical (Sect. 3). From the position of the nuclei in the [FORMULA] diagram and comparison with theoretical tracks, we can estimate the mass of the ionizing nuclei and their theoretical ages, compared with their kinematic ages (Sect. 4). The case of the binary central star of A 35 is discussed (Sect. 5).

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© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998