First results on RR Lyrae stars with the TESS space telescope: untangling the connections between mode content, colors and distances

TL;DR

This study analyzes TESS observations of 118 RR Lyrae stars, revealing diverse mode content, modulation properties, and correlations with physical parameters, advancing understanding of their pulsation behaviors and classifications.

Contribution

It presents the first detailed analysis of RR Lyrae stars observed by TESS, highlighting mode diversity, modulation patterns, and a new classification scheme based on combined TESS and Gaia data.

Findings

Many RR Lyrae stars show low-amplitude modes with different distributions from bulge stars.

A significant fraction of fundamental-mode RR Lyrae stars are modulated, but some lack the Blazhko effect.

Mode amplitude ratios distinguish between classical double-mode and stars with low-amplitude extra modes.

Abstract

The TESS space telescope is collecting continuous, high-precision optical photometry of stars throughout the sky, including thousands of RR Lyrae stars. In this paper, we present results for an initial sample of 118 nearby RR Lyrae stars observed in TESS Sectors 1 and 2. We use differential-image photometry to generate light curves and analyse their mode content and modulation properties. We combine accurate light curve parameters from TESS with parallax and color information from the Gaia mission to create a comprehensive classification scheme. We build a clean sample, preserving RR Lyrae stars with unusual light curve shapes, while separating other types of pulsating stars. We find that a large fraction of RR Lyrae stars exhibit various low-amplitude modes, but the distribution of those modes is markedly different from those of the bulge stars. This suggests that differences in physical parameters have an observable effect on the excitation of extra modes, potentially offering a way to uncover the origins of these signals. However, mode identification is hindered by uncertainties when identifying the true pulsation frequencies of the extra modes. We compare mode amplitude ratios in classical double-mode stars to stars with extra modes at low amplitudes and find that they separate into two distinct groups. Finally, we find a high percentage of modulated stars among the fundamental-mode pulsators, but also find that at least 28% of them do not exhibit modulation, confirming that a significant fraction of stars lack the Blazhko effect.