Hot Star Wind Astrophysics

UNDER CONSTRUCTION!

Who are we?

At the Bartol Research Institute, our group presently consists of:

• Dr. Stanley Owocki, Associate Professor
• Dr. Kenneth Gayley, Research Scientist
• Mr. Steven Cranmer, Graduate Fellow

Recent colleagues and collaborators include researchers from Universitäts Sternwarte München, University College London, the University of Wisconsin Astronomy Department, and the Université de Montréal, in addition to our neighbors here at Bartol and the University of Delaware Department of Physics and Astronomy.

Additional hot-star colleagues with interesting and informative WWW pages include: Mike Corcoran, Derck Massa, and the Landessternwarte in Heidelberg.

Who are you?

We will soon have a Guest book to sign. Email with questions to owocki@bartol.udel.edu.

Hopefully, this overview has been formatted to be accessible to both the specialist and the layman. Links to a set of notes on Introductory Stellar Astronomy will be provided throughout these pages, but they can be skipped without losing any of the details of our research program.

Overview: Hot Star Winds

Although few in number, hot massive stars are important constituents of the universe. Because of their extremely high luminosities (10,000 to a million times the sun's luminosity), they act as ideal ``standard candles'' which allow us to determine distances to other galaxies. Hot stars also have prodigious supersonic winds which inject large amounts of gas into the interstellar medium. Winds from O-type stars often have terminal outflow velocities of 1000 to 3000 km/sec (of the order of 1% of the speed of light) and mass loss rates of 10^-8 to 10^-5 solar masses per year. Because these stars only have main-sequence lifetimes of only several million years, they can lose a substantial fraction (typically about 50%) of their own mass over this time. This material contributes to the energy balance of the surrounding interstellar medium and can induce the formation of new stars, as well as have a strong impact on the star's own evolution.

The winds from hot stars are also important because they represent an ideal ``laboratory'' for the relatively unexplored field of radiation hydrodynamics. Often this term is used in a broad sense to refer to the common case where radiation plays an important role in the energy balance of a plasma; but here it applies in the stricter sense that the star's radiation imparts momentum (as well as energy) to the plasma, and so drives its supersonic outflow. In hot stars, both the continuum radiation and that due to spectral lines can transfer momentum to gas particles, via the absorption and scattering of photons. In fact, it is the opacity in the lines which dominates the momentum transfer, even though line transitions only occur in very narrow ranges of photon frequency. This efficiency comes from the presence of the rapidly accelerating wind, which Doppler shifts the line's opacity over a wider range of frequencies than it would have ``seen'' otherwise, thus providing a fresh supply of unattenuated flux from the star.

A few useful and comprehensive references are:

• Cassinelli, J. P. 1979, ``Stellar Winds,'' Ann. Rev. Astron. Astrophys., 17, 275-308.
• Mihalas, D. and Mihalas, B. W. 1984, Foundations of Radiation Hydrodynamics (Cambridge: Oxford University Press).
• Moffat, A. F. J., et al., ed. 1994, ``Instability and Variability of Hot-Star Winds,'' Proceedings of an International Workshop held at Isle-aux-Coudres, Quebec, August 23-27, 1993, reprinted in Astrophys. Space Sci., vol. 221.

Hot Star Wind Research Topics:

1. Fundamental physics of radiative driving
2. Small-scale line driven instabilities
3. Large-scale circumstellar structure
4. Wind collisions in binary systems
5. Observational diagnostics

Recent Publications:

First, check out our Preprints Page.

The following links to published papers go either to online e-prints (none yet!), or to the Astrophysical Data System (ADS) abstract archive.

