Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.

Details Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability. Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.

Jan 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...305..887k&link_type=abstract

Astronomy and Astrophysics, v.305, p.887

Astronomy and Astrophysics

Astrophysics

88

Stars: Early-Type, Supergiants, Emission-Line, Rotation, Oscillations

Scientific paper

We have obtained time series of spectra in the wavelength range 4000-6800 A over several months with high S/N and high resolution in wavelength (λ/{DELTA}λ=~20000) and time ({DELTA}t=~1d) of the late-type B and early-type A supergiants HD91619 (B7Ia), βOri (B8Ia), HD96919 (B9Ia), HD92207 (A0Ia), HD100262 (A2Ia) and αCyg (A2Ia). Halpha_ is found to show broad emission extended to about +/-1200km/s for all objects except αCyg. Due to the lack of strong line-emission in Halpha_ the electron-scattered photons are expected to originate in deep atmospheric layers. In all of the objects the Halpha_-line profiles are found to be highly variable on different time scales reaching from days to months. Patterns of variation in Halpha_ are found to be quite symmetric about the systemic velocity and are mainly due to variable blue and red-shifted emission superimposed on almost constant photospheric and/or wind profiles. These V/R variations are interpreted in terms of axial symmetry of the envelopes of these objects. Time-series analyses of the variations reveal Halpha_ time scales up to a factor of 6 longer than expected radial fundamental pulsation periods but consistent with rotational periods. Therefore, rotational modulation as a possible source of variability is concluded. Corotating weak magnetic surface structures are suggested as the source for a rotationally modulated lower wind region. Suddenly appearing deep and highly blue-shifted absorptions in Halpha_ are ascribed to instabilities of the ionization structure of the wind. Outwards propagating discrete absorption components have been observed only once in HD92207.

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