Aperiodic Ordered Sequences and Multiperiodicity in Semiregular Variable Stars

The use of aperiodic ordered sequences described by Lindenmayer systems in the study of the strings of periods for multiperiodic semiregular variables is proposed. Fibonacci sequences play a central role in the light curve analysis of UW Herculis.

Period-Gravity Relation for Semiregular Variable Stars

Red giant stars located on the AGB are intrinsically variable, which is usually associated with stellar pulsation. The complex light variation of semiregular variables (SRVs) has many alternative explanations. Besides the pulsation, other contributors to variability cannot be solidly excluded, such as time-dependent surface inhomogeneities, ellipsoidal deformation due to the presence of a close companion, or spots on a rotating star. The identification of ultra-short period M-giants with periods of a few days raised the possibility of very high-order overtone pulsation of these stars. Thus, it is very important to draw various constraints on the stellar pulsation in semiregular variables and to separate other physical causes. Here we present new empirical evidence for radial pulsation in SRVs through studying their period-gravity relation, following the ideas outlined by Fernie (1995, F95). F95 studied a log P versus log g relation for various types of radially pulsating variable stars. He found a well-defined linear relation, which might serve to test whether the pulsation is radial or nonradial and, in the former case, fundamental or overtone. The main goal of our study is to extend the relation into the domain of SRVs.

OH masers in semiregular variables: Insights from long-term monitoring

Drifts in radial velocities of OH maser features of the three semiregular variable stars R Crt, RT Vir and W Hya have been analyzed. The radial velocities of the extreme blue- and red-shifted features drifted by about 0.2 kms−1 to 1 km s−1 on time-scales of few months to several years. In the case of W Hya a blending effect of spectral features can account for those drifts. In the two other sources the velocity drifts are likely to be intrinsic to the clumps for which the velocities of peak emission vary due to appearance or disappearance of maser emission in the regions where circumstellar matter is still accelerated.