Non-adiabatic theoretical observables in δ Scuti stars

Abstract

Phase differences and amplitude ratios at different colour photometric bands are currently being used to discriminate pulsation modes to facilitate mode identification of κ-driven non-radial pulsating stars. In addition to physical inputs (e.g., mass, Teff, etc.), these quantities depend on the non-adiabatic treatment of the atmosphere. This paper presents theoretical results concerning δ Scuti pulsating stars. The envelope of each of these stellar structures possesses a convection zone whose development is determined by various factors. An interacting pulsation-atmosphere physical treatment is introduced which supplies two basic non-adiabatic physical quantities: the relative effective temperature variation and the phase lag φT, defined as the angle between effective temperature variation and radial displacement. These quantities can be used to derive the phase differences and amplitude ratios. Numerical values for these quantities depend critically on the α MLT parameter used to calculate the convection in the envelope. The dependence on α was analyzed and it was found that the use of colour observations may be of considerable importance in testing the MLT. Finally, examples are given of how α introduces uncertainties in the theoretical predictions regarding phases and amplitudes of photometric variations in δ Scuti pulsating stars.