Extensive study of HD 25558, a long-period double-lined binary with two SPB components

Sódor, Ádám and De Cat, P. and Wright, D. J. and Neiner, C. and Briquet, M. and Lampens, P. and Dukes, R. J. and Henry, G. W. and Williamson, M. H. and Brunsden, E. and Pollard, K. R. and Cottrell, P. L. and Maisonneuve, F. and Kilmartin, P. M. and Matthews, J. and Kallinger, T. and Beck, P. G. and Kambe, E. and Engelbrecht, C. A. and Czanik, R. J. and Yang, S. and Hashimoto, O. and Honda, S. and Fu, J. N. and Castanheira, B. and Lehmann, H. and Sódorné Bognár, Zsófia and Behara, N. and Scaringi, S. and Van, Winckel H (2014) Extensive study of HD 25558, a long-period double-lined binary with two SPB components. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 438 (4). pp. 3535-3556. ISSN 0035-8711

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Abstract

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ≈2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about nine years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. 11 independent frequencies were identified in the data. All the frequencies were attributed to one of the two components based on pixel-by-pixel variability analysis of the line profiles. Spectroscopic and photometric mode identification was also performed for the frequencies of both stars. These results suggest that the inclination and rotation of the two components are rather different. The primary is a slow rotator with ≈6 d period, seen at ≈60° inclination, while the secondary rotates fast with ≈1.2 d period, and is seen at ≈20° inclination. Spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field can be detected in the primary.

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