A multisite photometric study of two unusual beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph

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Handler G., Shobbrook R. R., Uytterhoeven K., Briquet M., Neiner C., Tshenye T., ...Daha Fazla

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, cilt.424, sa.3, ss.2380-2391, 2012 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 424 Sayı: 3
  • Basım Tarihi: 2012
  • Doi Numarası: 10.1111/j.1365-2966.2012.21414.x
  • Dergi Adı: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.2380-2391
  • Anahtar Kelimeler: stars: early-type, stars: individual: V2052 Oph, stars: individual: V986 Oph, stars: magnetic field, stars: oscillations, stars: rotation, DRIVEN STELLAR WINDS, MODE-IDENTIFICATION, DYNAMICAL SIMULATIONS, NU-ERIDANI, ASTEROSEISMOLOGY, PULSATION, FIELD, SPECTROSCOPY, OSCILLATION, VARIABILITY
  • Akdeniz Üniversitesi Adresli: Evet

Özet

We report a multisite photometric campaign for the beta Cep stars V2052 Oph and V986 Oph. 670?h of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry was obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l = 4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental mode. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54 degrees< i < 58 degrees and the magnetic obliquity 58 degrees < beta < 66 degrees The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l = 3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating beta Cep stars, which appear to prefer modes of higher l, are briefly discussed.

We report a multisite photometric campaign for the β Cep stars V2052 Oph and V986 Oph. 670 h of high-quality differential photoelectric Strömgren, Johnson and Geneva time-series photometry was obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l = 4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental mode. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54° < i < 58° and the magnetic obliquity 58° < β < 66°. The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l = 3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating β Cep stars, which appear to prefer modes of higher l, are briefly discussed.