Asteroseismology of Delta Scuti stars

Abstract

This paper presents recent results for δ Scuti stars based on measurements obtained by WET/Delta Scuti Network as well as theoretical modeling of the pulsation modes. In particular, the two stars in different stages of evolution, FG Vir and 4 CVn, are discussed. For 4 CVn, the XCOV13 campaign has revealed 34 frequencies, which sets a new record for δ Scuti stars. Preliminary mode identifications are presented, indicating pulsation in low radial order and low degree (ℓ = 0 to 2). The star shows strong amplitude variability with timescales of ten years or longer, although for neighbouring years the amplitudes usually are similar. The cyclic behavior of the amplitude variations excludes an evolutionary origin. The pulsation mode at 7.375 c/d exhibits the most rapid decrease found so far: the V amplitude dropped from the highest known value of 15 mmag in 1974 to 4 mmag in 1976 and 1 mmag in 1977. After that the mode has been increasing in amplitude. There exists a phase jump between 1976 and 1977, suggesting the growth of a new mode.