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Photometric observations of the nucleus of IC 418.
We discuss the observational characteristics of a recently proposedclass of variable central stars of planetary nebulae. We summarizeprevious observations of the nucleus of IC 418, a prototype star of thisclass, and we analyze new photometry of this object, obtained in 1989and 1991. We confirm that the characteristic timescale of thephotometric variations is a few hours. No single period can fit all ofour observational runs, implying that the variability is eitherirregular or multimodal. We discuss two possible explanations of theobserved phenomena: (i) an unstable, radiatively driven wind and (ii)pulsational instability driven by the ?-mechanism. We alsoconsider the possibility that the observed variability is produced by acombination of both mechanisms and that they may influence each other.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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