Nonradial and radial period changes of theδScuti star 4 CVn

Abstract

Aims. Radial and nonradial pulsators on and near the main sequence show period and amplitude changes that are too large to be the product of stellar evolution. The multiperiodic Delta Sct stars are well suited to study this, as the period changes of different modes excited in the same star can be compared. This requires a very large amount of photometric data covering years and decades as well as mode identifications. Methods. We have examined over 800 nights of high-precision photometry of the multiperiodic pulsator 4 CVn obtained from 1966 through 2012. Because most of the data were obtained in adjacent observing seasons, it is possible to derive very accurate period values for a number of the excited pulsation modes and to study their systematic changes from 1974 to 2012. Results. Most pulsation modes show systematic significant period and amplitude changes on a timescale of decades. For the well-studied modes, around 1986 a general reversal of the directions of both the positive and negative period changes occurred. Furthermore, the period changes between the different modes are strongly correlated, although they differ in size and sign. For the modes with known values of the spherical degree and azimuthal order, we find a correlation between the direction of the period changes and the identified azimuthal order, m. The associated amplitude changes generally have similar timescales of years or decades, but show little systematic or correlated behavior from mode to mode. Conclusions. A natural explanation for the opposite behavior of the prograde and retrograde modes is that their period changes are driven by a changing rotation profile. The changes in the rotation profile could in turn be driven by processes, perhaps the pulsations themselves, that redistribute angular momentum within the star. In general, different modes have different rotation kernels, so this will produce period shifts of varying magnitude for different modes.

The Delta Scuti star 38 Eri from the ground and from space

“…The method avoids the use of numerous two-colour diagrams. In one of the latest example (Breger et al 2017), instead of the color index value (φv−y − φy) the colour phase differences (Av/Ay versus φv − φy) were used for mode identification. The amplitudes and phases are more precisely determined from the colour light curves of highest amplitudes than from the colour index curves.…”

“…We followed Breger et al (2017) in using the colour values instead of the color index values. Unfortunately, we do not have such a previleged situation as Breger et al (2017) had for 4 CVn. They calculated the amplitude and phase values from season to season and presented the scatter as an error.…”

An Observer's View on the Future of Asteroseismology

“…In more general, amplitude and/or frequency variations had been found among nearly all types of non-stochastically excited pulsators (Guzik et al, 2015). The long-term follow-up of the famous δ Scuti star, 4 CVn, showed that most pulsation modes exhibited a systematic significant period and amplitude changes on a timescale of decades (Breger et al, 2017). The reasons of the period and amplitude variability will definitely be investigated as space data on a longer and longer time base will be available in the future.…”

Modelling stochastic signatures in classical pulsators

“…Kilkenny 2010;Zong et al 2018), as well as in a diverse range of main-sequence pulsators, including β Cepheid (Pigulski & Pojmański 2008;Degroote et al 2010), δ-Scuti (e.g. Breger & Pamyatnykh 1998;Bowman et al 2016;Breger et al 2017), and rapidly oscillating Ap stars (e.g. Kurtz et al 1997;Holdsworth et al 2014;Balona et al 2019).…”