• Owocki, S. P., Cranmer, S. R., and Fullerton, A. W. 1995, ``Periodic Variations in UV Spectral Lines of the B0.5 Ib Star HD 64760: Evidence for Corotating Wind Streams Rooted in Surface Variations,'' Ap. J. Letters, 453, L37.
• Gayley, K. G., Owocki, S. P., and Cranmer, S. R. 1995, ``Momentum Deposition in Wolf-Rayet Winds: Nonisotropic Diffusion with Effective Gray Opacity,'' Ap. J., 442, 296.
• Cranmer, S. R. and Owocki, S. P. 1995, ``The Effect of Oblateness and Gravity Darkening on the Radiation Driving in Winds from Rapidly Rotating B Stars,'' Ap. J., 440, 308.
• Gayley, K. G. and Owocki, S. P. 1994, ``Acceleration Efficiency in Line-driven Flows,'' Ap. J., 434, 684.
• Owocki, S. P., Cranmer, S. R., and Blondin, J. M. 1994, ``Two-dimensional Hydrodynamical Simulations of Wind-compressed Disks around Rapidly Rotating B Stars,'' Ap. J., 424, 887.
• Cooper, R. G. and Owocki, S. P. 1994, ``X-ray emission in wind instability simulations,'' Ap. Sp. Sci., 221, 427.
• Puls, J., Feldmeier, A., Springmann, U., Owocki, S. P., and Fullerton, A. W. 1994, ``Synthesis of line profiles from models of structured winds,'' Ap. Sp. Sci., 221, 409.
• Fullerton, A. W. 1994, ``Photospheric variability of O stars,'' Ap. Sp. Sci., 221, 105.
• Massa, D., Fullerton, A., and Prinja, R. 1994, ``Wind variability in intermediate luminosity B supergiants,'' Ap. Sp. Sci., 221, 77.
• Prinja, R. K. and Fullerton, A. W. 1994, ``Observations of structure in the stellar wind of HD 152408,'' Ap. Sp. Sci., 221, 67.
• Puls, J., Owocki, S. P., and Fullerton, A. W. 1993, ``On the synthesis of resonance lines in dynamical models of structured hot-star winds,'' Astron. Astrophys., 279, 457.
• Howarth, I. D., Bolton, C. T., Crowe, R. A., Ebbets, D. C., Fieldus, M. S., Fullerton, A. W., Gies, D. R., McDavid, D., Prinja, R. K., Reid, A. H. N., Shore, S. N., and Smith, K. C. 1993, ``Time-Series Observations of O Stars. III. IUE and HST Spectroscopy of zeta Ophiuchi and Implications for the `Photospheric Connection,' '' Ap. J., 417, 338.
• Reid, A. H. N., Bolton, C. T., Crowe, R. A., Fieldus, M. S., Fullerton, A. W., Gies, D. R., Howarth, I. D., McDavid, D., Prinja, R. K., and Smith, K. C. 1993, ``Time-Series Observations of O Stars. II. Optical Observations of zeta Ophiuchi,'' Ap. J., 417, 320.
• Fullerton, A. W., Gies, D. R., and Bolton, C. T. 1992, ``Propagating absorption enhancements in the wind of the extreme Of supergiant HD 151804,'' Ap. J., 390, 650.
• Prinja, R. K., Balona, L. A., Bolton, C. T., Crowe, R. A., Fieldus, M. S., Fullerton, A. W., Gies, D. R., Howarth, I. D., McDavid, D., and Reid, A. H. N. 1992, ``Time series observations of O stars. I - IUE observations of variability in the stellar wind of Zeta Puppis,'' Ap. J., 390, 266.
• Owocki, S. P. and Zank, G. P. 1991, ``The effect of viscosity on steady transonic flow with a nodal solution topology,'' Ap. J., 368, 491.
• Fullerton, A. W., Gies, D. R., and Bolton, C. T. 1991, ``Detection of small-amplitude pulsations in HD 34656 (O7 II),'' Ap. J. Letters, 368, L35.
• Poe, C. H., Owocki, S. P., and Castor, J. I. 1990, ``The steady state solutions of radiatively driven stellar winds for a non-Sobolev, pure absorption model,'' Ap. J., 358, 199.
• Rybicki, G. B., Owocki, S. P., and Castor, J. I. 1990, ``Instabilities in line-driven stellar winds. IV - Linear perturbations in three dimensions,'' Ap. J., 349, 274.
• Owocki, S. P., Castor, J. I., and Rybicki, G. B. 1988, ``Time-dependent models of radiatively driven stellar winds. I - Nonlinear evolution of instabilities for a pure absorption model,'' Ap. J., 335, 914.
• Owocki, S. P. and Rybicki, G. B. 1986, ``Instabilities in line-driven stellar winds. III - Wave propagation in the case of pure line absorption,'' Ap. J., 309, 127.
• Owocki, S. P. and Rybicki, G. B. 1985, ``Instabilities in line-driven stellar winds. II - Effect of scattering,'' Ap. J., 299, 265.
• Owocki, S. P. and Rybicki, G. B. 1984, ``Instabilities in line-driven stellar winds. I - Dependence on perturbation wavelength,'' Ap. J., 284, 337.

GO FORWARD to the Introductory Stellar Astronomy Tutorial.

For the curious, the image at the top of this page is indeed our own sun, but with its lovely G-type yellow color shifted to light blue - the color of O and B stars. (Aren't computers great?) Our apologies to solar physicists for appropriating their star, but it may be some time until we can get images as good as this of other stars!

Questions about this page? Send them to cranmer@bartol.udel.edu.