The Impact of Observing Strategy on Reliable Classification of Standard Candle Stars: Detection of Amplitude, Period, and Phase Modulation (Blazhko Effect) of RR Lyrae Stars with LSST

TL;DR

This paper evaluates how LSST's observing strategy impacts the ability to reliably detect and classify RR Lyrae stars and their Blazhko effect, emphasizing the importance of cadence and survey design for variable star studies.

Contribution

It introduces metrics to assess the impact of LSST's observing strategy on the detection and classification of RR Lyrae stars and their amplitude, period, and phase modulations.

Findings

LSST will enable detailed studies of RR Lyrae stars and the Blazhko effect.

Survey cadence and footprint significantly influence detection capabilities.

Optimized strategies improve the reliability of variable star classification.

Abstract

The Vera C. Rubin Observatory will carry out its Legacy Survey of Space and Time (LSST) with a single-exposure depth of $r{\sim}24.7$ and an anticipated baseline of 10 years, allowing to access the Milky Way's old halo not only deeper, but also with a longer baseline and better cadence than e.g. PS1 3$\pi$ (Chambers et al. 2016). This will make LSST ideal to study populations of variable stars such as RR Lyrae stars (RRL). Here, we address the question of observing strategy optimization of LSST, as survey footprint definition, single visit exposure time as well as the cadence of repeat visits in different filters are yet to be finalized. We present metrics used to assess the impact of different observing strategies on the reliable detectability and classification of standard-candle variable stars, including detection of amplitude period, phase modulation effects of RR Lyrae stars, the so-called Blazhko effect (Blazhko 1907, Kollath et al. 2011), by evaluating metrics for simulated potential survey designs. So far, due to depth and cadence of typical all-sky surveys, it was nearly impossible to study this effect on a larger sample. All-sky surveys with relatively few observations over a moderately long baseline allow only for fitting phase-folded RRL light curves, thus integrating over the complete survey length and hiding any information regarding possible period or phase modulation during the survey. On the other hand, surveys with a cadence to detect slightly changing light curves usually have a relatively small footprint. LSST's survey strategy, however, will allow for studying variable stars in a way that makes population studies possible.