Astron. Astrophys. 349, 532-536 (1999)

Light variations of the blue hypergiants HD 168607 and HD 168625 (1973-1999) ^*

C. Sterken ¹, T. Arentoft ¹, H.W. Duerbeck ¹ and E. Brogt <sup>2

1</sup> University of Brussels (VUB), Pleinlaan 2, B-1050 Brussels, Belgium
² University of Groningen, Kapteyn Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 11 July 1999 / Accepted 3 August 1999

Abstract

Strömgren differential photometry of HD 168607 and HD 168625 collected during the previous 27 years is analysed. We bring to an end our quarter of a century monitoring of these objects and conclude that HD 168607 shows typical variability of an uneventful LBV, whereas HD 168625 remains to be classified as a variable hypergiant, or a marginally-dormant LBV. The long-term light- and colour behaviour of HD 168607 indicates the possible presence of a very slowly-developing S Dor phase - that is, a bright phase that coincides with redder colours. Besides the  Cygni-type microvariability, no other signs of ultrashort-periodic variability has been observed.

Key words: stars: early-type stars: individual: HD 168607 stars: individual: HD 168625 stars: oscillations stars: variables: general

* Based on observations obtained at the European Southern Observatory at La Silla, Chile (applications ESO 56D-0249, 58D-0118, 60D-0148, 61D-0128 and 62H-0110)

Send offprint requests to: C. Sterken

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Contents

• 1. Introduction
• 2. The data
  • 2.1. The discovery data
  • 2.2. LTPV uvby photoelectric photometry
  • 2.3. Walraven VBLUW photometry
  • 2.4. Hipparcos photometry
  • 2.5. LTPV uvby CCD photometry
• 3. The light- and colour curves
  • 3.1. The character of the light variations
  • 3.2. High-frequency variability
  • 3.3. Frequencies in the light variation
• 4. Discussion and conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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