Radial Pulsation Modes Research Articles

Radial pulsation modes as a possible cause for the heterogeneity of the Delta Scuti stars

On the basis of observational data (Breger, 1979), a radial pulsation mode of 83 Delta Scuti stars is estimated in two ways. These stars can pulsate in four lowest modes—F, 1H, 2H, 3H— and, perhaps, in 4H and 5H. Our earlier suggestion—that the apparent heterogeneity of these objects in both the period-luminosity plane and the period-frequency distribution may be explained by means of pulsations in various modes—is confirmed. Semi-empirical period-luminosity relations for the four lowest modes are derived and the semi-empirical period ratios are compared with the theoretical ones.

PERIOD DISTRIBUTIONS OF IRREGULARITY VARIABLE RR LYR STARS.

ABSTRACT The occurrence of irregularly variable RR Lyrae stars in four globular clusters and the Draco dwarf spheroidal galaxy are examined in order to determine their period distributions. Two of the clusters are of Oosterhoff type I, M3 and M5, and two are of Oosterhoff type II, M15 and omega-Cen. Draco does not fit into either Oosterhoff group, having a medium ab-type period of 0.611 days, but few C-type variables. Irregular variability is more frequent among the shorter period ab-type RR Lyraes (P less than 0.65 days) and, at least in M15 and omega-Cen, among the longer period c-type variables. These period distributions are consistent with some mode-mixing explanations for irregular variability. It is suggested that the Blazhko effect in ab-type RR Lyraes is a nonlinear mixture of the fundamental and third overtone radial pulsation modes (Borkowski, 1980). This accounts for the occurrence of irregular ab-variables only at shorter periods, but yields RR Lyrae star masses larger than those predicted by stellar evolution theory.

Pulsational mode-typing in line profile variables. I - Four Beta Cephei stars

The detailed variations of line profiles in the Beta Cephei-type variable stars Gamma Pegasi, Beta Cephei, Delta Ceti and Sigma Scorpii are modeled throughout their pulsation cycles in order to classify the dominant pulsation mode as radial or nonradial. High-dispersion Reticon observations of the variables were obtained for the Si III line at 4567 A, and line profiles broadened by radial or nonradial pulsations, rotation and radial-tangential macroturbulence were calculated based on a model atmosphere. It is found that only a radial pulsation mode can reproduce the radial velocity amplitude, changes in line asymmetry and uniform line width observed in all four stars. Results are in agreement with the color-to-light arguments of Stamford and Watson (1978), and suggest that radial pulsation plays the dominant role in the observed variations in most Beta Cephei stars. Evidence for shocks or moving shells is also found in visual line data for Sigma Scorpii and an ultraviolet line of Beta Cephei, together with evidence of smooth, secular period changes in Beta Cephei and Delta Ceti.