Strahlungstransport und Hydrodynamik inhomogener Medien in Anwendung auf strahlungsbeschleunigte Stern- und Akkretionsscheibenwinde
Final Report Abstract
Conventional stellar atmosphere models approximate the wind inhomogeneities as structures of enhanced density but with sizes smaller than the photon mean free path. This "microclumping" approximation is not confirmed by modern observations, and seriously affects the empirical diagnostics of mass-loss rates, the latter being a chief parameter governing stellar evolution and feedback. Among the key achievements of this project is the development of a stochastic radiative transfer formalism that allows to overcome the microclumping approximation and to use a more realistic description of wind structures. The stellar wind spectral diagnostics developed in the framework of this project are applied to the X-ray, UV, and optical spectra of massive stars resulting in a concordance of the mass-loss estimates from analysis of multi-wavelength observations. Moreover, our new formalism allows to constrain the geometry and density of the wind structures from a comparison of the observed and model spectral line profiles. From the analysis of modern X-ray observations of hot stars we infer that the stellar wind "clumps" are compressed in radial direction. There is meanwhile broad agreement in the literature that "porosity" is a central physical property of hot-star winds. Little is known from hydrodynamic simulations about the shape and size of wind clumps, largely because the relative importance of the basic processes involved (Rayleigh-Taylor instability, wind turbulence, lateral line-drag effect) is unknown in the non-linear regime. We have written a new computer program for time-dependent radiation-hydrodynamic simulations, which calculates the radiative line force in two spatial dimensions at each hydrodynamic time step using the method of short characteristics. With this program it will be possible in the near future to perform first direct hydrodynamic simulations of clump formation due to the line-driven instability of hot-star winds. Often gasdynamic shocks and clumps in simulations of hot-star winds are accompanied by socalled kinks. We derive analytically that kinks are a new type of radiative shock wave, and propagate at super-critical speed upstream through the flow. From our 1-D hydrodynamic simulations it appears that in thin winds, metal ions and the bulk H/He plasma do not undergo a joint transition to a shallow wind solution, as was suggested by Krticka &; Kubat (2000), but decouple from each other and form a two-component flow. Our simulations also show that the strong equatorial density enhancement found in Be stars cannot be explained as a consequence of the transition from a radiation-driven to a centrifugally driven wind at a certain stellar rotation rate, as was suggested by Cure (2004).
Publications
- Barniske A., Oskinova L.. & Hamann W.-R. 2006, in: Stellar Evolution at Low Metalicity, ASP Conf. Series, 353, 241 Spitzer mid-IR spectroscopy of Wolf-Rayet stars
- Feldmeier A., Hamann W.-R., Rätzel D., &; Oskinova L, 2008, in: Clumping in hot star winds, eds.: Hamann W.-R., Feldmeier A., &: Oskinova L.. Univ. Verlag, Potsdam, p. 115 Hydrodynamic simulations of clumps
- Feldmeier A., Rätzel D-, & Owocki S.P. 2008, ApJ, 679, 704 The propagation of kinks in line-driven winds
- Hamann W.-R., Feldmeier A., & Oskinova L. (eds.) 2008, Univ. Verlag, Potsdam, Clumping in hot-star winds (Siehe online unter: http://nbn-resolving.de/urn:nbn.de)
- Hamann W.-R., Grafener G., Feldmeier A., Oskinova L., Barniske A., & Liermann A. 2008, in: Hydrogen-deficient stars, eds.: Werner K. & Rauch T., ASP, San Francisco Wolf-Rayet Analyses
- Hamann W.-R., Oskinova L., & Feldmeier A. 2008, in: Clumping in hot star winds, eds.: Hamann W.-R., Feldmeier A., & Oskinova L., Univ. Verlag, Potsdam, p. 75 Spectrum formation in clumpy stellar winds
- Ignace R., Oskinova L-, Waldron W., Hoffman J., & Hamann W.-R. 2008, AfeA, 477, L37 Phase-dependent X-ray observations of the ß Lyrae system
- Ignace R., Oskinova L., Waldron W., Hoffman J., & Hamann W.-R. 2006, AAS 20923005 An X-ray View of the Interacting Binary Beta Lyrae with Suzaku
- Madura T.I., Owocki S.P., & Feldmeier A. 2007, ApJ, 660, 687 A nozzle analysis of slow-acceleration solutions in one-dimensional models of rotating hotstar winds
- Oskinova L. 2005, in: Massive Stars and High-Energy Emission in OB Associations, JENAM 2005, p. 99 X-raying the super star clusters in the Galactic center
- Oskinova L. 2005, MNRAS 361, 679 Evolution of X-ray emission from star dusters
- Oskinova L. 2006, in: High Resolution X-ray Spectroscopy: towards XEUS and Con-X, p. E27 0 Star X-ray Line Profiles Explained by Radiation Transfer in Inhomogeneous Stellar Wind
- Oskinova L. 2007, ASPC, 367, 637 Evolution of X-ray Emission from Young, Massive Stellar Clusters
- Oskinova L., Feldmeier A., & Hamann W.-R. 2006, in: The X-ray Universe 2005, ed.: Wilson A., ESASP, 604, 57 0 star X-ray line profiles explained by radiation transfer in inhomogeneous stellar wind
- Oskinova L., Feldmeier A., & Hamann W.-R. 2006, MNRAS, 372, 313 High resolution X-ray spectroscopy of bright 0-type stars
- Oskinova L., Hamann W.-R., & Feldmeier A. 2007, A&A, 476, 1331 Neglecting the porosity of hot-star winds can lead to underestimating mass-loss rates
- Oskinova L., Hamann W.-R., &; Feldmeier A. 2008, in: Clumping in hot star winds, eds.: Hamann W.-R., Feldmeier A., & Oskinova L., Univ. Verlag, Potsdam, p. 203 X-raying clumped stellar winds
- Rauw G., Naze Y., & Oskinova L. 2008, AN, 329, 222 X-ray spectroscopy of early-type stars: The present and the future
- Votruba V., Feldmeier A., Kubat J., & Rätzel D. 2007, A&A, 474, 549 A hydrodynamic scheme for two-component winds from hot stars
- Waldron W.L., Cassinelli J., Oskinova L., & Lamers H. 2007, AAS 211, 8005 The B Supergiant Discontinuous Drop in X-ray Luminosity at Spectra Type Bl
