My general research interests are in astrophysical fluid dynamics and magnetohydrodynamics of the Sun and other stars. While most of my research is theoretical in nature, I also carry out telescopic observations of dynamical phenomena in the solar atmosphere. Some of my research is done in collaboration with colleagues in the Department of Physics and Astronomy, at the University of Cambridge in England, LAEFF in Madrid, and elsewhere. Specific topics of current research interest include:
Sunspot Structure and Dynamics
Theoretical models of intense magnetic flux tubes on the Sun. Calculations of siphon flows along magnetic flux tubes, including the effects of radiative transfer and variable ionization and the behavior of shock waves in supercritical flows. Theory and observation of the structure and dynamics of sunspots, especially the filamentary structure and Evershed flow in the penumbra. Numerical simulations of magnetic flux pumping in the photosphere around a sunspot.
Theory and observations of the interaction of a sunspot with the resonant acoustic modes of the Sun, as a means of probing the subsurface structure of a sunspot. The theoretical work involves the study of waves in a stratified, compressible, magnetized atmosphere.
Solar and Stellar Dynamos
Dynamo generation of magnetic fields in the Sun and other stars. Nonlinear and chaotic stellar dynamos.
- Sunspots: Theory and Observations, ed. J. H. Thomas & N. O. Weiss (Dordrecht: Kluwer), 428 pp., 1992.
- Localized Sources of Propagating Acoustic Waves in the Solar Photosphere (with T. M. Brown, T. J. Bogdan, and B.W. Lites), Astrophys. J. (Letters), Vol. 394, p. L65, 1992.
- The Absorption of p-Modes by Sunspots: Variations with Degree and Order (with T. J. Bogdan, T. M. Brown, and B. W. Lites), Astrophys. J., Vol. 406, p. 723, 1993.
- A Siphon-Flow Model of the Photospheric Evershed Flow in a Sunspot (with B. Montesinos), Astrophys. J., Vol. 407, p. 398, 1993.
- Dynamo Generation of Magnetic Fields in White Dwarfs (with J. A. Markiel and H. M Van Horn), Astrophys. J., Vol. 453, p. 403, 1995.
- The Vector Magnetic Field, Evershed Flow, and Intensity in a Sunspot (with D. C. H. Stanchfield and B. W. Lites), Astrophys. J., Vol. 477, p. 485, 1997.
- Simple Solar Dynamo Models with Variable Alpha and Omega Effects (with C. B. Roald), Mon. Not. Roy. Astron. Soc., Vol. 288, p. 551, 1997.
- The Evershed Effect in Sunspots as a Siphon Flow Along a Magnetic Flux Tube (with B. Montesinos), Nature, Vol. 390, p. 485, 1997.
- Velocity and Magnetic Field Fluctuations in the Photosphere of a Sunspot (with B. W. Lites, T. J. Bogdan, and P. Cally), Astrophys. J., Vol. 497, p. 464, 1998.
- Solar Interface Dynamo Models With a Realistic Rotation Profile (with J. A. Markiel), Astrophys. J., Vol. 523, p. 827, 1999.
- Fine-Scale Magnetic Effects on p-modes and Higher Frequency Acoustic Waves in a Solar Active Region (with D. C. H. Stanchfield, II), Astrophys. J., Vol. 537, p. 1086, 2000.
- Dynamos in Asymptotic-Giant-Branch Stars as the Origin of Magnetic Fields Shaping Planetary Nebulae (with E. G. Blackman, A. Frank, J. A. Markiel, and H. M. Van Horn), Nature, Vol. 409, p. 485, 2001.
- A New Look at the Relationship Among Activity, Dynamo Number, and Rossby Number in Late-Type Stars (with B. Montesinos, P. Ventura, and I. Mazzitelli), Mon. Not. Roy. Astron. Soc., Vol. 326, p. 877, 2001.
- [PDF] Downward Pumping of Magnetic Flux as the Cause of Filamentary Structures in Sunspot Penumbrae (with N. O. Weiss, S. M. Tobias, and N. H. Brummell) Nature, Vol. 420, p. 390, 2002.
- Fuel-Supply-Limited Stellar Relaxation Oscillations: Application to Multiple Rings Around Asymptotic Giant Branch Stars and Planetary Nebulae (with H. M. Van Horn, A. Frank, and E. G. Blackman), Astophys. J., Vol. 585, p. 983, 2003.
- [PDF] The Origin of Penumbral Structure in Sunspots: Downward Pumping of Magnetic Flux (with N. O. Weiss, N. H. Brummell, and S. M. Tobias), Astrophys. J., Vol. 600, p. 1073, 2004.
- [PDF] Fine Structure in Sunspots (with N. O. Weiss), Ann. Rev. Aston. Astrophys., Vol. 42, p. 517, 2004.
- [PDF] Flux Pumping and Magnetic Fields in the Outer Penumbra of a Sunspot. (with N.H. Brummell, S.M. Todias, and N.O. Weiss), Astrophys. J., Vol. 686, p. 1454, 2008.
- Sunspots and Starspots (with N.O. Weiss), Cambridge University Press (Cambridge Astrophysics Series), 275 pp., 2008.
- [PDF] Theoretical Models of Sunspot Structure and Dynamics, in Magnetic Coupling Between the Interior and the Atmosphere of the Sun. ed. S.S. Hasan and R.J. Rutten, Springer-Verlag, p. 239, 2010.