Envelope tomography of long-period pulsating stars

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Project objective

Research objcctives and content The optical spectra of pulsating stars of the Mira kind are dominated bv atomic lines. whose shapes are changing along the . pulsation cycle. These comple.Y profiles reflect the velocity stratification of the atmosphere in the line-forming region. caused by the shock wave associated uith the pulsation and propagating through the atmosphere. The aim of the present proJect is to make full use of the powerful technique of cross-correlating the stellar spectrum with carefullv designed numerical masks to extract the phase variations of specific sets of spectral lines forming at different depths in the pulsating atmosphere. It allou s to perform a tomography of the envelope. Slate-of-the-art stellar-atmosphere models uill be used to design these numencal masks. These models y ill allo- us to define sets of lines forming at a given depth in the atmosphere. The spectra of a dozen MiM stars at different phases in the pulsation cycle ( I y) will be acquired on'the CORALIE (installed on the Geneva 1.2-m telescope at the European Southern Obsenator ) and ELODIE (installed on the 1.93-m telescope at the the Haute-Provence Obsenaton) spectrographs. These high-resolution spectrographs (R = l00()()) have been specially designed to perform high-accuracy on-line radial-velocity measurements through numerical correlation. Previous test studies on the Mira star RZ Peg have demonstrated the feasibility of the mcthod. From the comparison bet- een lhe observed depth- and time-variations of the line profiles with dynamical modcls of the pulsating atmospllere. a better understanding of thc formation and propagation of the shock uavc through the envelope should be gained. along uith insights into the relationship between the shock-uave properties and thc stellar surface propertics. Training content (objective, benefit and expected impact) The training aspect of this project residcs in its large obser-ational content. after a Ph.D. thesis of a purely theoretical naturc. Links with industy / industrial relevance (22)

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Participants

• UNIVERSITE LIBRE DE BRUXELLES · BRUXELLESCoordinatorBelgium

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