Short-term variability and mass loss in Be stars I. BRITE satellite photometry of $\eta$ and $\mu$ Centauri

Abstract

Empirical evidence for the involvement of nonradial pulsations (NRP's) in the mass loss from Be stars ranges from (i) a singular case (\object{$\mu$ Cen}) of repetitive mass ejections triggered by multi-mode beating to (ii) several photometric reports about enormous numbers of pulsation modes popping up during outbursts and on to (iii) effective single-mode pulsators. The BRITE Constellation of nanosatellites was used to obtain mmag photometry of the Be stars $\eta$ and \object{$\mu$ Cen}. In the low-inclination star \object{$\mu$ Cen}, light pollution by variable amounts of near-stellar matter prevented any new insights into the variability and other properties of the central star. In the equator-on star \object{$\eta$ Cen}, BRITE photometry and {\sc Heros} echelle spectroscopy from the 1990s reveal an intricate clockwork of star-disk interactions. The mass transfer is modulated with the frequency difference of two NRP modes and an amplitude three times as large as the amplitude sum of the two NRP modes. This process feeds a high-amplitude circumstellar activity running with the incoherent and slightly lower so-called Štefl frequency. The mass loss-modulation cycles are tightly coupled to variations in the value of the Štefl frequency and in its amplitude, albeit with strongly drifting phase differences. The observations are well described by the decomposition of the mass loss into a pulsation-related engine in the star and a viscosity-dominated engine in the circumstellar disk. Arguments are developed that large-scale gas-circulation flows occur at the interface. The propagation rates of these eddies manifest themselves as Štefl frequencies. Bursts in power spectra during mass-loss events can be understood as the noise inherent to these gas flows.

Recommended for publication in Astronomy & Astrophysics

References in corpus (10)

• A unifying explanation of complex frequency spectra of gamma Dor, SPB and Be stars: combination frequencies and highly non-sinusoidal light curves
• Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity
• MOST detects corotating bright spots on the mid-O type giant ξ Persei
• Massive pulsating stars observed by BRITE-Constellation. I. The triple system Beta Centauri (Agena)
• Time-series photometry of the O4 I(n)fp star zeta Puppis
• Angular momentum transport by stochastically excited oscillations in rapidly rotating massive stars
• Pulsating B and Be stars in the Small Magellanic Cloud
• Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis
• Amplitude variability in satellite photometry of the non-radially pulsating O9.5V star zeta Oph
• Oscillation modes in the rapidly rotating Slowly Pulsating B-type star $\bmu$ Eridani

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