Delta-Scuti Seismology with the AFOE


The Delta Scuti stars are a class of young variables, somewhat hotter and more massive than the Sun, which lie in an extension of the Cepheid instability strip at the main sequence. The periods of these objects range from half an hour to several hours. Variations in brightness are typically on the order of 0.01 magnitudes or less while the corresponding mass motions at the surface of these stars are characterized by velocity amplitudes of a few km/s or less. With careful observations, such variations can be easily detected and studied using modern methods. To date, there are more than 250 known Delta Scuti stars.

Many Delta Scuti stars are multi-periodic and for this reason, the stars have been studied with increased interest in recent years. In the same way that the sound made by a bell depends on the bell's size and density, the frequencies of a Delta Scuti star carry information about its structure. In general, the variations of these stars are described by nonradial oscillations which may be expressed in terms of spherical harmonics. Because the detail to which stellar structure can be studied depends on the number and properties of the observed modes, multi-periodic Delta Scuti stars are attractive candidates for study. The investigation of stellar structure based on information provided by a star's natural oscillations is called asteroseismology.

Until now, efforts in Delta Scuti seismology have been concerned with the difficult task of mode and frequency identification. To this end, photometric observations have been organized as extensive multi-site campaigns (e.g., DSN and STEPHI) in order to provide the precise frequency determinations necessary for mode identification. On the other hand, spectroscopic observations can provide an alternative picture of the oscillations. Because the stars are rotating, velocity variations resulting from oscillations at the stellar surface introduce distortions in the Doppler-broadened absorption profiles providing a 'Doppler Image' of the star's oscillations in each profile. By analyzing a time series of stellar line-profile variations, information about the oscillation modes can be uncovered. To obtain continuous coverage of these variations, Delta Scuti stars have been included as targets for MUSICOS.

The AFOE (Advanced Fiber Optic Echelle) spectrograph is well suited for the study of delta Scuti line-profile variations as it satifies the necessary requirements of high spectral resolution, good wavelength coverage, and good temporal stability.


The AFOE has been used to study the oscillations of several rotating Delta Scuti stars. Work on some of these projects is still in progress.


Publications based on AFOE observations are available as compress postscript file.
  1. Nightly variations of nonradial oscillations in the Delta Scuti star upsilon Ursae Majoris, Korzennik, S.G., Noyes, R.W., Brown, T., Nisenson, P., and Horner, S., 1995, Ap.J.L., 443, 25
  2. The Oscillations of tau Pegasi, E.J. Kennelly, T.M. Brown, T.A.A. Sigut, R.W. Noyes, S.G. Korzennik, P. Nisenson, S.D. Horner, S. Yang, and A. Walker, in preparation.

More Information

For more information on Delta Scuti stars, check out the following pages. ____________________________________________
Edward J. Kennelly (
Sylvain G. Korzennik (
Last modified: Tue Aug 24 16:20:51 1999