MOST1 detects g- and p-modes in the B supergiant HD 163899 (B2 Ib/II)

H. Saio, R. Kuschnig, A. Gautschy, C. Cameron, G. A.H. Walker, J. M. Matthews, D. B. Guenther, A. F.J. Moffat, S. M. Rucinski, D. Sasselov, W. W. Weiss

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85 Citations (Scopus)


The Microvariability and Oscillations of Stars (MOST) satellite observed the B supergiant HD 163899 (B2 Ib/II) for 37 days as a guide star and detected 48 frequencies ≲ 2.8 cycles day-1 with amplitudes of a few millimagnitudes (mmag) and less. The frequency range embraces g- and p-mode pulsations. It was generally thought that no g-modes are excited in less luminous B supergiants because strong radiative damping is expected in the core. Our theoretical models, however, show that such g-modes are excited in massive post-main-sequence stars, in accordance with these observations. The nonradial pulsations excited in models between 20 M at log T eff ≈ 4.41 and 15 M⊙ at log Teff ≈ 4.36 are roughly consistent with the observed frequency range. Excitation by the Fe bump in opacity is possible because g-modes can be partially reflected at a convective zone associated with the hydrogen-burning shell, which significantly reduces radiative damping in the core. The MOST light curve of HD 163 899 shows that such a reflection of g-modes actually occurs and reveals the existence of a previously unrecognized type of variable, slowly pulsating B supergiants (SPBsg) distinct from α Cyg variables. Such g-modes have great potential for asteroseismology.

Original languageEnglish
Pages (from-to)1111-1118
Number of pages8
JournalAstrophysical Journal
Issue number2 I
Publication statusPublished - 2006 Oct 20
Externally publishedYes


  • Stars: early-type
  • Stars: individual (HD 163899)
  • Stars: oscillations
  • Supergiants

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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