Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...277..524b&link_type=abstract
Astronomy and Astrophysics, Vol. 277, NO. 2/OCT(I), P. 524, 1993
Astronomy and Astrophysics
Astrophysics
21
Stars: Variables: Cepheids - Line: Profiles - Turbulence - Shock Waves - Stars: Individual: Δ Cephei
Scientific paper
We present 43 high resolution spectra of the classical cepheid star δ Cephei at two different spectral domains, one including Hα and the other one including the sodium D lines. The interstellar component of the sodium D1 line at about 13 km s-1 heliocentric velocity has been removed and the radial velocity as well as the FWHM of the Na I(D1) line and four photo spheric iron lines are measured with good precision (σ < 2 km s-1) There is no evidence for a bump in any of the curves mentioned before. A simple nonlinear nonadiabatic radial pulsational description is used to calculate versus phase the maximum possible "turbulence" necessary to explain the observed line widths and to estimate the upper limit of the rotational velocity υrot sin i ≃ 9 km s-1. In this context we define turbulence as the "difference" between the observed and the computed thermal-pulsational-rotational FWHM. Furthermore we try to give a qualitative interpretation of the calculated turbulence curve and try to explain what is going on in the stellar atmosphere. It appears that the turbulence strongly varies with pulsational phase. This is certainly a direct consequence of the pulsating atmospheric motion where propagating shock waves play an important role. Other broadening mechanisms, which are not taken into account in our calculations because they need a much more complex model, are discussed. They can possibly reduce the amount of our so-called turbulent velocity.
Breitfellner M. G.
Gillet Denis
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