Nonradial modes in RR Lyrae stars from the OGLE Collection of Variable Stars

TL;DR

This study analyzes OGLE data of over 38,000 RR Lyrae stars, revealing numerous non-radial pulsation modes, especially in RRc and RRd types, and identifying new patterns in their period ratios and mode sequences.

Contribution

It reports the detection of over 260 double-mode RR Lyrae stars with non-radial modes, significantly expanding the known sample and revealing multiple mode sequences in the Petersen diagram.

Findings

Discovered over 260 stars with non-radial modes.

Identified three nearly parallel sequences in the Petersen diagram.

Some stars exhibit multiple non-radial modes simultaneously.

Abstract

The Optical Gravitational Lensing Experiment (OGLE) is a great source of top-quality photometry of classical pulsators. Collection of variable stars from the fourth part of the project contains more than 38 000 RR Lyrae stars. These stars pulsate mostly in the radial fundamental mode (RRab), in radial first overtone (RRc) or in both modes simultaneously (RRd). Analysis of the OGLE data allowed to detect additional non-radial modes in RRc and in RRd stars. We have found more than 260 double-mode stars with characteristic period ratio of the additional (shorter) period to first overtone period around 0.61, increasing the number of known stars of this type by factor of 10. Stars from the OGLE sample form three nearly parallel sequences in the Petersen diagram. Some stars show more than one non-radial mode simultaneously. These modes belong to different sequences.