Mass loss from OB-stars
نویسندگان
چکیده
We review recent developments regarding radiation driven mass loss from OB-stars. We first summarize the fundamental theoretical predictions, and then compare these to observational results (including the VLT-FLAMES survey of massive stars). Especially we focus on the mass loss-metallicity dependence and on the so-called bi-stability jump. Subsequently we concentrate on two urgent problems, weak winds and wind clumping, that have been identified from various diagnostics and that challenge our present understanding of radiation driven winds. We discuss the problems of “measuring” mass-loss rates from weak winds and the potential of the NIR Br-alpha-line as a tool to enable a more precise quantification, and comment on physical explanations for mass-loss rates that are much lower than predicted by the standard model. Wind clumping, conventionally interpreted as the consequence of a strong instability inherent to radiative line-driving, has severe implications for the interpretation of observational diagnostics, since derived mass-loss rates are usually overestimated when clumping is present but ignored in the analyses. Simplified techniques to account for clumping indicate overestimates by factors of 2 to 10, or even more. If actually true, these results would have a dramatic impact on the evolution of, and the feedback from, massive stars. We discuss ongoing attempts (including our own work) to interprete the corresponding observations in terms of more sophisticated models. By allowing for porosity in density and velocity space, and for a non-void inter-clump medium, such models might require only moderate reductions of mass-loss rates.
منابع مشابه
Search for OB stars running away from young star clusters . I . NGC 6611
N-body simulations have shown that the dynamical decay of the young (∼ 1 Myr) Orion Nebula cluster could be responsible for the loss of at least half of its initial content of OB stars. This result suggests that other young stellar systems could also lose a significant fraction of their massive stars at the very beginning of their evolution. To confirm this expectation, we used the Mid-Infrared...
متن کاملFundamental parameters of Galactic luminous OB stars VI. Temperatures, masses and WLR of Cyg OB2 supergiants
We have analyzed six OB supergiants and one giant covering spectral types from O3 to B1 in the Galactic OB association Cyg OB2 by means of an updated version of FASTWIND (Santolaya–Rey et al., 1997) that includes an approximate treatment of metal line blocking and blanketing. This large coverage in spectral type allows us to derive a new temperature scale for Galactic O supergiants that is lowe...
متن کاملMass-loss rates for hot luminous stars: the influence of line branching
The effect of photon frequency redistribution by line branching on mass-loss rates for hot luminous stars is investigated. Monte Carlo simulations are carried out for a range of OB-star models which show that previous mass-loss calculations which neglect nonresonance line scattering overestimate mass-loss rates for luminous O stars by ∼ 20 per cent. For luminous B stars the effect is somewhat l...
متن کاملFundamental Parameters of Massive Stars
We discuss the determination of fundamental parameters of ‘normal’ hot, massive OB-type stars, namely temperatures, luminosities, masses, gravities and surface abundances. We also present methods used to derive properties of stellar winds – mass-loss rates and wind velocities from early-type stars.
متن کاملOn the metallicity dependence of Wolf-Rayet winds
We have performed a pilot study of mass loss predictions for late-type Wolf-Rayet (WR) stars as a function of metal abundance, over a range between 10−5 ≤ (Z/Z ) ≤ 10. We find that the winds of nitrogen-rich Wolf-Rayet stars are dominated by iron lines, with a dependence of mass loss on Z similar to that of massive OB stars. For more evolved, carbon-rich, WR stars the wind strength is also foun...
متن کامل