Asteroseismology with the WIRE satellite

I give a summary of results from the WIRE satellite, which has been used to observe bright stars from 1999-2000 and 2003-2006. The WIRE targets are monitored for up to five weeks with a duty cycle of 30-40%. The aim has been to characterize the flux variation of stars across the Hertzsprung-Russell diagram. I present an overview of the results for solar-like stars, delta Scuti stars, giant stars, and eclipsing binaries.Comment: Accepted for publication in CoAst. Proceedings of the Vienna Workshop on the Future of Asteroseismology (September 2006). 8 pages, 2 figure

Infrared Polarimetry Of Very Young Objects Including Becklin-Neugebauer Source

NSFAstronom

Evidence of resonant mode coupling and the relationship between low and high frequencies in a rapidly rotating A star

In the theory of resonant mode coupling, the parent and child modes are directly related in frequency and phase. The oscillations present in the fast rotating Delta Scuti star KIC 8054146 allow us to test the most general and generic aspects of such a theory. The only direct way to separate the parent and coupled (child) modes is to examine the correlations in amplitude variability between the different frequencies. For the dominant family of related frequencies, only a single mode and a triplet are the origins of nine dominant frequency peaks ranging from 2.93 to 66.30 cycles per day (as well as dozens of small-amplitude combination modes and a predicted and detected third high-frequency triplet). The mode-coupling model correctly predicts the large amplitude variations of the coupled modes as a product of the amplitudes of the parent modes, while the phase changes are also correctly modeled. This differs from the behavior of 'normal' combination frequencies in that the amplitudes are three orders of magnitude larger and may exceed even the amplitudes of the parent modes. We show that two dominant low frequencies at 5.86 and 2.93 cycles per day in the gravity-mode region are not harmonics of each other, and their properties follow those of the almost equidistant high-frequency triplet. We note that the previously puzzling situation of finding two strong peaks in the low-frequency region related by nearly a factor of two in frequency has been seen in other Delta Scuti stars as well.Comment: To be published in the Astrophysical Journa

Observations of pulsations in roAp stars

I review recent results of the observations of magnetoacoustic p-mode oscillations in roAp stars with the focus on time-resolved spectroscopic studies. Time-series spectroscopy of roAp stars reveals unexpected and diverse pulsational behaviour in the spectral lines of different chemical elements. These unique pulsational characteristics arise from an interplay between short vertical length of pulsation waves and extreme chemical stratification in the atmospheres of peculiar stars. This enables a tomographic reconstruction of the depth-dependence of chemical composition and pulsation wave properties. Combination of magnetoacoustic tomography with the Doppler imaging of the horizontal non-radial pulsation pattern opens possibility for an unprecedented three-dimensional mapping of roAp atmospheres.Comment: To appear in the proceedings of Vienna Workshop on the Future of Asteroseismology, eds. G. Handler and G. Houdek, Comm. in Asteroseismolog

Theory of rapidly oscillating Ap stars

I review recent theoretical work on rapidly oscillating Ap stars and discuss key aspects of the physics of the oscillations observed in this class of pulsators.Comment: 8 pages, 2 figures, accepted for publication in CoAs

The Future of Computational Asteroseismology

The history of stellar seismology suggests that observation and theory often take turns advancing our understanding. The recent tripling of the sample of pulsating white dwarfs generated by the Sloan Digital Sky Survey represents a giant leap on the observational side. The time is ripe for a comparable advance on the theoretical side. There are basically two ways we can improve our theoretical understanding of pulsating stars: we can improve the fundamental ingredients of the models, or we can explore the existing models in greater computational detail. For pulsating white dwarfs, much progress has recently been made on both fronts: models now exist that connect the interior structure to its complete evolutionary history, while a method of using parallel computers for global exploration of relatively simple models has also been developed. Future advances in theoretical white dwarf asteroseismology will emerge by combining these two approaches, yielding unprecedented insight into the physics of diffusion, nuclear burning, and mixing.Comment: 8 pages, 1 fig, Communications in Asteroseismology (invited review