TY - CHAP A1 - Davies, B. A1 - Vink, J. S. A1 - Oudmaijer, R. D. T1 - Modelling the polarimetric variability of hot stars N2 - Many hot stars exhibit stochastic polarimetric variability, thought to arise from clumping low in the wind. Here we investigate the wind properties required to reproduce this variability using analytic models, with particular emphasis on Luminous Blue Variables. We find that the winds must be highly structured, consisting of a large number of optically-thin clumps; while we find that the overall level of polarization should scale with mass-loss rate – consistent with observations of LBVs. The models also predict variability on very short timescales, which is supported by the results of a recent polarimetric monitoring campaign. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17939 ER - TY - CHAP A1 - Kubát, Jiří A1 - Saad, S. M. T1 - Moving absorption bumps in the spectra of Be stars N2 - Several Be binaries exhibit an absorption bump moving across the blue wing of hydrogen emission lines towards the line center. This bump is demonstrated for the case of two bright Be stars, κ Dra and 4 Her. It is not clear what is the reason for this travelling bump. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17879 ER - TY - CHAP A1 - Nielsen, K. E. T1 - On irregular line profiles in the optical spectrum of Eta Carinae N2 - The optical spectrum of Eta Carinae (η Car) is prominent in H I, He i and Fe ii wind lines, all of which vary both in absorption and emission with phase. The phase dependance is a consequence of the interaction between the two objects in the η Car binary (η Car A & B). The binary system is enshrouded by ejecta from previous mass ejection events and consequently, η Car B is not directly observable. We have traced the He i lines over η Car’s spectroscopic period, using HST/STIS data obtained with medium spectral, but high angular, resolving power, and created a radial velocity curve for the system. The He I lines are formed in the core of the system, and appear to be a composite of multiple features formed in spatially separated regions. The sources of their irregular line profiles are still not fully understood, but can be attributed to emission/absorption near the wind-wind interface and/or a direct consequence of the η Car A’s, massive, clumpy wind. This paper will discuss the spectral variability, the narrow emission structure of the He i lines and how clumpiness of the winds may impede the construction of the reliable radial velocity curve, necessary for characterizations of especially η Car B. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18227 ER - TY - CHAP A1 - Cohen, David H. A1 - Leutenegger, M. A. A1 - Townsend, R. H. D. T1 - Quantitative analysis of resolved X-ray emission line profiles of O stars N2 - By quantitatively fitting simple emission line profile models that include both atomic opacity and porosity to the Chandra X-ray spectrum of ζ Pup, we are able to explore the trade-offs between reduced mass-loss rates and wind porosity. We find that reducing the mass-loss rate of ζ Pup by roughly a factor of four, to 1.5 × 10−6 M⊙ yr−1, enables simple non-porous wind models to provide good fits to the data. If, on the other hand, we take the literature mass-loss rate of 6×10−6 M⊙ yr−1, then to produce X-ray line profiles that fit the data, extreme porosity lengths – of h∞ ≈ 3 R∗ – are required. Moreover, these porous models do not provide better fits to the data than the non-porous, low optical depth models. Additionally, such huge porosity lengths do not seem realistic in light of 2-D numerical simulations of the wind instability. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18115 ER - TY - CHAP A1 - Morrison, N. D. A1 - Rother, R. A1 - Kurschat, N. T1 - Hα line profile variability in the B8Ia-type supergiant Rigel (β Ori) N2 - Hα observations of Rigel obtained on 184 nights during the past ten years with the 1-m telescope and ´echelle spectrograph of Ritter Observatory are surveyed. The line profiles were classified in terms of morphology. About 1/4 of them are of P Cygni type, about 15% inverse P Cygni, about 25% double-peaked, about 1/3 pure absorption, and a few are single emission lines. Transformation of the profile from one type to another typically takes a few days. Although the line stays in absorption for extended intervals, only one high-velocity absorption event of the intensity reported by Kaufer et al. (1996a) was observed, in late 2006. Late in this event, Hα absorption occurred farther to the red than the red wing of a plausible photospheric absorption component, an indication of infalling material. In general, as the absorption events come to an end, the emission typically returns with an inverse P Cygni profile. The Hα profile class shows no obvious correlation with the radial velocity of C II λ6578, a photospheric absorption line. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18120 ER - TY - CHAP A1 - Chené, A.-N. A1 - Moffat, Anthony F. J. A1 - Crowther, P. A. T1 - Rapidly accelerating clumps in the winds of the very hot WNE Stars N2 - We study the time variability of emission lines in three WNE stars : WR 2 (WN2), WR 3 (WN3ha) and WR152 (WN3). While WR 2 shows no variability above the noise level, the other stars do show variation, which are like other WR stars in WR 152 but very fast in WR 3. From these motions, we deduce a value of β ∼1 for WR 3 that is like that seen in O stars and β ∼2–3 for WR 152, that is intermediate between other WR stars and WR 3. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18163 ER - TY - CHAP A1 - Kholtygin, A. F. T1 - Modelling the induced clumping stochastic line profile variability N2 - We model the line profile variability (lpv) in spectra of clumped stellar atmospheres using the Stochastic Clump Model (SCM) of the winds of early-type stars. In this model the formation of dense inhomogeneities (clumps) in the line driven winds is considered as being a stochastic process. It is supposed that the emission due to clumps mainly contributes to the intensities of emission lines in the stellar spectra. It is shown that in the framework of the SCM it is possible to reproduce both the mean line profiles and a common pattern of the lpv. Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18180 ER - TY - CHAP A1 - Cassinelli, Joseph P. T1 - Discussion: Magnetic fields, variability Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18195 ER - TY - CHAP A1 - St-Louis, N. T1 - Discussion: Binaries, colliding winds, LBVs and high energy radiation N2 - Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007 Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18155 ER - TY - GEN A1 - Frese, Michael A1 - Garst, Harry A1 - Fay, Doris T1 - Making things happen : reciprocal relationships between work characteristics and personal initiative in a four-wave longitudinal structural equation model N2 - The authors used the frameworks of reciprocal determinism and occupational socialization to study the effects of work characteristics (consisting of control and complexity of work) on personal initiative (PI)--mediated by control orientation (a 2nd-order factor consisting of control aspiration, perceived opportunity for control, and self-efficacy) and the reciprocal effects of PI on changes in work characteristics. They applied structural equation modeling to a longitudinal study with 4 measurement waves (N = 268) in a transitional economy: East Germany. Results confirm the model plus 1 additional, nonhypothesized effect. Work characteristics had a synchronous effect on PI via control orientation (full mediation). There were also effects of control orientation and of PI on later changes in work characteristics: As predicted, PI functioned as partial mediator, changing work characteristics in the long term (reciprocal effect); unexpectedly, there was a 2nd reciprocal effect of an additional lagged partial mediation of control orientation on later work characteristics. T3 - Zweitveröffentlichungen der Universität Potsdam : Humanwissenschaftliche Reihe - paper 028 KW - personal initiative KW - job characteristics KW - reciprocal relationship KW - transition economy KW - selfefficacy Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18278 ER -