# Delta Scuti Star Newsletter

## Issue 1, October 1989

#
Nonradial pulsation of the Delta Scuti variable 4 CVn

The results of a multisite campaign undertaken during the
years 1983 and 1984 have resulted in a solution for the complex
variable 4 CVn = Al Cvn = HR4715. M Breger, B. J. McNamara,
F.Kerschbaum, Huang Lin, Jiang Shi-yang, Guo Zi-he, and E. Poretti
have made multisite observations at four observatories on three
continents McDonald and Tortugas (USA), Xing-Long (China), and
Merate (Italy). These two campaigns cover 136 hours and avoid the
serious one-cycle per day aliasing present in single-observatory data.

Multiple-frequency least-squares and single-frequency Fourier
techniques reveal five frequencies with constant amplitudes for
the two years. A sixth frequency near 5.5 c/d (actually predicted
by the nonradial pattern found below) is also present, but was not
included into the solution because its exact value was ambiguous.

A clue to the pulsation of 4 CVn is given by the observed
frequency differences of 0.40 and 0.80 cycles per day, respectively.
The factor of two suggests that we are dealing with rotational
splitting and modes with different m values. Consideration of first
and second-order rotational splitting as well as the theoretical
values and ratios of the pulsation constants, Q, given by Fitch,
allows an identification of the modes. All the frequencies are
matched well with the same l value of 2 or 3. The identification
given below may not be unique (within the observational
uncertainties of determining the radius and Q values), but
gives the best fit among the different combinations modelled.

Pulsation frequencies and p modes for l= 2

`Frequency Q value Amklitude k m`

(c/d) (dqys) (mag)

8.5950 0.016 0.013 3 0

6.9763 0.020 0.006 2 0

7.3778 0.019 0.005 2 -1

5.0475 0.028 0.028 1 1

5.8508 0.024 0.008 1 -1

The mode identification is consistent with the observed
rotational frequency of 20.31 revs/d and predicts an inclination, i,
of the rotational axis to the line of sight of 42 degrees.
A comparison with published and unpublished data for earlier
years shows that over 18 years the amplitudes of pulsation are
slowly variable on a time scale of years.

sperl@astro.ast.univie.ac.at