Most Detects G- and P-Modes in the B Supergiant HD 163899 (B2Ib/II)

Abstract

The {\it 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 $\la$ 2.8 c d${}^{-1}$ with amplitudes of a few milli-magnitudes (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 $20M_{\odot }$ at $\log T_{\mathrm{eff}}\approx 4.41$ and $15M_{\odot }$ at $\log T_{\mathrm{eff}}\approx 4.36$ 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 {\it MOST} light curve of HD 163899 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 $\alpha$ Cyg variables. Such g-modes have great potential for asteroseismology.

24 pages, 9 figures, Astrophysical Journal in press

References in corpus (2)

• delta Ceti is not monoperiodic: seismic modeling of a beta Cephei star from MOST spacebased photometry
• Discovery of the new slowly pulsating B star HD 163830 (B5II/III) from MOST spacebased photometry

Cited by in corpus (27)

• Low-frequency gravity waves in blue supergiants revealed by high-precision space photometry
• Asteroseismology and Interferometry
• Statistical properties of a sample of periodically variable B-type supergiants - Evidence for opacity-driven gravity-mode oscillations
• Variability of OB stars from TESS southern Sectors 1-13 and high-resolution IACOB and OWN spectroscopy
• Photometric detection of internal gravity waves in upper main-sequence stars. II. Combined TESS photometry and high-resolution spectroscopy
• Beyond the Kepler/K2 bright limit: variability in the seven brightest members of the Pleiades
• MOST photometry of the RRd Lyrae variable AQ Leo: Two radial modes, 32 combination frequencies, and beyond
• Asteroseismic Signatures of Small Convective Cores
• MOST Detects g-Modes in the Late-Type be Star beta CMi (B8Ve)
• MOST detects SPBe pulsations in HD 127756 & HD 217543: Asteroseismic rotation rates independent of vsini
• Automated supervised classification of variable stars II. Application to the OGLE database
• Main-sequence variable stars in young open cluster NGC 1893
• Magnetic inhibition of convection in O star envelopes
• Sher 25: pulsating but apparently alone
• The IACOB project: IV. New predictions for high-degree non-radial mode instability domains in massive stars and connection with macroturbulent broadening
• Pulsations in B-type supergiants with masses $M<20M_{\odot }$ before and after core helium ignition
• Massive Star Asteroseismology in Action
• Wind properties of variable B supergiants. Evidence of pulsations connected with mass-loss episodes
• Revising the evolutionary stage of HD 163899: the effects of convective overshooting and rotation
• Variability in Optical Spectra of epsilon Orionis
• Unveiling the evolutionary state of three B supergiant stars: PU Gem, $\epsilon$ CMa and $\eta$ CMa
• Onboard Dynamic Image Exposure Control for the Star-Planet Activity Research CubeSat (SPARCS)
• The SMC B-type supergiant AzV322: a g-mode pulsator with a circumstellar disc
• Asteroseismology of Massive Stars : Some Words of Caution
• Variability of Galactic blue supergiants observed with TESS
• Recent MOST space photometry
• Variable Stars in M31 Stellar Clusters from the Panchromatic Hubble Andromeda Treasury