Delta-Scuti Seismology with the AFOE

Introduction

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.

Results

• Nightly Variations of upsilon UMa.
  Observations of upsilon UMa taken during 5 successive nights.
• Observations of epsilon Cep from Two Sites.
  Successive observations collected at the Whipple Observatory and Dominion Astrophysical Observatory.
• Observations of the MUSICOS '94 target theta^2 Tau.
  Spectroscopic observations taken in support of the 1994 MUSICOS multi-site campaign.
• Observations of the DSN '95 target FG Vir.
  Short time series observations taken over a few nights in support of the DSN multi-site photometric campaign.
• The Oscillations of tau Peg.
  Time series observations taken during six consecutive nights with the AFOE. The new technique of Doppler Deconvolution is introduced to analyze the observations.
• Observations of the MUSICOS '96 target V480 Tau.
  Spectroscopic observations taken in support of the 1996 MUSICOS multi-site campaign.

Publications

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

• The Delta Scuti Network (DSN).
  Results from multi-site photometric observations (University of Vienna).
• The Delta Scuti Star Newsletter.
  An electronic publication devoted to new results in Delta Scuti research (University of Vienna).