Metal emission lines as diagnostic tools for shock waves in outer atmospheres of M-type Mira stars

He. Richter, E. Sedlmayr, P.R. Wood

AG Tagung München 2001

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Abstract:

One way to reveal the thermo- and hydrodynamical conditions in M-type Mira atmospheres is to study the various emission lines which are emitted behind a shock front and can be observed over a substantial portion of the pulsation period. Analysing a time-resolved series of these emission lines offers the possibility to determine these conditions in different atmospheric layers influenced by the passing shock wave. In particular, the metal emission lines are a diagnostic tool to probe the hydrodynamical conditions of the outer, dust-forming layers of the atmosphere, because they appear late in the pulsation cycle when the shock wave has reached these layers.

We present quantitive data on radial velocities, shapes, widths and fluxes of metal emission lines obtained by spectral observations in the optical wavelength region for a sample of six M-type Miras (periods 281-389 days), namely R Aql, RR Sco, R Car, R Leo, S Scl and R Hya (cf. Richter & Wood 2001, A&A, 369, 1027-1047). Because of the multiple phase coverage of our observations, the data shows the history of the shock as it emerges through the deep photosphere and then moves out through the atmosphere. The observations are analysed and discussed with regard to the atmospheric conditions.

Keywords:

line: profiles -- shock waves -- stars: circumstellar matter -- stars: late-type -- stars: variables: general