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Astron. Astrophys. 319, 161-165 (1997)

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Photometric observations of the nucleus of IC 418

E. Kuczawska 1, K. Wlodarczyk 1 and S. Zola 2, 1

1 Institute of Physics, Cracow Pedagogical University ul. Podchoraych 2, PL-30084 Kraków, Poland (sfkuczaw@cyf-kr.edu.pl)
2 Astronomical Observatory, Jagiellonian University, ul. Orla 171, PL-30244 Kraków, Poland

Received 15 October 1994 / Accepted 7 July 1996


We discuss the observational characteristics of a recently proposed class of variable central stars of planetary nebulae. We summarize previous observations of the nucleus of IC 418, a prototype star of this class, and we analyze new photometry of this object, obtained in 1989 and 1991. We confirm that the characteristic timescale of the photometric variations is a few hours. No single period can fit all of our observational runs, implying that the variability is either irregular or multimodal. We discuss two possible explanations of the observed phenomena: (i) an unstable, radiatively driven wind and (ii) pulsational instability driven by the [FORMULA] -mechanism. We also consider the possibility that the observed variability is produced by a combination of both mechanisms and that they may influence each other.

Key words: stars: post-AGB, oscillations, mass-loss, individual: HD 35914 – planetary nebulae: IC 418

Send offprint requests to: E. Kuczawska

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998