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
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.,
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
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.
- 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
- 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
Publications based on AFOE observations are available as compress
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
- 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.
For more information on Delta Scuti stars, check out the following pages.
Edward J. Kennelly (firstname.lastname@example.org)
Sylvain G. Korzennik (email@example.com)
Last modified: Tue Aug 24 16:20:51 1999