Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...240..308b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 240, no. 2, Dec. 1990, p. 308-316.
Astronomy and Astrophysics
Astrophysics
36
Stellar Oscillations, Variable Stars, Frequency Shift, Light Curve, Stellar Models, Stellar Spectrophotometry, Stars: Δ Scuti, Stars: Oscillations Of, Stars: Variables, Stars: Photometry, Stars: 4 Cvn
Scientific paper
The δ Scuti variable 4 CVn pulsates with seven frequencies with values of 8.59, 7.37, 6.98, 6.19, 5.85, 5.53, and 5.05 cycles per day. These seven frequencies are independently found and confirmed in different subsets of the 114 nights of photometric data covering the years 1966 to 1984. Five of these frequencies had already been detected during a multisite campaign of 1983 and 1984 and they should be free of possible 1 cycle d-1 aliasing problems. Previously unpublished photometric data obtained during 31 nights in 1976, 1977, and 1978 at McDonald Observatory can be fit by the multifrequency solution to ±0.003mag.
Even a cursory visual inspection of the light curves for different years reveals that the pulsation amplitude is variable. The numerical multifrequency solutions show that this amplitude variability can be traced to specific frequencies with long-term amplitude changes, although for neighboring years their amplitudes are usually very similar. If the frequencies are matched with specific nonradial p modes through the observed Q values, the observed amplitude variation can be described by a decrease of the amplitudes of the p1 modes after 1966, as well as a slow increase and subsequent decrease of the amplitude of the p3 mode with maximum amplitude reached during 1978.
Between 1966 and 1984 the two main periods are slowly decreasing their values at the rates of dP/dt = - 3.4 10-10 and -1.4 10-9 dd-1, respectively. The available data cannot unambiguously distinguish between interpretations of a constant period decrease or a small period shift around 1980.
The observed long-term variations show that the Blazhko Effect, known for other types of pulsating variables such as RR Lyrae stars, some short-period cepheids and β Cephei variables, also exists in δ Scuti stars.
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