Non-adiabatic theoretical observables in Delta Scuti stars

Abstract

Phase differences and amplitude ratios at different colour photometric bands are currently being used to discriminate pulsation modes in order to facilitate mode identification of kappa-driven non-radial pulsating stars. In addition to physical inputs (e.g., mass, T_eff, etc.), these quantities depend on the non-adiabatic treatment of the atmosphere. This paper presents theoretical results concerning Delta 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 phi^T, defined as the angle between effective temperature variations 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 alpha MLT parameter used to calculate the convection in the envelope. The dependence on alpha was analized 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 alpha introduces uncertainties in the theoretical predictions regarding phases and amplitudes of photometric variations in Delta Scuti pulsating stars.