Astron. Astrophys. 359, 1068-1074 (2000)

PG 1618+563B: A new bright pulsating sdB star ^*

R. Silvotti ¹, J.-E. Solheim ², J.M. Gonzalez Perez ², U. Heber ³, S. Dreizler ⁴, H. Edelmann ³, R. Ostensen ² and R. Kotak <sup>5

1</sup> Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
² Institutt for Fysikk, Universitetet i Tromso, 9037 Tromso, Norway
³ Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, 96049 Bamberg, Germany
⁴ Institut für Astronomie und Astrophysik, Waldhäuser Straße 64, 72076 Tübingen, Germany
⁵ Lund Observatory, Box 43, 22100 Lund, Sweden

Received 28 March 2000 / Accepted 18 May 2000

Abstract

The results of two runs of time-series photometry made at the Nordic Optical Telescope clearly show that the sdB star PG 1618+563B is a new member of the EC 14026 class of sdB pulsators. Its power spectrum shows a doublet of frequencies at about 6.95 and 7.18 mHz (P 144 and 139 s respectively), which produce a modulation effect in the light curve with a beat period of about 1.2 hours. The amplitudes of the two signals are very low, not more than 2 mma. Thanks to its brightness (B=13.4), which makes PG 1618+563B one of the brightest objects of its class, we were able to observe the star also in different colours and measure its UBV pulsation amplitudes and phases. The comparison of these "nonadiabatic observables" with models may help the identification of the oscillation modes. The spectral analysis of the sdB star and the spectral classification of PG 1618+563A suggest that both stars form a wide visual binary ( 2500 A.U. separation), at a distance of about 680 pc from the sun.

Key words: subdwarfs stars: oscillations stars: individual: PG 1618+563

* Based on observations obtained at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. And on observations obtained at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy

Send offprint requests to: R. Silvotti (silvotti@na.astro.it)

SIMBAD Objects

Contents

• 1. Introduction
• 2. PG 1618+563: A new spectral analysis
• 3. Is PG 1618+563 a visual binary?
• 4. PG 1618+563: photometry
  • 4.1. Calibrations
  • 4.2. Time-series: observations and data reductions
  • 4.3. Amplitude spectrum
    • 4.3.1. No-filter data
    • 4.3.2. UBV data
• 5. Summary and discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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