MOST photometry of the RRd Lyrae variable AQ Leo: Two radial modes, 32 combination frequencies, and beyond

TL;DR

This study presents highly precise MOST satellite photometry of the RR Lyrae star AQ Leo, revealing 42 frequencies including multiple combination modes, evidence of period changes, and potential nonradial pulsations, providing new insights into stellar pulsation theories.

Contribution

First detailed space-based photometry of AQ Leo uncovering numerous pulsation modes and combination frequencies, advancing understanding of RR Lyrae stellar oscillations.

Findings

Detected 42 pulsation frequencies, including 32 combination modes.

Evidence of period changes in fundamental and overtone modes.

Potential identification of nonradial pulsation modes.

Abstract

Highly precise and nearly uninterrupted optical photometry of the RR Lyrae star AQ Leo was obtained with the MOST (Microvariability & Oscillations of STars) satellite over 34.4 days in February-March 2005. AQ Leo was the first known double-mode RR Lyrae pulsator (RRd star). Three decades after its discovery, MOST observations have revealed that AQ Leo oscillates with at least 42 frequencies, of which 32 are linear combinations (up to the sixth order) of the radial fundamental mode and its first overtone. Evidence for period changes of these modes is found in the data. The other intrinsic frequencies may represent an additional nonradial pulsation mode and its harmonics (plus linear combinations) which warrant theoretical modeling. The unprecedented number of frequencies detected with amplitudes down to millimag precision also presents an opportunity to test nonlinear theories of mode growth and saturation in RR Lyrae pulsators.