The magnificent past of RR Lyrae variables

TL;DR

This paper reviews the historical observations of RR Lyrae variables, analyzing period changes and the Blazhko effect over more than a century using a comprehensive database, revealing insights into their stellar evolution and pulsation behaviors.

Contribution

It provides a long-term analysis of RR Lyrae stars' period variations and Blazhko effect using a newly compiled database, offering new insights into their evolutionary and pulsation characteristics.

Findings

Most RRab stars show no significant period change.

Period increases in 27 stars and decreases in 21.

The Blazhko effect exhibits diverse behaviors, including decoupled pulsation and amplitude variations.

Abstract

The history of the observations of RR Lyr variables started in the XIXth century, more than 120 years ago. The very long time baseline of available data combined with the short period of RR Lyrae variables offer an unique opportunity to look at their past as a treasure of valuable information. At this purpose, the amateur/professional association Groupe Europeen d'Observations Stellaires (GEOS) has built a database aimed to gather all the published maxima. We could study the period changes due to stellar evolution. Most of the 123 scrutinized RRab stars does not show any significant period variation. This reflects the fact that the rapid evolution is confined in short evolutionary phases. Notwithstanding this, we could put in evidence period increases in 27 stars and decreases in 21 ones. We also used the GEOS database to study the Blazhko effect of galactic RRab stars. The closed curves representing the Blazhko effect are constructed by plotting the magnitudes at maximum vs. the O-C values. We obtained a variegate family of Blazhko "potatoes". We could also reconstruct the changes in the pulsational and Blazhko periods of RR Lyr itself, resulted to be completely decoupled. Moreover, the amplitude of the Blazhko effect decreased so much to be hardly detectable by looking at the maxima collected in 2014 only. The effect seems to start again in the 2015 data.