Delta Scuti Star Newsletter

Issue 1, October 1989


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Nonradial pulsation of the Delta Scuti variable 4 CVn

by: Michel Breger, M.Breger, B.J.McNamara, F.Kerschbaum, H.Lin, J.Shi-yang, E.Poretti.

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A comparison with published and unpublished data for earlier years shows that over 18 years the amplitudes of pulsation are slowly variable on a time scale of years.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