Aerts, C.; Símon-Díaz, S.; Bloemen, S.; Debosscher, J.; Pápics, P. I.; Bryson, S.; Still, M.; Moravveji, E.; Williamson, M. H.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Pallé, P. L.; Christensen-Dalsgaard, J.; Rogers, T. M.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 602, id.A32, 14 pp.
Fecha de publicación:
6
2017
Revista
Número de citas
39
Número de citas referidas
34
Descripción
Stellar evolution models are most uncertain for evolved massive stars.
Asteroseismology based on high-precision uninterrupted space photometry
has become a new way to test the outcome of stellar evolution theory and
was recently applied to a multitude of stars, but not yet to massive
evolved supergiants.Our aim is to detect, analyse and interpret the
photospheric and wind variability of the O9.5 Iab star HD 188209 from
Kepler space photometry and long-term high-resolution spectroscopy. We
used Kepler scattered-light photometry obtained by the nominal mission
during 1460 d to deduce the photometric variability of this O-type
supergiant. In addition, we assembled and analysed high-resolution high
signal-to-noise spectroscopy taken with four spectrographs during some
1800 d to interpret the temporal spectroscopic variability of the star.
The variability of this blue supergiant derived from the scattered-light
space photometry is in full in agreement with the one found in the
ground-based spectroscopy. We find significant low-frequency variability
that is consistently detected in all spectral lines of HD 188209. The
photospheric variability propagates into the wind, where it has similar
frequencies but slightly higher amplitudes. The morphology of the
frequency spectra derived from the long-term photometry and spectroscopy
points towards a spectrum of travelling waves with frequency values in
the range expected for an evolved O-type star. Convectively-driven
internal gravity waves excited in the stellar interior offer the most
plausible explanation of the detected variability.
Based on photometric observations made with the NASA Kepler satellite
and on spectroscopic observations made with four telescopes: the Nordic
Optical Telescope operated by NOTSA and the Mercator Telescope operated
by the Flemish Community, both at the Observatorio del Roque de los
Muchachos (La Palma, Spain) of the Instituto de Astrofísica de
Canarias, the T13 2.0 m Automatic Spectroscopic Telescope (AST) operated
by Tennessee State University at the Fairborn Observatory, and the
Hertzsprung SONG telescope operated on the Spanish Observatorio del
Teide on the island of Tenerife by the Aarhus and Copenhagen
Universities and by the Instituto de Astrofísica de Canarias,
Spain.
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