Nonradial and radial period changes in the Delta Scuti star 4 CVn I. 700+ nights of photometry

TL;DR

This study presents extensive high-precision photometry of the Delta Scuti star 4 CVn over eight years, revealing detailed period and amplitude changes in multiple pulsation modes, with implications for stellar rotation and mode interactions.

Contribution

It provides the first long-term, high-precision photometric analysis of 4 CVn, identifying 64 pulsation frequencies and analyzing their period and amplitude variations over eight years.

Findings

Significant period and amplitude changes detected in dominant modes.

Prograde and retrograde modes show opposite signs of period change.

Radial mode exhibits small, cyclical period changes.

Abstract

The nature of period and amplitude changes in nonradial pulsators is presently unknown. It is therefore important to examine the correlations between these changes in stars with a large number of simultaneously excited pulsation modes. However, the small amplitudes require extensive high-precision photometry covering many years. We present 702 nights of high-precision photometry of the evolved Delta Scuti variable 4 CVn obtained from 2005 - 2012 with a dedicated telescope. We detected 64 frequencies, of which 38 can be identified as combinations and harmonics. The relative amplitudes of the combination frequencies are similar to those found in 44 Tau and show no evidence for resonant mode coupling. Significant period and amplitude changes are detected for the dominant modes. The known prograde and retrograde modes show period changes with opposite signs, while the radial mode exhibits only small, cyclical period changes. For each mode, the period changes are constant over the eight years and range from (1/P)dP/dt = -16 to +13 parts per million. On the other hand, the amplitude variations show no systematic behavior between different pulsation modes. The behavior of the prograde, axisymmetric, and retrograde modes indicates a constant decrease in the rotational splitting over the eight years.